Partial Freezing as a Means of Preserving Pacific Salmon Intended for Canning

Abstract

Proteolysis of the flesh surrounding the visceral cavity ("belly-burn") can cause serious spoilage in Pacific salmon. The condition usually occurs in uneviscerated fish that were feeding when caught and develops during storage at temperatures above freezing when storage must be prolonged beyond a few days.The possibility that the proteolysis might be prevented by partial freezing of the fish in salt-reinforced refrigerated sea water at various temperatures between 25 and 29 F was investigated. Round fish, containing large quantities of food in the stomach and intestine could be held at 25 F for 2 weeks without the appearance of belly-burn or bacterial spoilage. Between 25 and 29 F there was a delay in the appearance and a reduction in the incidence of belly-burn.Partial freezing was effective in preventing a darkening of the flesh adjacent to the visceral cavity, a defect that is sometimes observed in fish canned after being stored in an uneviscerated condition for several days at temperatures above freezing. This darkening is apparently the result of the diffusion of pigment from the kidney, liver, and spleen into adjacent flesh.The lipid of the red lateral muscle in partially frozen fish was found to be very susceptible to rancidity, but this defect was overcome by excluding air from the storage tank.Free drip from partially frozen fish after storage (3.2–4.5%) was approximately double that from unfrozen fish, while weight increases during storage tended to be a little greater in unfrozen than in partially frozen fish. Spoilage odours that developed in unfrozen fish during storage were greatly reduced or eliminated in partially frozen fish. Sodium uptake and potassium loss during storage were similar in fish stored under either condition, but magnesium uptake was less in partially frozen than in unfrozen fish.A comparison of the influence of prior storage of the fish, either unfrozen in refrigerated sea water or partially frozen in salt-fortified, refrigerated sea water on the quality of the canned product, showed that each method had some advantages over the other. When the fish were of initially good quality, those stored partially frozen yielded a product quite comparable in quality to those stored unfrozen. Judgment of quality was based on the results of a number of organoleptic and objective tests, including colour, curd formation, firmness of flesh, quantity of free oil, and odour.