| Banana (Musa parasdisiac) is a most famous tropic fruit, which is widely favored for its abundant nutrition, cheerful flavor and aroma. The total yield of bananas reached 68,279,192 tons and was the second largest fruit in the world in 2003. Its yield in our country increases year by year, and our country has become the third largest producer of bananas in the world. Normally, bananas are consumed freshly; but there is a great deal of decay and loss because of poor postharvest handling, packaging, poor and inadequate storage facilities and uncompetitive freight rates. Therefore, to develop processed banana products would be an alternative method for reducing the loss of fresh fruit. Clear banana juice, with highly acceptable aroma, can be used in various foods and drinks and can be well developed. The objective of this dissertation is to develop an enzymatic technology for processing clear banana juice and investigated its stability. The main results are as follows.Mature degree of banana for processing clear juice was determined. There were about 1% starch and 20oBrix of soluble solid content in entirely yellow banana. The largest press supported by entirely yellow bananas was lower than 600g. This kind of banana was found to be suitable for processing clear juice and therefore selected for this study.Thermal stability of polyphenol oxidase (PPO) from banana pulp was studied primarily. The results showed that PPO of banana pulp had a relatively high thermal stability. Therefore, inactivation of peroxidase (POD) was not a suitable index for the complete blanching of banana pulp. PPO had a relatively higher activity in the pH range from 4.0 to 8.4, and peeled bananas should be immerged in 0.05% citric acid solution immediately before blanching.Processing technology of banana juice was established. After blanching at 100℃ for 8min, banana pulp was cooled and mashed. Two orthogonal experiments were designed to optimize conditions for mixed enzymes liquefying banana puree. The optimal processing conditions were obtained as follows: adding 0.08% Pectinex SMASH (v/w), 0.02% acidic α-amylase (w/w) and 0.1% cellulase (w/w) into the puree, the latter was firstly liquefied at 45℃ for 2 hours and then centrifuged; final yield of juice could be reached to 76.43% and the juice was highly clarified (T670>95%) juice yield of was obtained. Component analysis indicated that clear banana juice retained most of the nutritional components in fresh banana.Browning of banana juice during processing was investigated. The results showed that enzymatic browning was the main cause for change in juice color when banana pulps were not entirely blanched. But when banana pulps were highly blanched, non-enzymatic browning was the main cause for browning of banana juice during processing. Oxidation of polyphenols induced browning of banana juice during enzymatic liquefaction, while caramelization and Maillard reaction induced browning during sterilization. The mechanism on banana puree liquefied by enzyme blends was investigated. The relative viscosity of banana puree decreased during enzymatic liquefaction, so juice could be easily separated from banana puree. According to Sepharose CL-6B gel filtration chromatography, the relative molecular weight of alcohol insoluble polysaccharides in banana puree decreased during liquefaction; the relative molecular weight was about 537kDa before liquefaction and about 9kDa after treatment for 120min with enzyme blends. Results showed that enzyme blends could degrade puree polysaccharides significantly. Contents of pectin, starch and alcohol insoluble polysaccharides in banana puree decreased after liquefaction based on component analysis. And content of galactose, the basic neutral sugar in pectin, aribonogalactans, galactomannans and galactans, also decreased evidently. The results demonstrated that cell wall and starch in puree could be decomposed by enzyme blends. Microstructures of banana pulp during processing were observed by optical microscope, it was revealed that enzyme blends...
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