Selective hydrolysis of α-lactalbumin by Acid Protease A offers potential for β-lactoglobulin purification in whey proteins

Whey protein (WP) purification exploits selective heat and salt stabilities. Proteins are denatured. WP α-lactalbumin (α-La) and β-lactoglobulin (β-Lg) are resistant to trypsin (EC 3.4.21.4) and pepsin (EC 3.4.23.1), respectively. This work was to selectively hydrolyse α-La in WP isolate (WPI) using Acid Protease A in acid pH in order to selectively remove α-La while retaining high amounts of native β-Lg. WPI was hydrolysed over a range of temperature (30 °C, 37.5 °C and 45 °C) and pH (2.5, 3.0 and 3.5). The enzyme reaction was stopped using 1 mol L−1 NaOH. Residual protein was quantified using RP-HPLC. Under low pH (2.5) and low temperature (30 °C), the degree of hydrolysis (DH) was lowest (1.90 ± 0.16%), with limited hydrolysis and incomplete depletion of α-La. In high pH of 3.5 at 45 °C, a DH of 7.35 ± 0.06% was reached (with 50 g L−1 substrate), and α-La was depleted. Electrophoresis and RP-HPLC revealed selective depletion of α-La while β-Lg was resistant. Optimal depletion of α-La was 50 g L−1 WPI hydrolysed at 37.5 °C at pH 3.0 for 120 min. With this method, enzymatic purification of native β-Lg and co-production of potentially bioactive peptides from α-La is demonstrated.