Chemical, Microbiological and Sensory Properties of Plain Nonfat Yogurt

Chemical and microbiological properties of plain nonfat yogurt were determined after 2, 6 and 12 days refrigerated storage. Sensory properties were determined after 6 days storage. Viable culture bacteria concentrations ranged from 140 to 8,000 × 10 6 /g and ratios of lactobacillus to streptococcus ranged from 0.18 to 15.4. Chemical criteria used to characterize products included: pH, titratable acidity, lactic and four other organic acids and lactose by HPLC, and 23 major volatile organic compounds by dynamic headspace analysis. Lactic acid concentrations ranged from 7.5 to 9.9 mg/g. Major flavor volatiles in all yogurts included: acetaldehyde, heptane, acetone, diacetyl, and benzothiazole. Untrained sensory panels showed differences for flavor, aroma and acceptability.