Use of macroporous adsorption resin for simultaneous desalting and debittering of whey protein hydrolysates

Whey protein isolate (WPI) was hydrolysed to whey protein hydrolysates (WPH) of degree of hydrolysis equal to 15% using Protease N 'Amano' G (IUB 3.4.24.28) in a batch reactor at 55 degrees C and pH 7.0 according to the pH-stat procedure. Ash was removed by adsorbing WPH onto macroporous adsorption resins (MAR). Following rinsing with deionised water, desorption was achieved by washing with 20%, 40% and 75% alcohol (v v(-1)) to obtain the three fractions HS20, HS40 and HS75. Ash reduced from 15.71% (WPH) to 4.38% (HS20), 2.02% (HS40) and 2.38% (HS75). Similarly, the protein content was enriched from a low of 64.89% (WPH) to 94.74% (HS20), 95.32% (HS40) and 92.00% (HS75). The fractions were analysed for surface hydrophobicity (SHo), angiotensin-I converting enzyme (ACE) inhibition, emulsifying activity index, total amino acids composition and molecular weight distribution. Fraction HS75 was objectionably bitter, showed superior ACE inhibition (lowest IC50), had the highest content of hydrophobic and essential amino acids and contained about 71% of < 600 Da with no fractions exceeding 4142 Da. Desorption with alcohol weakened the hydrophobic interaction forces between the peptides and resins and hence eluted the peptides, with the bitter HS75 being extracted.