LIQUEFYING COD FISH FRAMES UNDER ACIDIC CONDITIONS WITH A FUNGAL ENZYME

An acidic protease (Newlase A from Rhizopus niveus, Amano) was evaluated as to its ability to reduce viscosity of ground cod fish frames without excessive hydrolysis. Newlase A had an optimal pH of 3.5 and an optimal temperature of 60C with Azocoll as substrate. The enzyme was more stable in the ground fish mixture at pH 3.5 than it was in citrate:phosphate buffer of the same pH. The enzyme hydrolyzed the fish proteins more extensively and decreased the viscosity of the ground fish more between 40-50C over an extended time period than at its optimal temperature of 60C. It is likely that the lower optimal temperature under these conditions is related to its greater stability at the lower temperatures. The energy of activation of the deactivation of the enzyme was 44.5 Kcal per mol-degree. Over a period of 75 min at 45C there was a decrease in viscosity of the groundfish with added enzyme of some two orders of magnitude. After a 3-h incubation, total soluble protein increased from 30% to 48%; the amount of each molecular size fraction produced decreased in the following order: 1-3, > 10, < 1, and 3-10 kdaltons.