The paper deals with refrigeration at peri-cryoscopic temperatures as a measure to preserve rainbow trout.
Effects of superchilling and storage at -2 "C on sensory, physico-chemical, and microbiological changes in the fish are analysed.
The industrial practice has been till now concerned with preventing fish spoilage especially by means of icing or freezing. Additionally, as early as before the World War 11, superchilling began to be used, particularly to preserve marine fish. Rather extensive studies on the latter method and its application were carried out in the sixties, following the introduction of the method on board of Portuguese vessels [ 131. British workers improved the system and produced new technological developments [14, 17, 181. At the same time, superchilling was being studied in the Federal Republic of Germany [20], Canada [28], USA [29], and Soviet Union [l 1, 12, 21, 22, 231, the experimental work being extended to include some other food products.
A marked development in freshwater-fish production has been recently observed in Poland and other countries. Regardless of marketing these fish when live, preserving them by refrigeration becomes important. Freezing, commonly used for fish, is not always purposeful and desired. In some cases, particularly during a short-time storage, superchilling may be more useful and feasible as it produces less damage then freezing does.
The aim of the present work was to evaluate the keeping potentials of superchilled rainbow trout.
Material and methods
Matkrial
The work was carried out on rainbow trout (Satmo gairdneri Richardson), about 25 cm long, caught in autumn from culturing ponds. Some fish were superchilled whole and the others were gutted before superchilling. Superchilling was effected at -30 @C in a Feutron experimental air tunnel. When the fish thermal centre reached -I 'C, the fish were packed in polythene bags and stored for 30 days at --2 "C. The material was analysed at intervals of 5 days, after allowing the fish to thaw for 1 h at room temperature. Microbiological assays of the fish skin were performed on smears taken with sterile cotton wool swabs from a standard 10 cm2 area. Microbiological assays of gills and muscles were made on samples of 2 g taken aseptically and homogenized with an appropriate amount of peptone water. The raw material for chemical assays was broken down in a laboratory grinder.