Comparative analysis on the distribution of protease activities among fruits and vegetable resources

In this study, a comparative analysis on the distribution of protease activities among 90 plant resources, including fruits and vegetables, has been performed. Protease activities of plant extracts were assayed at different pH values (pH 3.0, pH 7.5 and pH 10.5) using casein as a substrate. Ten fruits and thirteen vegetables show protease activities above 10 U/g. Pineapple, fig and papaya, which are used for commercial protease production, exhibited high protease activities. Additionally, high protease activities were detected in kiwifruit (28.8 U/g), broccoli (16.9 U/g), ginger (16.6 U/g), leek (32.7 U/g) and red pepper (15.8 U/g) at different pH values. SDS-PAGE and zymograms confirmed that various types of proteases existed in the five plant extracts and might be explored. Furthermore, five plant extracts were treated by different protease inhibitors. These results show that there are still many plant resources unexplored, which may be promising candidates for plant-derived protease production.