Effets des galactomannanes de graines de caroube sur la viscosité d’un lait écrémé et sur le développement de souches bénéfiques

Abstract

This study is an exploration of the effects of carob galactomannans and starters cultures (Streptococcus thermophilus and Lactobacillus delbrueckii ssp bulgaricus of reference YFL811) on the parameters of growth and synthesis of organic acids, the rheological properties of a milk with 0% (W/V) fat and 10% (W/V) of dry matter fermented in the presence of two beneficial bacteria (of the kind Bifidobacterium, animalis ssp lactis = Bb12 and of the kind of Lactobacillus: rhamnosus = LbRE-LSAS). The post-evolution (post-acidification of fermented milk and survival of the various bacteria) as well as the viscosity and synaeresis were evaluated. The obtained results show that the clotting time of milk (one that achieves a pH close to 5) is reduced when there is presence of Locust bean gum. The improvement rate of growth of the strains by the galactomannans used at 0.01 to 0.1% (W/V) varies from 14.38 to 36.27% according to the strains and the concentration of LBG. A level of 0.1% of LBG is proved to be most effective in the accumulation of biomass. The study of the lactic strains survival during 28 days of storage at 4°C, shows that the best rates of survival rates was recorded in the presence of galactomannanes and it varies from 64.59 to 88.99%. The measurements of viscosity of fermented milk indicate that these polymers improve viscosity and the contents of 0.1% allow to reach strongest viscosities (1.586 Pa.s) after two weeks of cooled storage. The evaluation of the consistency an rheological properties of the fermented milk by the determination of the whey separation showed that a rate of 0.05 to 0.1% of locust baen gum prevent the problem of syneresis during all the period of refrigeration, whereas it is attenuated at low levels in presence of 0.01 to 0.02% of LBG. Indeed, these polymers improve texture, the viscosity and the smooth-feel of the end product and have the ability to retain the water molecules, thus decreasing the separation of the whey and coagulated caseins of milk.