It has been demonstrated that in fresh sausage different microbial populations, dominated by either M. thermosphactum, yeasts or lactobacilli, may develop on storage in response to the storage history of the meat used in manufacture and other factors such as the level(s) of HSO3- or SO32- contained. In sausages with a typical microbial content sulphite does not affect significantly the growth of the most numerous contaminants, except during chilled storage when the growth of the Gram negative mesophiles is significantly reduced by sulphite. Experimental data suggests that sulphite reduces the growth rate, but not necessarily the growth yield of microbes. Evidence both statistical, from routine sampling, and from model experiments using sausage components, suggests that microbes principally grow in association with the meat particles, their growth rates and ability to produce metabolites capable of binding sulphite being enhanced by their proximity to meat particles. Considerable amounts of sulphite are lost irreversibly from the sausage during storage (probably by a first-order oxidative reaction). Chilled storage does not reduce the rate of sulphite loss, but it does reduce the rate of sulphite binding. Bound sulphite can be recovered experimentally, as free SO2, by an alkalisation procedure. The existence of oxygen tension gradients within a pack of sausages axe shown by the presence of oxymyoglobin at the periphery and metmyoglobin at the core. The depth of the oxygenated layer decreased during storage, although chilled storage slowed the rate of decrease. The atmospheric oxidation of sulphite which is catalysed by meat pigments (pro- or anti-oxidative) may be affected by the availability of oxygen at the various sampling sites. Sulphite may also be oxidised by the hydroperoxides produced during the similarly catalysed oxidation of unsaturated fats. Such reactions, exhibiting first order kinetics, were demonstrated in model systems by measurement of both free sulphite loss and oxygen uptake rates. In commercially produced sausages the extent of sulphite binding increases during storage. The ability of microbes isolated from sausages, to bind sulphite with their metabolic products was demonstrated using a Schiff's base reaction. Sulphite binding by the solids in sausage (separated by chilled centrifugation) could not be demonstrated consistently. Good correlation, but not equivalence, could be demonstrated between the two methods, steam distillation and electrometric assay, used for the determination of free and bound sulphite levels. The reliability of the estimate of the bound sulphite levels determined was dependent on the procedure used to alkalise the sample. A reduction in the dry weight component of the buoyant layer (obtained from sausage by chilled centrifugation) during storage was noted; its proportional composition (fibrous material v material extracted with propan-2-ol) also altered. Compositional changes, detected using t.l.c., suggested that lipolysis of triglycerides occurred during storage. The rate and extent of such changes was dependent on sampling site, the presence or absence of sulphite and storage temperature. Changes in the level of glycerol in the sausage suggested that large quantities are metabolized during storage.
|Date of Award||1977|