Capitain Charlotte C, Nejati Fatemeh, Zischka Martin, Berzak Markus, Junne Stefan, Neubauer Peter, Weller Philipp
Institute for Instrumental Analytics and Bioanalytics, Mannheim University of Applied Sciences, 68163 Mannheim, Germany.
Bioprocess Engineering, Institute of Biotechnology, Technische Universität Berlin, Ackerstrasse 76 ACK 24, 13355 Berlin, Germany.
Metabolites. 2022 Mar 28;12(4):299. doi: 10.3390/metabo12040299.
Fermented foods, such as yogurt and kefir, contain a versatile spectrum of volatile organic compounds (VOCs), including ethanol, acetic acid, ethyl acetate, and diacetyl. To overcome the challenge of overlapping peaks regarding these key compounds, the drift tube temperature was raised in a prototypic high-temperature ion mobility spectrometer (HTIMS). This HS-GC-HTIMS was used for the volatilomic profiling of 33 traditional kefir, 13 commercial kefir, and 15 commercial yogurt samples. Pattern recognition techniques, including principal component analysis (PCA) and NNMF, in combination with non-targeted screening, revealed distinct differences between traditional and commercial kefir while showing strong similarities between commercial kefir and yogurt. Classification of fermented dairy samples into commercial yogurt, commercial kefir, traditional mild kefir, and traditional tangy kefir was also possible for both PCA- and NNMF-based models, obtaining cross-validation (CV) error rates of 0% for PCA-LDA, PCA-NN ( = 5), and NNMF-NN ( = 5) and 3.3% for PCA-SVM and NNMF-LDA. Through back projection of NNMF loadings, characteristic substances were identified, indicating a mild flavor composition of commercial samples, with high concentrations of buttery-flavored diacetyl. In contrast, traditional kefir showed a diverse VOC profile with high amounts of flavorful alcohols (including ethanol and methyl-1-butanol), esters (including ethyl acetate and 3-methylbutyl acetate), and aldehydes. For validation of the results and deeper understanding, qPCR sequencing was used to evaluate the microbial consortia, confirming the microbial associations between commercial kefir and commercial yogurt and reinforcing the differences between traditional and commercial kefir. The diverse flavor profile of traditional kefir primarily results from the yeast consortium, while commercial kefir and yogurt is primarily, but not exclusively, produced through bacterial fermentation. The flavor profile of fermented dairy products may be used to directly evaluate the microbial consortium using HS-GC-HTIMS analysis.
发酵食品，如酸奶和开菲尔，含有多种挥发性有机化合物（VOC），包括乙醇、乙酸、乙酸乙酯和双乙酰。为了克服这些关键化合物峰重叠的挑战，在原型高温离子迁移谱仪（HTIMS）中提高了漂移管温度。这种顶空固相微萃取-气相色谱-高温离子迁移谱（HS-GC-HTIMS）用于对33个传统开菲尔、13个商业开菲尔和15个商业酸奶样品进行挥发性成分分析。模式识别技术，包括主成分分析（PCA）和非负矩阵分解（NNMF），结合非靶向筛选，揭示了传统开菲尔和商业开菲尔之间的明显差异，同时显示出商业开菲尔和酸奶之间有很强的相似性。基于PCA和NNMF的模型也能够将发酵乳制品样本分类为商业酸奶、商业开菲尔、传统温和开菲尔和传统浓郁开菲尔，PCA-LDA、PCA-NN（=5）和NNMF-NN（=5）的交叉验证（CV）错误率为0%，PCA-SVM和NNMF-LDA的交叉验证错误率为3.3%。通过NNMF载荷的反向投影，鉴定出了特征物质，表明商业样品具有温和的风味组成，含有高浓度的奶油味双乙酰。相比之下，传统开菲尔显示出多样的VOC谱，含有大量风味醇（包括乙醇和甲基-1-丁醇）、酯（包括乙酸乙酯和乙酸3-甲基丁酯）和醛。为了验证结果并进行更深入的了解，使用定量聚合酶链反应（qPCR）测序来评估微生物群落，证实了商业开菲尔和商业酸奶之间的微生物关联，并强化了传统开菲尔和商业开菲尔之间的差异。传统开菲尔多样的风味特征主要源于酵母群落，而商业开菲尔和酸奶主要但并非完全通过细菌发酵产生。发酵乳制品的风味特征可用于通过HS-GC-HTIMS分析直接评估微生物群落。
