Selective enrichment of bioactive properties during ultrafiltration of a tryptic digest of β-lactoglobulin

Whey proteins are rich sources of bioactive peptides which may play a role in the dietary management of chronic diseases. Fractionation via ultrafiltration (UF) was investigated for the enrichment of antioxidant, dipeptidyl peptidase IV (DPP-IV) and angiotensin converting enzyme (ACE) inhibitory activity in a tryptic hydrolysate of β-lactoglobulin (β-Lg TH). UF processing selectively enhanced the biofunctional properties of β-Lg TH with the permeate obtained using a 1 kDa polyethersulfone (HFP-1) membrane having highest in vitro multifunctional bioactivity. Compared to β-Lg TH, the antioxidant activity was 1.7-fold higher (46,765 ± 2504 vs. 77,251 ± 5124 μmol Trolox equivalent/100 g dw; P < 0.05), DPP-IV half maximal inhibitory concentration (IC₅₀) decreased threefold (1.6 ± 0.31 vs. 0.53 ± 0.05 mg/mL; P < 0.05) and there was a twofold reduction in ACE IC₅₀ (0.131 ± 0.005 vs. 0.068 ± 0.018 mg/mL; P < 0.05). The multifunctional peptide VAGTWY, β-Lg f(15-20) was shown to have potent antioxidant activity (5.63 μmol TE/μmol peptide). Two new ACE inhibitory peptides, IIAEK and IPAVFK, having IC₅₀ values of 63.7 ± 7.22 and 144.8 ± 25.3 μM, respectively, were also identified in β-Lg TH. This study demonstrates the multifunctional bioactive properties of a β-Lg TH and its associated UF fractions.