Influence of fermentation temperature on the exopolysaccharides characteristics and the rheological properties of fermented milks obtained with Lactobacillus paracasei

LLAMAS G; ABRAHAM A G; HAMET F; GARROTE G L,; BENGOA A; DUEÑAS M T

Tucumán

Simposio; SIBAL 2016 - V Simposio Internacional de Bacterias Lácticas.; 2016

CERELA

Exopolysaccharides (EPS) produced by lactic acid bacteria are of great interest for the dairy food industry since these biomolecules are able to improve the rheological properties, texture and mouthfeel of fermented milks, yogurts and cheeses. Since growth conditions, such as time, culture media, temperature or pH could modify the characteristics of the EPS synthesized in situ, the aim of this work was to evaluate the effect of fermentation temperature on the EPS characteristics and rheological properties of the acid gels obtained by milk fermentation with L. paracasei strains.L. paracasei CIDCA 8339, 83123 and 83124, characterized as EPS-producing and potentially probiotics strains, were inoculated in UHT low fat milk at 5% v/v. Acid gels were obtained by milk fermentation with each strain at 20ºC, 30ºC and 37ºC until pH was lower to 4. Rheological characterization was performed in a Haake rheometer in rotational mode and apparent viscosities were determined at 300 s-1. The EPS were isolated from supernatants of fermented milks by precipitation with ethanol and then characterized by gel permeation High Performance Liquid Chromatography.L. paracasei CIDCA 83123 require between 3 (at 30 and 37ºC) and 7 days (at 20ºC) to obtain acids gels, whereas 8339 and 83124 needed not more than 2 days even when the temperature was 20ºC. With regard to the rheological properties, all the acid gels showed a pseudoplastic and thixotropic behavior. The apparent viscosity of the fermented milk obtained with CIDCA 83124 at 37ºC (167mPa.s) was significantly lower than the values obtained at 30ºC (217mPa.s) and 20ºC (223 mPa.s). Besides, these fermented milks showed apparent viscosities much higher than the ones obtained with CIDCA 8339 (30-38 mPa.s) and 83123 (25-36mPa.s). The chromatograms showed changes in the EPS produced by the strains at different temperatures. In all cases, it was evidenced an increase in the relative amount of the high molecular weight fraction when the temperature fermentation was lower. In this work, we demonstrated that fermentation temperature actually influences on the characteristics of the EPS produced and that these changes can modify the rheological properties of the acid gel depending on the EPS-producing L. paracasei strain. Thus, we conclude that the fermentation temperature must be taken into account to improve the technological properties of fermented dairy products.