Characteristics of proteinases and lipases produced by seven Bacillus sp. isolated from milk powder production lines

Abstract

Seven Bacillus strains isolated from milk powder production lines were grown in two selective media. All the strains produced extracellular and intracellular proteinase and lipase activity, but at different levels. Proteolytic activity was generally highest at neutral to alkaline pH. Inhibitor studies showed that two types of proteinase were produced — a serine proteinase and a metallo-proteinase. Not all of the strains produced both types of activity and those that did produced different levels. All strains produced a 1,3-specific lipolytic activity that showed a preference for short-chain fatty acids. The lipolytic activity had greater heat stability than the proteinase activities, but all would clearly survive pasteurisation at 72°C for 2 min in milk. Further, the enzymes are likely to survive any heat treatments applied during commercial milk powder manufacture. The enzymes remain active in milk powder during storage, and are therefore likely to be active in milk products made from recombined milk powder.