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Lawrence et al. (1984) noted that cheese with a salt-in-moisture concentration Succimer propionic acid concentration during ripening of cheese seem to follow crossover times between starter lactococci and NSLAB. The control and 10% K cheeses (both with typical Cheddar cheese Na levels) had a more rapid decline in starter populations, which allowed NSLAB to become dominant earlier during storage. Nonstarter LAB activity has been reported to increase propionic acid concentration in cheese during storage (St-Gelais et al., 1991; Bouzas et al., 1993). The control and 10% K cheeses had elevated propionic acid concentrations at 6?mo and both had crossover times Dehydrogenase inhibitor check details 2A) corresponding to the 40?mM increase in propionic acid ( Figure 2B) was observed between 3 and 6?mo for the control and 10% K cheeses or between 6 and 9?mo for the other high-salt cheeses. The low-salt cheese had the greatest increase in propionic acid concentration between 6 and 9?mo, and lactic acid concentration was the same at 6 and 9?mo, whereas most of the other cheeses had a further increase in lactic acid concentration over that time period ( Figure 2A). Alternatively, proteolysis of amino acid side chains and nonspecific esterase activities by NSLAB have also been suggested as sources of propionic acid (Gonz��lez de Llano et al., 1996). Propionic acid can be produced from branched-chain amino acids that are used as an energy source by LAB under sugar starvation conditions prevalent in aged cheese (Ganesan et al., 2004). In Cheddar cheese augmented with ��-ketoglutarate (a transaminase acceptor that enhances amino acid catabolism), propionic acid concentration was higher at 24?wk of aging than in untreated cheeses (Banks et al., 2001). In our study, at 9?mo, the NSLAB populations were similar in all cheeses and by then propionic acid concentrations in all the high-salt cheeses were also the same.