Physiological And Biochemical Changes In Fresh-cut Shoots Of Daemonorops Margaritae During Preservation

Daemonorops margaritae belongs to the family Palmae. As the only one Daemonorops species native to China, it is widespread in tropical and south subtropical parts of southern China, occurring on Hainan Island, southern Guangdong and Guangxi Provinces, and in cultivation extending to southern Fujian and Yunnan Provinces. D. mrgaritae shoots refer to the heart part of its young stems, which have been traditionally consumed by local residents in Guangxi, Hainan and Yunnan. Results of previous analysis of nutritional contents showed that D. margaritae shoots are a good forest vegetable with rich protein and low fat. However, the harvetsed D. margaritae shoots are not easy to store, transport and sell as there are sharp thorns on external multi-leaf sheaths. Development of appropriate postharvest processing and preservation technologies has become an obligatory to prevent postharvest losses of D. margaritae shoots. In studies reported in this paper, the fresh cut technology was employed to process D. margaritae shoots and preservatives or their mixtures were used to treat the packaged fresh-cut shoots stored at a low temperature of 10 degrees C to determine physiological and biochemical changes in the test shoots so as to find out practical preservation methods for D. margaritae shoots. The results and conclusions are shown as follows:1. In the first study, the fresh-cut D. margaritae shoots treated with 1.0% ascorbic acid, 0.25% oxalic acid, 1.0% citric acid, 0.5% potassium sorbate, 2.0% sodium chloride (NaCl), 0.3% calcium chloride, vacuumizing and nitrogen flushing were stored for 21 days and percentage of weight loss, colority, hardness, relative electronical conductivity, and activities of polyphenol oxidase (PPO), peroxidase (POD) and catalase (CAT) were measured at an interval of 7 days for the selection of preservatives. Results showed that 1.0% ascorbic acid, 0.5% potassium sorbate and 0.3% calcium chloride could effectively reduce the increaments of weight loss, hardness, relative electronical conductivity, PPO and POD activities, and decrements of colority and CAT activity. They can be seen as appropriate preservatives for preservation of D. margaritae shoots.2. In the second study, three concentrations of the selected preservatives, ascorbic acid (0.5%, 1.0% and 1.5%), potassium sorbate (0.5%, 1.0% and 1.5%) and calcium chloride (0.3%, 0.5% and 1.0%) used to treat the fresh-cut D. margaritae shoots during storage for 28 days. The colority, hardness, relative electronical conductivity, and activities of PPO, POD and CAT were measured every 7 days for the selection of optimum concentration of preservatives. Results showed that 1.0% ascorbic acid, 0.5% potassium sorbate, 0.3% calcium chloride could effectively maintain the storage quality of frush-cut D. margaritae shoots.3. In the third study, the packaged fresh-cut D. margaritae shoots were treated with 1.0% ascorbic acid, 0.5% potassium sorbate, 0.3% calcium chloride, 0.5% potassium sorbate + 1.0% ascorbic acid, and 0.5% sorbic acid + 0.3% potassium chloride. Percentage of weight loss, colority, hardness, relative electronical conductivity, the activities of PPO, POD, CAT and phenylalanine ammonia lyase (PAL), and contents of vitamin C, soluble total sugar and cellulose were measured once a week during a storage period of 28 days. Results showed that the 0.5% potassium sorbate + 1.0% ascorbic acid could reduce the increments of weight loss, browning degrees and activities of PPO, POD and PAL, and the decrements of colority and CAT activity of the fresh-cut D. margaritae shoots; the treatment of 0.5% potassium sorbate + 0.3% calcium chloride could reduce the weight loss, hardness, relative electronical conductivity, cellulose content and POD activity, and slow down color reduction, decomposition of vitamin C and decrement of CAT activity of the fresh-cut D. margaritae shoots. The optimum preservation period of fresh-cut D. margaritae shoots was 14 to 21 dyas and effectiveness of preservation of mixed preservatives was better than that of a single preservative.4. In the fourth study, the relationship between browning and related enzyme activity of fresh-cut D. margaritae shoots was studied during storage for 28 dyas. The colority and activities of PPO, POD and PAL were measured. The correlation of browning degree and the activities of POD, PPO and PAL were analysised by the Gray correlation analysis method. Results showed that POD and PPO activities play a major role in enzymatic browning of fresh-cut D. margaritae shoots.