Metabolism of Volatile Compounds by Lactic Starter Culture Microorganisms. A Review

Cultured dairy products are accepted by the consumer primarily on the basis of flavor.During the last several years there has been a rapid proliferation of knowledge on the flavor compounds produced and utilized by starter culture organisms.This has led to a more thorough understanding of cultured product flavors and the role of starter bacteria in formation and degradation of these flavors.Volatile compounds produced by the common lactic culture organisms include acetaldehyde, diacetyl, ethanol, and volatile organic a~ids.Acetaldehyde arises from decarboxylation of pyruvate and it can be reduced to ethanol.Diacetyl is produced by citrate-fermenting organisms which also are able to reduce this compound to odorless products.Some of these organisms produce acetic acid by hydrolysis of acetylphosphate and by cleavage of citrate.This paper attempts to discuss recent findings in this area with reference to the most common microorganisms found in lactic starter cultures.A_ section on practical aspects of culture selection based on flavor compound production is included.Recent advances in micro-analytical techniques, especially gas chromatography, have led to a rapid and productive expansion in research concerning production and utilization of volatile compounds by microorganisms.This has led to a more thorough understanding of the involvement of microorganisms in the formation and deterioration of food flavor.In this review, we note recent findings concerning metabolism of volatile compounds by organisms common to lactic dairy cultures.Lactose fermentation is considered only as it relates to production of flavor compounds.