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AbstractConvective air-drying assisted radio frequency drying (CARFD) is an innovative method with the merits of rapid volumetric heating, energy efficiency, as well as high quality food products. However, knowledge about how pretreatment methods impact on the physicochemical characteristics of pretreated apples and the performance of subsequent CARFD is limited. In present work, apple slices were subjected to osmotic pretreatment (OP) and ultrasonic-assisted osmotic pretreatment (USOP) with different intensities (1.0, 2.0 and 3.0 W/g); and the physicochemical properties of pretreated samples (such as mass transfer behavior, water migration status, dielectric loss factor and the others) were compared. The drying duration, energy consumption and a series of quality characteristics (color index, texture, nutrient compositions, antioxidant activity, and so on) of the CARFD produced apple slices were also investigated. The microstructure observations revealed that acoustic waves induced the structural changes and created microchannels. Meanwhile, physicochemical properties of pretreated samples also demonstrated that OP and USOP methods significantly facilitated the water migration status and heightened the dielectric loss factor. In comparison with control and OP methods, three USOP methods were successful in reducing the drying time (14.6%∼27.1%) and total energy consumption (4.5 ∼ 19.8%) of entire processing steps. Concomitantly, USOP (2.0 W/g) samples after drying showed an enhanced quality characteristics in terms of good texture, higher retention of bioactive compounds, higher rehydration ratio, better antioxidant capacity. This study highlights the application of USOP as an effective pretreatment method for enhancing the process efficiency and quality of CARFD produced apple slices. [ABSTRACT FROM AUTHOR]

To improve the drying efficiency and quality of hot air-dried apple slices with blanching pretreatment, this study systematically evaluated the effects of two blanching pretreatments, hot water blanching and vacuum steam pulsed blanching, on the macroscopic drying performance of apple slices. The results indicated that under the conditions of 0.07 MPa vacuum, two blanching cycles, and blanching time of 3 minutes, vacuum steam pulsed blanching significantly enhanced the rehydration rate and textural quality of apple slices while reducing the drying time. Paraffin sectioning, microscopic observation and image processing were used to compare the microstructural changes of apple slices in terms of cell cross-sectional area, perimeter, equivalent diameter, cell roundness, wall roughness factor, and porosity under different branching conditions (temperature and time for hot water blanching; vacuum level, number of cycles, and time for vacuum steam pulsed blanching). The results showed that with the increase in temperature, blanching time and number of blanching cycles, apple cells exhibited changes that accelerated water evaporation during subsequent drying, thus shortening the drying time. Additionally, the relationship between microstructural parameters and rehydration ratio was fitted to a polynomial regression model. The findings of this study provide a theoretical basis for understanding the mechanisms by which vacuum steam pulsed blanching affects the microstructure and quality of dried apple slices.

Copyright of Shipin Kexue/ Food Science is the property of Food Science Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Hot air–assisted radio frequency drying (HARFD) is a recently developed food dehydration method to enhance thermal efficiency while retaining the quality of the fresh produce. This investigation is aimed at exploring the potential for the application of portable near-infrared (NIR) spectroscopy for rapid real-time assessment of the quality of apple slices during HARFD. Both moisture content (MC) and vitamin C content (VCC) were selected as the critical indicators to assess the quality of the dried apple slices. Principal component regression (PCR), partial least squares regression (PLSR), and back propagation-artificial neural network (BP-ANN) models were developed and compared to establish the relationships between the NIR spectrum and the selected quality indicators of dried products. Model fitting results indicate that the BP-ANN model achieved the highest prediction accuracy for MC (lowest RMSEP = 0.331 and highest R P 2 =0.976) and VCC (lowest RMSEP = 0.605 and highest R P 2 =0.933) of apple slices during HARFD. This work highlights the use of portable NIR spectroscopy as an efficient and non-destructive tool for smart prediction of the quality parameters of apple slices during the HARFD process via optimized statistical modeling. [ABSTRACT FROM AUTHOR]

The combination of pretreatment with ultrasonic technology and air‐frying could improve the quality and efficiency of apple slice processing. This research aimed to explore how ultrasonic treatment prior to frying and varying temperatures during air‐frying impact the drying and thermodynamic characteristics of apple slices. The study also aimed to assess mathematical models that explain the moisture transfer kinetics and to numerically simulate the moisture distribution in apple slices during air‐frying operation. The results revealed that the moisture content and water activity (aw) of apple slices consistently decreased with longer frying times, regardless of the temperature. The mathematical models' precision was confirmed through regression analysis, which accurately represented the dynamics of moisture transfer, activation energy (Ea), and Gibbs free energy (ΔG) throughout the frying process. The results of the statistical analysis showed that the two‐term (exponential) model was effective in predicting moisture transfer in apple slices throughout air‐frying process, while the spatial distribution of moisture was successfully illustrated by the diffusion model under different conditions. Additionally, numerical simulations showed that moisture removal is faster at higher frying temperatures, and ultrasonic pretreatment led to a shorter frying time. Ultrasonic pretreatment combined with higher frying temperatures led to reduced differential enthalpy, along with an increased effective moisture diffusivity and Gibbs free energy difference. These findings are essential for improving and optimizing the frying process in food manufacturing. [ABSTRACT FROM AUTHOR]

This study aimed to improve apple slices' color and drying kinetics by optimizing the hot-air drying process, utilizing machine and deep learning models. Different steam blanching times (30, 60, 90, and 120 s), drying temperatures (50, 55, 60, 65, and 70 °C), and humidity control methods (full humidity removal or temperature–humidity control) were examined. These factors significantly affected the quality of apple slices. 60 s blanching, 60 °C temperature, and full dehumidification represented the optimal drying conditions for apple slices' dehydration, achieving better drying kinetics and the best color quality. However, the fastest drying process (40 min) was obtained at a 60 °C drying temperature combined with complete dehumidification after 90 s blanching. Furthermore, machine and deep learning models, including backpropagation (BP), convolutional neural network–long short-term memory (CNN-LSTM), temporal convolutional network (TCN), and long short-term memory (LSTM) networks, effectively predicted the moisture content and color variation in apple slices. Among these, LSTM networks demonstrated exceptional predictive performance with an R2 value exceeding 0.98, indicating superior accuracy. This study provides a scientific foundation for optimizing the drying process of apple slices and illustrates the potential application of deep learning in the agricultural processing and engineering fields. [ABSTRACT FROM AUTHOR]

This study investigated the impacts of a drying process under low temperature and reduced pressure (non-thermal drying) on the final dehydrated products characteristics. This process is based on the retention of water on molecular sieves with a good selectivity against these molecules. In this study, drying experiments of 7mm thick apple slices (AS) were performed and compared to apple slices pretreated by freezing. It was concluded that the dehydrated apple slices were depleted of the maximum amount of water after 12 hours of drying, with a final water content equal to 12 ± 1.75%, whereas after freezing pretreatment, a decrease in drying time to 7 hours was observed, as well as a decrease in water content to 10 ± 0.5%. This explains the effect of freezing pretreatment on accelerating water transfer. In addition, a convective drying was performed on the apple slices at 60°C, which allows comparison with the slices dried by our non-thermal drying process. In order to characterize the obtained fruits, characteristic analyses such as water activity (Aw), color, texture (hardness), and dimensions (diameter and thickness) were performed before and after each drying experiment. Thus, continuous measurements of temperature, humidity, and pressure, within the enclosure, were determined during the experiments using a wireless sensor system controlled by a programming Arduino. Finally, mathematical modeling by various models (Newton, Page, Midilli, etc.) was performed to determine the most suitable model describing the non-thermal and convective drying of apple slices. [ABSTRACT FROM AUTHOR]

