Experimental Study On The Effect Of Freezing-thawing Strategy On Physicochemical Properties Of Red Fuji Apple

With the improvement of residents' living standards,residents' demand for food types is increasing day by day,and the quality requirements are becoming more and more demanding.This requires more and more frozen and fresh-keeping fruits and vegetables.However,in the process of refrigerated transport,food processing and marketing,it is difficult to avoid the freezing-thawing process of fruits and vegetables.In this process,the properties of fruits and vegetables will decrease.It has very important social and economic benefits by adopting effective freezing and thawing measures.In this way,good nutritional properties was ensured,the decay and damage were reduced,and the contradiction between supply and demand of fruits and vegetables was resolved.(1)Experimental research on the temperature-changing rate strategy of freezingthawing process:by using the PLC control system,the constant temperature and humidity test chamber is used to control the red Fuji apples with different temperature-changing rate strategies for freezing-thawing treatment,respectively,to change the influence freezing rate and thawing rate during the freezing-thawing process,and each hardness,color difference,soluble solid content,titrate acid content and vitamin C content of the group of fruits are measured.The changes of physicochemical properties were researched.It was found that when the red Fuji was treated by freezing-thawing at different freezing rates,the higher freezing rate treatment had less damage to the hardness,brightness and vitamin C content of Red Fuji,and the a*(the degree of red and green)value,b*(the degree of yellow and blue)value and titrate acid content increased relatively slowly.The properties of the fruit is relatively better preserved;when the red Fuji is treated by freezing-thawing at different thawing rates,the higher freezing rate is less harmful to the hardness,brightness and vitamin C content of Red Fuji,a*value,b*value,titrate acid content and soluble solids content rise relatively slowly,and the properties of the fruit remains relatively good.(2)Experimental study on the temperature strategy of the freeze-thawing process:In this paper,the freezing and thawing treatment of Red Fuji apples with different temperature strategies was carried out by controlling the constant temperature and humidity test chamber,and the freezing temperature and the method in the freezing-thawing process were respectively changed to measure the hardness,color difference,soluble solid content,titrate acid content and vitamin C content of each group of fruits and vegetables.The changes of physicochemical properties were researched.It was found that Shandong Crystal Red Fuji,which was stored in different freeze temperature strategies for freezing-thawing treatment,had lower freezing temperature and thawing treatment of apple fruit,and the fruit propertiesloss would be relatively less;the red Fuji apple for the freeze-thawing treatment The physicochemical properties changes were studied by one-time cooling and stepwise cooling.When the apple fruit was treated by step-down cooling and thawing,the hardness,brightness and vitamin C content of the fruit were less damaged,a*value,b* value,the titrate acid content and soluble solids content rise relatively slowly,and the overall properties retention is relatively better.(3)Measurement of Glass Transition Temperature of Red Fuji Apple:The flesh slice of Shandong Crystal Red Fuji apple were dried by circulating drying oven,and the apple flesh slices with different water content were taken by DSC differential scanning calorimetry.The continuous scanning method with annealing-constant temperature was used to treat the crystal red Fuji.The partial glass transition temperature of the apple flesh slice was measured,the glass transition temperature of the red Fuji apple flesh slice increases with the decrease of water content.The relationship model between water content and glass transition temperature is established to predict accurately the glass transition temperature of crystal red Fuji apple flesh slice under different water content conditions,and provide a theoretical basis for fruit and vegetable vitrification temperature storage.