Effect of blackberry and raspberry juice on whey protein emulsion stability

The effect of raspberry and blackberry juice on oil-in-water (o/w) emulsion oxidative stability was investigated with different concentrations of whey proteins and rapeseed oil. The extent of lipid oxidation was measured by determining conjugated diene hydroperoxides and thiobarbituric acid reactive substances and that of protein oxidation by loss of natural tryptophan fluorescence and formation of protein carbonyl compounds. In addition, the anthocyanin colour stability and emulsion turbidity were measured. The increasing concentration of whey proteins and berry juices led to enhanced stabilization of the interface formed during emulsification. The anthocyanin concentration and colour decreased during oxidation leading to whiter emulsions. Raspberry juice provided a better overall antioxidant protection towards lipid and protein oxidation compared to blackberry juice. The antioxidant activity of berry juices towards lipid oxidation varied with concentration. The antioxidant activity increased with increasing concentration of berry juices. In conclusion, red berry juice anthocyanins, as well as other phenolic compounds, act as antioxidants improving the oxidative stability of whey protein emulsions. However, the antioxidant protection is different towards protein and lipid oxidation, and is also affected by other components present.