The effect of legume protease inhibitors on native milk and bacterial proteases

Abstract

Protease inhibitors from legume seed extracts (soybean, cowpea and marama beans) and purified soybean protease inhibitor were evaluated with regards to their abilities to inhibit proteases produced by important milk contaminating bacteria, i.e. Bacillus spp. and Pseudomonas spp., and native milk protease, plasmin. Although heattreatment is the most common mean of inactivating enzymes, some heat-stable enzymes can survive the ultra-high temperature (UHT) processing of milk and cause sensory and consistency defects during storage at room temperature. The legume protease inhibitors reduced the activity of plasmin and proteases produced by Bacillus spp. by up to 94% and 97%, respectively, while it showed low inhibitory activity towards P. fluorescens proteases (19%) in a buffer system. The protease inhibitors reduced the activity of plasmin (41%) and Bacillus proteases (50%) in UHT milk, however to a lesser extent as compared to inhibition in the buffer system; while it had little or no effect on proteases from Pseudomonas spp. Legume protease inhibitors show great potential in preventing or reducing proteolytic activity of Bacillus proteases and plasmin and may be exploited in various applications where these proteases cause sensory or consistency defects in the product.