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Chai C., Kim H., Park S., Hwang J., Jhoo J., Kim G.
Kangwon National University, South Korea

Substitution of sugars generally added to Greek-style yogurt with a noncaloric natural sweetener such as Stevia rebaudiana extract may be a good way to promote the value of Greek-style yogurt. Greek-style yogurt where sucrose was substituted with Stevia rebaudiana extract was prepared, and its quality and fermentation characteristics during storage at 4 oC were investigated in this study.

Stevia rebaudiana extracts were prepared in two different methods. Dried Stevia rebaudiana leaves (100 g) were put into water (3 L) and heated at 100 oC for 6 h. Hot water extract was concentrated using a rotary evaporator and freeze-dried. Ethanol extract from Stevia rebaudiana leaves (100 g) was prepared via three consecutive treatments in 70% ethanol (3 L). Ethanol extract was concentrated and freeze-dried in a same manner applied to hot water extract.
Greek-style yogurt was manufactured via incubation of reconstituted milk inoculated with yogurt starter. Hot water extract or ethanol extract (0.5% w/v) was added to prior to the incubation, which were used as treatments. Greek-style yogurt with sucrose (0.5% w/v) without any supplement were prepared and used as controls. Prepared Greek-style yogurts were stored at 4 oC for 15 days.
Number of lactic acid bacteria in Greek-style yogurt during the incubation and storage was enumerated using plate counts on MRS agar. The pH of Greek-style yogurt was also monitored.
Sensory properties of Greek-style yogurt were evaluated after the storage for 3 days. Sensory properties were color, flavor, sweetness, bitterness, sourness, stickiness, after taste, and overall acceptability in 5 point scale.

The numbers of lactic acid bacteria and pH of all treatments were gradually increased and decreased, respectively, during the incubation. Although there was no significant difference in the numbers of lactic acid bacteria between treatments and controls, the pH of Greek-style yogurt supplemented with Stevia rebaudiana extracts and sucrose were likely to be less than that of Greek-style yogurt without any supplement. Especially, the pH of Greek-style yogurt supplemented with hot water extract after the incubation for 12 h reached to 4.50 that was least value of pH than those of others. During the storage, the pH of all treatments and controls decreased slightly and reached to 4.38-4.56, but the difference in the pH between day 0 and day 15 of storage was not exceed 0.3. Sensory evaluation reveals that Greek-style yogurt supplemented with hot water extract scored greatest in sweetness. However its overall acceptability scored least. Poor evaluation of Greek-style yogurt supplemented with hot water extract was probably due to unfamiliar herb flavor.

Inclusion of Stevia rebaudiana extracts in fermentation of Greek-style yogurt promoted the production of lactic acid, which resulted in less value of pH than those of controls. But the difference in the pH was not obvious. As Greek-style yogurt supplemented with Stevia rebaudiana extracts scored better in sweetness than controls, Stevia rebaudiana extracts may be a good substitute with sucrose for Greek-style yogurt.

Keywords: Greek-style yogurt, Sugar substitute, Fermentation characteristics, Herb extract, Probiotics, Sensory evaluation

Chai C., et al. (2016). Quality and fermentation characteristics of Greek-style yogurt added with herb extract. Conference Proceedings of IPC2016. Paper presented at the International Scientific Conference on Probiotics and Prebiotics, Budapest (p. 88.). IPC2016

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