Low-calorie sugars produced by lactic acid bacteria

Abstract

Mannitol, sorbitol, and erythritol are naturally occurring sugar alcohols. Mannitol is produced by bacteria, yeasts, fungi, algae, and several plants. This polyol might help these organisms to cope with different environmental stresses such as osmotic and oxidative stress. Sorbitol is produced by a variety of both plants and microorganisms. Erythritol production is usually associated with yeasts but has also been reported for some lactic acid bacteria (LAB). All these polyols — mannitol, sorbitol, and erythritol — display properties that are benefi cial to human health as they are non - metabolizable, insulin - independent sweeteners, or low - calorie sugars, which make them applicable in dietetic and diabetic food products. In addition, mannitol is used in the pharmaceutical industry as a powerful osmotic diuretic agent and as an osmotic agent for decreasing brain and cellular edema. Mannitol biosynthesis through bacterial fermentation has become an interesting alternative to existing chemical production. Chemical synthesis using nickel catalyst - assisted hydrogenation shows several economic disadvantages, such as high production costs and low product recovery. Furthermore, the capability of certain LAB, belonging to both homofermentative and heterofermentative species, to synthesize mannitol offers the possibility of in situ production in foods. For this reason, different fermentation technology - based strategies for improving mannitol production by LAB have been reported. To date, 93 – 97 mol% mannitol yields are reached using a bioprocess with a heterofermentative LAB strain. Moreover, metabolic engineering of food - grade lactate dehydrogenase - deficient mutants has been reported, in particular for sorbitol production by LAB. This chapter deals with the state of the art of sugar alcohol (mannitol, sorbitol, and erythritol) production by LAB as interesting low - calorie food ingredients. In addition, the strategies employed to increase the production and application of sugar alcohols in food and pharmaceutical products, or to design new functional foods naturally enriched in mannitol will be discussed.