The influence of microwave blanching (MWB) at different times (30–120 s) on the physicochemical properties, microstructure, and drying characteristics of apple slices, compared to steam blanching (SB) was investigated. Results showed that MWB resulted in greater weight loss and more efficient enzyme inactivation efficiency than SB. The MWB process facilitated the moisture diffusion, resulting in a significant (p < 0.05) reduction in drying time of up to 27.78 % and specific energy consumption of up to 50.00 %. Microstructural observations confirmed that this result stemmed from the development of microporous channels within the cellular tissue structure. The Page model exhibited a higher applicability to the drying of apple slices. Moreover, MWB was more effective than SB in inhibiting browning and retaining phenolic compounds. However, concerning amino acid retention, the dried samples treated with SB for 30 s (21.36 ± 0.83 mg/g DW) showed superior performance compared to dried samples treated with MWB. In addition, molecular docking results suggested that amino acids could form the distinctive flavor of dried apple slices through hydrogen bonding with taste receptors. [ABSTRACT FROM AUTHOR]

Copyright of Revista Brasileira de Engenharia Agricola e Ambiental - Agriambi is the property of Revista Brasileira de Engenharia Agricola e Ambiental and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to reveal the change laws of microstructure in apple slices during hot air‐explosion puffing drying, the microstructure images and parameters of apple slices under different drying conditions were obtained by using paraffin sectioning, microscopic observation, and image processing techniques with apples as raw material and CO2 as drying medium. Subsequently, the changes in internal cell and pore structure of dried apple slices were analyzed, as well as the relationship between micro‐parameters of apple slices and macro‐measurement indicators was further obtained. Results indicated that the overall cross‐sectional area, cross‐sectional perimeter, equivalent diameter, and porosity of cells increased by explosion puffing drying, while the cell roundness and wall roughness factors changed relatively little. Meanwhile, macro–micro parameters of expanded apples were fitted and analyzed. Then, the obtained mathematical model showed a nonlinear correlation as experimental and predicted results exhibited good agreement, with determination coefficients R2 more significant than 0.8, which could better expect the macro–microparameters to change in the drying process. The results of this research could provide an essential reference for exploring the change laws of tissue microstructure parameters in apples dried by hot air‐explosion puffing drying, with expansion and rehydration ratios under different experimental conditions, as well as optimizing the puffing drying process and designing corresponding drying equipment. Practical Applications: Fresh apples have high moisture content and are not easy to store, so drying is usually used to reduce the moisture content to extend shelf time and increase economic benefits. For the drying process of fruit and vegetable products, scholars mainly focused on the influence of microstructure parameters on moisture migration, drying rate, heat and mass transfer and other factors, but did not give a quantitative description of how microstructure parameters affect macroscopic parameters. In this article, the relationship between microstructural changes and macroscopic indicators was investigated by taking puffed apple slices as an example. Research could provide an essential reference for exploring the change laws of tissue microstructure parameters in apples dried by hot air‐explosion puffing drying, with expansion and rehydration ratios under different experimental conditions, as well as optimizing the puffing drying process and designing corresponding drying equipment. [ABSTRACT FROM AUTHOR]

In an aim to examine water content, distribution, and state of apple slices during hot air drying, this study determined the inversion spectra of transverse relaxation time (T2) of apple slices during the drying process at different temperatures using low‐field nuclear magnetic resonance (LF‐NMR) and magnetic resonance imaging (MRI). The results showed that drying temperatures was negatively correlated with water content and positively correlated with drying rate. The relaxation peak area of free water decreased, while those of semi‐bound and bound water increased and subsequently decreased. The water content of apple slices had quadratic polynomial correlations with signal amplitudes of LF‐NMR (peak areas of total, free, and semi‐bound), R2 of these regression fitting equations were basically above 0.8 and 0.9. The models of total and free water had good prediction performance, suggesting that LF‐NMR is suitable for rapid non‐destructive testing of water in apple slices during hot air drying. Practical applications: In this work, the amount of water in apple slices at any given time during hot air drying can be predicted well‐using regression fitting equation models of the peak areas of total, free, and semi‐bound water. This information can then be used to improve the quality of dried products and clarify the distribution and states of water during drying. Therefore, LF‐NMR can be used for rapid non‐destructive testing of water in apple slices during hot air drying. And it provided references for further investigation of optimized drying methods and conditions for different apple species and achieved accurate and non‐destructive monitoring of water in fruits during processing based on LF‐NMR. [ABSTRACT FROM AUTHOR]

To clarify the key aroma compounds of Fuji apples and the influence of drying temperatures, the volatile compounds of Fuji apple slices dried by hot-air at 50, 60, 70 and 80 ℃ were characterized by head space solid-phase micro-extraction gas chromatography-mass spectrometer (HS-SPME-GC-MS) combined with electronic nose. The results showed that 64 volatile compounds were identified in fresh and four kinds of dried apple samples, including 23 esters, 18 alcohols, 8 aldehydes, 2 alkenes, 2 ketones, 3 lactones, 1 acid, 3 sulfur-containing compounds and 4 heterocyclic compounds. The differences between types and contents of volatile compounds in different samples were great. The content of aroma compounds in fresh samples was 397.059 mg/kg. Total volatile compounds contents in four hot-air dried samples from high to low were 64.189 mg/kg at 50 ℃, 57.703 mg/kg at 80 ℃, 32.124 mg/kg at 70 ℃ and 32.020 mg/kg at 60 ℃, respectively. Odor-active value (OAV) analysis showed that there were 8 key aroma compounds both in fresh apple sample and hot-air dried apple samples. They were α-farnesene (12746.11~1597.75), hexyl 2-methylbutyrate (755.62~6.90), hexanol (2988.00~168.54), 1-octene-3-ol (53.12~12.08), nonanal (1534.99~47.36), trans-2-nonenal (1202.98~189.38), linalool (1264.30~212.75) and 6-methy-5-hepten-2-one (11.27~3.90). The key aroma compounds identified in hot-air dried samples included 2-methyl-1-butanol (32.26~7.16), 3-methyl-4-heptanol (14.39~6.90), phenylethanol (11.11~4.67), octanal (211.25~84.36), 3-hydroxy-2-butanone (64.57~21.86), 3-methylthiopropanol (13.52~5.88) and 2-pentylfuran (26.44~14.88). Electronic nose analysis showed that there were differences in aroma profiles between fresh apple and apple slices dried by hot-air at different temperatures. The fresh samples and dried apple slices could be effectively distinguished by principle component analysis (PCA). Considering aroma and energy consumption, 80 ℃ hot air dehydration apple slices had better characteristic aroma than 50 ℃ hot air treatments. Therefore, 80 ℃ hot air drying was the optimal drying condition.

