Study On The Degradation Kinetic Of VC In Kiwi Fruit And The Dry Processing Technology Of Fruit Powder

With ’Walter’ species of kiwifruit from Wenzhou as raw material, the degradation factor and mechanism of vitamin C (referred to VC) in kiwifruit were studied, and in order to decrease the loss of VC, we also optimized the squeezing processing and spray drying processing. The purpose of this article is to provide a new way for deep processing of kiwifruit. The main contents and the results of this paper were as follows:The nutritive value and officinal hygienically value was high in kiwi fruit, the VC content of the’Walter’species was significantly higher than ordinary kiwi fruit, and its content is five times more than others, which is known as the king of VC. But the natural VC was vulnerable to degradation, which was affected by environment condition in the processing. In this study, we chosen the common factors, such as light, pH, metal ions, air and temperature, and the degradation mechanisms of VC in kiwifruit were discussed. The results showed that, natural light promoted VC decrease, tAA(total ascorbic acid) loss was mainly caused by the oxidation of AA, and generated DHAA(dehydroascorbic acid) and other products. The preservation rate of tAA was higher under acidic conditions, and tAA was the most stable in the solution of pH3.8. The degradation velocity of AA was fastest in the role of Fe3+, compared with other metal ions such as K+, Na+, Ca2+and Al3+. VC was more affected by temperature easily, which followed the model of first-order degradation kinetics, and the activation energy of reversible reaction of AA and DHAA was11.0269kJ·mol-1and32.9584kJ·mol-1, respectively. The influence order of the four factors on VC was:pH> temperature> light> oxygen> metal ions.The free radical absorbers BHT and VE could block the free radical chain reactions by absorbing free radicals. In addition, sodium hexametaphosphate would react with alkaline metal ion (Ca2+, Mg2+) thus generated soluble compounds. Moreover, EDTA-2Na is a metal chelating agent. Hence, the four substances were selected to add to the squzeeing processing for reducing the degradation of VC. What’s more, according to the single factor experiment, VE, EDTA-2Na and BHT were used as the antioxidant additives in squzeeing processing. To optimize the adding amount by using Box-Behnken response surface methodology, the content of AA as the response value, a regression model was made and the equation of expression was showed as follow:Y=-2.6713+156.4303Xi+30.7011X2+99.2276X3+606.3750XiX2-23 8.2500XiX3-145.6875X2X3-1203.5563X12-572.9938X22-864.6188X32.The researches showed that, the main effect relationship of three kinds of antioxidants on the degradation of VC was VE> BHT> EDTA-2Na, and the optimal concentrations of VE, EDTA-2Na and BHT were0.07%,0.04%,0.035%, respectively. Therefore, the preservation rate of AA in kiwifruit was94.17%after squeezing.Concerned with the pre-treated kiwi juice, we developed kiwifruit powder by using spray drying processing. Maltodextrin was selected as drying aids, and the ratio of soluble solids of kiwi juice and maltodextrin was4:6by pre-experiment and single factor experiment. The optimal levels of the parameters in spray drying processing were determined:the temperature of inlet air:175℃, the temperature of outlet air:50℃, the feed quantity:1200mL/h and the feed concentration was25%. The yields of fruit powder, moisture, content of VC as well as color values were the key indicators of kiwifruit powder. Therefore, the above multi-index normalized principal component analysis for a comprehensive index, and the regression model equation was Z=0.6933Y1+0.2193Y2. Through the table with four factors and three levels orthogonal experiment design, it was found that, the optimum condition for the spray drying processing was, the temperature of inlet air:180℃, the temperature of outlet air:55℃, the feed quantity:1000mL/h and the feed concentration:25%. The quality and storage temperature of the fruit powder by spray drying were compared with the ones by freeze-drying. It was showed that, the fruit powder by freeze-drying was more viscous and had higher moisture content than spray drying. Considered the quality of the two kinds of kiwifruit powder and the production costs, results was found that, spray drying was more suitable for developing kiwifruit powder, which was best stored in low temperature.