The effects of gas-atmosphere packaging (a gas ratio of 80% O₂: 20% CO₂) on keeping quality of raw beef was studied in comparison with stretch-packaging for 12 days of storage at 5°C.
1) The growth of various bacteria on the gas-packaged raw beef was suppressed; the bacterial population was 1/10-1/1.000 lower than that on the stretch-packaged raw beef.
2) On the gas-packaged raw beef, Lactobacillus became predominant with the lapse of storage time, whereas Pseudomonas became predominant on the stretch-packaged raw beef.
3) After 12 days of storage, the volatile basic nitrogen value of the stretch-packaged raw beef was 31.8mg/100g and that of the gas-packaged raw beef 11.9mg/100g.
4) The surface discoloration appeared on the stretch-packaged raw beef after 4 or 5 days of storage, whereas the gas-packaged raw beef showed no change during 8 days of storage.
Thus, the shelf-life of the raw beef packaged with a gas ratio of 80% O₂: 20% CO₂was extended about twice that of the stretch-packaged one.

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Thermal inactivation of Clostridium botulinum type A and B toxins produced in various food samples was determined by the time-to-death method by iv injection into mice. Factors influencing the heat stability of the toxin were further examined. Generally, botulinum toxin produced in vegetables was stable as compared with that in meat. Type B (strain Okra) toxin produced in string beans was especially resistant and the activity was detected even after heating at 80°C for 30min. Heating at 90°C for 10min was necessary for complete inactivation. Its high stability was not shown in the supernatant fluid which did not cotnin the particle of string beans and botulinal cells. By heating purified toxin in some menstrua, string beans extract was protective against heat to some extent. The protection afforded by reduced pH was more prominent for type A toxin than type B toxin. No significant difference was seen in the stability of L toxin (16S) and M toxin (12S).

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