The Combined Analysis of GC-IMS and GC-MS Reveals the Differences in Volatile Flavor Compounds between Yak and Cattle-Yak Meat

In order to investigate the composition and differences in volatile organic compounds (VOCs) in yak and cattle-yak meat and determine the key metabolites and metabolic pathways related to flavor formation. In this study, the VOCs and non-volatile metabolites in Longissimus dorsi muscle of two groups of samples were detected and analyzed by gas chromatography-ion migration spectrometry (GC-IMS) and gas chromatography-mass spectrometry (GC-MS). The results showed that 31 VOCs were identified by GC-IMS, including 5 alcohols, 5 ketones, 5 esters, 3 aldehydes, 2 furans, 2 hydrocarbons, 1 amine, 1 acid, 1 thiazole, 1 pyrazine, and 5 others. Most of them were alcohols, ketones, esters, and aldehydes. A total of 75 non-volatile metabolites with significant differences were obtained by GC-MS screening, among which amino acid contents such as serine, glycine, phenylalanine, and aspartic acid were significantly up-regulated in cattle-yak, and glutamic acid and tyrosine were significantly up-regulated in yak. The non-volatile differential metabolites in the two groups were significantly enriched in the metabolic pathways of arginine biosynthesis and oxidative phosphorylation. By combining GC-IMS and GC-MS, this study comprehensively and intuitively reflected the differences in VOCs between yak and cattle-yak meat, and clarified the metabolomic reasons for the differences in VOCs, so as to provide a theoretical basis for meat quality improvement.

Identification of characteristic flavor compounds and small molecule metabolites during the ripening process of Nuodeng ham by GC-IMS, GC-MS combined with metabolomics

To investigate effects of metabolites and volatile compounds on the quality of Nuodeng ham, gas chromatography-mass spectrometry (GC-MS), ultra-high performance liquid chromatography-Q exactive orbitrap-mass spectrometry (UHPLC-QE-MS), and gas chromatography-ion transfer spectroscopy (GC-IMS) were used to analyze the differences of free fatty acids, small molecule metabolites and volatile compounds of Nuodeng ham at different ripening stages (the first, second and third year sample). 40 free fatty acids were detected. 757 and 300 metabolites were detected in positive and negative ion modes, respectively. 48 differential metabolites (VIP ≥ 1.5, P < 0.05) might important components affecting flavor differences of Nuodeng ham. Metabolic pathways revealed that fermenting-ripening of ham was associated with 31 metabolic pathways, among, 19 pathways were significant (Impact > 0.01, P < 0.05). 58 volatile compounds were identified, combined with PCA and PLS-DA, 15 flavor markers were screened out. These findings provide a scientific basis for further research on the flavor formation mechanism of Nuodeng ham.

Quantitative Proteomics Reveals the Relationship between Protein Changes and Volatile Flavor Formation in Hunan Bacon during Low-Temperature Smoking

This study aimed to investigate the changes in proteins and volatile flavor compounds that occur in bacon during low-temperature smoking (LTS) and identify potential correlations between these changes. To achieve this, a combination of gas chromatography-mass spectrometry and proteomics was employed. A total of 42 volatile flavor compounds were identified in the bacon samples, and, during LTS, 11 key volatile flavor compounds with variable importance were found at a projection value of >1, including 2',4'-dihydroxyacetophenone, 4-methyl-2H-furan-5-one, Nonanal, etc. In total, 2017 proteins were quantified at different stages of LTS; correlation coefficients and KEGG analyses identified 27 down-regulated flavor-related proteins. Of these, seven were involved in the tricarboxylic acid (TCA) cycle, metabolic pathways, or amino acid metabolism, and they may be associated with the process of flavor formation. Furthermore, correlation coefficient analysis indicated that certain chemical parameters, such as the contents of free amino acids, carbonyl compounds, and TCA cycle components, were closely and positively correlated with the formation of key volatile flavor compounds. Combined with bioinformatic analysis, the results of this study provide insights into the proteins present in bacon at various stages of LTS. This study demonstrates the changes in proteins and the formation of volatile flavor compounds in bacon during LTS, along with their potential correlations, providing a theoretical basis for the development of green processing methods for Hunan bacon.