Dried red-fleshed apples are considered a promising high-quality product from the functional foods category. The objective of this study was to compare the flesh features of freeze-dried red-fleshed apples belonging to the 'Alex Red', 'Trinity', '314', and '602' genotypes and indicate which parameters and shapes of dried samples are the most useful to distinguish apple genotypes. Apple samples were at the stage of harvest maturity. The average fruit weight, starch index, internal ethylene concentration, flesh firmness, total soluble sugar content, and titratable acidity were determined. One hundred apple slices with a thickness of 4 mm and one hundred cubes with dimensions of 1.5 cm × 1.5 cm × 1.5 cm of each genotype were subjected to freeze-drying. For each apple sample (slice or cube), 2172 image texture parameters were extracted from images in 12 color channels, and color parameters L*, a*, and b* were determined. The classification models were developed based on a set of selected image textures and a set of combined selected image textures and color parameters of freeze-dried apple slices and cubes using various traditional machine-learning algorithms. Models built based on selected textures of slice images in 11 selected color channels correctly classified freeze-dried red-fleshed apple genotypes with an overall accuracy reaching 90.25% and mean absolute error of 0.0545; by adding selected color parameters (L*, b*) to models, an increase in the overall accuracy to 91.25% and a decrease in the mean absolute error to 0.0486 were observed. The classification of apple cube images using models including selected texture parameters from images in 11 selected color channels was characterized by an overall accuracy of up to 74.74%; adding color parameters (L*, a*, b*) to models resulted in an increase in the overall accuracy to 80.50%. The greatest mixing of cases was observed between 'Alex Red' and 'Trinity' as well as '314' and '602' apple slices and cubes. The developed models can be used in practice to distinguish freeze-dried red-fleshed apples in a non-destructive and objective manner. It can avoid mixing samples belonging to different genotypes with different chemical properties. Further studies can focus on using deep learning in addition to traditional machine learning to build models to distinguish dried red-fleshed apple samples. Moreover, other drying techniques can be applied, and image texture parameters and color features can be used to predict the changes in flesh structure and estimate the chemical properties of dried samples. [ABSTRACT FROM AUTHOR]

The effects of temperature, air velocity, and infrared radiation distances on the drying characteristics and quality of apple slices were investigated using infrared-assisted-hot air drying (IRAHAD). Drying temperature and air velocity had remarkable effects on the drying kinetics, color, total phenol content, total flavonoid content, and vitamin C content (VCC) of apple slices. Infrared radiation distance demonstrated similar results, other than for VCC and color. The shortest drying time was obtained at 70 °C, air velocity of 3 m/s and infrared radiation distance of 10 cm. A deep neural network (DNN) was developed, based on 4526 groups of apple slice drying data, and was applied to predict changes in moisture ratio (MR) and dry basis moisture content (DBMC) of apple slices during drying. DNN predicted that the coefficient of determination (R2) was 0.9975 and 1.0000, and the mean absolute error (MAE) was 0.001100 and 0.000127, for MR and DBMC, respectively. Furthermore, DNN obtained the highest R2 and lowest MAE values when compared with multilayer perceptron (MLP) and support vector regression (SVR). Therefore, DNN can provide new ideas for the rapid detection of apple moisture and guide apple processing in order to improve quality and intelligent control in the drying process. [ABSTRACT FROM AUTHOR]

In this work, the kinetics of drying and rehydration of green apple slices peeled and unpeeled (Granny Smith cv) were studied. The apple slices were dried at 50, 60, and 70 °C, and after that, rehydrated at ambient (Ta) and boiling temperature (Tb). The drying kinetics were adjusted with the Dincer and Dost model, giving a good fit. Effective diffusivity (Deff) and the convective mass transfer coefficient (hm) were also determined, both coefficients increase with drying temperature, being 1.25 × 10−9 m2 s−1 and 9.53 × 10−7 m2 s−1 the highest values obtained for the peeled apple slices respectively. Peleg and Weibull models were adjusted to the rehydration experimental data obtaining a good fit (R2 > 0.99). Deff values increase significantly with rehydration temperature but take similar values between peeled and unpeeled samples. Acidity, pH, moisture content, solid soluble content, and equivalent diameter were determined to compare the fresh apple slices with those after dehydration and the post-rehydration process. The apple slices rehydrated at boiling temperature better preserved the characteristics of fresh samples due to the short immersion times in water, no significant differences were observed between peeled and unpeeled apples. According to the results, it is convenient to dry the apple slices unpeeled at 70 °C and rehydrate them at Tb. [ABSTRACT FROM AUTHOR]

In this study, the drying properties of apple slices dried at different microwave powers and in different hot air were investigated and compared. Depending on the increase in microwave power, an increase in drying rate and effective moisture diffusivity and a decrease in drying time were determined. Effective moisture diffusivity were found in the range of 9.72x10-10 - 2.36x10-9 m² s-1 at different microwave powers, and between 3.80×10-10 - 7.40x10-10 m² s-1 in hot air drying. Longer drying time, slower drying rate and less effective moisture diffusivity were obtained from drying hot air when compared to different microwave powers. Depending on the increase in temperature, an increase in drying rate and effective moisture diffusivity was determined. While Page model has the best fit for the drying curves at different microwave powers, the drying curves of hot air dried apple slices were defined by Parabole model. [ABSTRACT FROM AUTHOR]

In this work, two novel models have been proposed based on semi-empirical and factional calculus incorporating non-integer time derivatives in the Fick’s first law of anomalous diffusion. The experimental data has been collected from literature of 15 kinetics investigated in a convective dryer under the effect of temperatures ranging from 40 to 80 °C at 10 °C interval, and thickness of the slices of 2 to 6 mm at 2 mm interval. The collected experimental dataset was of apple slices (Golab variety). Results from this study were compared with a set of 64 thin-layer drying models previously published in the literature. The fitting capability of the models was compared using the mean of root mean square error MRMSE (%) of all kinetics and the global determination coefficient R2. All models’ constants and coefficients were optimised by dragonfly algorithm programmed in MATLAB software. Results showed that the fractional model is highly capable of describing the drying curve of the apple slices with a determination coefficient (R2) of 0.99981, and average root mean square error (MRMSE) of 0.43 % in comparison to the best empirical models with R2 of 0.99968 and MRMSE of 0.61 %.

The current study covers drying of 500 g of apple slices of uniform thickness by forced convection mixed solar drying unit integrated with paraffin wax and natural sand as energy storage (thermal) material. The experimental setup consists of solar collector (for heating inlet air) and drying chamber in which heated air removes moisture content of apple slices from 80 to 21.7% (wet basis) in 3.5 h during April 2021. The average moisture diffusivity for lower tray was 1.018 × 10−8 m2/s which was 16.3% and 28.6% greater than upper tray and open sun drying, respectively. The average drying rate for lower tray (0.5318 kg water/kg dried product/h) was higher than upper tray and open sun drying. At the same drying time of 3.5 h, the final moisture content in lower tray, upper tray and open sun drying were obtained as 21.7%, 22.64% and 25.61%, respectively, which indicates that present solar drying is better than open sun drying. The average drying exergy efficiency was obtained as 48.14% with maximum value as 74%. The maximum (& average) drying efficiency and collector efficiency were 13% (& 5.56%) and 83.3% (& 66.39%), respectively. Wang and Singh model was found the best suitable among 14 thin layer drying models. [ABSTRACT FROM AUTHOR]

