Changes in Some Quality Properties of Kefir during Storage and Inhibition Effect of Water Soluble Extracts on Angiotensin-I Converting Enzyme Purified by Human Plasma

Angiotensin converting enzyme (ACE)-inhibitory activity in water soluble extracts (WSEs) of kefir was investigated. Kefir was produced traditionally using kefir grains and stored at refrigerated temperature for 20 days. During storage period (on 1, 5, 10, 15 and 20 days) in vitro ACE-inhibitory activity in WSEs was determined. ACE was purified from human plasma to determine kinetic parameters. Purified ACE had a specific activity of 20.75 EU.mg(-1), a yield of 16.6% with a factor of 22100. The inhibition effects of kefir on ACE increased at 15 storage days than other storage days. Some microbiological and physicochemical characteristics of kefir were also studied. Counts of presumptive LAB on M-17 and presumptive LAB on MRS in the kefir were about 10(8) CFU.ml(-1) throughout the storage period. Yeast counts were lower than lactic acid bacteria counts and the average of the counts was approximately 10(6) log CFU.ml(-1). Storage period had a significant effect (P < 0.05) on titratable acidity and pH values. On the contrary, it had no significant effect (P > 0.05) on viscosity and serum separation values of kefir.