Evaluation of antioxidant and antimicrobial activity in peptide fractions of water soluble extract of Koopeh cheese produced in northwest Iran

Abstract

Background: In recent years bioactive peptides in foods and their role in improving consumer health have attracted the attention of food industries. Due to the various biological effects of these peptides, they are known as bioactive compounds and have a high potential to extract and isolate from food sources and applied in the production of new products. The present study was carried out to evaluate the antioxidant and antimicrobial activity of peptide fractions extracted from water soluble extract of Koopeh cheese. Also, peptides were separated into three fractions according to their molecular weight by using ultrafiltration and the best sample was subjected to reverse phase HPLC. Material and Method: In this research, traditional Koopeh cheeses of western Azerbaijan wich prepared from cow's milk, were randomly sampled and physicochemical properties (acidity-salt-fat-total protein-moisture content -ash -PH ) and bacterial (Total counting of bacteria on Plate Count Agar medium) and molds / yeasts (on YGC medium) determined for all samples according to Iranian national standards. Water-soluble extract of all sample were converted to a powder by liofiliser. Electrophoresis analysis was performed to determine the accuracy of separation of peptides and removal of proteins in water-soluble extract after centrifuging and filtration. The peptides concentration in the powder was determined by buret method with the standard curve of bovin serum albumin, and then the antioxidant and anti-microbial activity of peptides was determined in 200 μl of samples with the same concentrations. Activity of peptides on inhibiting free radicals of ABTS, 2 and 2 Azinobis-Ethylbenzothiazolin-6 sulfonic acid and DPPH 2,2-Diphenyl-1- Pyridine Hydrazyl as well as Metal Scalping were studied. Also the antimicrobialactivity of peptides in preventing the growth of E.coli, Bacillus cereus, Staphylococcus aureus, Listeria monocytogenes, Pseudomonas aeruginosa and Salmonella typhi-murium was investigated by Minimal inhibitory concentration metod (MIC). Result: According to the results of the experiments, cheeses produced in different regions differed in physicochemical characteristics, (acidity (0.24-4.2%), protein (12.8- 20.8%),fat (12-35%), ash (2.2-5.9%), salt (2.2-8.04%), moisture (33-51%), pH (4.2-4.9)) which directly affected the process of ripening, proteolysis and formation of peptides. After extraction of water soluble peptides, antioxidant and antimicrobial activity of the extracts were investigated. Also, after examining the antimicrobial properties against the six bacteria, some extracts, especially extracts No. 4 and 5, showed antimicrobial effects against all bacteria especially Pseudomonas and Bacillus. After selecting the extracts No. 4 and 6, according to the total bioactivity characteristics, three fractions (below 2), (between 2 and 10) and (above 10) kDa were prepared by ultrafiltration and re-evaluated by antioxidant methods. Also, after examining MIC fractions on Pseudomonas bacteria, peptides above 10 kDa showed the best performance compared to other fractions. Conclusion: This study found that Koopeh cheese contains bioactive peptides that produced during its unique ripping period (under the soil) with antioxidant and antimicrobial activity. The high antioxidant properties of Koopeh cheese can be the basis for further studies to purify and larg scale production of selected peptides.