Dried red-fleshed apples are considered a promising high-quality product from the functional foods category. The objective of this study was to compare the flesh features of freeze-dried red-fleshed apples belonging to the ‘Alex Red’, ‘Trinity’, ‘314’, and ‘602’ genotypes and indicate which parameters and shapes of dried samples are the most useful to distinguish apple genotypes. Apple samples were at the stage of harvest maturity. The average fruit weight, starch index, internal ethylene concentration, flesh firmness, total soluble sugar content, and titratable acidity were determined. One hundred apple slices with a thickness of 4 mm and one hundred cubes with dimensions of 1.5 cm × 1.5 cm × 1.5 cm of each genotype were subjected to freeze-drying. For each apple sample (slice or cube), 2172 image texture parameters were extracted from images in 12 color channels, and color parameters L*, a*, and b* were determined. The classification models were developed based on a set of selected image textures and a set of combined selected image textures and color parameters of freeze-dried apple slices and cubes using various traditional machine-learning algorithms. Models built based on selected textures of slice images in 11 selected color channels correctly classified freeze-dried red-fleshed apple genotypes with an overall accuracy reaching 90.25% and mean absolute error of 0.0545; by adding selected color parameters (L*, b*) to models, an increase in the overall accuracy to 91.25% and a decrease in the mean absolute error to 0.0486 were observed. The classification of apple cube images using models including selected texture parameters from images in 11 selected color channels was characterized by an overall accuracy of up to 74.74%; adding color parameters (L*, a*, b*) to models resulted in an increase in the overall accuracy to 80.50%. The greatest mixing of cases was observed between ‘Alex Red’ and ‘Trinity’ as well as ‘314’ and ‘602’ apple slices and cubes. The developed models can be used in practice to distinguish freeze-dried red-fleshed apples in a non-destructive and objective manner. It can avoid mixing samples belonging to different genotypes with different chemical properties. Further studies can focus on using deep learning in addition to traditional machine learning to build models to distinguish dried red-fleshed apple samples. Moreover, other drying techniques can be applied, and image texture parameters and color features can be used to predict the changes in flesh structure and estimate the chemical properties of dried samples.

The objective of this study was to determine and compare the effect of five different pretreatments including sulfite treatment (ST), osmotic dehydration (OD), steam blanching (SB), steam blanching plus osmotic dehydration (SB+OD), and ultrasound treatment (UT), on the microwave vacuum drying (MVD) kinetics, the physicochemical properties, and sensory quality of the apple slices. The results showed that the pretreatments prior to MVD could reduce the drying time of apple slices by 25-45% as compared to the non-pretreated apple slices, and the drying time in the SB+OD apple slices sample was shortest. Whether pretreated or not, MVD process was controlled by diffusion and characterized by a two-stage falling-rate drying. As calculated according to the Fick's law of diffusion, the moisture diffusivities ( D eff ) ranged from 1.64×10 -8 to 3.46×10 - 8 m 2 /s. Different pretreatment methods had a significant influence on the physicochemical properties and sensory qualities of the dried products (pSB>UT>OD>ST>the control. ntrol.

The effects of temperature, air velocity, and infrared radiation distances on the drying characteristics and quality of apple slices were investigated using infrared-assisted-hot air drying (IRAHAD). Drying temperature and air velocity had remarkable effects on the drying kinetics, color, total phenol content, total flavonoid content, and vitamin C content (VCC) of apple slices. Infrared radiation distance demonstrated similar results, other than for VCC and color. The shortest drying time was obtained at 70 °C, air velocity of 3 m/s and infrared radiation distance of 10 cm. A deep neural network (DNN) was developed, based on 4526 groups of apple slice drying data, and was applied to predict changes in moisture ratio (MR) and dry basis moisture content (DBMC) of apple slices during drying. DNN predicted that the coefficient of determination (R2) was 0.9975 and 1.0000, and the mean absolute error (MAE) was 0.001100 and 0.000127, for MR and DBMC, respectively. Furthermore, DNN obtained the highest R2 and lowest MAE values when compared with multilayer perceptron (MLP) and support vector regression (SVR). Therefore, DNN can provide new ideas for the rapid detection of apple moisture and guide apple processing in order to improve quality and intelligent control in the drying process.

Copyright of Kemija u Industriji is the property of Croatian Society of Chemical Engineers and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Summary: This work aimed to incorporate prebiotic FOS from yacon in apple slices using vacuum impregnation (VI). Three FOS concentrations (10.3, 14.1 and 18.9 g per 100 g of dry matter (DM)), two temperatures (25 and 35 °C), reuse of extracts and stability of the impregnated slices were evaluated. The highest impregnation level (30.5 g per 100 g DM) was obtained at 35 °C with 14.1% FOS extract while levels of common sugars were reduced. Total phenolics and ABTS antioxidant capacity (AC) slightly decreased while ORAC AC was reduced by 55%. Reuse of the impregnation solution in successive cycles after restoring the FOS level maintained the FOS concentration and profile (GF2–GF7), sugars and phenolic antioxidants. FOS in apple slices remained stable during 4 week storage, while aw, colour and fracture point changed during storage. This work demonstrated the feasibility of yacon FOS to improve the functional properties of dehydrated apple slices. [ABSTRACT FROM AUTHOR]

The influence of intermittent-microwave drying and hot-air drying on drying characteristics and rehydration properties of apple slices were compared. Microwave powers have crucially affected the drying rate, effective moisture diffusivity and drying time. As microwave power increased, the drying rate and effective moisture diffusivity increased while the drying time reduced. In intermittent-microwave drying, the effective moisture diffusivities were estimated between 4.47 × 10−9 and 2.54 × 10−8 m2 s−1. Longer drying time, slower drying rate and less effective moisture diffusivity were obtained from hot-air drying when compared to intermittent-microwave drying. Higher temperatures provided higher drying rate and effective moisture diffusivity. Effective moisture diffusivities of hot-air dried-apple slices were calculated in the range of 3.38 × 10−10–6.25 × 10−10 m2 s−1. Moreover, Page model gave the best fitting to intermittent-microwave drying curves, while hot-air drying curves were suitably described by Parabolic Model. On the other hand, the rehydration ratio of intermittent-microwave dried-apple slices was higher than hot-air dried-apple slices. Additionally, Peleg model was defined to be the best model predicting experimental rehydration data in both drying techniques. [ABSTRACT FROM AUTHOR]

The strong physical effects of ultrasound can change the state of water in food. In order to study the effect of ultrasound on the microwave drying of apple slices, an ultrasonic online-assisted microwave vacuum drying (UOAMVD) device was designed. The curves of moisture content versus drying time, the change in dielectric constant and dielectric loss factor, and the flow characteristics of water molecules were obtained during microwave vacuum drying (MVD), microwave vacuum drying with the apple slices pretreated by ultrasound (MVDPU), and UOAMVD, was measured by a vector network analyzer and a low-field nuclear magnetic resonance and imaging analyzer. The differences in color and microporous structure of the different dehydrated products were determined. Compared with MVD and MVDPU, apple slices that underwent UOAMVD had a higher drying rate and improved drying uniformity, and the dielectric constant was significantly reduced. In addition, the color of the UOAMVD dehydrated samples was the closest to that of fresh apple slices, whereas the microporous structure was not obvious and there was granular starch overflow. UOAMVD significantly improved the microwave drying efficiency and quality of apple slices. This work provides a reference for enhancing the application of ultrasonic microwave combination drying. [ABSTRACT FROM AUTHOR]

