SUGARS, ORGANIC ACIDS AND GLYCEROL METABOLISM OF LACTIC ACID BACTERIA FROM FRUITS AND FERMENTED BEVERAGES. INFLUENCE ON THE PRODUCTS QUALITY

MARIA CRISTINA MANCA DE NADRA, FABIANA MARIA SAGUIR AND ANA MARIA STRASSER DE SAAD,

Red Wine and Health

NOVA SCIENCE PUBLISHERS, INC.

Lugar: Hauppauge, NY 11788-3619; Año: 2009; p. 235 - 278

Growth and metabolism of lactic acid bacteria (LAB) are essential in the quality of many fermented beverages like cider and wine. In these cases, they convert L-malic acid into L-lactic acid during the malolactic fermentation (MLF). In addition to malic acid, some other organic acids, sugars and carbon sources as glycerol may be utilized by LAB modifying the sensory quality of these products. In fruits juice and related product, they are considered spoilage microorganisms. Carbohydrates metabolism by LAB follows the homofermentative or heterofermentative pathways with formation of lactate, or lactate, acetate, ethanol and CO2, respectively. Studies on tomatoes microflora demonstrate that it is mainly constituted by obligatory heterofermentative LAB. D, L-lactic and acetic acids, CO2, ethanol and diacetyl formed from glucose and fructose by LAB, affect the sensory properties of tomato purée by producing undesirable buttermilk and fermented flavor. In Oenococcus oeni strains from Argentinian wines  growing in synthetic medium with acetate, equimolecular amount of D-lactate and ethanol in molar relation higher than 1 are produced from glucose. In deficient nutritional condition, glucose is diverted to the cysteine biosynthesis with decreased D-lactate recovery. In these strains the favorable effect of L-malic acid on the growth in synthetic medium and without essential amino acids is correlated with the energy gain associated with MLF. Heterofermetative LAB from wine can metabolize citrate mainly to acetate, lactate, and carbon dioxide. Cells of O. oeni co-metabolizing citrate-glucose increase rate and molar yield growth. End products from glucose change: ethanol decreases and acetate is formed with ATP production via acetate kinase. It have been also demonstrated in this bacterium that citrate avoid essential amino acids requirement for growth. Fermentation balances indicate that part of citrate is diverted to the amino acids synthesis derived from aspartic acid. Glycerol, produced during alcoholic fermentation in beverages, brings desirable properties (body, softness). But if it is used by LAB, depending on the pathway involved, the products formed can affect the product quality.  Apparently the pathways to degrade glycerol in the species Pediococcus pentosaceus are variable. In the wine Ped. pentosaceus N5p strain, glycerol is incorporated by an energy-dependent mechanism. It is degraded by the glycerol kinase (GK) pathway producing D-lactate, acetate and aroma compounds which can alter the flavor balance. Ped. pentosaceus CAg from beer degrade glycerol simultaneously by GK and glycerol dehydratase pathways producing high volatile acidity and aroma compounds that confer unacceptable flavors.