GC-MS metabolomics comparison of yoghurts from sheep's and goats' milk

A chemical study of yoghurt produced under isostatic pressure during storage

Yoghurt fermented under sub-lethal high pressure (10, 20, 30 and 40 MPa at 43 °C), and afterward placed under refrigeration (4 °C for 23 days) was studied and compared with yoghurt fermented at atmospheric pressure (0.1 MPa). For a deeper analysis, metabolite fingerprinting by nuclear magnetic resonance (NMR), sugars and organic acids assessment by high performance liquid chromatography (HPLC), total fatty acids (TFA) determination and quantification by gas chromatography with a flame ionization detector (GC-FID) were performed. Metabolomic analyses revealed that only 2,3-butanediol, acetoin, diacetyl and formate vary with the increase of pressure and probable relation with pressure influenced diacetyl reductase, acetoin reductase and acetolactate decarboxylase. Yoghurts fermented at 40 MPa had the lowest content in lactose (39.7 % of total sugar reduction) and the less content in TFA (56.1 %). Further research is of interest to understand more about fermentation processes under sub-lethal high pressure.

Mass spectrometry-based techniques for identification of compounds in milk and meat matrix

Food including milk and meat is often viewed as the mixture of different components such as fat, protein, carbohydrates, moisture and ash, which are estimated using well-established protocols and techniques. However, with the advent of metabolomics, low-molecular weight substances, also known as metabolites, have been recognized as one of the major factors influencing the production, quality and processing. Therefore, different separation and detection techniques have been developed for the rapid, robust and reproducible separation and identification of compounds for efficient control in milk and meat production and supply chain. Mass-spectrometry based techniques such as GC-MS and LC-MS and nuclear magnetic resonance spectroscopy techniques have been proven successful in the detailed food component analysis owing to their associated benefits. Different metabolites extraction protocols, derivatization, spectra generated, data processing followed by data interpretation are the major sequential steps for these analytical techniques. This chapter deals with not only the detailed discussion of these analytical techniques but also sheds light on various applications of these analytical techniques in milk and meat products.

Impact of lactic acid bacteria and their metabolites on the techno-functional properties and health benefits of fermented dairy products

After conversion of lactose to lactic acid, several biochemical changes occur such as enhanced protein digestibility, fatty acids release, and production of bioactive compounds etc. during the fermentation process that brings nutritional and quality improvement in the fermented dairy products (FDP). A diverse range of lactic acid bacteria (LAB) is being utilized for the development of FDP with specific desirable techno-functional attributes. This review contributes to the knowledge of basic pathways and changes during fermentation process and the current research on techniques used for identification and quantification of metabolites. The focus of this article is mainly on the metabolites responsible for maintaining the desired attributes and health benefits of FDP as well as their characterization from raw milk. LAB genera including Lactobacillus, Streptococcus, Leuconostoc, Pediococcus and Lactococcus are involved in the fermentation of milk and milk products. LAB species accrue these benefits and desirable properties of FDP producing the bioactive compounds and metabolites using homo-fermentative and heterofermentative pathways. Generation of metabolites vary with incubation and other processing conditions and are analyzed and quantified using highly advanced and sophisticated instrumentation including nuclear magnetic resonance, mass-spectrometry based techniques. Health benefits of FDP are mainly possible due to the biological roles of such metabolites that also cause technological improvements desired by dairy manufacturers and consumers.

