Exploring the Characteristic Aroma Components of Traditional Fermented Koumiss of Kazakh Ethnicity in Different Regions of Xinjiang by Combining Modern Instrumental Detection Technology with Multivariate Statistical Analysis Methods for Odor Activity Value and Sensory Analysis

Effect of Capsaicin Stress on Aroma-Producing Properties of Lactobacillus plantarum CL-01 Based on E-Nose and GC-IMS

Capsaicin stress, along with salt stress, could be considered the main stressors for lactic acid bacteria in traditional fermented pepper products. Until now, insufficient attention has been paid to salt stress, while the effect of capsaicin on the aroma-producing properties of Lactobacillus plantarum (L. plantarum) is unclear. The present study attempted to illustrate the effect of capsaicin stress on the aroma-producing properties of L. plantarum CL-01 isolated from traditionally fermented peppers based on E-nose and GC-IMS. The results showed that E-nose could clearly distinguish the overall flavor differences of L. plantarum CL-01 under capsaicin stress. A total of 48 volatile compounds (VOCs) were characterized by means of GC-IMS, and the main VOCs belonged to acids and alcohols. Capsaicin stress significantly promoted L. plantarum CL-01 to produce alpha-pinene, ethyl crotonate, isobutyric acid, trans-2-pentenal, 2-methyl-1-butanol, 3-methyl-3-buten-1-ol, 1-penten-3-one, 2-pentanone, 3-methyl-1-butanol-D, and 2-heptanone (p < 0.05). In addition, under capsaicin stress, the contents of 1-penten-3-one, 3-methyl-3-buten-1-ol, 5-methylfurfuryl alcohol, isobutanol, 2-furanmethanethiol, 2,2,4,6,6-pentamethylheptane, 1-propanethiol, diethyl malonate, acetic acid, beta-myrcene, 2-pentanone, ethyl acetate, trans-2-pentenal, 2-methylbutyl acetate, and 2-heptanone produced by L. plantarum CL-01 were significantly increased along with the fermentation time (p < 0.05). Furthermore, some significant correlations were observed between the response values of specific E-nose sensors and effective VOCs.

Discriminant Analysis of Aroma Differences between Cow Milk Powder and Special Milk Powder (Donkey, Camel, and Horse Milk Powder) in Xinjiang Based on GC-IMS and Multivariate Statistical Methods

In order to explore the aromatic differences between Xinjiang cow milk powder and specialty milk powder (donkey, camel, and horse milk powder), Gas Chromatography-Ion Mobility Spectrometry (GC-IMS) analysis was employed to investigate the volatile compounds in these four types of milk powders. A total of 61 volatile substances were detected, with ketones, aldehydes, and alcohols being the primary flavor components in the milk powders. While the aromatic components of the different milk powders showed similarities in terms of types, there were significant differences in their concentrations, exhibiting distinct characteristics for each type. The Partial Least Squares Discriminant Analysis (PLS-DA) showed that there were 15, 14, and 23 volatile compounds that could be used for discrimination of cow milk powder against specialty milk powders, respectively. And it was validated by Receiver Operating Characteristic (ROC) analysis, and finally, 8, 6, and 19 volatile compounds were identified as valid differential marker substances. To facilitate visual discrimination between the different milk powders, we established GC-IMS fingerprint spectra based on the final discriminant markers. These studies provide theoretical guidance for the application of volatile compounds to discriminate adulteration of milk powder marketed in Xinjiang.