Ultrasonic Sugar Soaking And Variable-temperature Gas Jet Impingement Drying Technology For Kiwifruit Slices

Kiwifruit is a kind of fruit with fresh quality,soft texture and sweet and sour taste,which is rich in organic compounds and trace elements.And the vitamin C content is far more than other fruits,known as the "the world’s precious fruit",favored by consumers of all ages.The fresh fruit of kiwifruit is prone to decay and deterioration,which is easy to cause a large amount of fresh fruit backlog,seriously affecting the development of kiwifruit planting.The deep processing technology of kiwifruit plays an important role in the further development of kiwifruit industry.Kiwifruit slices are currently processed products with large demand in the international and domestic markets,which have broad development prospects.However,traditional techniques for processing kiwifruit slices have the shortcomings of poor quality and high energy consumption.Based on the problems in the processing technology of the above kiwifruit slices,the paper studied the effects of ultrasound on the sugar permeability effect,drying energy consumption and quality of kiwifruit slices,and analyzed the impact of constant temperature and variable temperature air-impingement jet drying on the drying characteristics and quality of kiwifruit slices,and optimized the process parameters of segmentally variable temperature air-impingement jet drying.The main results were as follows:1.The characteristic indexes of kiwifruit slices were selected by factor analysis as resilience,AE,sugar content,WL,titratable acid,vitamin C preservation rate.The established models could be applied to analyze and predict the effects of ultrasonic treatment parameters on the osmotic effect,drying energy,and quality of kiwifruit slices.The optimal process parameters for ultrasonic infiltration were ultrasonic time 58 min,temperature 47 ℃,sucrose concentration of 40 ° Brix,and ultrasonic density of 0.7 W/mL.2.The air-impingement jet of kiwifruit slice was mainly the falling rate drying,and there is no obvious constant speed drying stage.By fitting the selected five models with the measured data,it was found that the selected models could describe the change of moisture of kiwifruit slices during air-impingement jet drying.The Modified Henderson and Pabis model had the best fit,which was the optimum model of the kiwifruit slice in air-impingement jet drying.Different air-impingement jet drying temperature had different influence on the quality of kiwifruit slices.Variable temperature drying methods were superior to constant temperature drying methods,and the kiwifruit slices of each index was better under the 70-40 ℃ cooling method.3.The established quadratic polynomial regression model of various quality characteristic indexes and segmental temperature-changing drying process parameters could be applied to predict the indexes of kiwifruit slices under the condition of segmental variable temperature air-impingement jet drying of kiwifruit slices.The optimal process parameters for segmental variable temperature air-impingement jet drying were:first stage drying temperature 62 ℃,water conversion point 32%,second stage drying temperature 47 ℃.Compared with hot air drying,microwave vacuum drying and vacuum freeze drying,the kiwifruit slices obtained by segmental variable temperature air-impingement jet drying have the lowest energy consumption,sweet and sour taste,higher VC preservation rate,good taste and best sensory score.Ultrasonic osmosis and segmental variable temperature air-impingement jet drying technology applied to the processing of kiwifruit slices could improve the quality and reduce energy consumption.The research plays an important role in increasing the added value of kiwifruit,improving the full development and utilization of kiwifruit resources,and promoting the further development of the kiwifruit industry.