Qualitative & quantitative analysis of amino acids & peptides of whey in selected curd brands produced in Sri Lanka

Abstract

Objective: Consuming curd reduces hypertension by inhibiting the enzyme Angiotensin Converting Enzyme (ACE). ACE inhibiting peptides in curd (mainly containing proline amino acid) vary with the bacterial species used and milk type. A preliminary study was carried out to analyze qualitatively and quantitatively amino acids and peptides in two commercially available brands of Sri Lankan curd.

Methods: Whey fractions were isolated from two different brands using high speed centrifuge and amino acids and peptides present were analyzed using paper chromatography. The amino acid and peptides were identified matching with the distance migrated by standard amino acids and the peptides and by absorbance method. Concentrations of each amino acid were calculated against the amino acid standard that matched the most.

Results: Whey fractions of both brands had seven different fractions. First two were peptides and other five were amino acids. The amino acids matched with glycine, tyrosine, proline, valine and isoleucine standards.  Third amino acid and second peptide gave yellowish purple colour with higher absorbance at 440 nm indicating the presence of proline residues. Total amino acid concentration was higher in brand 2 (4.66 mg/mL) than brand 1 (4.25 mg/mL). Peptide concentration was higher in brand 2.  Peptide containing proline amino acid was also higher in brand 2 suggestive of higher ACE inhibiting activity.

Conclusion: The amino acid and peptide concentration varies with different brand of curd and hence contribute to different extent of ACE inhibiting properties