Physico-Chemical Properties of Milk Powders Treated With Proteolytic Enzymes

Abstract

The use of thermolysin, flavourzyme or trypsin (at their optimal pH and temperature) was studied for the production of milk powder with angiotensin converting enzyme (ACE) inhibitory activity. The treated milk samples were evaluated for non-protein nitrogen (NPN) and ACE inhibitory activity. Milk powders were prepared from each protease, spray dried and evaluated for color, median size, size distribution and bulk density. The reconstituted milk samples were then re-evaluated for ACE inhibition. There was an increase in milk protein digestion with increasing digestion time. A steep increase in ACE inhibition during the first 3 hr (from 0 to 30%) was observed in the samples treated with thermolysin and flavourzyme. From 3–24 hr, fluctuation in the ACE inhibition was observed between 30 and 50%. Therefore, a digestion time of 3 hr was selected for milk powder production. There was no significant (P > 0.05) difference in the bulk density and ACE inhibition among samples. Differences in the particle size and distribution among samples were found. However, the ACE inhibitory activity of reconstituted milk decreased by 10 times compared with samples prior to the drying process. This corresponded with an increase in yellowness (b*) as a result of a Maillard reaction during milk powder production.