Foaming properties of barley protein isolates and hydrolysates

Foaming properties of the barley protein isolates (BPI) and barley protein hydrolysates (BPH) were investigated by using gas sparging method. BPIs were produced from hulled (BPI-1) and hull-less (BPI-2) barley flours by extracting with 70% (v/v) ethyl alcohol. BPI-2 was hydrolyzed with Subtilisin enzyme using pH-stat technique in order to produce hydrolysates at 3% (BPH-1) and 6% (BPH-2) degree of hydrolysis. Barley flour, BPI-1 and the pellets and supernatants obtained from centrifugation of BPI-1 were examined by SDS-PAGE. The foaming properties of BPIs and BPHs were determined as a function of pH and protein concentration. The results showed that foaming properties were affected by the changes in pH of the medium in isolates and hydrolysates. Foaming properties of isolates were improved below and above the isoelectric pH. The lowest values were observed at pH 6, which is close to the isoelectric pH of BPIs. The protein hydrolysates displayed improved foam stability at basic pH values, while stability was very low at acidic pH values. Generally, at all pH values in both isolates, the highest foam volumes and stability were observed for 1% (w/v) protein concentrations.