Thermal death time studies on anaerobic spore formers : investigations on Australian strains of clostridium botulinum.

Canning is the general term applied to the heat preservation Of foodstuffs in sealed containers from which air is partially excluded. The heat treatment (process) is given in order to destroy the normal Microbial flora of the fresh food that would otherwise grow and spoil it. Of the various types of micro-organisms found on fresh material, vegetative forms and the spores of moulds and yeasts are easily destroyed but bacterial spores are more resistant and if they survive the heat, processes may spoil the canned product. Only light processes are given to acid products, i.e. pH values lower than 4.5, such as canned fruits and preserves, because the spores of the majority of bacterial species are unable to develop in these acid products. For the non-acid foods like vegetables and soups, longer processes are required to destroy all spores. In order to determine adequate heat processes for destruction of the spores, it is necessary to know the resistance to heat in a liquid substrate of a known number of spores. At any temperature the time taken to destroy all of a given number of spores is known as the Thermal Death Time (T.D.T.). If supplied with the thermal death time data and the rate of penetration of heat into the can, it is possible to calculate an adequate heat process for the heat preservation of canned non-acid foodstuffs. However, not only is it necessary to destroy the spores of common spoilage types but also the spores of Clostridium botulinum which produces a toxin dangerous to man, and the development of this organism within the product would be a serious health hazard. Therefore, in determining adequate heat sterilising processes for canned foods, a kftowledge of the maximum heat resistance of spores of Cl. botulinum is of the utmost importance. A process for the absolute destruction of this organism is a minimum standard for all products with pH values greater than 4.5.