Freeze drying (FD) usually provides the best final quality but results in the high drying energy consumption, and the slow drying speed. To improve the FD efficiency, a two-stage dehydration strategy using a radio frequency-vacuum assisted freeze-drying process (FD + RFVD) was explored by taking apple slices as the representative samples. The drying rate changes during the FD treatment process of apple slices were experimentally determined. The best transition point of the two drying stages was also clearly obtained based on the changes of drying speed and product quality. The best processing parameters would be the FD drying time of 10.5 h followed by the RF-vacuum treatment at the electrode gap of 100 mm and vacuum pressure of 0.02 MPa. The optimized FD + RFVD process required only 81.25% of the FD drying time to achieve the same target moisture content, and similar or better product quality as compared to FD alone. This study may provide a technical guidance for developing effective and practical FD + RFVD technology to improve singe FD processes. • A two-stage FD + RFVD process was explored to improve the FD efficiency. • The best transition point of the two drying stages was also clearly obtained. • The best processing parameters of FD + RFVD process were determined. • The optimized FD + RFVD process provided shorter drying time and similar quality. [ABSTRACT FROM AUTHOR]

Study of fruit by-products is increasing because they contain several bioactive compounds which can add value to food products. In this study, the effect of mango peel powder addition (0, 2, and 4%) on physical, structural, and antioxidant properties of starch edible films and their effectiveness as edible coatings on apple slices during storage (4 °C) were evaluated. The addition of mango peel powder increased the penetration resistance and a* and b* color parameters of edible films and reduced the numbers of holes in them. The higher antioxidant properties were obtained with the highest amount of mango peel added. For example, increases in 178.4 and 830.7% for total phenolic compounds (TPC) and antioxidant capacity (AC) were obtained, respectively. Suspensions (0, 2, and 4% of mango peel powder) applied as edible coating increased the firmness, browning index (BI), TPC, and AC of apple slices. In storage, the edible coating application did not inhibit the increase of BI and decrease of firmness of apple slices. However, the bioactive compounds and antioxidant capacity remained constant. Although further studies have to be conducted, mango peel powder may be used to improve the mechanical, physical, and antioxidant properties of edible films, and these could be used as an edible coating on apple slices. [ABSTRACT FROM AUTHOR]

Abstract Polyphenols are closely related to the nutritional value, flavor, and color of dried apple products. In present work, the correlation of polyphenol accumulation with apple slices browning in hot air drying (65 °C, 2 m/s air velocity) process was investigated. Polyphenols composition were distinguished in different apple varieties, among which chlorogenic acid, epicatechin were the most abundant constitutes, accounting for 44.47–75.45 g/100 g, 30.31–35.16 g/100 g of total polyphenols respectively in apple flesh. Browning characteristic distribution of 7 varieties dried apple in PCA analysis model were similar to their fresh counterparts. The average browning degree were 22.31 and 6.72 in dried and fresh apple slices respectively, revealing that hot air drying treatment accelerated and extended the effects of polyphenol enzymatic browning process. High chlorogenic acid and/or catechin content induced redness value (a* value) variation, while lower total polyphenol content and higher polyphenol diversity mainly induced brightness (L* value) and yellowness (b* value) variation in drying process. Specifically, in Fuji apple slices, quercetin-3-O-galactoside significantly correlated to L* variation (r = 0.838, **P < 0.01), while catechin, chlorogenic acid, phlorizin successively contributed to the variation of a* (r = 0.877, 0.906, 0.848, **P < 0.01) and b* (0.919, 0.953, 0.906, **P < 0.01). These results would be the reference for predicting and controlling the color quality of dehydrated apple products by polyphenol content and composition. Highlights • Apple slices surface browning is more related to its polyphenol composition. • Polyphenols selectively accumulated in apple slices in hot air-drying process. • Polyphenols variation correlate to surface color value L * , a * , b * in different way. • Correlation of polyphenol variation with surface color of apple slices was variety dependent. [ABSTRACT FROM AUTHOR]

In this study, dehydration kinetics of ultrasound and microwave combined vacuum frying (UMVF) of apple slices was investigated and the most suited model predicting the drying kinetics was determined. The variation in dielectric properties (DPs) during frying of apple slices was determined to understand the heating behavior in microwave electric fields. In addition, oil uptake, texture properties and color parameters were also measured and analyzed. Two microwave (MW) power levels (800 and 1000 W) were used at a constant ultrasound power and frequency of 600 W and 28 kHz, respectively. The experimental frying data of apple slices were used to fit ten different mathematical models and non-linear regression analysis was used to determine model parameters. The goodness of fit was determined using the coefficient of determination (R2), reduced chi-square (Σ2), root mean square error (RMSE). The Logarithmic model was found to be the most suitable for describing the frying process. By increasing MW power, the effective moisture diffusivity values increased from 1.7791 to 2.2761 × 10−9 m2/s. The results have shown that the dielectric constant (e′) and loss factor (e″) of the apple slices decreased significantly with increasing frying time and the combination of ultrasound in both MW power levels. The combination of ultrasound with microwave significantly increased the penetration depth compared to when microwave vacuum frying (MVF) was used. The oil uptake of fried apple slices was reduced in UMVF compared to MVF. At the same time textural crispiness and color perimeters significantly improve in UMVF process. UMVF had greater advantages on moisture evaporation rate and uniform heating compared to MVF and it can be confidently used to produce crispy, desirable texture, healthier, and visually appealing fried foods in short time. [ABSTRACT FROM AUTHOR]

Abstract Food materials with high moisture content were prone to occur drying shrinkage-deformation during dying process. In-depth understanding of drying shrinkage-deformation mechanism for food materials was crucial for optimizing drying parameters as well as for obtaining better quality dried foods. Therefore, the main aim of the present work was to investigate the drying shrinkage-deformation mechanism of apple slices during process of heat and mass transfer. Hot air drying experiment of freshed apple slices was conducted and the shrinkage-deformation values of apple slices were obtained by image analysis. Simultaneously, Heat-mass transfer coupled with stress-strain mathematical model were constructed and solved by COMSOL Multiphysics software. Results showed that the mathematical models of heat-mass transfer and stress-strain can be used to simulate the hot-air drying process of apple slices effectively, and the maximum relative errors of simulated value and experimental value were less than 10%. Temperature distribution and moisture distribution of apple slices during hot-air drying process were uniform. The maximum value of thermal stress and moisture stress were occurred at the middle period of the whole drying process; and the moisture stress during the whole drying process of apple slices were higher than thermal stress, which indicated that moisture stress was the main factor causing the drying shrinkage deformation of apple slices. Highlights • The heat-mass transfer and stress-strain mechanism are analyzed for creating the mathematical model. • The drying shrinkage-deformation of apple slices are obtained experimentally by image processing technology. • The heat-mass transfer and stress-strain mathematical model are numerically solved by COMSOL Multiphysics software. • Experimental and predicted values are in close agreement with each other. • Moisture stress is the main factor causing the drying shrinkage-deformation of apple slices. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the impact of vacuum (VC) and ultrasound (US) treatments during osmotic hydration (OD) at 25 °C on the impregnation of calcium into apple tissues. The VC and US treatments were applied in two modes: a) VC or US at the first 10 min of the OD process and b) treatment with 10-min intervals during OD. Under the experimental conditions used in this study, the results revealed that the interval ultrasound treatment was the most effective in enhancing mass transfer and calcium uptake among all the treatments. It exhibited the highest efficiency in moisture removal and calcium uptake, resulting in a calcium content of 3,644.19 μg/g dry basis, over 18 times higher than that found in fresh apples. The calcium content in OD-treated apple slices remained well-preserved after hot air finish drying. Additionally, the samples treated with VC and US exhibited high total phenol content and antioxidant capacity, suggesting their ability to retain bioactive compounds in the apple slices. Overall, this study highlights the efficacy of VC and US treatments during OD in promoting calcium impregnation into apple tissues, with the interval ultrasound treatment yielding the most favorable results in terms of calcium uptake, moisture removal, and nutrient preservation. • Osmotic dehydration (OD) is an effective method for calcium fortification of apples. • Pulse ultrasound in OD was the most effective in enhancing calcium content in apples. • Calcium content in OD-treated apple slices was well-preserved after hot air drying. • OD apple slices have exhibited high total phenol content and antioxidant capacity. [ABSTRACT FROM AUTHOR]

