| Due to freshness and convenience, Fresh-cut fruits and vegetables are becoming more and more popular with people of all ages. But compared with the perfect ones, the quality of fresh-cut fruits and vegetables is easy to deteriorate. The research of finding safe and non-toxic natural preservation has becoming a hot topic because of people's safety awareness. OCS, as a biosafe amino polysaccharides, also have the properties of antioxidant and antimicrobial. This study is about the antioxidant of OCS, the effect of browning of fresh-cut apples and the inbition of PPO.The details are as follow.1. The radical scavenging activity of OCS. There have been some reports about the radical scavenging activity of OCS. This study set the ASA and cysteine as the control. The results showed that OCS has a good scavenging activity on DPPH radical, hydroxyl radical and superoxide anion. The IC50 of OCS on DPPH radical scavenging activity is 26.06ug/ml, well the ASA is 2.47ug/ml, the cysteine is 2.43ug/ml. The IC50 of OCS on hydroxyl radical scavenging is 0.27mg/ml, well the ASA is 0.04mg/ml, the cysteine is 0.07mg/ml. Although ASA and cysteine can scaveng superoxide anion at a low concentration, they did't have a thorough scavenging ability. The maximum clearance rate of ASA is 50%, the cysteine is 26.89%. The OCS can reach 58%. In short, the OCS has a lower radical scavenging activity compared with ASA and cysteine.2. The effect of OCS on the browning of fresh-cut apples. The fresh-cut apples which have a thickness of 2.5mm has been separately dipped in solution of distilled water, 1%ASA, 1%OCS for 5min, then, been dryed by absorbent paper. After this treatment, the fresh-cut apples were used to measure all indicators about the qulity of the apples within 10h. All the results made the ASA as positive control, and made the distilled water as negative control. This study has found that oligocatosan can inhibit the browning of fresh-cut apples. Compared with the apples treated by distilled water, the browning index of apples treated by OCS was lower within 4 hours. The OCS treatment had a lower PPO activity than the ASA and distilled water treatment. The content of POD is significantly improved within 10h compared with the other treatments. OCS can also maintain the quality of fresh-cut apples. The weight loss of OCS group is slightly lower than the other groups. The OCS has little effect on total sugar content of fresh-cut apples, but can reduce the titratable acidity, so the sugar to acid ratio has been increased. OCS can inhibit the growth of bacteria on the surface of fresh-cut apples. The content of bacteria on apples treated by OCS is significantly lower than the other groups.3. The inhibition effect from OCS on PPO. From the study above, we know the OCS can inhibit browning and reduce the activity of PPO. The study about the inhibition from OCS on PPO is working through the method of reaction dynamics in vitro. The OCS can inhibit the activity of PPO, and the inhibition rate will increase with the increasing of the concentration of OCS. When the concentration is 5mg/ml, the inhibition rate is 77%. The figure has been made with different concentrations of PPO as abscissa, the reaction rate as ordinate, when the reaction has been added OCS, the curve through the same point, has a smaller sope than the control one. This indicates that OCS is a reversible inhibitor of PPO. The double-reciprocal graph is a set of parallel lines, which indicate the OCS is the anti-competitive inhibitor of PPO.The OCS can inhibit the browning of fresh-cut apples and improve the quality of fresh-cut apple. Although it has a lower activity of radical scavenging, it can improve the activity of POD.The results of inhibition kinetics show that the OCS is the anti-competitive inhibitor of PPO. This study indicates that the major role of OCS on fresh-cut apples is to prevent browning. |
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