Analysis of Aroma Components in Water Extract of Eucommia ulmoides Leaf Fermented by Different Lactobacillus Species

In order to research the effect of different Lactobacillus species on the aroma components of water extract of Eucommia ulmoides leaf, electronic nose (E-nose) and simultaneous distillation extraction (SDE) combined with gas chromatography-mass spectrometry (GC-MS) was used to analyze the volatile flavor composition of water extract of Eucommia ulmoides leaf fermented by Lactobacillus plantarum, Lactobacillus bulgaricus, Lactobacillius acidophilus and Streptococcus thermophilus. The results of SDE-GC-MS showed that 31 aroma components were identified in unfermented samples, with aldehyde being the most abundant constituents (14.3591%). The volatile components identified by Lactobacillus plantarum, Lactobacillus bulgaricus, Lactobacillius acidophilus and Streptococcus thermophilus after fermentation were 45, 38, 51 and 43, with ketones (18.8255%), heterocycles (25.7828%), alcohols (18.3376%) and alcohols (14.1481%) as the highest relative contents, respectively. In principal component analysis (PCA) and Loading Analysis (LoA) the cumulative contribution of the first 2 principal components accounted for greater than 95%, suggesting that the E-nose sensors had good recognition performance and discrimination between samples on the basis of their flavor characteristics was excellent with clear distinctions.The relative odor activity value (ROAV) indicated that Lactobacillus fermentation increased the content of key aroma components in Eucommia ulmoides leaf extract, and reduced its green leaf flavor. After Lactobacillus fermentation, the extract of Eucommia ulmoides leaf not only had more volatile components, but also significantly increased the content of key aroma components, which was more conducive to the improvement of aroma in the extract of Eucommia ulmoides. The results of this study provide a reference for the later research and development of Eucommia ulmoides leaf.