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To investigate the effects of different microwave drying conditions on the texture and nutritional quality of candied strawberries in a vacuum environment. This study investigated the effects of three different vacuum microwave treatment conditions (2.5 w/g-1.5 h, 3.5 w/g-1 h, 4.5 w/g-0.5 h) on moisture migration characteristics, texture, microstructure, color, anthocyanins, and phenolics of candied strawberries, which were evaluated by hot air drying. The results showed that the time required for vacuum microwave drying to dry candied strawberries to 20%±2% moisture content was significantly lower than that of hot air, and the higher the microwave power, the shorter the drying time. In addition, the water in the candied strawberries obtained after drying mainly appeared in two states, namely, bound water and water not easy to flow. The relaxation time T2 of strawberry candied strawberries obtained by vacuum microwave drying increased with the increase of microwave power, which indicated that the degree of freedom of water increased. Cross-sectional microscopic observation found that vacuum microwave drying caused cell wall rupture, and the higher the microwave power, the closer the site of fissure formation to the medullary core, and the bigger the fissure, and the smaller the porosity, whereas the cellular integrity and the porosity of the samples dried by the hot air were higher than that of microwave drying. In addition, the hardness, viscosity, and a* value of vacuum microwave-dried dried strawberry preserves were lower than those of hot air-dried samples, but the L* value, total sugar, anthocyanin, and phenolic content were higher. In conclusion, vacuum microwave drying had higher drying efficiency and could better retain the nutrients such as anthocyanins in candied strawberries.

The purpose of this study was to discover the quality properties of the commercially available candied strawberries. Fifteen samples with different brands were purchased, and the physicochemical parametes, such as color, texture, sugar and acid content were determined using colorimeter, texture analyzer and HPLC. In addition, sensory scores were evaluated using intensity scale method. The results showed that the moisture content of these preserved strawberries were between 12.49% and 23.86%, and the colorimetric values distribution ranges of L*, a* and b* were 23.25~34.39, 5.17~19.83, and 5.78~17.04, respectively. For the texture characters, there were significant differences (P

In order to clarify the content and structural changes of different pectin fractions in grape cell walls under ultrasonic treatment, the grapes were treated with different ultrasonic time and ultrasonic power in this study, and the content of pectin fractions, composition of monosaccharides and structural changes of grape cell walls were analyzed by means of carbazole sulfuric acid method, PMP pre-column derivatization, high-performance liquid gel chromatography , scanning electron microscopy, Fourier transform infrared spectroscopy and circular dichroism. Results showed that the highest and the lowest contents in fresh grape cell walls were alkali-soluble pectin (NSP) and chelate pectin (CSP), respectively, and they were 27.41 mg/g AIR and 8.25 mg/g AIR. The total pectin decreased after ultrasonic treatments, in which the water-soluble pectin (WSP) increased and the CSP and NSP decreased. A total of six monosaccharides were detected in three pectins, and the monosaccharides of different pectin were not the same. The galactose and arabinose were high in WSP, the glucuronic acid was the most abundant of CSP and the rhamnose were the highest in NSP. After ultrasonic treatment, the contents of monosaccharides decreased, while the composition did not change, and the main chain structure of pectin was no change, but the linear structure and the degree of branch chain were changed. With the increase of ultrasonic times and powers, the molecular weight of different pectins declined gradually. And in the microstructure showed a more loose morphology. In addition, ultrasonic treatment had an effect on the structure and chain conformation of CSP and NSP, which made their maximum response values shift, and the effect of ultrasonic power was more significant. In conclusion, ultrasonic treatment could reduce the pectin and monosaccharide contents in grape cell walls, and affect the molecular linear structure and molecular chain conformation of pectin. These results can provide theoretical basis for the quality change of grape products under ultrasonic treatment.

In order to discover the moisture distribution and migration during the drying process of strawberries at constant or gradient temperatures and the effect on the quality of dried strawberries, the strawberries which had experienced osmotic dehydration were dried under constant temperatures (60 °C-12 h, flip it over when dry to 6 h) and gradient temperature (65 °C-2 h, 60 °C-2 h, 55 °C-2 h, flip it over, 65 °C-2 h，60 °C-2 h，55 °C-2 h) during hot air drying. Low-field nuclear magnetic resonance (LF-NMR) was used and the physicochemical (texture, VC, total phenols) and sensory qualities (flavor, texture, taste, color) of the preserved strawberries obtained by the two drying programs were compared. The results showed that the water content of the dry base of strawberries at both programs decreased with time extending gradually, but the rate of gradient temperature was higher than that of constant temperature drying. From the T2 inversion spectra and peak areas of LF-NMR, it illustrated that the free water was the main form of water in the osmotically dehydrated strawberries, and there were also a small amount of bound water and immobile water. With the drying procedure proceeded, the T2 peak of the strawberry gradually decreases, which indicates a decrease in the mobility of the water. However, the total relaxation peak area of constant temperature drying and gradient drying was reduced to 31.3% and 26.4% of the original at the end of the drying programs, which showed that the gradient drying had higher drying efficiency. Magnetic resonance imaging (MRI) showed that the water in strawberries was firstly enriched to the broken tip of the fruit and dispersed, then in the medium of the drying process, the peel took the main position for the water evaporation, and finally some water left in the pith. From the imaging results, the main difference between the two drying programs was that there was an obvious homogeneous wetness phenomenon in the strawberries after 6 h drying i.e. the water was redistributed evenly in the fruit at that time, while this process did not appeared in the gradient drying. In addition, the VC and total phenolic contents of dried strawberries were significantly higher (P

In order to explore the water diffusion characteristics of green bananas during the microwave drying process, a microwave drying test was conducted to investigate the green bananas drying characteristics under different microwave power densities (3, 5, 7 and 9 W/g), and the microwave drying test model of green bananas was established. Low-field nuclear magnetic resonance (LF-NMR) was used to investigate the internal moisture distribution and change law of green bananas during the drying process. Results showed that drying rate of green bananas in the microwave drying process increased first and then decreased, the effective diffusion coefficient was between 1.082×10−8 and 7.708×10−8 m2/s, and also increased with the increasing of microwave power density. The nuclear magnetic resonance experiments showed that, during the drying process, the free water was removed first, the non-flowing water showed an overall upward trend and then a downward trend, while the combined water showed an overall upward trend. With the extension of microwave drying time, the water peak area of the three states decreased and the total peak moved in the direction of the decrease of relaxation time, at the end of drying, the free water in green banana was basically removed, and the internal water mainly existed in the state of combined water and non flowing water. By fitting green banana drying kinetics model, it was found that the Page model fitted best (R2>0.9), which could provide a basis for effectively describing the variation law of water with time during the microwave drying process of green bananas.