Study On Extending The Shelf-life Of Minimally Processed Water Bamboo Shoots By Ultra High Pressure Treatment

In recent years, ultra high pressure (UHP) technology has received considerable attention as a new nonthermal method for food processing and preservation. UHP processing has good potential for food preservation not only because it favored to overcome the disadvantages caused by traditional heat treatment, but also deal with the problems of energy resources and chemical pollution. In addition, UHP processing was able to satisfy the social requirement of higher quality food, especially for people's higher demand of food freshness, which promoting the emerging of minimally process foods (MPF) and the further research on nonthermal technologies.Minimally processed water bamboo shoots were taken as research object in this paper. The Effect of different pressure and time on the activities of phenylalanine ammonia lyase (PAL) and peroxidase (POD) and the changes of some other quality parameters were evaluated, then the optimum conditions of UHP processing for water bamboo shoots were determined. During storage, the parameters of water bamboo shoots, including weight losing rate, respiratory intensity, relative cell membrane permeability, ascorbic acid content, cellulose content and color value, were measured under the optimum UHP conditions and then the preservation effect of UHP on minimally processed water bamboo shoots was evaluated. In addition, the optimal temperature of storage was confirmed by analyses of respiration intensity, ascorbic acid content and chlorophyll content under different temperature conditions of storage. Minimally processed water bamboo shoots tend to lignification during storage. PAL and POD activities are related with lignin synthesis during the process of lignification, and phenolics are the precursor for the synthesis of lignin. In view of this problem, changes of lignin content, related enzyme activity and phenolics content were researched and their correlation were also studied. Meanwhile, the effect of UHP treatment on these three factors were analyzed for understanding the mechanism of lignification and the reason why UHP treatment was able to inhibit the lignification process.The results showed that the residual activities of PAL and POD were decreased obviously under 600MPa for 10min and the nutrition and quality of water bamboo shoots were preserved well at room temperature (18～20°C). Compared with control, UHP treatment not only had lower weight losing rate, respiratory intensity, relative cell membrane permeability and cellulose content, but also higher retention ratio of ascorbic acid content and stable change of whole color value. At the same time, storage in low temperature (4°C) was better for extending the shelf-life of minimally processed water bamboo shoots and improving the storage quality. Lignin is a complex polymer derived from three precursor substances, including coumaric acid, caffeic acid and ferulic acid. With the regulation of PAL and POD activities through UHP treatment, there was a significant effect on the content changes of three precursor substances. So UHP treatment was able to inhibit the increase of lignin content obviously, and then delay the lignification process of minimally processed water bamboo shoots.These studies suggested that UHP treatment might be an efficient nonthermal alternative for the quality retention of minimally processed water bamboo shoots.