Optimization of extraction conditions for crude antibacterial proteins/peptides from clarias gariepinus by-products

Abstract

In this paper, acetic acid was used for extracting crude antimicrobial proteins/peptides from by-products of healthy Clarias gariepinus reared at high stocking density. For the extraction process, three variables, namely the concentration of acetic acid, extraction time, and the ratio of liquid to solid were optimized by using orthogonal design L9(33) with the yield and antibacterial activity of the crude proteins/peptides extracts as test indices. The yields of extracted crude proteins were analyzed by range analysis. The results showed that the yield of crude proteins/peptides was different among nine groups, the highest was group 7, producing 1.5842 g (dialyzed in 1,000 MWCO and lyophilized) per 100 g raw material. All the nine extracted samples had similar inhibitory activity against Aeromonas hydrophila, Escherichia coli, Staphylococcus aureus, Citrobacter sp., and Microbacterium sp. except that groups 7 and 9 exhibited higher inhibitory activity against A. hydrophila and E. coli; moreover, the inhibitory activity of group 7 was higher than group 9 against the two bacteria strains. Nine groups did not display obvious different patterns on the SDS-PAGE gel. Based on these results above, the final conclusion was that group 7, namely 10% acetic acid, 12 h extraction, and 5:1 liquid to solid ratio was the best combination for isolating the crude antimicrobial proteins/peptides from by-products of C. gariepinus.