Physicochemical characterization and in vitro digestibility of β-lactoglobulin/β-Lg f142-148 complexes

The hypotensive peptide β-lactoglobulin (β-Lg) f142-148, known as lactokinin, was shown to bind to bovine β-lactoglobulin variant A (β-Lg A). Complexes of β-Lg A:β-Lg f142-148 were prepared at pH 6.8 and 40 °C in a molar ratio of 1:5, and recovered subsequently by ultrafiltration. Under these conditions 0.9 moles of β-Lg f142-148 bound per mole of β-Lg A. The analysis of the complexes by high performance size exclusion chromatography and laser light scattering revealed that particle size of the complexes was smaller than the β-Lg A particle size. β-Lg A formed polydispersed aggregates at pH 6.4, while a single aggregate peak was observed in the case of the complexes. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry confirmed the presence of the peptide β-Lg f142-148 in the complexes. The in vitro digestibility of β-Lg A and of the complexes determined using pepsin, trypsin, pancreatin, pepsin/trypsin and pepsin/pancreatin were similar, whereas chymotrypsin and pepsin/chymotrypsin digested the complexes more slowly. The binding of β-Lg f142-148 to β-Lg A could delay the hydrolysis of this peptide by digestive enzymes.