Kefir제품으로부터 slime생성력이 우수한 Str. thermophilus LFG를 분리하여 이 유산균과 상업균주인 Str. thermophilus TH3 및 Str. thermophilus LFG와 L. delbrueckii subsp. bulgaricus LB12 혼합균주로 산양유 및 우유를 이용하여 발효유를 제조하고 제품특성을 조사하였다. 젖산 함량은 산양유 발효유(743.9-1043.8 mg/100 g)가 우유 발효유(441.6-709.9 mg/100 g)보다 높았다. 저장 중 발효유의 생균수는 Str. thermophilus LFG로 배양한 발효유에서 가장 높았다. 점도는 우유 및 산양유 발효유에서 Str. thermophilus LFG 균주를 사용한 발효유에서 가장 높았으며 Str. thermophilus TH3를 사용시에 가장 낮았다. 우유 및 산양유 발효유의 syneresis는 Str. thermophilus LFG를 이용한 발효유가 9.6-16.1%이었으나 Str. thermophilus TH3를 발효시킨 발효유는 28.2-31.8%이었다. 산양유의 향기성분으로 acetone, ethylbutanoate, ethyl-3-methyl butyrate, ethyl-2-butenoate, ethylhexanoate 등이 분리되었으며, 우유의 향기성분으로는 ethylbutanoate, acetone, 2-heptanone, acetoin 등이 분리되었다. 산양유 및 우유 발효유에서 acetic acid, butanoic acid, butanol, diethylcarbinol, acetone, diacetyl, decane, 2-methyl-3-pentanone, hexanal, 2-heptanone, acetoin, benzaldehyde, dimethyldisulfide, dimethyltrisulfide 등 14개의 성분이 검출되었다. 관능평가에서 Str. thermophilus LFG로 발효시킨 산양유 발효유가 우유 발효유보다 전반적인 기호도와 조직감에서 높은 평가를 받았다. 특히 혼합균주를 사용한 발효유에서 가장 높았으며 풍미특성도 향상 시키는 효과를 보였다.
This study was carried out to investigate the characteristics of goat and cow milk yogurts containing high-exopolysaccharide fermented by Streptoccous thermophilus LFG isolated from kefir. The pH of cow milk yogurt was higher than that of goat milk yogurt. The contents of lactic acid was greater in goat milk yogurt (743.9-1043.8 mg/100 g) than in cow milk yogurt (441.6-709.9 mg/100 g). The numbers of survival lactic acid bacteria were the greatest in goat milk yogurt fermented by Str. thermophilus LFG. Viscosity was greater in cow and goat milk yogurts cultured by Str. thermophilus LFG than in yogurts by Str. thermophilus TH3. Syneresis of yogurt fermented by Str. thermophilus LFG was 9.6-16.1% and 28.2-31.8% in yogurt fermented by Str. thermophilus TH3 after 10 d storage at $4^{\circ}C$. Flavor compounds identified from goat milk were acetone, ethylbutanoate, ethyl-3-methylbutyrate, ethyl-2-butenoate and ethylhexanoate, and those from cow milk were ethylbutanoate, acetone, 2-heptanone and acetoin. Flavor compounds detected from goat milk and cow milk yogurts were acetic acid, butanoic acid, butanol, diethylcarbinol, acetone, diacetyl, decane, 2-methyl-3-pentanone, hexanal, 2-heptanone, acetoin, benzaldehyde, dimethyldisulfide, and dimethyltrisulfide. In sensory evaluation, overall preference and texture values were higher in goat milk yogurt fermented by Str. thermophilus LFG than in cow milk yogurts and the yogurt fermented by mixed culture resulted in the highest score.