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 beta-lactoglobulin (beta-LgTH). UF processing selectively enhanced the biofunctional properties of beta-Lg TH with the permeate obtained using a 1 kDa polyethersulfone (HFP-1) membrane having highest in vitro multifunctional bioactivity. Compared to beta-Lg TH, the antioxidant activity was 1.7-fold higher (46,765 +/- 2504 vs. 77,251 +/- 5124 mu mol 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, beta-Lg f(15-20) was shown to have potent antioxidant activity (5.63 mu mol TE/mu mol peptide). Two new ACE inhibitory peptides, IIAEK and IPAVFK, having IC50 values of 63.7 +/- 7.22 and 144.+/- 8 25.3 mu M, respectively, were also identified in beta-Lg TH. This study demonstrates the multifunctional bioactive properties of a beta-Lg TH and its associated UF fractions. (C) 2014 Elsevier Ltd. All rights reserved.