Endogenous protease activity in byproducts of pink salmon (Oncorhynchus gorbuscha)

Authors: Bower, Cynthia; MALEMUTE, CHARLENE - 5341-05-00; Bechtel, Peter

Submitted to: Journal of Food Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/26/2009
Publication Date: 3/4/2011
Citation: Bower, C.K., Malemute, C., Bechtel, P.J. 2011. Endogenous protease activity in byproducts of pink salmon (Oncorhynchus gorbuscha). Journal of Food Biochemistry. DOI:10.1111/j.1745-4514.2010.00406.

Interpretive Summary: Hydrolysate production is a low-cost method of preservation that could be employed to decrease the amount of fish byproducts discarded by Alaska’s salmon industry. However, endogenous enzymes within salmon vary with spawning maturity, and must be controlled in the raw material to ensure a consistent hydrolysate. The objective of this study was to evaluate the changes in proteolytic activity of pink salmon as they approach spawning maturity. Both male and female adult pink salmon (Onchorhynchus gorbuscha) were harvested at three different levels of spawning maturity from four different tissue groups (fillets, heads, livers, and viscera). Crude extracts of each tissue were tested for proteolytic activity at three pH levels (pH 3.5, 6.5, and 7.3) using spectrophotometric methods hydrolyzing either casein or hemoglobin as a substrate. Corresponding protein, fat, moisture, and ash levels were also determined. Ocean bright salmon (premium quality with silver scales and no watermark) displayed lower proteolytic activity per mg soluble protein than spawning salmon in their fillets at all three pH levels regardless of gender. Mature salmon (displaying prominent watermarks and loss of scales) generally contained higher quantities of proteases than freshwater spawning salmon in fillet and liver tissues, but not in heads and viscera. This research demonstrated that proteolytic activity changes significantly as salmon move from salt water to their freshwater spawning grounds, which may have implications for processing hydrolysates when pink salmon of different maturity levels are used.

Technical Abstract: Hydrolysate production is a low-cost method of preservation that could be employed to decrease the amount of fish byproducts discarded by Alaska’s salmon industry. However, endogenous enzymes within salmon vary with spawning maturity, and must be controlled in the raw material to ensure a consistent hydrolysate. The objective of this study was to evaluate the changes in proteolytic activity of pink salmon as they approach spawning maturity. Both male and female adult pink salmon (Onchorhynchus gorbuscha) were harvested at three different levels of spawning maturity from four different tissue groups (fillets, heads, livers, and viscera). Crude extracts of each tissue were tested for proteolytic activity at three pH levels (pH 3.5, 6.5, and 7.3) using spectrophotometric methods hydrolyzing either casein or hemoglobin as a substrate. Corresponding protein, fat, moisture, and ash levels were also determined. Ocean bright salmon (premium quality with silver scales and no watermark) displayed lower proteolytic activity per mg soluble protein than spawning salmon in their fillets at all three pH levels regardless of gender. Mature salmon (displaying prominent watermarks and loss of scales) generally contained higher quantities of proteases than freshwater spawning salmon in fillet and liver tissues, but not in heads and viscera. This research demonstrated that proteolytic activity changes significantly as salmon move from salt water to their freshwater spawning grounds, which may have implications for processing hydrolysates when pink salmon of different maturity levels are used.