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.
