Impact of lyophilized soapwort extract on the physicochemical, textural and sensory properties of nonfat yogurt.

This study investigated the potential use of lyophilized soapwort (Gypsophila sp.) extract as a functional ingredient in set-type nonfat yogurt. Yogurt samples were supplemented with lyophilized soapwort extract at four different concentrations (Control: 0%, 0.025%, 0.050% and 0.100% w/w) and stored for 30 days at 4°C. The effects of the extract on the physicochemical (acidity, dry matter, protein and fat), textural, rheological, microstructural (scanning electron microscopy [SEM]) and sensory properties of the yogurts were evaluated. The addition of soapwort extract did not significantly affect the pH, titratable acidity, total solids, protein content or colour parameters (L*, a*, b*) of the samples. Although the total colour difference (ΔE*) was significantly influenced by the extract, the values remained below the visual detection threshold (ΔE* < 2). Regarding textural properties, the extract did not significantly affect viscosity or serum separation. However, gel hardness decreased significantly with increasing soapwort extract concentration, from 343.8 g in the control sample to 279.7 g in the sample containing the highest level of soapwort extract (0.100%). SEM revealed that the extract interfered with the casein network, leading to an irregular gel structure characterized by larger pores and smaller aggregates compared to the control. Sensory evaluation indicated that while higher concentrations reduced consumer acceptability due to textural changes and bitterness, the sample containing 0.025% extract was statistically comparable to the control. Consequently, 0.025% was identified as the optimum inclusion level. These findings suggest that dried soapwort extract can be successfully incorporated into yogurt at low concentrations to develop a novel functional dairy product.