Leuconostoc mesenteroides is a bacterium that plays a significant role in various natural processes, particularly in food environments. It is a common, naturally occurring microorganism often found in association with plant materials and within fermented settings. This bacterium is recognized for its contributions to the characteristics of many fermented foods.
Key Characteristics and Natural Habitats
Leuconostoc mesenteroides is classified as a lactic acid bacterium (LAB). This bacterium is an obligate heterolactic fermentative LAB, meaning it converts sugars into a mix of byproducts, including lactic acid, carbon dioxide, and ethanol. When grown in a sucrose solution, it also produces dextran, a polysaccharide with various industrial uses.
This bacterium thrives in natural environments. It is found on fruits and vegetables, such as cabbage and cucumbers. It also occurs in dairy products. The optimal temperature for its growth is around 30°C, but it can grow in temperatures ranging from 10°C to 30°C and can survive within a pH range of 4.5-7.0, with an optimum pH of 5.5-6.5.
Its Role in Food Fermentation
Leuconostoc mesenteroides contributes to food fermentation through its heterofermentative metabolism. This process involves the breakdown of hexose sugars like glucose, producing D-lactate, ethanol, and carbon dioxide. It can also convert citrate into diacetyl and acetoin, important flavor compounds.
These byproducts contribute to several aspects of fermented foods. Lactic acid lowers the pH, preserving food by inhibiting spoilage organisms. Carbon dioxide contributes to texture changes, such as porosity in fermented products. Furthermore, the various acids and flavor compounds, like diacetyl, contribute to the aroma and taste profiles of fermented foods.
Common Food Products Where It Thrives
Leuconostoc mesenteroides plays a significant role in the fermentation of several common food products. In sauerkraut, it initiates cabbage fermentation, contributing to firm texture and reducing off-flavors. It is also predominant in kimchi fermentation, converting fructose into mannitol for a refreshing taste.
It is also used in sourdough bread fermentation, contributing to its unique flavor and leavening. In cheeses, L. mesenteroides is included in dairy starter cultures because it produces metabolites like diacetyl, a main source of aroma and flavor in products like buttermilk and butter. The carbon dioxide it produces is also important for “eyes” or holes in cheeses like Havarti.
Beyond Food and Its Safety
Beyond its role in food fermentation, Leuconostoc mesenteroides is notable for its ability to produce dextran. Dextran is an extracellular polysaccharide synthesized from sucrose by the enzyme dextransucrase, which is secreted by the bacterium. This polysaccharide has various industrial applications, including its use as a blood plasma expander in medicine and as a chromatographic medium for separating and purifying proteins.
Dextran also finds uses in the food industry as a thickener for items like jam and ice cream, where it helps prevent sugar crystallization and improves moisture retention. Generally, L. mesenteroides is recognized as safe for food use. While some strains have been explored for their probiotic potential due to their ability to survive gastrointestinal conditions and inhibit certain pathogens, it is considered non-pathogenic for the average person.