Microbial physiology, fermentation kinetics, and process engineering of heteropolysaccharide production by lactic acid bacteria

Many species of lactic acid bacteria (LAB) produce extracellular heterotype polysaccharides, the so-called hetero polysaccharides (HePS). Biosynthesis and secretion of the HePS from the LAB occur during different growth phase s, and both the amount and type of the polymer is influenced by growth cond itions. The total yield of exopolysaccharides produced by the LAB depends o n the composition of the medium (carbon and nitrogen sources, growth factor s, etc.) and the conditions in which the strains grow, i.e. temperature, pH , oxygen tension, and incubation time. It is never higher than 1.5g of poly mer dry mass per litre of fermentation medium. Whereas mesophilic strains p roduce maximal amounts of HePS under conditions not optimal for growth, the HePS production from thermophilic LAB strains is growth-associated, i.e. m aximum production during growth and under conditions optimal for growth. Th e HePS degradation often takes place upon prolonged incubation of the HePS- producing LAB strains due to glycohydrolase activity. Primary, secondary, a nd tertiary modelling unravel the functionality of the HePS-producing LAB s trains in a food environment. Finally, appropriate process engineering can lead to an industrial breakthrough of the HePS production and applications: a high and stable high-molecular-mass HePS production by appropriate feedi ng strategies through fed-batch cultivation on the one hand, and the applic ation of a two-step fermentation process in yoghurt manufacture on the othe r hand. (C) 2001 Elsevier Science Ltd. All rights reserved.