Study of the effects of temperature, pH and yeast extract on growth and exopolysaccharides production by Propionibacterium acidi-propionici on milk microfiltrate using a response surface methodology

Aims: To study the effects of temperature, pH and yeast extract (YE) concen tration on growth and exopolysaccharide (EPS) production by Propionibacteri um acidi-propionici DSM 4900 cultivated on milk microfiltrate. Methods and Results: A multifactorial approach using a Response Surface Met hodology (RSM) was followed. The results indicated that both growth, and EP S and organic acids production, were influenced by pH, temperature and YE c oncentration. Biomass and organic acids production occurred in all the test ed domains, whereas EPS production was only possible in a narrow pH range ( 5.3-6.5). The results clearly showed that the optimal conditions for EPS pr oduction were different to those for optimal growth. The effect of YE on EP S production was not only due to an increase in growth but also to a direct effect on the production of EPS. The temperature played a major role. A de crease of temperature induced a slowing down of both growth and organic aci ds production, making the essential factors of the medium and the precursor s of EPS biosynthesis more available and hence, leading to an increase in E PS production. Conclusions: The effects of pH, temperature and YE were determined, allowin g the definition of favourable, though non-optimal, conditions for EPS prod uction: 23 degreesC, pH 6 and 3 g 1(-1) YE concentration. Significance and Impact of the Study: The use of a multifactorial approach for investigating the effect of fermentation conditions on EPS production h as been demonstrated.