Effect of gamma irradiation on the overall quality of a commercial plain-type yogurt products

To develop a yogurt for sensitive consumer such as infants, children or immuno-compromised patients using gamma radiation, the effects of gamma irradiation on the microbiological, chemical, and sensory quality in a commercial plain yougurt were investigated. No viable coliform bacteria were detected in the sample and approximately a 6 decimal reduction was achieved in the number of total aerobic bacteria by irradiation at 5 kGy. The initial population of lactic acid bacteria observed in the commercial plain yogurt was 8.95 log CFU/g. Gamma irradiation significantly reduced the initial microbial level to 6.47 and 2.85 log CFU/g after irradiation at 1 and 3 kGy, respectively (p<0.05). However, irradiation dose up to 5 k-Gy could not completely eliminate the lactic acid bacteria in commercial plain yogurt. pH, color, lactose and lactic acid content, and sensory quality were not affected by irradiation treatment and storage. Our results suggest that irradiation can improve the microbial quality of commercial plain yogurt without impairing the physicochemical and sensory quality.Y

Reduction of the antigenicity of powdered milk by gamma irradiation

The aim of this work was to examine the reduction in antigenicity of milk proteins in powdered milk by gamma irradiation which is increasingly used for food safety. Skim milk powder samples were exposed to irradiation doses of 1, 5, and 10 kGy. A greater reduction of alpha(S1)-casein and beta(A1)-casein was found than alpha(S0)-casein and beta(A2)-casein by capillary electrophoresis. Competitive indirect ELISA and passive cutaneous anaphylaxis tests using guinea pigs showed a reduction in antigenicity of powdered milk by 10 kGy gamma irradiation. These results indicated that gamma irradiation reduce allergenicity of milk proteins by structural changes of alpha(S1)-casein and beta(A1)-casein, and can be useful for dairy products.Y