Study On Antibacterial Activities Of Enzymatic Hydrolysates Of Bovine Casein And Application On Chilled Fresh Duck Preservation

Several antibacterial peptides are generated from bovine casein with protease.H aving high antibacterial effect and safty , it is going to be widely used as a kind of natural antibacterial agents.The study compared antibacterial activities of enzymatic hydrolysate produced with various commercially available proteases.Casein hydrolysates were prepared with trypsin,pepsin and papain and both their antibacterial activities towards E.coli ATCC 25922 and hydrolyzing degree were determined.Pepsin was observed to be the only protease to produce antibacterial peptides,while casein hydrolysates generated by the other 2 proteases almost had no antibacterial effect,and there was no positive correlation between their antibacterial activity and hydrolyzing degree.As a result, pepsin was choosen to hydrolyse casein.Single factor level test was adopted to optimize the hydrolysis conditions(pH, substrate concentration,enzyme dosage, and hydrolysis time) of casein hydrolysates by pepsin.The results showed that the high antibacterial activity of casein hydrolysates would be obtained at pH2.0,substrate concentration 9%, enzyme dosage E/S 1:10 and hydrolyzing 5h at 37℃.Using the optimum condition to hydrolysis casein by pepsin. The casein hydrolysates were isolated by ultrafiltration ,then determined the antibacterial effect of each parts. The antibacterial activity of casein hydrolysates toward various bacteria was determined and the influence of conditions including temperature,pH,thermal treatment on antibacterial effects of casein hydrolysate were studied.The results were as follows: The part which molecular weight between 3000Da to 5000Da had the highest antibacterial activity;Casein hydrolysates could inhibit to all three bactenal:Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginoso.And it had most effectively inhibition to Escherichia coli, the inferior inhibition to Pseudomonas aerginoso; Casein hydrolysates was still active against E.coli at 4℃,25℃and 37℃,and the antibacterial activity at 4℃was lower than 25℃and 37℃;,casein hydrolysates performed high antibacterial activity when heated 30min at 63℃,80℃and 100℃, and it exhibited a good thermal stability; Casein hydrolysates had antibacterial activity at pH5.0～pH8.0,but it had more prominent antibacterial activity at pH6.0～pH8.0 than pH5.0.Researching the application of casein hydrolysates on chilled duck preservation, observing the effect of casein hydrolysates used in duck preservation. The results showed that during the storage period casein hydrolysates showed a good bactriostatic action, and it could decreased the loss of duck's juice,and deferred the speed of shearing force fall and fat oxidation to a certain extent. As a result, casein hydrolysates had a certain preservative effect on chilled duck preservaition .The antibacterial effect of casein hydrolyastes increased with the growth of the concentration of casein hydrolysates.The study made experimental basis for the further study of antibacterial peptides used as natural food preservatives in the food industry and provided reliable experimental data for developing casein antibacterial peptides in the future and a new way to chilled duck preservation.