Role of Scleroglucan Produced by Sclerotium rolfsii in Shaping the Microstructure, Rheology, and Flavour Profile of Full-Fat Yoghurts

This study evaluated the effects of different concentrations (0.25%, 0.5%, and 1.0% w/w) of highly purified (90%) β-glucan (scleroglucan—SCGL) produced by Sclerotium rolfsii on the physicochemical, rheological, microbiological, and sensory properties of full-fat yoghurt (3.2% fat). The fermentation dynamics, titratable acidity, apparent viscosity, hardness, adhesiveness, colour, microstructure, and volatile compound profiles of the studied yoghurts were analysed. The addition of SCGL increased gel hardness and viscosity, while preserving its pseudoplastic flow behaviour (n = 0.10–0.15). In samples containing 1.0% SCGL, yield stress (τ0) increased from 0 Pa in the control to 739 Pa after 28 days of storage, pointing to the formation of a dense protein–polysaccharide network. The analysed polysaccharide slowed down lactose hydrolysis and acidification, but increased the counts of Streptococcus thermophilus (7.7 log CFU·g−1) compared to the control (5.8 log CFU·g−1). The volatile compound analysis showed increased acetaldehyde (5.6 mg·L−1) and diacetyl (5.0 mg·L−1) levels and reduced acetoin (~1.0 mg·L−1) concentration, which enhanced the intensity of the buttery aroma. The sensory evaluation revealed that yoghurts containing 1% SCGL had the most desirable smooth consistency and a balanced, fresh aroma, whereas yoghurts with lower SCGL concentrations (0.25–0.5%) were characterised by a mealy mouthfeel and thinner consistency. Scleroglucan proved to be an effective natural stabiliser and flavour modulator that improved the structure, stability, and sensory quality of full-fat yoghurts.