ABSTRACT
The microbiological safety, refrigeration shelf-life, and nutritional quality of chicken breast meat were investigated following combined electron-beam irradiation and cooking under vacuum (sous-vide). Chicken breast meat inoculated with 106 CFU/g of Listeria monocytogenes was irradiated with an electron beam at doses up to 3.1 kGy under vacuum in barrier bags, cooked in a boiling water bath for 3 min 45 s (previously determined to achieve an internal temperature of 71.1°C), and stored at 8°C for up to 5 weeks. Listeria was undetectable in samples treated with combined sous-vide and irradiation at 3.1 kGy, but the organism survived the sous-vide treatment without irradiation and multiplied during storage. A similar study, conducted with uninoculated chicken breast meat, revealed that the product which received both irradiation (3 kGy) and sous-vide treatment had a shelf-life of at least 8 weeks at 8°C, whereas the unirradiated samples treated sous-vide spoiled in 16 days. Listeria was undetectable in combination treated samples, but some of the unirradiated sous-vide samples tested after long storage showed high levels of Listeria . Some loss of thiamine occurred with the combined treatments.
ABSTRACT
The influence of suspension in a phosphate buffer and various lipid media on the heat and radiation resistance of Clostridium sporogenes PA3679 was examined. Lyophilized spores were suspended in vegetable oils, animal fats, synthetic triglycerides, glycerol, or phosphate buffer, and their radiation and heat D]0 values (dose or time required for 90% inactivation) were determined. Radiation D10 values in the lipids were much higher than in the phosphate buffer. Radiation D10 values in glycerol and animal fats were higher than in the vegetable oils and the synthetic triglycerides. The D10 values in triolein and tributyrin were close to each other, suggesting that chain length may not be a significant factor in radiation resistance. The heat D10 value of the spores in a phosphate buffer at 95 ± 1°C was close to that in beef fat and was much higher than in any of the other lipid media tested. The heat D10 value in triolein was greater than twice that in tributyrin, suggesting that the fatty acid chain length is an important factor in the heat resistance of the spores in triglycerides. The effects of various nonaqueous suspension media on the radiation-induced thermosensitivity of spores were also determined. A comparison of the heat D10 values of the spores with and without prior irradiation in various media showed that irradiation at 5.0 kGy greatly increased their heat sensitivity.
ABSTRACT
Radiobiological studies were carried out with three strains of Listeria monocytogenes . Resistance characteristics were determined under a variety of conditions. For one strain (CFPDC), the D10 values were 0.18, 0.21, and 0.44 kGy when subjected to gamma irradiation in phosphate buffer (pH 7.0), trypticase soy broth containing yeast extract (TSB-YE), and in poultry feed, respectively. For this strain, D10 values in poultry feed determined by using 60Co gamma rays or 10 MeV electrons as radiation sources were almost identical. D values for gamma irradiation of TSB-YE cultures were 0.21, 0.25, and 0.46 kGy for CFPDC, Scott A, and 81-861 strains, respectively.
