Method of improving the efficacy of lactic acid bacterial starter cultures and improved starter culture compositions

The present invention relates to the field of lactic acid bacterial starter cultures and in particular there is provided the means of enhancing the growth rate and/or controlling the metabolic activity of lactic acid bacteria by cultivating the lactic acid bacteria in association with a lactic acid bacterial helper organism which has a defeat in its pyruvate metabolism. Such a helper organism is also useful as a means of improving the shelf life and/or quality of edible products. Methods of enhancing the growth rate and/or controlling the metabolic activity of lactic acid bacteria and of improving the shelf life and/or the quality of an edible product using lactic acid bacterial organisms which are defective in their pyruvate metabolism. There is also provided starter culture compositions comprising such defective lactic acid bacteria as helper organisms and lactic acid bacterial starter culture strains. Useful helper organisms are Lactococcus strains which are defective with respect to pyruvate formate lyase (Pfl) and/or lactate dehydrogenase (Ldh) activity. The helper organisms may overexpress a gene coding for an NADregenerating enzyme such as NADH oxidase encoded by nox gene.