Commercial yogurt can be classified as fermented milk (FM) and condensed fermented milk (CFM). A selection of commercial yogurt was collected from domestic markets and the quality characteristics were compared by analyzing total acidity, viscosity, organic acids, sugars, conjugated linoleic acid (CLA), and aroma pattern. Total acidity and viscosity in FM were significantly lower than those in CFM (p<0.05). The major organic acid of commercial yogurt was lactic acid, the content of which was 8.15-4.72 times and 26.83-47.20 times higher than that of citric acid and acetic acid, respectively. CFM contained 1.47 times more lactic acid and 2.53 times more citric acid than FM. The total sugar content in FM was two times higher than that in CFM and the major sugars measured were sucrose, lactose, glucose, and maltose. The sucrose content was the highest in FM. CFM contained 23.65 times more CLA and 10.81 times more lipid than FM. The aroma patterns of yogurt analyzed with an electronic nose were clustered into Therefore, among commercial yogurt, CFM had higher viscosity, organic acid and CLA content, but lower sugar content than FM, which resulted in a relatively strong sour and weak sweet taste.

Yogurt is produced by fermentation of milk using bacteria known as “yogurt cultures”. Most of these bacteria are probiotics such as Lactobacillus delbrueckii subsp. bulgaricus, Lb. rhamnosus, Streptococcus thermophilus, and Bifidobacterium. The domestic fermented milk market is increasing, and about 30 companies are producing yogurt. The purpose of this study was to analyze the quality characteristics of domestic commercial liquid yogurt. Total 30types of commercial yogurts were sampled and their physicochemicial properties, including pH, sugar content, acidity, viscosity, and microbial characteristics of lactic acid bacteria counts, were measured. Commercial liquid type yogurt showed a pH of 4.5, sugar content of 7.4-21.2%, total acid content of 0.4-0.9%, and viscosity of 0.1-250 cP. In terms of microbial populations, lactic acid bacteria counts were 7.2-11.3 log CFU/mL and anaerobic lactic acid bacteria counts were 8.0-11.5 log CFU/mL. The quality characteristics differed depending on the constituents of the sample and the microorganisms used. These results are related to the quality characteristics of yogurts and are useful for identifying new trends in the domestic fermented milk industry.