Effects of casein- and whey protein–dextran conjugates on the stability of bog bilberry anthocyanin extract

Bog bilberry ( Vaccinium uliginosum ) contains a high concentration of anthocyanins. Anthocyanin stability depends on many factors, including pH, temperature and composition of food matrices in a product, such as protein and polysaccharide. The effect of casein–dextran and whey protein–dextran conjugates on the stability of bog bilberry anthocyanin extract (BBAE) was investigated in an accelerated model system. Cyanidin-3-glucoside was the main anthocyanin (79%) found in BBAE. The cyanidin-3-glucoside content, absorbance and ABTS [2, 2-Azinobis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt] radical scavenging activity of BBAE significantly ( P  < 0.05) decreased after heating at pH 8.0 and 80 °C for 60 min. The addition of casein–dextran and whey protein–dextran conjugates significantly ( P  < 0.05) prevented cyanidin-3-glucoside from degradation, and increased the absorbance and ABTS radical scavenging activity of heated BBAE. The protection of casein–dextran conjugate on BBAE was significantly higher ( P  < 0.05) than that of whey protein–dextran conjugate. The results suggest that protein–dextran conjugates have the ability to stabilise BBAE.