Diacetyl production and growth of Lactobacillus rhamnosus on multiple substrates

Lactobacillus rhamnosus is a heterolactic acid bacterium, which can be used to produce flavour compounds like diacetyl and acetoin. Various startegies have been applied to improve the growth rate and diacetyl yield. The use of multiple substrates affected growth as well as the yield of diacetyl. Growth on a medium containing glucose demonstrated a diauxic growth profile, with the second phase of growth being on the product, lactic acid. L. rhamnosus also grew on a medium containing citrate. Growth on medium containing glucose+citrate demonstrated simultaneous utilization of carbon sources. L. rhamnosus did not grow in a medium containing acetate and also did not co-metabolize it with glucose. Maximum specific growth rate (mu(max)) was found to increase in the case of simultaneous utilization of glucose+citrate (0.38 h(-1)) as compared to glucose as the sole carbon source (0.28 h(-1)). The yields of diacetyl were also found to increase for glucose+pyruvate and glucose+citrate (0.10 and 0.05 g g(-1) of glucose, respectively) as compared to glucose alone (0.01 g g(-1) of glucose). The productivity of diacetyl on medium containing glucose and citrate was double that of a medium containing only citrate, although the yields were comparable.