Digestive lipases from Chinook salmon (Oncorhynchus tshawytscha) and New Zealand hoki (Macruronus novaezelandiae ) -- purification, characterization, application and immobilization

Lipases from two New Zealand commercial fish species, Chinook salmon (Oncorhynchus tshawytscha) and New Zealand hoki ( Macruronus novaezelandiae) were investigated. The lipases were extracted from the pyloric ceca and purified by affinity chromatography and gel filtration. Calcium ions and sodium cholate were absolutely necessary both for lipase stability in a polyacrylamide gel and for optimum activity against p-nitrophenol esters. Both fish lipases had a pI value of 5.8 +/- 0.1, were most active at 35°C, were thermally labile, had a pH optimum of 8-8.5, were more acid stable compared to other fish lipases studied to date, and showed good stability in several water-immiscible solvents. The salmon enzyme was an overall better catalyst for the hydrolysis of p-nitrophenyl caprate based on its higher turnover number and lower activation energy for the hydrolysis reaction. Based on their chemical and catalytic properties, the salmon and hoki enzymes were classified as carboxyl ester lipases. Chinook salmon and hoki lipases were then evaluated as flavour modifying agents in dairy products. Cream was either incubated with the fish lipases or two commercially available lipases used in dairy flavour development. The fish enzymes were more similar to calf pregastric esterase in terms of the total amount and types of fatty acids released (mainly short chain) over the course of the reaction. The highest specificity was towards the key dairy product flavour and odour compounds, butanoic and hexanoic acids. Immobilization of the salmon lipase was then carried out on two hydrophobic supports. Salmon lipase immobilized on octyl-Sepharose had 40- and 10-fold higher activity (on a dry weight basis) against a tributyrin emulsion than the same lipase immobilized on Lewatit VP OC 1600 and a microbial lipase immobilized on Lewatit (Novozym 435), respectively. Salmon lipase-octyl-Sepharose was highly active against both ghee and fish oil emulsions, but salmon lipase-Lewatit and Novozym 435 had very low activities against the fish oil emulsion.;The potential for flavour enhancement in dairy products with both fish lipases was demonstrated based on the free fatty acid composition and sensory characteristics of lipase-treated creams. In addition, the immobilized salmon lipase showed potential for low temperature modifications of emulsified lipids.