Comparison of antioxidant activities of bovine whey proteins before and after simulated gastrointestinal digestion

Oxidative stress caused by free radicals has been implicated in several human disorders. Dietary antioxidants can help the body to counteract those reactive species and reduce oxidative stress. Antioxidant activity is one of the multiple health-promoting attributes assigned to bovine whey products. The present study investigated whether this activity was retained during upper gut transit using a static simulated in vitro gastrointestinal digestion (SGID) model. The capacity to scavenge free radicals and reduce ferric ion of whey protein isolate (WPI), individual whey proteins, and hydrolysates pre- and post-SGID were measured and compared using various antioxidant assays. In addition, the free AA released from individual protein fractions in physiological gut conditions were characterized. Our results indicated that the antioxidant activity of WPI after exposure to the harsh conditions of the upper gut significantly increased compared with intact WPI. From an antioxidant bioactivity viewpoint, this exposure negates the need for prior hydrolysis of WPI. The whey protein alpha-lactalbumin showed the highest antioxidant properties post-SGID (oxygen radical absorbance capacity = 1,825.94 +/- 50.21 mu mol of Trolox equivalents/g of powder) of the 4 major whey proteins tested with the release of the highest amount of the antioxidant AA tryptophan, 6.955 mu mol of tryptophan/g of protein. Therefore, alpha-lactalbumin should be the preferred whey protein in food formulations to boost antioxidant defenses.