Research On Key Technology Of The Litchi Juice Crushing

Traditionally litchi is mainly considered as a fresh fruit for eating, a small part for processing. Because of its short harvest period, exuberant metabolism and easy to decay after harvest in hot summer, it is difficult to store and transport litchi, so processing of litchi is important to extend the supply period. During the production of litchi juice, litchi is easy to brown staining by enzyme catalysis during the crushing, pressing process which was influent the flavor and the nutrition of litchi. It is also the important reason to hinder the development of litchi industry.According to the series methods in this experiment, it tested the polyphonic oxidase's characteristics and determined the best enzymatic environment of litchi juice. According to the change of litchi juice which was tested by different methods during the storage period, the optimal storage parameters were determined. At the same time replacing oxygen with nitrogen as blanket gas during the litchi juice processing, which inhibit the activities of oxidase catalysis and control browning. The conclusions were as followed:1. If pH is too high or too low, it both goes against the extraction of PPO. Adjusting pH can effectively inhibit the activity of PPO. The Inhibitor can also control the activity of PPO to some degree. Relative strength index of inhibitors were:ascorbic acid> citrate> EDTA,40℃is the optimum reactive temperature of litchi PPO activity.2. The browning of litchi juice is the major factor for the color change. The output of litchi juice is high by cold squeezing in room temperature which can not be saved easily. The color of the litchi juice by cold squeezing is clear. The speed of browning is slow during the storage. The Vc in litchi juice is unstable and would lost seriously during the storage. Browning index of litchi juice is positively correlated to the transmittance and the coloring intensity, and is negatively correlated to the total acid content.3. Gernerally the PPO of litchi juice in air is 11000U·g-1·min-1, the PPO of litchi juice in the nitrogen is 2333U·g-1·min-1.Replacing the air with nitrogen in the device which reduce the Oxygen Concentration of the environment. This behavior can obviously affect the browning degree of litchi pieces and the PPO of it.