Short communication: Effect of kefir grains on proteolysis of major milk proteins

Abstract 

The effect of kefir grains on the proteolysis of major milk proteins in milk kefir and in a culture of kefir grains in pasteurized cheese whey was followed by reverse phase-HPLC analysis. The reduction of κ-, α-, and β-caseins (CN), α-lactalbumin (α-LA), and β-lactoglobulin (β-LG) contents during 48 and 90h of incubation of pasteurized milk (100mL) and respective cheese whey with kefir grains (6 and 12g) at 20°C was monitored. Significant proteolysis of α-LA and κ-, α-, and β-caseins was observed. The effect of kefir amount (6 and 12 g/100mL) was significant for α-LA and α- and β-CN. α-Lactalbumin and β-CN were more easily hydrolyzed than α-CN. No significant reduction was observed with respect to β-LG concentration for 6 and 12g of kefir in 100mL of milk over 48h, indicating that no significant proteolysis was carried out. Similar results were observed when the experiment was conducted over 90h. Regarding the cheese whey kefir samples, similar behavior was observed for the proteolysis of α-LA and β-LG: α-LA was hydrolyzed between 60 and 90% after 12h (for 6 and 12g of kefir) and no significant β-LG proteolysis occurred. The proteolytic activity of lactic acid bacteria and yeasts in kefir community was evaluated. Kefir milk prepared under normal conditions contained peptides from proteolysis of α-LA and κ-, α-, and β-caseins. Hydrolysis is dependent on the kefir:milk ratio and incubation time. β-Lactoglobulin is not hydrolyzed even when higher hydrolysis time is used. Kefir grains are not appropriate as adjunct cultures to increase β-LG digestibility in whey-based or whey-containing foods.

Key words: milk protein, high-performance liquid chromatography, kefir, proteolysis