Oxidative stress and antioxidant systems in Guava (Psidium guajava L.) fruits during ripening.

Two varieties of guava viz., L-49 and Hisar Safeda differing in their shelf lives were analyzed for various components of oxidative stress and of enzymatic and non-enzymatic antioxidative system at different stages of fruit ripening. Indices of oxidative stress viz., lipoxygenase activity, malondialdehyde value and H2O2 content increased throughout during ripening in both the varieties. The extent of oxidative stress was more pronounced in Hisar Safeda (shelf life 3-4 days) than in L-49 (shelf life 7-8 days). Except for superoxide dismutase, activities of all other antioxidative enzymes viz., catalase, peroxidase, ascorbate peroxidase and glutathione reductase increased up to color turning stage and decreased thereafter. Superoxide dismutase activity, however, increased upto ripe stage followed by a decline. Contents of ascorbic acid and glutathione (total, oxidized and reduced) were found to be the maximum at turning and mature stage, respectively. It is inferred that ripening of guava fruit is accompanied by a progressive increase in oxidative/peroxidative stress which induces antioxidant system but not until later stages of ripening. Over-accumulation of ROS due to dysfunctioning of ROS scavenging system at later stages of fruit ripening appears to be responsible for loss of tissue structure as observed in ripened and over-ripened fruits.