Determination of appropriate concentrations of Stevia sweeteners in vanilla yogurt and effect on viability of yogurt and probiotic cultures

Today, yogurt is recognized as a popular functional food to deliver probiotics and is consumed in 'lite', low-fat and non-fat variants because of a variety of natural and artificial sweeteners available in the market. With the emergence of new sweeteners like Stevia (available in a variety of different formulations), their suitability for yogurt needs to be validated. The present study aimed to determine the preferred concentration level (out of low (C1), high (C2) and intermediate (C3) levels) of four processed Stevia sweeteners/supplements in vanilla yogurt. The Stevia sweeteners included Ery-Reb and Mdx-Glyc (contain steviol glycoside(s) and bulk sweetener formulations); supplements included Gln-Glyc (90% steviol glycosides in water) and CW (a cold water extract of Stevia leaves); two control sweeteners included sucrose (CS) and aspartame (CA). This study determined the Just-About-Right (JAR) level for each sweetener for use in vanilla yogurt, and consumer acceptability of the same yogurts. In general, consumers were not very accepting of any of the vanilla yogurts, regardless of sweetener type or level. JAR sensory results were analyzed using Penalty AnalysisRTM with significant differences (p<0.1) among JAR levels. Results from Penalty Analysis RTM indicated that the attributes sweetness and sourness influenced mean drop in overall liking more than color and flavor. Since the C3 concentration of sweeteners scored the lowest penalties, this level was chosen for subsequent microbial analysis. Growth rate and total log cfu/mL of yogurt cultures (S. thermophilus and L. bulgaricus ) and probiotic cultures (L. acidophilus and B. lactis) were evaluated using BioScreenRTM. Results demonstrated that a polyphenol-rich CW extract of Stevia promoted growth of LAB in both individual and mixed cultures. The study also verified that the steviol glycosides did not inhibit growth of LAB within 72 hours. Overall, commercial Stevia sweeteners had little or no effect on growth of LAB compared to CW extract, sucrose, and aspartame. Filler components such as erythritol, maltodextrin used in commercial Stevia sweeteners were found to differentially influence growth of LAB. Although commercial stevia sweeteners do not negatively influence growth of commercial yogurt and probiotic cultures within 72 hours, these sweeteners do not demonstrate a positive effect on growth of yogurt and probiotic cultures.