A collection of glycerol-degrading lactic acid bacteria from spoiled cider was isolated. The most wide-spread species was Lactobacillus collinoides, a heterofermentative species which mainly produced the D-lactic acid isomer from glucose. Conditions of glycerol assimilation by such bacteria were investigated for strain Lb. collinoides IOEB 9527. It could not be cultivated with glycerol alone as carbon source. Sugars were necessary for growth, and fructose was preferred to glucose. Glycerol was degraded, mainly to 1,3-propanediol. Small amounts of acrolein, produced from 3-hydroxypropion-aldehyde (3-HPA) during distillation of samples, were detected. When Lb. collinoides was cultivated with glucose or fructose alone, it produced the usual compounds of the heterofermentative pathway, notably D-lactic acid and small amounts of L-lactic acid, acetic acid and ethanol. When glycerol was present, the amounts of lactic acid were surprisingly much lower and acetic acid + ethanol much higher than expected. Oxidation of D-lactic acid, and to a lesser extent of L-lactic acid, was coupled to degradation of glycerol to 1,3-propanediol. This co-metabolism leading to acetic acid provided energy. Consequently, in fermented beverages spoiled by such strains, glycerol is degraded and 3-HPA plus acetic acid are produced. Both components are undesirable for health and sensorial quality.
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