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This study examines the performance of a parabolic greenhouse-type solar dryer used for drying of cayenne pepper (Capsicum annuum) in Nan (northern Thailand). The dryer has a base area of 6.0 m × 8.2 m and a height of 3.25 m with the loading capacity of 100–200 kg for fruit or vegetables. It has a parabolic roof structure covered with polycarbonate sheets and is placed on a concrete floor. It is ventilated by three DC fans powered by a 50-Watt solar cell module. The produce is placed on trays with wire mesh base and located on steel supports. Among the advantages of this type of dryer is that the product is protected from rain, dust and insects. The pepper samples consisted of whole pods or cut pods. The drying experiments were carried out in the solar dryer and in an electrical (convective) tray dryer. The study was focusing on drying kinetics and on the effects of the drying treatments on one of the main quality attributes namely the capsaicin content in the dried products.

A new drying approach to enhance physical quality of konjac glucomannan extracted from Amorphophallus muelleri was studied. It consisted of a comparison between microwave vacuum drying and conventional hot-air drying. The effects of microwave vacuum drying and hot-air drying on drying kinetics and physical and structural properties such as color, bulk density, particle density, porosity, viscosity, and morphology of konjac glucomannan (KGM) flour were investigated. It can be concluded that microwave vacuum drying significantly reduced drying time and increased porosity of dehydrated products which have a positive effect on the viscosity of the KGM solution. In contrast, it decreased bulk density and particle density when compared with conventional hot-air drying. Microstructure observations revealed the presence of large cavities in the granules of microwave-vacuum-dried KGM samples. However, there was a slight change in color of the microwave-vacuum-dried samples, resulting in a lower whiteness index tha...

Fluidized bed dryers (FBDs) and spouted bed dryers (SBDs) are considered efficient dryers for drying seeds from high moisture content (MC; 20–25%wb) to medium MC (≈18%wb). In this work, a number of drying experiments and seed quality tests were conducted using rice and wheat seeds in order to compare the FBD and SBD with regard to drying rate, product quality, and specific energy consumption. It was found that FBD was better in terms of a faster drying rate and SBD was better in terms of specific energy consumption. However, it could not be clearly concluded which dryer provided a better product quality in terms of germination percentage.

Macadamia nuts are well known for their unique flavor and taste. They contain a high level of monounsaturated fatty acids such as oleic acid, which is claimed to have an effect on reducing blood cholesterol. This study focuses on monitoring the changes in the physical and chemical qualities of macadamia nuts during drying, roasting, and storage. A combination of heat pump drying and tunnel drying was selected for this study to provide a comparison with convectional hot air drying. After completion of all drying treatments, the dried nuts were subjected to roasting at 125°C for 20 min and storage in ethylene vinyl alcohol copolymer (EVOH) bags at 4°C for 3 months. After each stage of processing, nut samples were taken to assess the quality in terms of fatty acids, moisture content, water activity, peroxide value, free fatty acids, color, and volatile compounds. The experimental results showed that drying treatments using heat pump combined with tunnel drying can reduce drying time significantly. It appears...

Thin-layer drying studies were conducted on two peanut varieties, Middleton and Sutherland. The range of inlet conditions used were drying air temperatures between 35 and 55°C, air humidities of 5 to 10 g/kg, and an air velocity of 2.5 m/s. The initial product moisture contents were 39 ± 3% (Middleton) and 43 ± 4% (Sutherland). A two-compartment drying model was fitted to the experimental data. The goodness of fit was assessed by comparing correlation coefficients and sums of squares. The coefficients of determination (R 2) were greater than 0.94 for both varieties, indicating that the models were adequate to describe the drying process. The results showed that the drying air temperature was the predominant factor in peanut drying. No significant difference in drying rates was found between the two varieties.

This paper describes the effects of spray drying temperature and wall materials on functional properties of kaffir lime oil microcapsules. The effects of spray drying were studied at inlet air temperatures at 160, 180, and 200°C. Two coating materials (konjac glucomannan and gum arabic) were employed in this study. The results indicate that kaffir lime oil had antibacterial activity against all tested pathogens and was able to inhibit Vibrio cholerae comparable to a standard antibiotic. The combination of konjac glucomannan and gum arabic (KGM+GA) can enhance the yield and retention of total oil in the microcapsules more than using konjac glucomannan alone as a wall material. Increasing inlet air temperature resulted in a decrease of antibacterial activity and amount of bioactive volatile compounds. Physical and chemical properties of the microcapsules did not differ significantly (p > 0.05) in terms of process yield, a w , moisture content, efficiency in retention of total, surface and inner oil, water s...

