Heat stress (HS) damages the global dairy industry by reducing milk yields and quality, harming health, and damaging the reproduction of dairy cows, causing huge economic losses each year. However, an understanding of the physiological mechanism of HS lactating dairy cows remains elusive. Here, a metabolomics study using LC-MS and 1H NMR spectroscopy was performed to analyze the metabolomic differences in the milk between HS-free and HS dairy cows, and discover diagnostic biomarkers and changes in the metabolic pathway. A total of 53 discriminating metabolites were significantly up- or down-regulated in the HS group compared with the HS-free group (P < 0.05). These biomarkers were involved in pathways of carbohydrate, amino acid, lipid, and gut microbiome-derived metabolism. Comparing these potential biomarkers with previously identified HS candidate biomarkers in plasma, significant correlations between the levels of lactate, pyruvate, creatine, acetone, β-hydroxybutyrate, trimethylamine, oleic acid, linoleic acid, lysophosphatidylcholine 16:0, and phosphatidylcholine 42:2 in milk and plasma were found, indicating that the blood-milk barrier became leaky and the levels of these 10 biomarkers in milk can reflect HS-induced metabolomic alterations in blood. These novel findings can support more in-depth research to elucidate the milk-based changes in metabolic pathways in HS lactating dairy cows.

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The aroma chemical composition of commonly planted kiwifruit cultivars in China was analyzed. The combination of 2-octanone with 3-octanone was the most suitable dual internal standard for quantitative analysis in GC-MS. A total of 172 aroma components in 23 kiwifruit cultivars were detected, and ethyl butanoate, (E)-2-hexen-1-ol, and (E)-2-hexenal could be considered the core aroma components in kiwifruit, but still need further confirmation using Sensomics. E-nose could effectively distinguish different cultivars of kiwifruit. Clustering based on GC-MS and E-nose results tends to be consistent and demonstrate a certain degree of similarity. Kiwifruit cultivars with different flesh colors cannot be effectively distinguished by their aroma chemical compositions. Different species of kiwifruit can be distinguished to some extent by their aroma chemical compositions, but the effect was not satisfactory. These results could prove valuable in the breeding, planting, and marketing of kiwifruits.

Reactive carbonyl species (RCS), such as acrolein (ACR), glyoxal (GO), and methylglyoxal (MGO), have received extensive attention recently as a result of their high activity and toxicity in vitro and in vivo. In the present study, propyl gallate (PG), a common food antioxidant, was found to effectively trap more ACR than butylated hydroxytoluene and butylated hydroxyanisole through the formation of mono-ACR adducts (PG−ACR) and di-ACR adducts (PG−2ACR). The two adducts were successfully purified, and their structures were elucidated on the basis of their high-resolution mass spectrometry and 1 H, 13 C, and two-dimensional nuclear magnetic resonance data. We further identified that PG−ACR had the ability to continue to trap GO and MGO to form PG−ACR−GO and PG−ACR−MGO, respectively, by liquid chromatography−tandem mass spectrometry (LC−MS/MS). Furthermore, we verified that PG could inhibit the production of ACR, GO, and MGO via trapping these RCS simultaneously to form the corresponding adducts in pound cakes using LC−MS/MS.

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Commercial milk products worldwide come not only from cows, but also from goats, buffaloes, camels, and yaks. Milk from non-bovine animals is important culturally and economically. Pseudomonas spp. are frequently linked to milk spoilage under storage temperatures. The objectives of this study were to identify Pseudomonas spp. isolated from goat, buffalo, camel, and yak milks, and to measure proteolytic activity of Pseudomonas spp. under different storage temperatures. Raw milk samples of goat (n = 50), buffalo (n = 25), camel (n = 25), and yak (n = 25) were collected from 5 provinces in China. Pseudomonas spp. were analyzed by Pseudomonas-specific 16S, universal 16S rRNA, and rpoB gene sequence analyses. Proteolytic activity on milk agar, quantification via the trinitrobenzenesulfonic acid assay at 2°C, 4°C, 7°C, 10°C and 25°C, as well as alkaline peptidase gene (aprX) identification were performed to ascertain the proteolytic activity of these isolates. Pseudomonas spp. were found in 46 samples out of total 125 samples. A total of 67 Pseudomonas spp. were identified. Of Pseudomonas isolates, we obtained extracellular peptidase activity in 7 (10.4%) at 2°C, 17 (25.4%) at 4°C, 24 (35.8%) at 7°C, 39 (58.2%) at 10°C, and 41 (61.2%) at 25°C. The results revealed that a wide diversity of Pseudomonas spp. were present in different non-bovine raw milks, with the ability to produce peptidases at storage temperatures. However, proteolytic activity varied widely among the peptidase-positive isolates. A majority of isolates from yak milk had high proteolytic activity.