| Fresh-cut fruits and vegetables were a newly developed product, with the characteristics of fresh, convenient and safe and accepted by consumers. Cutting bringed lots of injure to fruits and vegetables which enhanced a series of biochemical reactions, and resulted in nutritional lose and senescence, Furthermore, cutting destroyed membrane integrity that result in combining phenols and PPO which were isolated by membrane in intact fruits and vegetables, this arised the browning of cut tissue and quality deterioration of fresh-cut products and shortened shelf life.Fresh-cut burdock was one of the most important export products in our country. There were rich phenols in burdock so that it was easy to be brown after cut, which restricted the processing industry of fresh-cut burdock; meanwhile, the content of moisture was in a tendency to decrease which resulted in softening. This thesis studied the browning and quality during storage; furthermore we touched the phenolic substance and PPO of fresh-cut burdock to offer the bases of the browning control during storage.1. Put the burdock under different storage temperature(20℃,10℃and 1℃) to study the browning and senescence, exploreed the influence of storage temperature to browning and quality, the results showed that more lower the temperature led more slight browning and better quality. Low temperature storage inhibited the activity of PPO, then delayed the browning of fresh-cut burdock, at the same time, low temperature storage inhibited the increase of Malondialdehyde(MDA) and total pheno(TP) content, protected the stability of membrane, inhibited the activity of peroxidae(POD), phenylalanine ammonia lyase(PAL), ascorbate peroxidase(Apx), Polygalacturonase (PG), Pectin methylesterase(PE) andβ-Galactasidase(β-GAL) while maintained the activity of superoxidedismutase(SOD) , catalase(CAT) and good appearance.2. The effect of different concentration of 4-HR (50mg/kg,100mg/kg and 150mg/kg) treatment on the browning and the change of enzymes activity during storage at 1℃were studied. The results showed that 4-HR treatment can control the browning of burdock. 50mg/kg treatment was approach the CK, the activity of PPO by 150mg/kg treatment was strong than 100mg/kg treatment during the end storage, resulted in the browning was more serious. 100mg/kg treatment had the best effect, the browning process was significant delayed, and the activity of PPO, POD, PAL and Apx were inhibited. While levels of MDA and the content of TP were decreased. So 100mg/kg 4-HR can effectively inhibited tissue browning and maintain good appearance.3. The effect of different concentration of Ca(AsA)2 (10mM,20mM,30mM) treatment on the quality of burdock during storage at 1℃were studied. The results showed that Ca(AsA)2 treatment can control the browning of burdock, inhibit ethylene production and the activity of PPO, POD, PG, PE,β-GAL, decrease the levels of MDA and the content of TP. 20mM and 30mM treatment had better effect while 20mM treatment maintained the activity of CAT and SOD, so delayed deterioration, promised better quality.4. The phenols extracted from fresh-cut burdock were investigated by ultraviolet scanning and HPLC, the results showed that there is chlorogenic acid. The characteristics of PPO in burdock were studied, it indicated that the optimal pH of PPO was 6.0(there is no activity when pH<3.0 or >9.0); the optimal temperature was 30℃. The PPO had bad heat resistance, the activity quickly decreased after 3 minutes under 60℃and it thoroughly lost after 15 minutes under 80℃. The PPO had greatest activity when chlorogenic acid was used as substrate at low concentration. It indicated chlorogenic acid is important to browning of burdock.Four kinds browning inhibitors on PPO were studied. The results showed that 4-HR was more effective; L-cys can not completely inhibit the activity when the concentration reaches 1mM; Ca(AsA)2 obtained good effect at high concentration. |
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