Instrumental texture of set and stirred fermented milk. Effect of a ropy strain of lactobacillus delbrueckii subsp. Bulgaricus and an enriched substrate

Texture profile analysis (TPA) of stirred and set cultured milk were evaluated, using an exopolysaccharide producing strain of Lactobacillus delbrueckii subsp. bulgaricus (NCFB 2772) and a protein enriched substrate (retentate). In both cases, samples were compared respectively with a nonropy strain (NCFB 1489) and reconstituted skim milk substrate. The retentate fermented products were firmer in comparison with skim milk products, both at 10% of total solids. A loss of structure occurred when the retentate products were stirred causing a nine-fold decrease in hardness, whereas in cultured milk products the loss was of around three-fold. The main differences were found in adhesiveness and fracture characteristics. Set retentate ropy product was five times more adhesive than the nonropy one, whereas in stirred retentate and set skim milk products the difference was two-fold. No differences in adhesiveness were detected when skim milk products were stirred using either strain. The fracture force on ropy retentate samples increased after fracture while the nonropy ones showed a decrease, implying more structural breakdown in the latter. On set products, cohesiveness increased slightly due to the ropy strain. Changes in texture observed between ropy and nonropy strains can be attributed to exopolysaccharide attachment to the casein matrix being increased when the protein content is higher. Le sujet de cette etude est d'evaluer la difference entre des laits fermentes brasses ou non, en determinant la contribution de souches de lactobacillus delbrueckii subsp. Bulgaricus NCFB 2772, productrices d'exopolysaccharides, sur la consistance particuliere de lait ecreme fermente et de retentat d'ultrafiltration de lait et en comparant les souches productrices aux souches non productrices. Elle etudie en particulier l'interaction entre ces polysaccharides et les proteines laitieres conduisant a un effet synergique.