Okara residue as source of antioxidants against lipid oxidation in milk enriched with omega-3 and bioavailability of bioactive compounds after in vitro gastrointestinal digestion.

The residue from soy processing (okara) was evaluated for phenolic compounds, flavonoids, radical scavenging activity and reducing power ability. The ability of okara to decelerate the oxidation of omega-3 fatty acids caused by light exposure in a milk matrix, as well as its bioavailability after in vitro digestion, were investigated. Okara contained phenolic compounds (106.7 mg gallic acid equivalents (GAE)/100 g) and flavonoids (32.7 mg quercetin equivalents/100 g) and showed antioxidant activity. The addition of okara to omega-3 fatty acids-enriched milk inhibited the production of conjugated dienes and malonaldehyde during 8 days of storage compared to the control (without okara), particularly at the higher (3 g/L) than lower inclusion concentrations studied (1 and 2 g/L). The bioavailability assay demonstrated that polyphenols (41 mg GAE/100 g) were still present after in vitro digestion and had antioxidant activity. Okara, which is considered a residue and is discarded, can potentially be used as an antioxidant ingredient for the enrichment of foods.