| High pressure sterilization technology is one of the research hotspots in the non-thermal sterilization in agricultural products. It has been put much emphasis on juice drinks industry, because of its advantages of maintaining the original aroma, flavor, and nutrients of the fruits. In this study, fresh kiwifruit was used as raw material, and the formula of kiwifruit pulp beverage was optimized. The effects of pressure, treatment time, various pressure treatments and the sugar content on sterilization of kiwifruit pulp beverage were investigated. The effects of high pressure processing (HPP) on the quality of kiwifruit pulp beverage and the quality changes of kiwifruit pulp beverage during the storage were studied. Finally, the changes of ascorbic acid content in pulp drinks (kiwifruit and citrus) during the storage were analyzed. The main methods and results were as follows.(1) The kiwifruit pulp beverage formula was optimized by orthogonal tests, and the best kiwifruit pulp beverage formula obtained with fuzzy mathematical method was 45% of pulp content,12% of sugar content, and 0.15% of thickener content.(2) The effects of pressure, treatment time, various pressure treatments and the sugar content on sterilization of kiwifruit pulp beverage were investigated. Results showed that the sterilization was improved significantly with the pressure and treatment time increasing. The total number of bacterial colony was less than 10cfu/mL at 300MPa for 5min. There were no molds and yeasts detected at 250MPa for 10min. There was no significant difference in bacteria inactivation rate among the various pressure treatments (200MPa,10 min and 200MPa,5+5 min), and the difference of bacteria inactivation rate was only 3.08%, for molds and yeasts, the inactivation rate was 5%. And the sugar content (Brix=17.30) could increase the resistance of bacteria against pressure. Bacteria inactivation rate of kiwifruit pulp beverage (Brix= 17.30) decreased from 80.34% (Brix=5.95) to 63.75%.Results indicated that the shelf life was longer at 400MPa-500MPa compared to pressure of 300MPa of kiwifruit pulp beverage. Under 300MPa, 10min, total bacteria was less than 10cfu/mL in kiwifruit pulp beverage during 80 days storage at 4℃, but the logarithm of total bacteria was up to 2.45 during 64 days storage at 25℃. Low temperature could inhibit growth of bacteria. Under 400MPa, 10min, total bacteria was less than 10cfu/mL in kiwifruit pulp beverage during 101 days storage at 4℃ or 25℃.(3) The effects of pressure (200MPa-500MPa, 10min) on the quality of kiwifruit pulp beverage were examined. The results indicated that changes in pH, total acid, soluble solids, reducing sugar, total sugar, and color of kiwifruit pulp beverage were not significant after HPP. The original taste, nutrients, and appearance of kiwifruit pulp beverage could be better maintained. Under 300MPa to 500MPa, total phenols, viscosity, and stability of kiwifruit pulp beverage increased.During the storage, there was little impact on pH, total acid, and soluble solids in kiwifruit pulp beverage after HPP (300MPa-400MPa, 10min). But total phenols gradually reduced. Total phenols in kiwifruit pulp beverage decreased by 25.37%(4℃) and 46.19%(25℃) respectively during 35 days storage after HPP of 400MPa for 10min. Pressure of 400MPa led to more distinct total phenols differences than pressure of 300MPa in kiwifruit pulp beverage. Whereas color indices such as total color difference, yellowness, and browning index increased during the storage. And lightness decreased with increased storage time. It was concluded that low temperature can effectively maintain the total phenols, color, and stability of kiwifruit pulp beverage.(4) The effects of HPP (200MPa-500MPa, 10min) on ascorbic acid content of pulp beverage drinks were investigated. The results showed that ascorbic acid content of pulp drinks was found to be not significant after HPP (the maximum different value between samples was 1.22mg/100g). But ascorbic acid content was of great differences during the storage with different pressures processing. The maximum difference between samples was up to 25.16mg/100g at 4℃ for 60 days storage. The retention rate of ascorbic acid content in pulp beverage was 76.77%(4℃) and 27.68%(25℃) respectively during 30 days storage after HPP of 300MPa for 10min. The ascorbic acid degraded faster at 400MPa～500MPa compared to pressure of 300MPa in kiwifruit pulp beverage. Under 4℃, ascorbic acid retention rate was much greater than that at 25℃ in the same processing. Ascorbic acid content was affected largely by the storage time and temperature. Low temperature was more conducive to preserve nutrients in pulp drinks. The same conclusion was obtained in citrus pulp beverage after HPP. As the constituents varied between different materials, the effect of HPP on ascorbic acid content should be specifically analyzed. |
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