Purpose: To date though, limited research has been conducted with respect to the structure-altering capabilities of S. carnosus in non-meat model systems. The purpose of this study was therefore to evaluate if the presence of this microorganism may affect the microstructure of a model O/W emulsion.
Methods: A sterile base emulsion was carefully prepared by mixing 15% (v/v) Miglyol, with filter sterilized 5% (w/v) whey protein isolate (WPI), and 80% phosphate buffer (0.01M pH 7.0). S. carnosus LTH 4410 was added to the emulsion at a concentration of 105 CFU/ml. Bacterial growth was monitored for 48 h at 30°C by plate enumeration. To assess proteolytic activity, a modified Lowry assay was used to determine the concentration of tyrosine in the emulsion. Structural changes in the emulsion related to proteolytic activity were measured by rheology and optical microscopy.
Results: The initial concentration of tyrosine was 38.99 µg/ml. After 48 h the tyrosine concentration in the inoculated emulsions increased to 43.89 µg/ml. The rheological behavior of the inoculated and non-inoculated emulsion did not differ from each other (P < 0.05). On a structural level, microscopic observations did not reveal any flocculation or aggregation. The results suggest that there was insufficient proteolytic activity, possibly due to the concentration of bacteria being too low or the metabolic activity of bacteria being limited.
Significance: The study of structural transformations caused by starter cultures such as S. carnosus should in general be of interest to food manufacturers interested in using starter cultures to transform a food template structure to a texturally different product.