Gas chromatography-mass spectrometry based metabolomic approach to investigate the changes in goat milk yoghurt during storage

The overall goal was to utilize a gas chromatography spectrometry based metabolomics approach to investigate the metabolite changes in goat milk yoghurt during storage. A total of 129 metabolites were identified in goat milk yoghurt during 28 days refrigerated storage. Among 129, 39 metabolites were differentially regulated (p < 0.05) wherein 22 were upregulated (UR) and 17 were downregulated (DR). 17 (9 UR, 8 DR), 20 (11 UR, 9 DR) and 2 (both UR) differential metabolites were identified during storage period of 0-14, 14-28, and 0-28 days, respectively. Metabolic pathway analysis revealed that aminoacyl-tRNA biosynthesis, phenylalanine, tyrosine and tryptophan biosynthesis and phenylalanine metabolism altered during 0-14 days storage; while fatty acid biosynthesis, and propanoate metabolism altered during 14-28 days of storage. Metabolite-gene interaction analysis identified genes regulated by differentially expressed metabolites. Functional annotation of interacted genes in corroboration with that of KEGG pathway analysis provided the probable mechanisms that altered the metabolites during storage. These findings reveal comprehensive insights into the metabolite alterations during storage. This research provides practical information for developing goat milk yoghurt with enhanced bio-activities and would aid in future investigations into the nutritional research and isolation of functional compounds.

Characterization and ACE Inhibitory Activity of Fermented Milk with Probiotic Lactobacillus plantarum K25 as Analyzed by GC-MS-Based Metabolomics Approach

Addition of probiotics to yogurt with desired health benefits is gaining increasing attention. To further understand the effect of probiotic Lactobacillus plantarum on the quality and function of fermented milk, probiotic fermented milk (PFM) made with probiotic L. plantarum K25 and yogurt starter (L. delbrueckii ssp. bulgaricus and Streptococcus thermophilus) was compared with the control fermented milk (FM) made with only the yogurt starter. The probiotic strain was shown to survive well with a viable count of 7.1 ± 0.1 log CFU/g in the PFM sample after 21 days of storage at 4°C. The strain was shown to promote formation of volatiles such as acetoin and 2,3-butanediol with milk fragrance, and it did not cause post-acidification during refrigerated storage. Metabolomics analysis by GC-MS datasets coupled with multivariate statistical analysis showed that addition of L. plantarum K25 increased formation of over 20 metabolites detected in fermented milk, among which γ-aminobutyric acid was the most prominent. Together with several other metabolites with relatively high levels in fermented milk such as glyceric acid, malic acid, succinic acid, glycine, alanine, ribose, and 1,3-dihydroxyacetone, they might play important roles in the probiotic function of L. plantarum K25. Further assay of the bioactivity of the PFM sample showed significant (p < 0.05) increase of ACE inhibitory activity from 22.3% at day 1 to 49.3% at day 21 of the refrigerated storage. Therefore, probiotic L. plantarum K25 could be explored for potential application in functional dairy products.

Study on the dynamic changes and formation pathways of metabolites during the fermentation of black waxy rice wine

Black waxy rice wine fermentation metabolites are closely related to the product's final quality. However, little is known about dynamic metabolite changes during fermentation. Here, we used gas chromatography time-of-flight mass spectrometry (GC-TOF-MS) metabolomics and multivariate statistical analysis to explore the relationship between metabolites and fermentation time. A total of 159 metabolites were identified during the entire fermentation process. The PCA analysis revealed a clear separation between the samples after 4 days and 2 days, and the samples after 4-24 days clustered together. This indicated that BGRW fermentation progresses rapidly in the first 48 hr of fermentation. A total of 40 metabolites were identified as differential during fermentation (VIP > 1 and p < .05), including 12 organic acids, four amino acids, one fatty acid, 17 sugars and sugar alcohols, one alcohol, and five other metabolites. Pathway analysis showed that the differential metabolites were involved in 28 metabolic pathways, and the most commonly influenced pathways (impact value > 0.1 and p < .05) were galactose metabolism, pyruvate metabolism; starch and sucrose metabolism; alanine, aspartic acid, and glutamate metabolism; the tricarboxylic acid cycle, glyoxylic acid, and dicarboxylic acid metabolism; and amino sugar and nucleotide sugar metabolism. Moreover, the integrated metabolic pathway was generated to understand the transformation and accumulation of differential metabolites. Overall, these results provide a comprehensive overview of metabolite changes during black waxy rice wine fermentation.