Manufacture, isolation and characterization of antibacterial peptides from rainbow trout (Oncorhynchus mykiss)
Trout by-products were used as a source of antibacterial peptides, which were obtained by enzymatic hydrolysis using trout pepsin. The protein hydrolysates exhibited different antibacterial activities against gram-positive and gram-negative bacteria that cause food spoilage and fish diseases. The degree of hydrolysis was found to exert a considerable influence on antibacterial activity, with a significant increase in the observed inhibitory effect at the beginning of hydrolysis. In contrast, a growth-promoting effect on the bacteria was observed for the raw substrate and for hydrolysates with low degrees of hydrolysis. To isolate antibacterial peptides from trout protein hydrolysate (DH 30 %), a combination of ion-exchange chromatography and gel filtration was used. The isolated peptides exhibited approximately nine-fold higher activity than the hydrolysate against the examined bacteria. Cationic peptides with molecular weights below 1 kDa showed the broadest spectrum of activity. One drawback of the use of enzymatic digestion is the high cost of enzymes; thus, the use of the fish’s own pepsin, which is currently not subject to industrial use, offers a cost-reducing alternative to the use of the microbial or mammalian enzyme. A prerequisite for utilization of this enzyme is determination of its enzymatic properties. Therefore, trout pepsin was isolated via the conventional enzyme isolation method , and a detailed enzyme characterization was performed. The isolation method consisted of a series of chromatographic separations preceded by ammonium sulphate precipitation. Apart from a detailed enzyme characterization, the development of an enzyme purification method with good scaling-up properties, low cost and high enzyme yield is important for increasing the potential of fish pepsin as an enzyme source for industrial use. Via aqueous two-phase (ATPs) extraction and polyelectrolyte precipitation with pectin, a cost-reducing method with high enzyme yields (25-30 %) was developed.