This study was conducted in order to provide information on drying behavior of seed destined for reproduction of corn, wheat, and rice. Drying experiments were conducted in a fluidized bed dryer (FBD) with corn, rice, and wheat and in spouted bed dryer (SBD) with wheat and rice at temperatures between 40 and 80°C. The experimental data were fitted into four thin-layer drying models by a least squares method. As a result, Page's model and a two-compartment model were the best-fitted models. However, due to the limitation of these models, Page's model and the two-compartment model were modified by adding the drying temperature term. Subsequently, these models could adequately predict the drying curves under a wider range of temperatures with root mean square (RMS) of the difference between model-predicted and experimental values of less than 0.035.

Two drying treatments were applied to slices of beef: superheated steam and hot air. Drying kinetics and quality attributes such as color, water activity, and peroxide value were investigated for different drying conditions (drying medium temperature 130, 160, or 180°C; flow rate of the drying medium of 35, 45, or 55 kg/h; and sample thickness 3 mm, 6 mm, 9 mm, or minced beef). The experimental results show that superheated steam drying generally leads to shorter residence times in the dryer when the moisture content needs to be decreased below 8%. Superheated steam drying distinguishes itself by longer constant rate periods, lower critical moisture contents, and higher drying rates for the falling rate period compared to air drying. Reducing the sample thickness or increasing the transferred heat, by increasing the temperature or velocity of the drying medium, result in accelerating the drying process. Temperatures above 160°C, however, cause changes within the and its surface and prevent the bound moist...

Corn, rice, and wheat seeds with an initial moisture content (IMC) of 20–25% wb were dried to moisture content below 18% wb at 40–80°C in a fluidized bed dryer (FBD) and spouted bed dryer (SBD) and the seeds with IMC 18% wb were dried to below 14% wb at air temperatures 18–30°C and relative humidity 60–70% by an in-store dryer (ISD). As a result, it appears that a two-stage drying concept is feasible in drying high-moisture-content seeds due to the high germination rate of dried seeds. Nonetheless, the drying temperature must be carefully selected. A drying temperature of 40°C was clearly safe for all samples, whereas more than 90% of wheat seeds still germinated after drying at 60°C in FBD. Furthermore, drying seeds with IMC 18% wb by ISD was safe under specified drying conditions.

The effects of drying treatments including dryer type, drying conditions, and sample preparation on the composition of volatile compounds in two cultivars of dried Australian nectarines were investigated in this study. A cabinet dryer, a tunnel dryer, and a heat pump dryer were evaluated. The sample preparation included halving or slicing the fruit to different slice thickness and in different directions. The volatile compounds in fresh and dried nectarines were isolated using Likens Nickerson simultaneous distillation and extraction technique and identified by gas chromatography. The results indicated that a heat pump dryer was the best system for preservation of volatile compounds in sliced dried fruit in terms of lactones and terpenoids followed by cabinet dryer and tunnel dryer.

A mathematical model of temperature and wheat moisture content distribution inside a triangular spouted bed dryer was developed. The model is based on analysis of heat and mass transfer inside the dryer. In addition to that, an empirical bulk density model has been developed for wheat and included in the drying simulation. A laboratory-scale triangular spouted bed (TSB) dryer was used to dry wheat grain to validate the model. The dryer was divided into three sections, namely spouting, downcomer, and fountain. A series of drying runs were conducted to record moisture and temperature profile. There were two distinct regions observed during wheat drying. A constant rate period was observed during the initial drying stage and the falling rate period took place at the later drying stage. Initial moisture content and operating drying temperature governed the timing of transition from constant rate period to falling rate period. The model can be used to accurately predict the moisture content of wheat during dry...

A triangular spouted-bed dryer has been designed as part of a hexagonal continuous dryer for paddy. In the triangular-bed dryer, the spout of drying air is placed in one corner of the drying chamber. Combining six triangular units with the spout located in the center of the dryer allows a continuous process and reduces energy consumption due to the reduction of heat losses. The current study focuses on the distribution of moisture and temperature in an individual triangular bed. Models of distribution have been developed in order to provide a better understanding of the phenomena and to help in scaling-up of the design.

