Production Of Cloudy Pear Juice And Cloudy Peach Juice By Enzymatic Liquefaction

Peach is one of most stone fruit, which is widely favored for its abundant nutrient, cheerful flavor and aroma due to its importance;it is the third largest fruit in China after apple and pear. Nevertheless, China is one of the country's productor of peach in the world. However pear is a pomes fruit occupied the second place among deciduous fruit crops grown in ChinaNormally these both fruits are consumed freshly, but there is a great deal of decay and loss because of poor post harvest handing packing, and inadequate storage facilities. Therefore to develop processed peach products or pear products would be an alternative method for reducing the loss of fresh fruit.The objective of this dissertation is to develop an enzymatic technology for processing cloudy pear juice and cloudy peach juice and to investigate their stabilities. The main results are as follows.Some physico-chemical properties of pear and peach were investigated, the dominant component of fresh pear and peach were carbohydrates. The soluble solid content was 9.75 and 12.25 respectively, and pH was 4.07 and 4.1 respectively. Shows obtained also indicated that there were a fair distribution of essential amino acid in both pear and peach.Thermal stability of polyphenol oxidase (PPO) from pear and peach were studied, Results showed that pear PPO was stable at 25 ℃ at pH 7 .However peach was stable at 25 ℃ pH 6.8, 7.0;7.2In peach, peroxidase (POD) was investigated but it was not a suitable index for the complete blanching of the pulp.Pear PPO had a wide activity in the pH range from 4~8 .However in peach PPO varied from the pH range of 4.5~8.The occurrence of enzymatic browning was found to be prominent in the both fruits and findings showed that it could be minimized by blanching with 0.5%citric acid at 100℃ for 7 min.With regards to the processing technology of pear and peach juices, Response Surface Methodology (RSM) and orthogonal experiments were used to optimize conditions of enzymatic liquefaction of pear puree and peach puree. The optimum processing conditions were obtained as follows:In the case of pear adding 0.1 %( v/w) of citozym cloud 100L (cc100L) at 40℃ for 1h and the juice yield could be reached to above 80%Adding 0.05 %( v/w) of enzyme pectinex ultra SPL at 40°C for 30 minutes, in peach puree can increased the juice yield at 78%.Browning of peach and pear juice during processing was investigated .The results showed that the enzymatic browning was main cause for change in juice color when the blanching were not complete .But when the pulps were highly blanched, non enzymatic browning was the main cause for browning of pear or peach juice during processing.The resulting juice exhibited an improved shelf-life and a more stabilized color, with an optimum retention of its components through the manipulation of some influencing factors such as pH, ascorbic acid concentration, storage temperature and degree of pasteurization.The optima pH levels that supported better juice characteristics and longer shelf life were pH 3.8 and pH 4.1 for pear and peach respectively.High temperature storage of 40°C had a negative effect on juice quality and shelf life whereas low temperature (4°C and 20°C) favored juice color stability and quality with the former been more favorable than latter.Cloudy pear juice and cloudy peach juice in this study have a shelf life of approximately 6months.