Mass transfer during the incorporation of probiotics protected within a double emulsion W 1 /O/W 2 using hypertonic solutions were analyzed. Osmotic dehydration (OD) and vacuum osmotic dehydration (VOD) were used to impregnate the fruit with probiotics. Fresh apple tissue was soaked in osmotic solutions at 40, 50 and 60 °Brix, using a ratio of 1:9 (w/w) emulsion: sucrose solution. The results showed that the survival of probiotics decreased with increasing osmotic pressure of the solution. Higher impregnation of microorganisms was promoted by the application of a period (20 min) of vacuum treatment. Afterwards the atmospheric pressure was restore. The number of viable cells in the osmodehydrated apple was in the range 10 6 –10 8 CFU/g d.b. Scanning electron microscope (SEM) images revealed the presence of microcapsules of 1–2 μm into apple tissue. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the antioxidant properties of apple slices stored in edible starch films enriched with white and green tea extracts. All results were compared to that obtained for apple slices stored in polyethylene films. The use of starch films, as carrier of antioxidants, prolonged the storage life and improved quality of fresh-cut apples at the end of storage; however, deteriorated their lightness and increased their browning. Apple slices coated in starch films enriched with tea extracts exhibited higher antioxidant properties than those without these additives, as well as those in polyethylene films. [ABSTRACT FROM PUBLISHER]

The accuracy of imaging for bulk volume estimation of apple slices in the process of drying at temperatures from 40 to 80°C was investigated and compared with physical caliper measurements. The initial hypothesis was to estimate bulk volume of cylindrically shaped apple slices from diameter and thickness imaging. Imaging of diameter showed strong agreement with caliper measurements throughout the entire drying process, however imaging of thickness was not accurate due to the irregular shrinkage and bending phenomena. A linear model reflecting the relationship between diameter and bulk volume was developed and validated at temperatures of 40, 60, and 80°C. It showed good correlation between imaging diameter and bulk volume changes in the range of moisture contents from 9.1 to 0.25 g/g. The relative percentage error of the prediction model was approximately 6.45%, which suggests that imaging can be used as a robust tool for bulk volume estimation of apple slices during convective drying. [ABSTRACT FROM PUBLISHER]

The effect of different concentrations of sugar solution (hypertonic) (30%, 45% and 60% w/v) and carboxyl methyl cellulose (CMC) (0%, 1% and 2% w/v) coating on freeze drying of apple slices was studied. In total, nine treatments with respect to concentrations of hypertonic solution and coating layer were prepared to analyze their influence on the physical and chemical properties of freeze dried apple slices. It was observed that increase in the sugar solution concentration, decreased the moisture content of the apple slices significantly impacting its water activity, texture and sugar gain. Application of different concentrations of CMC coating had no significant effect on the properties of dried apple slices. A significant change was observed for color of CMC coated freeze dried apple slices pretreated with 60% sugar solution. Drying kinetics of pretreated apple slices were fitted by using two drying models, Newton’s and Page’s. Page’s model showed higher R-square and lower root mean square error (RSME) compared to Newton’s model.

Vacuum drying is a preferred drying technology in food industry due to the higher quality of the final products than conventional hot air drying. However, the low drying efficiency significantly limits its application. The low heat transfer and high humidity under vacuum conditions are the main causes for the low drying rate. The present study innovatively focused on dehumidification inside the vacuum chamber to improve the drying rate, and created novel vacuum drying device assisted with a condensation unit (VD + C) by putting a cooling plate into the vacuum chamber to condensate the water vapor into liquid. The innovative device was used to study the drying rate on apple slices, the nutrients degradation and color changes comparing to hot air drying, vacuum drying and vacuum freeze drying. The results showed that VD + C significantly enhanced the drying effect of apple slices, the drying rate (D eff value) was the highest and the energy consumption (SEC value) was the lowest among the tested drying methods. Compared with hot air drying and vacuum drying, the water rehydration rate, the content of ascorbic acid, total phenol content and antioxidant activity were improved, and the color was obviously better than that of hot air drying and vacuum drying. Besides, the microstructure of apple slices by VD + C was better than that by hot air drying. • A vacuum drying device assisted with condensation unit (VD + C) was created. • VD + C significantly improved the drying rate of apple slices. • Lowest energy consumption was observed in VD + C. • Dried apple by VD + C had better Vc, phenolic content, antioxidant activity. • VD + C better retained the appearance and color of dried apple. [ABSTRACT FROM AUTHOR]

An intermittent microwave convective drying method combined with a real-time computer vision technique was employed to detect the effect of drying parameters on color properties of apple slices. The experiments were performed at air temperature of 40 to 80℃, air velocities of 1–2 m/s, microwave powers of 200–600 W, and pulse ratios (PRs) of 2–6. Drying rate and drying time varied from 0.014 to 0.000001 min−1 and 27 to 244 min, respectively. The normalized lightness values had ascending and descending parabolic trends with decrease in product moisture content. With descending dimensionless moisture content, redness, yellowness, color change, hue angle, and chroma were enlarged. The normalized redness values changed from −4 to 3. Models relating drying parameters with drying time, drying rate, and lightness were obtained and found to be significant (P < 0.01). Results indicated that microwave power and PRs had more influence on lightness and color change than other parameters. [ABSTRACT FROM AUTHOR]

An attempt was made to quantify the contribution of chemical pre-treatment on the color changes of apple slices during hot air drying. The monitored color attributes of apple slices were computed real time at drying air temperatures of 50, 60, and 70 °C. The apple slices dried in a computer vision system (CVS) assisted-hot air dryer both with and without pre-treatment. The quantities of measured color parameters for pre-treated (P.T.) samples were subtracted from the values obtained for untreated (U.T.) samples at the same water content. For this purpose, an artificial neural network was developed and used satisfactorily for mapping out the color parameters of P.T. samples at calculated moisture ratio for U.T. sample to compute the physio-chemically significant difference. From the results, it can be derived that a CVS seems to be a promising tool when it comes to detecting and monitoring the effects of various pre-treatments on being-processed foodstuffs . [ABSTRACT FROM AUTHOR]

