Résumé:
This study is an exploration of the comparative effects of various milk protein ingredients (sweet whey, promilk 852A2, promilk C502 and casein hydrolyzate CH2) and starter cultures (Streptococcus thermophilus ST B01 and a mixture of lactic ferment including Streptococcus thermophilus and Lactobacillus delbrueckii ssp bulgaricus of reference YF-L812) on the growth and synthesis parameters of organic acids, rheological properties of 25% fat milk (W/V) reconstituted to 10% (W/V) and fermented in the presence of different beneficial strains ( Bifidobacterium longum BLR, Lactobacillus rhamnosus LbRE-LSAS, Bifidobacterium animalis ssp lactis Bb12, Lactobacillus acidophilus, Lba CECT 4529, and lactobacillus plantarum Lbp CECT 748). The post acidification of fermented milk and the survival of different strains during the post fermentation 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 an association of a beneficial strain with both lactic ferments at the same time. Depending on the strain, the improvement rate of the growth of beneficial strains by 0.53% of different milk protein ingredients varies from 1.53 to 16.5%. Sweet whey was the most effective in the biomass accumulation (10.62 log UFC/ml as max with Lba CECT 4529).
The study of the beneficial strains survival during 28 days of storage at 4°C, shows that the best survival rates was recorded with sweet whey and promilk C502 , and vary from 72 to 89%.
The viscosity measures of fermented milk indicate that the beneficial strains associated with streptococcus achieve the highest viscosities (142 mPa.s) after two weeks of refrigerated storage. The evaluation of fermented milk texture using exopolysaccharides assay showed that the association between beneficial strain and Streptococcus thermophilus in the presence of sweet whey presented the highest level of exopolysaccharides ( 679 mg/l; over 80% more than the control).
