Effects of mimetic bio-membrane on free radical and protective enzymes of lightly processed grapes

Effects of mimetic bio-membrane treatments on "red-globe" grapes were investigated. Lightly processed grapes were stored at 0℃ after coating with (0%, 1.2%, 1.5%, 1.8%) chitosan. Dynamic changes in superoxide anion(O₂^-·) producing rate, activities of superoxide dismutase(SOD), peroxidase(POD) and catalase(CAT) were monitored, while malondialdehyde(MDA) contents and electrolyte leakage were measured. Results indicate that 1.5% chitosan mimetic bio-membrane can slow the decrease rate of SOD, POD and CAT activities, reduce the O₂^-· production and MDA accumulation, and maintain the stability of cell membrane. The ripening and senescence process of grape are decayed. Statistics analysis indicate that there is a significantly negative correlation among O₂^-· and SOD, CAT activities(r=－0.975^**，－0.546^**) and a significantly positive correlation between O₂^-· and POD(r=0.442^*). It is suggested that the defensive enzymes play an essential role in restraining O₂^-· production. 1.5% chitosan mimetic bio-membrane can inhibit the decrease of defensive enzyme activities and O₂^-· production. 1.2% or 1.8% chitosan mimetic bio-membranes have no beneficial effects.