Antioxidant, ACE-Inhibitory and antibacterial activities of Kluyveromyces marxianus protein hydrolysates and their peptide fractions

Background: There has been evidence that proteins are potentially excellent source of antioxidants, antihypertensive and antimicrobial peptides, and that enzymatic hydrolysis is an effective method to release these peptides from protein molecules. The functional properties of protein hydrolysates depends on the protein substrate, the specificity of the enzymes, the conditions used during proteolysis, degree of hydrolysis, and the nature of peptides released including molecular weight, amino acid composition, and hydrophobicity. Context and purpose of this study: The possibility of using strain of Kluyveromyces marxianus as a source of yeast extract with antioxidant, antibacterial, and ACE-inhibitory activity was the subject of this research. Results: Autolysis and enzymatic hydrolysis were completed respectively, after 96 h and 5 h. Overall, trypsin (18.52% DH) and chymotrypsin (21.59% DH) treatments were successful in releasing antioxidant and ACE inhibitory peptides. Autolysate sample (39.51% DH) demonstrated poor antioxidant and ACE inhibitory activity compared to trypsin and chymotrypsin hydrolysates. The chymotrypsin 3-5 kDa (301.6+/-22.81 mu M TE/mg protein) and trypsin < 3 kDa (280.16+/-39.16 mu M TE/mg protein) permeate peptide fractions showed the highest DPPH radical scavenging activity. The trypsin < 3 kDa permeate peptide fraction showed the highest ABTS radical scavenging (1691.1+/-48.68 mu M TE/mg protein) and ACE inhibitory (IC50=0.03+/-0.001 mg/mL) activities. The fraction (MW=5-10 kD) obtained after autolysis treatment showed antibacterial activity against St. aureus and Lis. monocytogenes in well diffusion screening. The minimum inhibitory concentration (MIC) value was 13.3 mg/mLagainst St. aureus and Lis. monocytogenes calculated by turbidimetric assay and it showed bactericidal activity against St. aureus at 21.3 mg/mL protein concentration. Conclusions: Altogether, the results of this study reveal that K. marxianus proteins contain specific peptides in their sequences which can be released by enzymatic hydrolysis and autolysis.