Adding α-Ketoglutarate to Semi-hard Cheese Curd Highly Enhances the Conversion of Amino acids to Aroma Compounds

St Paulin type cheeses made with three different starters were supplemented with alpha;-ketoglutarate, the main alpha;-ketoacid acceptor for amino acid transamination. Amino acid catabolism was monitored during ripening by free amino acid analysis and by analysis of metabolites produced from radiolabelled amino acids introduced as tracer into cheese curd. Also, odour development in cheese was evaluated by sniffing. Amino acid degradation in control cheeses was low and did not lead to aroma compounds. In contrast, adding alpha;-ketoglutarate in cheeses highly enhanced the degradation of aromatic and branched-chain amino acids and methionine. The degradation intensity was related to the amount of alpha;-ketoglutarate added, and alpha;-ketoglutarate used for amino acid transamination was transformed to glutamate. This degradation led to the formation of potent aroma compounds such as isovalerate for leucine and benzaldehyde for phenylalanine. As a result, cheese odour was significantly intensified by alpha;-ketoglutarate addition.