Studing On Physiology, Quality And Browning Mechanism Of Fresh-Cut Colocasia Esculenta (L.) Schott During Refrigeration Storage

Fresh-cut fruits and vegetables are a newly developed product, with the characteristics of fresh, convenient and safe and are accepted by consumers . Cutting brings lots of injure to fruits and vegetables which enhance a series of biochemical reactions , and result in senescence and nutritional lose. Furthermore, cutting destroyed membrane integrity that result in combining phenols and PPO which are isolated by membrane in intact fruits and vegetables. This arises the browning of cut tissue and qualify deterioration of fresh-cut products and shortened shelf life. The thesis studied the changes of biochemitry, physiology and quality in fresh-cut Colocasia esculenta (L. ) Schott to offer the bases of the browning control and new product development. The studied results were as following:1. The respiration rate and MDA content of Colocasia esculenta (L. ) Schott after cutting markedly increased during refrigerated storage. The contents of ascorbic acid and reducing sugar in fresh-cut Colocasia esculenta (L. ) Schott were lower than whole Colocasia esculenta (L. ) Schott. The starch content is about 11.34% of fresh weight in Colocasia esculenta (L. ) Schott which produced in Weihai in Shandong province. Cutting almost no effect on amylase and catalase activiting in Colocasia esculenta (L. ) Schott.2. The contents of total phenols in fresh-cut Colocasia esculenta (L. ) Schott was markedly higher than intact Colocasia esculenta (L. ) Schott, while the content of free phenols in all two Colocasia esculenta (L. ) Schott was not signification different. Cutting reduced the activities of catalase(CAT) and phenylalanine ammonia lyase(PAL) .TP in fresh-cut Colocasia esculenta (L. ) Schott was increased very fast during days in storage and then decreased quickly to the level in intact Colocasia esculenta (L. ) Schott at the day of 12. The ratios of FP to TP was real small in two. The color determined of the values of L~* a~* b~* changed greatly , especially the browning in fresh-cut Colocasia esculenta (L. ) Schott.3. Phenols of Colocasia esculenta (L. ) Schott were mostly located near the peel and in midrib, where the most serious browning presented. The main phenols in Colocasiaesculenta (L ) Schott were chlorogenic acid and tyrosine.4. The PPOof Colocasia esculenta (L ) Schott had its greatest activity at pH 8.0 and the second highest at pH 4.0, while POD had its greatest activity at pH 5.5. The optimal temperatures of PPO from Colocasia esculenta (L. ) Schott and POD were 40 ℃ and 60 ℃ respectively, higher or lower temperatures lose activities observed. Compared with POD, PPO was more heat tolerant.5. The PPO and POD activities were obviously affected by the substrate concentration , which is normally increased to highest level first and then dropped along with the increasing of the substrate concentration. The order of Colocasia esculenta (L. ) Schott PPO to different phenol substrate was xatechol > pyrogallic acid > chlorogenic acid > methyl catechol . The PPO had greatest activity when catechol is used as the substrate, while almost no activity existed when tyrosine and gallic acid as the substrate. The POD activity reached maximum when chlorogenic acid or methyl catechol as the substrate. Since chlorogenic acid was main phenol in Colocasia esculenta (L.) Schott. The effect of PPO on browning should be noticed.6. NaHSO3 and 4-HR inhibited PPO activity, and 4-HR was more effective at concentration less than 3.91 x 10~-5 mol/L. The inhibitory ascorbic acid and L-cysteine was also very effective to inhibit PPO at higher concentration, The inhibited effect of phytic acid citric acid and EDTA was only at high concentration for Colocasia esculenta (L. ) Schott PPO.