Addition of alpha-ketoglutarate enhances formation of volatiles by Staphylococcus carnosus during sausage fermentation

The effect of leucine and alpha-ketoglutarate addition on transamination of branched-chain amino acids was studied in model minces inoculated with Pediococcus pentosaceus and Staphylococcus carnosus. Leucine addition changed the ratio of volatile breakdown products of leucine, isoleucine and valine but not the total amount of the volatiles and it was concluded that the amount of free amino acids does not limit transamination of amino acids. The addition of alpha-ketoglutarate resulted in increased levels of methyl-branched aldehydes and insignificant positive changes in methyl-branched acid production. The results were verified in real fermented sausages with no, low (0.09% w/w) and high (0.36% w/w) addition of added alpha-ketoglutarate since the levels of the flavour intensive methyl-branched aldehydes and acids were drastically increased in sausages added a-ketoglutarate. The catabolism of phenylalanine was also induced by alpha-ketoglutarate and there were further indications of increased transamination of aspartate. A triangular test showed that the flavour of sausages with no and low addition of alpha-ketoglutarate could be clearly distinguished from one another. Altogether the results presented in this paper point to glutamate dehydrogenase, the enzyme catalyzing regeneration of a-ketoglutarate, as a key enzyme in catabolism of amino acids and thereby also in aroma formation during sausage processing.