Study On Hot Air-microwave Drying Technology Of Persimmon Crisps

Hot air-microwave drying(HAMD)was chosen to produce persimmon crisps by comparison of three different drying methods-including hot air drying(HAD),vacuum freeze drying(VFD)and HAMD,and the optimization process was studied.The effects of the cultivators and maturity stages of persimmon fruits on the quality of persimmon crisps were determined.Correlation analyses between raw materials and products were taken to find out the most suitable raw materials.The optimal packing material and packing method were selected,and the shelf life of persimmon crisps was predicted by the accelerated shelf life testing.The main results were as follows:(1)Study on process of persimmon crisps under HAMD.HAMD was compared with HAD and VFD in the aspect of color,texture,rehydration ratio,nutrient compositions and energy consumption.Persimmon slices produced by HAMD showed the best sensory quality.The energy consumption of HAMD was similar to HAD,and significantly lower than VFD.Therefore,HAMD is an appropriate drying method to produce persimmon crisps.The color,texture,rehydration ratio,nutrient compositions and sensory evaluation was used to optimize the HAMD technology.The optimal technological parameters were shown as follows:Persimmons were cutting into pieces of 1mm thickness.In the period of hot air drying,persimmon slices were dried at 70?for 2 hours and 40 minutes in a hot air dryer till the moisture content of the persimmon slices was about 5%-10%.After hot air drying,persimmon slices were dried under 10.7 W/g in a microwave oven.The on-off timings used in the intermittent microwave drying treatments were 20s on-10s off.It takes 8 minutes and 30 seconds to decrease the moisture content of persimmon slice to about 2%-5%and make the persimmon slices a crisp texture.(2)Effects of the characteristics of persimmon fruit on the quality of persimmon crisps.The L^*value of HAMD persimmon crisps was positively correlated with the L^*value of persimmon fruits and negatively correlated with reducing sugar and total soluble solid content of persimmons.The a^*/b^*value of persimmon crisps was positively correlated with the a^*/b^*value and beta-carotene content of persimmon and negatively correlated with reducing sugar and total soluble solid content of persimmons.The total soluble solid/titratable acidity ratio and reducing sugar/titratable acidity ratio of persimmon crisps was positively correlated with reducing sugar and total soluble solid content of persimmon and negatively correlated with titratable acidity content of persimmons.The rehydration ratio of persimmon crisps was positively correlated with pectin and titratable acidity content of persimmon and negatively correlated with total soluble solid content of persimmons.The hardness of persimmon crisps was positively correlated with total soluble solid content of persimmon and negatively correlated with pectin and titratable acidity content of persimmons.The crispness of persimmon crisps was positively correlated with reducing sugar and total soluble solid content of persimmon and negatively correlated with pectin,total polyphenol and titratable acidity content of persimmons.The reducing sugar and total soluble solid content were lower in‘gongchengyueshi'than in‘fuyu'and‘yangfeng',while the pectin,total polyphenol and titratable acidity content were higher.As for‘gongchengyueshi',the lower reducing sugar,total soluble solid and pectin content and the higher total polyphenol and titratable acidity content were found in persimmons at lower maturity stage.But the persimmon crisps produced by persimmons at low maturity stage in our study were considered a astringent aftertaste.Comprehensively,persimmons of‘gongchengyueshi'cultivator at medium maturity stage were selected as the raw material of persimmon crisps.(3)Study on the packing and preserving of HAWD persimmon crisps.The water activity,color,hardness and crispness of products could be kept in a better condition by nitrogen-infilling packing with polyamide composite bag.It was proved in the destructive test that the shelf life finished when the L^*value reduced to64.56.The kinetic model of L^*at 37?was y=73.30622e^-0.00079x,and that at 47?was y=73.05771e^-0.0180x.Q₁₀was 2.28.Therefore the shelf life of persimmon crisps,when stored at 25?,was suggested to be 460 days.