Effect Of Microwave Sterilization On The Quality Of Papaya(Carica Papaya L.) Puree

Papaya (Carica papaya L.) fruit had abundant nutrition and contained a variety of biological activity ingredients which were good for people's health. Puree was one of major process methods for fruit. The traditional sterilization of puree was conductive heat sterilization, which severely affected the quality and aroma of heat sensitive material products such as papaya due to its high temperature,long time, along with the cooking flavor. The microwave sterilization was a kind of radiation sterilization technology, which had the advantages of short heating time, fast heating, energy saving. Besides, the microwave sterilization could better preserve the original nutrients, color and flavor in food. The effect of different microwave power, treatment time, and sample initial temperature on the sterilization effect and quality in papaya puree were investigated and the optimal sterilization process parameters were determined. The article compared the physicochemical properties, storage stability and volatile flavor compounds in papaya puree by microwave sterilization and pasteurization. The main research results and conclusions were as follows:1. Based on the results of single factor experiments, made sure to total number of bacteria,ascorbic acid content, total carotenoids content, POD residual activity and color aberration as the judging indexes. The sterilization conditions were optimized by orthogonal experiment. The optimal sterilization process parameters were as follows:microwave power for 550 w, treatment time for 60 s, sample initial temperature at 25?.Under the sterilization process conditions, microwave treatment could effectively sterilize microorganisms in the papaya puree, and had little effect on the sensory quality indexes,such as nutrition,color and flavor,etc.2. Microwave sterilization (550 w/60 s/25?) and pasteurization (80?/15 min) all met the commercial sterilization requirements. Microwave sterilization and pasteurization all could make PPO and POD activity significantly decreased (p<0.05); microwave sterilization could make the browning degree of papaya puree decreased (p>0.05) while browning degree significantly increased after pasteurization (p<0.05); total phenols content significantly increased (p<0.05) in microwave sterilization samples while total phenols content decreased in pasteurization samples (p>0.05); two sterilization methods had no significant effect on reducing sugar and total acids contents(p>0.05) . The soluble solid content, pH and ?E value in papaya puree increased after microwave sterilization and pasteurization (p<0.05), while the contents of vitamin C, total flavonoids, total carotenoids and antioxidant activity decreased (p<0.05),vitamin C,total flavonoids,total carotenoids content and antioxidant activity were decreased greater and ?E value was increased greater by pasteurization. Those indicated that microwave sterilization could better maintain the color and nutrients of papaya puree; the results of sensory evaluation showed that the papaya puree after microwave sterilization treatment was more closer to control sample than that under pasteurization treatment in color, flavor and taste.3. The counts of total aerobic bacterial, and of yeasts and molds in different treated papaya puree samples nearly kept unchanged during storage at 4? and 25?, which still met the commercial aseptic requirements after 90 days' storage. And the PPO and POD residual activity remained stable during storage. The total soluble solids and reducing sugar content had no obvious change during storage at 4? and 25 ?. The browning degree and?E value of papaya puree increased with storage time increasing. The pH value of papaya puree gradually decreased with storage time increasing while total acid content gradually increased. Ascorbic acid,total phenols,total flavonoids and total carotenoids content in different treated papaya puree gradually reduced during storage,with retention rate of 65.32%, 78.14%, 71.75% and 84.78% respectively after 90 days' storage at 4?; and with retention rate of 47.56%, 70.05%, 65.35% and 78.07% respectively after 90 days' storage at 25? in microwave sterilization samples, which were obviously more than pasteurization samples. Therefore, microwave treatment combined with refrigeration could keep the quality of papaya puree well.4. Kinetic data of changes in ascorbic acid, total phenols, total flavonoids and total carotenoids during storage fitted well into a combined model for both microwave sterilization and pasteurization treated samples. The main contributors to the total antioxidant capacity in papaya puree were ascorbic acid, total phenols, total flavonoids and total carotenoids,which were positively correlated to the changes in antioxidant capacity regardless of storage temperature, with R being 0.868-0.961 for ascorbic acid, 0.965-0.984 for total phenols, 0.824-0.971 for total flavonoids and 0.913-0.982 for total carotenoids.5. The aroma components of different treated papaya puree samples were analyzed using headspace solid phase microextraction (HS-SPME) and gas chromatography mass spectrometry (GC-MS). The results showed that 39, 36 and 38 kinds of aromatic compounds were respectively identified from native papaya puree, microwave sterilized papaya puree and pasteurized papaya puree. The relative content of ketones and hydrocarbons increased significantly,while those of esters and acids decreased, and those of alcohols did not obviously change in microwave sterilization and pasteurization treated samples. The PCA analysis of E-nose and E-tongue indicated that there was obvious difference between pasteurized papaya puree and fresh papaya puree, while the microwave sterilization could keep the original flavor of papaya puree better.