The purpose of this research was to develop an approach for porosity estimation in the process of convective air drying. Fresh apple slices were exposed to 80°C drying to equilibrium moisture content 0.2 g/g. Porosity at different stages of drying was estimated using three approaches: (1) direct volume and mass measurements, (2) pycnometer measurements, and (3) theoretical model. All three approaches were in good agreement in the range of moisture contents above 1.0 g/g. However, at moisture contents below 0.26 g/g, significant deviation of pycnometer measurements from both experimental estimates and theoretical model was observed. This difference could be explained by transformation of open pores into closed pores due to glass transition phenomenon. This study presents an example of separate quantitative estimation of total, open-, and closed-pore porosity. [ABSTRACT FROM PUBLISHER]

Pectin is an important active polysaccharide in the matrix of dried fruit slices. Its components and structural character not only affect the texture but also impact the color of the dried fruit products. Present work studied the variation of pectin fractions of water-soluble (WSP), trans -cyclohexane-1,2-diaminetetraacetic acid-soluble (CSP), and sodium carbonate-soluble (NSP) from apple slices dried by using freeze-drying (FD), 60 °C hot air drying (HAD60), and 90 °C hot air drying (HAD90), to investigate the correlation of their monosaccharide composition, molecular weight distribution, Fourier transform infrared (FTIR) spectrum and small-angle X-ray scattering (SAXS) intensity plot of pectin fractions with the appearance browning of the apple slices. It was found that thermally process ruptures the cell wall structure and pectin component, leading to 12.57% less yield of WSP, and a maximum of 6.35% more yield of NSP pectin fractions. In FD, HAD60, and HAD90 apple slices, the linearity of WSP decreased but the branching extent of the rhamnogalacturonan I (RG-I) domain of WSP and NSP increased successively. The weight average molecular mass (Mw) and number average molar mass (Mn) of WSP and NSP increased as drying temperature increased, whereas they decreased in CSP. The thermal treatment promoted the dehydration of the pectin and caused higher methyl esterification, inducing the structure of pectin more compact and tighter. Moreover, the pectin structural characteristics of the degree of esterification (DE), the radius of gyration (Rg) value, conformational index (ν), and galactose content of three soluble pectin fractions were positively correlated with the a* and b* value of different dried apple slices. [Display omitted] • Different drying techniques induce different changes in three pectin fractions. • The change of pectin fractions notably impacts the browning of dried apple slices. • Thermal treatment induced methyl esterification of pectin fractions of dried apple. • Thermal treatment made the structure of pectin much more compact and tighter. [ABSTRACT FROM AUTHOR]

Apple is one of the most competitive agricultural exports in China, accounting for about 30% of the total production of fruits. Unsuitable preservation or storage methods can lead to the loss, which may amount for 30% of the total. To reduce the loss of apples after harvesting, deep processing is an appropriate method. As a kind of snack food, dried apple slice is produced by a drying process and the natural flavor of apple can be retained. During the drying process, the drying temperature and time have a great influence on the apple slice quality. To develop a new method to monitor and characterize the drying process of apple slices as well as evaluate the influence of the drying temperature and time on this process, the electrical impedance and moisture content of apple tissues were measured during the drying process under different conditions. The hot air temperature was set to 40, 50, 60 and 70℃, and the hot air speed was set to 0.5 and 1.0 m/s, respectively. The 6 same apple samples were placed in the drying chamber for drying test. One sample was to detect the change of the impedance characteristics, and the other samples were used to detect the change of the moisture content. The interval measurement time was 20 min. Until the mass difference of the 2 successive measurements for one sample was less than 0.01 g, the experiment was stopped. Results showed that the electrical impedance of apple slices increased with the increase in the drying time, and the increase rate was slow in the early stages and fast in the latter part of the drying process. The moisture content decreased during the drying process, and the decrease was fast at the beginning and slow in the latter part. Thus, the variation tendency of moisture content was contrary to that of electrical impedance during the process. The electrical impedance of apple slices showed a negative linear correlation with the moisture content when the moisture content was more than 20%. So electrical impedance measurement could provide a simple and rapid approach for predicting the moisture content, and furthermore it was capable of monitoring and evaluating the drying process of apple slices. The curves of the normalized electrical impedance and moisture content with the drying time could be approximated with the logarithmic drying model which could describe the characteristics of the drying process. The rate constant of the model at various temperatures was estimated by the normalized impedance and moisture content. The rate constant increased with the increasing of drying temperature. Then to analyze the effect of temperature on the drying rate constant, the rate constants at different temperatures were formulated by the Arrhenius equation. Based on the obtained rate constants at different drying temperature, the activation energy was calculated. It was found that when the speed of drying hot air was 0.5 and 1.0 m/s, the activation energy calculated from the normalized impedance was 33.925 and 28.912 kJ/mol, respectively; the calculated activation energy from the moisture content was 27.320 and 22.947 kJ/mol, respectively. The activation energy decreased with the increasing of hot air speed, which indicated that the higher the hot air speed, the faster the drying of apple slices. The findings are useful to monitor the drying process of apple slices and have the potential applications in the control of fruit drying process. [ABSTRACT FROM AUTHOR]

Fresh-cut ‘Braeburn’ apple slices were dipped into cold water (4 °C for 2 min) or hot water (HWT, 48 °C or 55 °C for 2 min) followed by dips into 0 or 6% w/v aqueous calcium ascorbate (CaAsc, 2 min, 0 °C) and stored in air up to 28 d at 4 °C. Microbial counts, changes in browning and sensory acceptance were determined to indicate changes in quality. Changes in antioxidant levels were measured using free radical scavenging activity (DPPH), reducing activity (FRAP), ascorbic acid content (AA) and polyphenolic content (by HPLC). CaAsc dips had a strong impact reducing the browning through increasing the flesh luminosity and hue angle. 6% CaAsc in fresh-cut apples extended the overall acceptability from less than 7 d to 14 d. Immediately after CaAsc treatment, AA content was 5 fold higher (0.25–1.25 g kg −1 ) than those not dipped into CaAsc. However, the combination of HWT treatments and CaAsc dips led to seven fold increased levels of AA inside the apple tissue (0.25–1.85 g kg −1 ) and consequently increased the antioxidant activity. HWT did not increase the AA content when not combined with CaAsc dips. The HWT CaAsc dip extended the overall acceptability to 21 d compared to 14 d for samples not heated but dipped into CaAsc. Shelf life was ultimately limited by sensory quality. At day 28, total plate counts were reduced from 5.3 log cfu/g (untreated slices) to 4.6 log cfu/g in the 6% CaAsc dips and further to 3.9 log cfu/g with the combination of HWT and CaAsc dip. Changes in the content of phenolic compounds with time, HWT and CaAsc dip were generally not significant except for slightly increased quercetin and phloridzin levels and decreased p -coumaric and procyanidins over time. The combination of HWT at 48 °C for 2 min followed by 6% CaAsc dip would be best for preserving the eating quality of apple slices. [ABSTRACT FROM AUTHOR]

