Abstract: Cholesterol-lowering Bifidobacteria and lactic acid bacteria were used as mixed starter cultures to produce yoghurt from a mixture of skim milk powder and saccharified potato pulp in this paper. The effect of 19 different strains on the quality of yoghurt was studied, and the effects of different combinations of selected strains and inoculum size on the concentration of acetaldehyde and diacetyl as the major flavor compounds, determined by titration and colorimetric assay using o-phenylenediamine, respectively, as well as sensory evaluation were also examined. The results showed that the sensory evaluation score and flavor compounds concentrations exhibited strain specificity. The interaction among Bifidobacterium animalis subsp. lactis BZ11, Lactobacillus pentosus MT-4, B. longum BL1 and Streptococcus thermophiles Q-1 affected flavor formation in yogurt fermented by their mixed cultures. The total probiotic count in the yogurt produced under the optimized conditions was 6.3 × 108 CFU/mL. Notably, the Bifidobacterium count was up to 3.6 × 108 CFU/mL. In addition, the contents of reducing sugar and free amino acids were 1.94% and 136.64 mg/100 g, both higher than those before fermentation and those of commercial yogurt. The degradation percentage of cholesterol in yoghurt containing the mixed culture was 20.45%, which was 1.86%–15.57% higher than that obtained using individual strains alone. The probiotic potato not only had an excellent flavor, but also could be expected to have health benefits due to its nutritional and functional properties.

Key words: potato incorporated yoghurt, cholesterol-lowering probiotics, acetaldehyde, diacetyl