The volatile composition of yogurt produced by Streptococcus thermophilus fermentation at different time points was investigated by gas chromatography-mass spectrometry combined with simultaneous distillation and extraction. A total of 53 volatile compounds including 11 aldehydes, 10 ketones, 8 acids, 7 benzene derivatives, 13 hydrocarbons, and 4 other compounds were identified in all of the samples. Ketones and hydrocarbons were the predominant volatile components in the early stage, whereas acids were the predominant volatiles in the late stage. The importance of each volatile was evaluated based on odor, threshold, and odor activity values (OAVs). Twenty-nine volatiles were found to be odor-active compounds (OAV > 1), among which (E, E)-2,4-decadienal had the highest OAV (14623–22278). Other aldehydes and ketones such as octanal, dodecanal, 2-nonen-4-one, and 2-undecanone also showed high odor intensity during fermentation. Heat map analysis was employed to evaluate the differences during fermentation. The results demonstrated that the volatile profile based on the content and OAVs of volatile compounds enables the good differentiation of yogurt during fermentation.

中文翻译：

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基于气味活性值和热图分析的嗜热链球菌对酸奶发酵过程中挥发性成分的评价。

嗜热链球菌产生的酸奶的挥发性成分通过气相色谱-质谱联用同时蒸馏和萃取研究了在不同时间点的发酵。在所有样品中共鉴定出53种挥发性化合物，包括11种醛，10种酮，8种酸，7种苯衍生物，13种烃和4种其他化合物。在早期，酮和碳氢化合物是主要的挥发性成分，而在后期，酸是主要的挥发性成分。根据气味，阈值和气味活性值（OAV）评估每种挥发物的重要性。发现有29种挥发物是具有气味活性的化合物（OAV> 1），其中（E，E）-2,4-癸二烯醛的OAV最高（14623-22278）。其他醛和酮，例如辛烷，十二烷，2-壬烯-4-酮，和2-十一烷酮在发酵过程中也表现出高气味强度。使用热图分析来评估发酵过程中的差异。结果表明，基于挥发性化合物的含量和OAV的挥发性分布图可在发酵过程中很好地区分酸奶。