Metabolism of amino acids by resting cells of non-starter lactobacilli in relation to flavour development in cheese

Amino acid metabolism by one strain each of Lactobacillus casei and Lactobacillus paracasei subsp. paracasei in resting cell suspensions was studied. The experiment was performed under cheese like conditions in terms of pH, salt concentration, temperature and carbohydrate starvation using a mixture Of L-amino acids as substrate. The effect of supplementing the amino acids mixture with alpha -ketoglutarate was estimated. Asparagine, serine and glutamine were utilised in the suspension with only amino acids. In the suspension with both amino acids and alpha -ketoglutarate, the degradation of leucine and lysine was observed. Production of metabolites that could be important for cheese flavour such as carbon dioxide, ammonia, organic acids and volatiles was measured. The suspensions with amino acids were characterised by high production of acetoin and ammonia and both increased even more when alpha -ketoglutarate was added. Carbon dioxide was produced in high amounts in the suspension with both amino acids and alpha -ketoglutaric acid. (C) 2001 Elsevier Science Ltd. All rights reserved.