OXYGEN Sterilisation

Sterilised sealed cans of foodstufifs, including fruit, vegetables, meat, fish and milk, which should contain only residual traces of oxygen. Cans for beer and soft drinks. 

Industrial bioreactors can withstand up to 3 atmospheres positive pressure. Large fermenters are equipped with a lit vertical sight glass for inspecting the contents of the reactor. Side parts for pH, temperature and dissolved oxygen sensors are a minimum requirement. A steam sterilisation sample port is provided. Mechanical agitators are installed on the top or bottom of the tank for adequate mixing. 

Commercial sterilisation is a more severe process than pasteurisation as the temperature is higher (70-90°C). The process is used to protect food during long-term storage. The oxygen residue should be minimised before heating to reduce deterioration of antioxidants or, in some cases, antioxidants... 

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To attain good distribution of the gas, the freeze-drying system is evacuated to a rough vacuum with its own vacuum pump system. After sterilisation, the H2O2 saturated steam is decomposed into water and oxygen with the help of a catalyser. There are no other by-products. For this reason, this process can be considered as completely harmless to the environment. 

Food products, which undergo undesirable colour changes in the presence of enzymes and oxygen, are sterilised to achieve the inactivation of enzymes, and stored in an inert atmosphere or in the presence of antioxidants. In cases where it is impossible to prevent the degradation of carotenoids (e.g. during the storage of flour or the manufacture of pasta, losses of carotenoids can reach 30-60%), the material can be coloured using synthetic carotenoids. 

The usual aerobic medium is plain nutrient broth, adjusted so that it has a final pH value after sterilisation of 7 2-7 8. The anaerobic medium is the same nutrient broth with the addition of 0 5 per cent cystine, 0 05-0 07 per cent agar, 0 05 per cent glucose, 0 05 per cent sodium thioglycollate and 0 1 per cent of a 1 in 1,000 aqueous solution of resazurin, and adjusted so that the final pH value after sterilisation is between 7-2 and 7 8. Both media may be filled in about 50-ml or 250-ml amounts into tubes plugged with cotton wool or into screw-capped bottles if bottles are used, they should be of such a size that they are not more than two-thirds filled with the aerobic medium, but for the anaerobic medium they should be filled to the neck to minimise the access of oxygen. If the anaerobic medium shows a pink colour extending to more than about one inch below the surface it should be heated in flowing steam for twenty to thirty minutes, and subsequently cooled immediately prior to use. 

Bracco P, Brach del Prever EM, Cannas M, Luda MP, Costa L. Oxidation behaviour in prosthetic UHMWPE components sterilised with high energy radiation in a low oxygen environment. Polym Degr Stab 2006 91 2030-6. 

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