Physical properties of synbiotic yogurts as affected by the acidification rate

Synbiotic yoghurts are fermented using a probiotic starter culture and prebiotics, which are claimed to promote health benefits. We have previously shown that new prebiotic oligosaccharides derived from lactulose (OsLu) are chemically stable during fermentation and cold storage. This study tested how physical properties are affected when adding OsLu and lactulose at concentrations reasonable for fermented milks' consumption (2% and 4%). Sixty six stirred yoghurts were produced from skimmed milk (<0.1% fat), as high-heated (95 °C, 256 s) after prebiotic supplementation. Protein content was standardized (4.5–5.2%) by skim milk powder (SMP) or total milk protein (TMP). Lactose and maltodextrin served as inert carbohydrate controls. Fermentation was significantly slowed by OsLu or lactulose, regardless of concentration, indicating substrate inhibition. Such gels were softer and resulted in less viscous yoghurt. Multivariate analysis revealed clustering into samples containing OsLu, lactulose, or the inert carbohydrates, with acidification rate being the most prominent feature.