The thermophysical properties of the stone fruits plum, peach, and nectarine were modeled from experimental data as functions of moisture content. Samples were dried to preset moistures in a laboratory cabinet dryer, and the thermal conductivity, specific heat, apparent density, bulk density, and porosity of the fruit were determined. The thermal conductivity and specific heat were found to be linear functions of moisture content, whereas apparent bulk density and porosity followed second-order polynomials. Temperature dependence was not found to be significant.

The desorption isotherms of peach, plum, and nectarine were obtained using the gravimetric method. The experimental data were fitted with Chung-Pfost, Oswin, and GAB models using nonlinear regression. The coefficient of determination, analysis of variation, distribution of residuals, and mean relative deviation were measured to determine the validity of each model. Of the models tested, the five-parameter GAB model was found to give the best representation of the data. The isothermal data were also used to calculate the energy required for evaporation from the product surface, by means of Othmer plots, resulting in a moisture-dependent equation for the heat of desorption.

Three varieties of paddy rice, namely Langi and Amaroo from Australia and Chainart I from Thailand, were dried from high initial moisture content of about 27% down to 13–14% wet basis using a two-stage drying system. A fluidized bed dryer reduced the moisture content down to 18%. Drying experiments were carried out at 100, 125, and 150°C. Further moisture content reduction down to 14% was achieved by shade drying. As a result of these treatments, head rice yield increased proportionally with the drying temperature. In contrast to that, the yellowness, measured by colorimeter in terms of b value, showed an opposite trend. Starch characteristics were studied by Rapid Visco Analyser (RVA), x-ray diffraction, and differential scanning calorimetry (DSC). Pasting properties were affected by the drying temperature. The peak viscosity and break down were decreasing with the increase of drying temperature in all varieties while the setback values were increasing in Langi and Amaroo only. All starch sample...

The effects of high-temperature drying on Thai Jasmine rice were investigated. Paddy was first rewetted and then dried using a two-stage drying process, involving a fluidized bed at high temperature, followed by shade drying (ambient air drying). Three high drying temperatures: 100, 125, and 150°C were studied. Volatile compounds were extracted by distillation and extraction in a Likens and Nickerson apparatus, and analyzed by gas chromatography–mass spectrometry. A total of 94 volatile compounds were identified. These included 21 alcohols, 19 aldehydes, 14 ketones, 12 acids, 9 heterocyclic compounds, 8 hydrocarbons, 5 esters, and 6 miscellaneous compounds. 2-Acetyl-1-pyrroline, a major constituent of volatiles in fragrant rice was identified and tended to increase in concentration with increasing drying temperature. The three different drying temperatures used in the fluidized bed dryer were found to have an effect on the volatile components of Thai Jasmine rice. The increase in drying temperatu...

In northeastern provinces of China, maize is one of the main sources of income in agriculture. After harvest, the grain is kept under subzero conditions for 3–4 months. Studies have been undertaken...

Drying using ambient subzero temperatures is of potential interest for thermosensitive products. Existing theoretical drying models have been used to predict the response of the system to different aeration systems. The model is based on enthalpy balances and includes water freezing and deposition of water on the surface of the commodity. It uses thermophysical properties of the commodity (i.e., maize in this study) and ambient weather data collected from northeastern China. Water within the grain is modelled as bound, free or frozen. The physical state of water under subzero temperatures has been investigated using a differential scanning calorimeter and nuclear magnetic resonance spectrometry. It has been established that the quantity of bound water was around 17%. Thermophysical properties characterizing the drying behavior of maize kernels cv. Huangmo 417, the most common variety grown in northeastern China, were determined under a wide range of moisture contents and drying temperatures. Thos...

Heat pump dryers were studied as an alternative to freeze drying for dehydration of lactic acid bacteria for starter cultures. Factors investigated were bacterial growth phase, addition of dehydro-protectants, drying conditions, drying media and storage life of the dried bacteria. The main criterion for evaluation was the activity of the dried product. Results indicated that single dehydro-protectants were not able to give high activities, but suitable combinations were found giving results at least equal to freeze-drying. Nitrogen purging was found to give a significant improvement in activity.

From the successful drying of paddy in a lab-scale triangular spouted bed (TSB), a pilot scale unit with a capacity of 500kg/batch was constructed and used to dry paddy of high moisture contents. The drying tests showed that air temperatures of up to 160°C in the first stage, followed by a lower temperature of 80–100°C in the second stage, can be used to dry paddy from more than 25% down to around 15% (w.b.) without significantly changing grain quality in terms of head rice recovery. Moisture distribution in the pilot-scale TSB was observed to be satisfactorily uniform.