Abstract: In this study, headspace solid phase microextraction in combination with comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (HS-SPME-GC × GC-TOFMS) was used to analyze the volatile compounds in whole (WM), low-fat milk (LFM) and non-fat milk (NFM). Altogether 49 volatile compounds were detected, among which methyl ketones with odd-numbered carbon chain lengths such as 2-nonanone and 2-undecanone constituted the main flavor compounds of WM. Using partial least squares discriminant analysis (PLS-DA), a model which could well differentiate among the 3 milks was developed and it was found to have good variance and cross-validation predictive ability. Nine differential key aroma compounds were identified using variable importance in the projection (VIP) > 1, P ≤ 0.05 and their contents ≥ 1% as criteria, which may be the main factors contributing to the differences in flavor profiles among the 3 milks. The heatmap from clustering analysis indicated that NFM had poor sensory performance due to the presence of off-flavor compounds (e.g., hexadecanal), whereas WM and LFM contained more aroma compounds, having a full and rich sensory aroma profile. The HS-SPME-GC × GC-TOFMS method can provide theoretical guidance for dairy flavor improvement and dairy flavoring formulation.

Key words: non-fat milk; flavor; headspace solid phase microextraction in combination with comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry; partial least squares discriminant analysis

摘要： 采用顶空固相微萃取-全二维气相色谱-飞行时间质谱（headspace solid phase microextraction in combination with comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry, HS-SPME-GC×GC-TOFMS）技术对全脂牛乳（whole milk, WM）、低脂牛乳（low-fat milk, LFM）和脱脂牛乳（non-fat milk, NFM）3 种牛乳样品进行挥发性化合物分析, 结果表明：共检测到49 种挥发性化合物, 其中2-壬酮、2-十一酮等奇数碳链的甲基酮构成WM的主要风味化合物；偏最小二乘法判别分析表明, 其模型可以很好地区分3 种牛乳样品, 并且有较好的方差和交叉验证预测能力；通过变量投影重要性＞1、P≤0.05且含量≥1%筛选出9 种化合物, 被认定为关键香气差异化合物, 这些化合物可能是导致3 种牛乳风味不同的主要因素；聚类热图结果表明, NFM因异味化合物（如十六醛）的存在可能导致不良感官表现, 而WM和LFM存在更多的香气化合物, 令其在感官方面具有饱满丰富的香气。本研究建立了HS-SPME-GC×GC-TOFMS分析牛乳的研究方法, 为乳制品风味改进和乳制香精调配提供了理论指导。

关键词: 脱脂牛乳；风味；顶空固相微萃取-全二维气相色谱-飞行时间质谱；偏最小二乘法判别分析