Drying is an effective method for the food industry to extend product's shelf life, which makes the moisture content of the food reduce to a certain extent to ensure microbial stability of the product. Compared to traditional air drying method, short and medium wave infrared drying takes shorter time to evaporate moisture. Water plays a critical role in the chemical and enzymatic reactions and alters material properties. Moisture transfer is therefore a governing factor in drying process. However, heat and moisture transfer in fruits and vegetables drying is a complex process. A better understanding of the mechanism of moisture transfer will be helpful to improve product quality and the efficiency of drying process. In order to investigate the changing rules of water characteristics and glass transition temperature in apple slices during short and medium wave infrared drying, low-field nuclear magnetic resonance (LF-NMR), differential scanning calorimetry (DSC) and other instruments were applied in the test. LF-NMR is commonly used to detect changes in water status with the advantages of fast and non-destructive analysis. It can explain the migration of water from microscopic point of view through its relaxation behavior of inner protons. Results showed that short and medium wave infrared temperatures had strong influence on water diffusion, and the ratio of average drying rates under 50, 70 and 90 °C was 1:1.5:2.3. Three kind of water states were obtained from the LF-NMR experiments using the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequences, and among the transverse relaxation time (T2), T21 (1-20 ms), T22 (20-200 ms) and T23 (200-1 000 ms) were corresponding to bound water, immobilized water and free water respectively, which implied that the longer the relaxation time, the stronger the water flow. The dramatically decreased content of free water content in vacuoles was accompanied by the sharp increase in the content of immobilized water in the cytoplasm and extra-cellular space, from 7.96% to 46.82%. Subsequently, the content of immobilized water decreased gradually with time increasing. Short and medium wave infrared drying elevated the glass transition temperature (P<0.05) and reduced water activity (P<0.01) appreciably by decreasing the content of immobilized water in apple tissues, which showed high correlation between glass transition temperature or water activity and water status. Obviously shrinkage occurred in apple slices along with the water loss in the process of drying, and volume and moisture content showed a significant correlation (R>0.99). This research provides the theoretical basis for understanding the water diffusion characteristics of short and medium wave infrared drying. [ABSTRACT FROM AUTHOR]

In this study, the effects of tray drying, heat-pump drying, freeze drying, and microwave drying methods on the quality characteristics of apple slices were investigated and energy efficiencies of drying methods were determined. Drying time of samples were calculated as 50 min, 90 min, 270 min, and 20 min for tray heat-pump freeze, and microwave drying respectively. Quality characteristics of apple slices were determined by physical (moisture content, color values, water activity, rehydration, bulk density), chemical (total phenolic, total and invert sugar, pectin) and sensory analysis. Energy efficiencies of drying methods were evaluated by calculating the Specific Moisture Extraction Rate (SMER), Moisture Extraction Rate (MER), Specific Energy Consumption (SEC) energy consumption, and energy cost. Considering the quality characteristics of the products, the results showed that dried apple slices which were produced by using microwave and freeze drying methods had a better quality comparing to the tray and heat-pump drying methods. On the other hand, the lowest energy consumption and the highest SMER and MER values were obtained from the heat-pump dryer. According to the purpose of the production obtained quality and cost values will help us in selecting the dryer. [ABSTRACT FROM AUTHOR]

A conveyor-belt dryer was developed using a combined infrared and hot air heating system that can be used in the drying of fruits and vegetables. The drying system having two chambers was fitted with infrared radiation heaters and through-flow hot air was provided from a convective heating system. The system was designed to operate under either infrared radiation and cold air (IR-CA) settings of 2000 W/m with forced ambient air at 30 °C and air flow of 0.6 m/s or combined infrared and hot air convection (IR-HA) dryer setting with infrared intensity set at 2000 W/m and hot at 60 °C being blown through the dryer at a velocity of 0.6 m/s or hot air convection (HA) at an air temperature of 60 °C and air flow velocity 0.6 m/s but without infrared heating. Apple slices dried under the different dryer settings were evaluated for quality and energy requirements. It was found that drying of apple (Golden Delicious) slices took place in the falling rate drying period and no constant rate period of drying was observed under any of the test conditions. The IR-HA setting was 57.5 and 39.1 % faster than IR-CA and HA setting, respectively. Specific energy consumption was lower and thermal efficiency was higher for the IR-HA setting when compared to both IR-CA and HA settings. The rehydration ratio, shrinkage and colour properties of apples dried under IR-HA conditions were better than for either IR-CA or HA. [ABSTRACT FROM AUTHOR]

BACKGROUND The postharvest life of fresh-cut apple slices is limited by browning on cut surfaces. Dipping in halide salt solutions was examined for their inhibition of surface browning on 'Granny Smith' apple slices and the effects on biochemical factors associated with browning. RESULTS Delay in browning by salts was greatest with chloride = phosphate > sulfate > nitrate with no difference between sodium, potassium and calcium ions. The effectiveness of sodium halides on browning was fluoride > chloride = bromide > iodide = control. Polyphenol oxidase ( PPO) activity of tissue extracted from chloride- and fluoride-treated slices was not different to control but when added into the assay solution, NaF > NaCl both showed lower PPO activity at pH 3-5 compared to control buffer. The level of polyphenols in treated slices was NaF > NaCl > control. Addition of chlorogenic acid to slices enhanced browning but NaCl and NaF counteracted this effect. There was no effect of either halide salt on respiration, ethylene production, ion leakage, and antioxidant activity. CONCLUSION Dipping apple slices in NaCl is a low cost treatment with few impediments to commercial use and could be a replacement for other anti-browning additives. The mode of action of NaCl and NaF is through decreasing PPO activity resulting in reduced oxidation of polyphenols. © 2014 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Abstract: Pullulan is a thickener that can form semipermeable films, and glutathione is an effective reducing agent, while chitooligosaccharide has antibacterial activity. In this study, effect of pullulan-based coatings in combination with antibrowning and antibacterial agents (1% pullulan; 0.8% glutathione+1% chitooligosaccharides; and 0.8% glutathione+1% chitooligosaccharides+1% pullulan) on apple slices was investigated during hypothermia storage. Pullulan-coating treatments effectively retarded enzymatic browning, maintained firmness, decreased weight loss, and inhibited microbial growth and respiration rate of apple slices during hypothermia storage compared with that of the control (p <0.05). Results indicate that using pullulan-based coatings in combination with glutathione and chitooligosaccharides is a promising way to extend the shelf-life of apple slices. [Copyright &y& Elsevier]

The purpose of this work is to quantify the energetic interest of convective and intermittent drying process of natural products. This drying mode has been achieved within a climatic tunnel blower. This laboratory device permitted us to achieve several tests for different conditions of the apple slices drying. In the intermittent case, a variation of the air temperature and air velocity values permitted us to find the most economic velocities for the drying of the apple thin slices. The numerical simulations in the intermittent tests, give us more information on what really happens to the product during periods of interruption. The drying kinetics at the resumption increases with the air temperature. Then, we gain in energy and in overall drying time. These studies show the considerable advantages of the intermittent drying of agricultural products and confirm the preservation of their qualities and the reduction of the drying time. [ABSTRACT FROM AUTHOR]

Abstract: Microstructural studies have played an important role in the comprehensive understanding of some food phenomena that occur during drying processes. The aim of this work was to study the effect of four pre-treatments (immersion in boiling water, vacuum impregnation, freezing/thawing, and uni-axial compression) on apple microstructure characterized by cell cavities size parameter and how the changes induced by these pre-treatments can affect the water loss rate during air drying. The quantitative structure analysis showed that freezing/thawing and compression pre-treatments caused more damage on the apple structure, yielding larger cell cavities in comparison to vacuum impregnation and immersion in boiling water and control. Apple slices that were frozen/thawed, compressed and immersed in boiling water displayed the higher drying rates and diffusivity coefficients than the vacuum impregnated and control samples. These results allow concluding that disruption of the cell walls can be considered as a factor that affects the drying rate. [Copyright &y& Elsevier]