Gamma radiation sanitation of fish and blood meals

Abstract

Trade samples of fish and blood meal containing 10–14 per cent moisture were inoculated with 0·2–0·4 × 105/g of Salmonella binza and 0·2 × 106/g of spores of a strain of B. subtilis which had at least the same heat resistance as those of B. anthracis. This material was sealed in Polythene bags, filling them to the maximum, and irradiated in a Co60 γ-cell at ca. 18°C with 0·50, 0·75 and 1·0 Mrad respectively. Bacteriological examinations made ca. 72 hr after irradiation revealed that 0·50 Mrad secured final counts of Salm. binza below 1/25 g (corresponding to ca. six decimal reductions), while 1·0 Mrad reduced viable counts of the spores used to less than 10/g (i.e. four decimal reductions). The latter dose also reduced numbers of naturally present viable Lancefield group D streptococci by at least three factors of ten.

No significant losses of available lysin occurred in any of the materials at any tested dose of γ-irradiation. Autoxidative changes in the lipid fraction of the materials were noticed in fish meal only, but even there solely at dosages ≥0·75 Mrad and limited to about a 100 per cent increase in peroxide value.

These results indicate that the treatment of contaminated dry products of animal origin with γ-radiation at a level up to 1 Mrad is a promising approach to the very much required terminal sanitation of many of such products.