Soybean protein isolate was hydrolyzed consecutively with pepsin and pancreatin followed by separation of the digest on a SP-Sepharose column to obtain angiotensin-converting enzyme (ACE)-inhibitory fractions. Three of the five fractions obtained inhibited ACE activity, with values of the concentration of hydrolysate fraction that inhibited 50% of ACE activity of 1.09, 0.42, and 0.25 mg/ml for fractions 2, 3, and 4, respectively. Kinetic analysis showed that fractions 2, 3, and 4 are non-competitive, competitive and mixed inhibitors of ACE, respectively. Fluorescence emission of ACE was quenched along with a red shift in wavelength of emission maxima in the presence of the protein hydrolysate fractions. Fraction 3 was the most potent free-radical scavenger, while fraction 4 had almost no scavenging effect. We concluded that fraction 3 had the most potential to be used as a bioactive ingredient because of its strong ACE-inhibitory and free-radical scavenging properties.

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Human milk (HM) contains antioxidants such as vitamins (A, C, E) and enzymes (SOD, GPx, CAT) which can reduce radical‐mediated diseases among infants. The current study is aimed at identifying novel antioxidants that might help to reduce some diseases of prematurity and to enhance infant formulas for babies who cannot be breastfed. To achieve our goal, pooled HM samples were freeze‐dried and initially separated into lipid, whey and casein proteins. The antioxidant power of each fraction was measured using the oxygen radical absorbance capacity (ORAC) assay: results were 67.2 μmol Trolox/g for whole milk; 7.1, 13.1, and 205.6 μmol Trolox/g for lipid, whey and casein, respectively. The HM sample was subsequently digested with pepsin, pancreatin and bile salt to mimic the infant digestion system. ORAC (μmol Trolox/g) values were 172.4 for the whole pepsin‐pancreatin digested milk, 234.3 for peptides above 3000 Da, and 146.9 for peptides below 3000 Da. The resulting fractions were separated by preparative HPLC and the fractions dried. Antioxidant capacity of each fraction was obtained and the identity of four antioxidant peptides confirmed by LC‐MS/MS. This work is supported by the Advanced Food and Material Network (AFMNet), the Manitoba Institute of Child Health and Canadian Institutes of Health Research (CIHR).

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