Effcet Of High Pressure Treatment On Sterilization, Enzyme Inavtivation And Qualities Of Strawberry Juice

In recently years, nonthermal food processing technology is a interesting topic in the food processing. Of these nonthermal food processing technologies, high hydrostatic pressure (HHP) has proven to be effective in eliminating microbes and maintaining a good food quality. Those complied with consumer demands for high quality foods with natural flavor and taste, fresh, health, and safe. In this paper, HHP technology was applied to strawberry juice, the effects of treatment pressure and time on strawberry juice microbes, enzymes, and nutritional qualities were investigated. The changes of physical and chemical quality of strawberry juice storage in different high pressure treatments were discussed. The main conclusions were summarized as follows:(1) Study on the bactericidal of HHP strawberry juice displayed that the treatment of300MPa for15min and400MPa for5min on strawberry juice, the total aerobic bacteria count, yeasts and molds count corresponded to commercial sterile. HHP treatment of300MPa for15min decreased the number of yeasts count from2.3×104cfu/mL reduced to1cfu/mL and the total aerobic bacteria count from3.17×104cfu/mL reduced to35cfu/mL. More than the treatment of500MPa with15min and20min with400MPa, the molds and yeasts were all killed in strawberry juice.(2) The effect of the high pressure processing on the polyphenol oxidase in strawberry juice had weak passivation effect, but the pectin methyl enzyme had a good passivation effect after HHP treatment. The best passivation condition of polyphenol oxidase was600MPa for40min, the residual enzyme activity was67.52%. More than600MPa pressure and HHP effect of blunt pectin methyl enzyme increased significantly. The critical point of high pressure treatment on PME inactivation of enzymes in strawberry juice was600MPa for20min. The best passivation condition of pectin methyl enzyme was600MPa for40min, the residual enzyme activity was42.14%.(3) The content of ascorbic acid was decreased with the increase of pressure and time, but the treatment of600MPa for40min retained83.8%of ascorbic acid. The values of L*, a*, b*were decreased by the treatment of400MPa. The values of L*, a*, b*were significantly increased by the other treatments. HHP treatment on strawberry juice had a little effect on the colour of strawberry juice. HHP treatment could maintain or improve the colour of strawberry juice well. The browning degree was significantly decreased by the treatment of300MPa and400MPa. However, the treatment of500MPa and600MPa were increased the value of browning degree of strawberry juice. The suspension stability and the viscosity of strawberry juice increased with pressure and time increasing. The turbidity decreased with pressure and time increasing.The pH, the total soluble solids, titratable acidity, total phenols and anthocyanins and other physical and chemical qualities of strawberry juice were not significantly influence of HHP treatment.(4) The treatment of300MPa increased the number of microbial significantly during the25℃storage. The rest treatments on strawberry juice made the colony of yeast and mold count corresponded to commercial sterile. Total soluble solids and titratable acid storage period had no obvious change. The value of pH decreased during4℃storage. However, the value of pH showed decreased from0to3days and increased3days later during the25℃storage.During the different storage condition, the contents of total phenol, ascorbic acid and anthocyanins were decreased significantly with the storage time increasing. The color of juice reduced gradually with storage time increasing. During the storage, the value of brightness, red light, yellow light was decreased. The value of brightness of strawberry juice increased by the heat-treatment, but the value of red light and yellow light decreased. The colour degradation of juice in low temperature storage had slower rate than that in room temperature storage. The impact of HHP treatment on total aberrations of strawberry juice was small. HHP treatment combined with low temperature keep the color of strawberry juice well. The suspension stability and viscosity of juice decreased with storage time increasing. The turbidity of strawberry juice increased with storage time increasing. However the heat-treatment made no obvious change of turbidity of strawberry juice in storage period. Compared with heat treatment, the HHP treatment maintains better quality of strawberry juice.