Identification of dynamic changes in volatile compounds and metabolites during the smoking process of Zhenba bacon by GC-IMS combined metabolomics

Zhenba bacon is a traditional cured bacon product with a rich history that originated from Zhenba County, Shaanxi Province. This study aimed to investigate the patterns of volatile compound formation and changes in metabolites during the smoking process in Zhenba bacon. Firstly, the sensory properties and physicochemical properties of Zhenba bacon were analyzed. Gas chromatography-ion mobility spectrometry (GC-IMS) and nontargeted metabolomics technology were used to analyze Zhenba bacon from different smoking stages. The results show a gradual increase in the sensory acceptance and volatile flavor compounds such as aldehydes, ketones, and esters with the prolongation of smoking of Zhenba bacon. LC-MS analysis identified 191 co-expressed differentially metabolites, with amino acid and lipid metabolism being the main metabolic pathways according to KEGG enrichment analysis. Temporal expression analysis of bacon metabolites at each stage revealed a decrease in harmful steroid hormones such as cortisone and an increase in amino acids and lipid metabolites, such as arginine, lysine, acid, and cholesterol, that contribute to the flavor of bacon. In summary, duration of smoking increased, the amount of flavor substances in Zhenba bacon gradually increased, and the safety and quality of bacon reached the optimal level after 32 days of smoking. This study provides valuable insights into the dynamic changes in volatile flavor compounds in Zhenba bacon and establishes a theoretical foundation for quality control during its production.

Perspective of sodium reduction based on endogenous proteases via the strategy of sodium replacement in conjunction with mediated-curing

NaCl is the main curing agent in dry-cured meat products, and a large amount of NaCl addition leads to high salt content of final products. Salt content and composition are important factors affecting the activity of endogenous proteases, which in turn could affect proteolysis as well as the quality of dry-cured meat products. With the increasing emphasis on the relationship between diet and health, reducing sodium content without sacrificing quality and safety of products is a great challenge for dry-cured meat industry. In this review, the change of endogenous proteases activity during processing, the potential relationship between sodium reduction strategy, endogenous proteases activity, and quality were summarized and discussed. The results showed that sodium replacement strategy and mediated-curing had a complementary advantage in influencing endogenous proteases activity. In addition, mediated-curing had the potential to salvage the negative effects of sodium substitution by affecting endogenous proteases. Based on the results, a sodium reduction strategy that sodium replacement in conjunction with mediated-curing based on endogenous proteases was proposed for the future perspective.

Non-target metabolomics reveals the changes of small molecular substances in duck breast meat under different preservation time

Poultry products are an essential animal source of protein for humans. Many factors could destroy the balance of the poultry production chain and cause an overstock of products, which need to be stored in the frozen storage warehouse for a long time. The long-term frozen storage may affect the quality of meat products. In this study, the changes of small molecular substances were revealed in duck meat during long-term storage using non-targeted metabolomics. The results showed that compared with fresh meat, even if the meat is stored under frozen storage conditions, the number of differential metabolites of frozen storage meat continues to increase with the prolongation of storage time, indicating that the meat composition has changed significantly with the storage time increased. With the increase in storage time, the nitrogen-containing small molecular compounds in duck meat increased (carnosine and anserine, aspartic acid, and tyrosine, 1H-indole-3-acetamide, 2-Hydroxyphenethylamine, 2-Naphylamine, allocystathionine, and O-phosphoethanolamine), the nucleotides decomposition process strengthened (IMP and AMP, GMP and UMP), and the content of organic acid increased (5-hydroxy indole acetic acid, 5-hydroxypentanoic acid and phenylacetate, taurine) and carbohydrate (1-O-sinapoyl-beta-d-glucose, 4-O-beta-d-glucopyranosyl-d-mannose, and alpha-d-glucose). These small molecular substances can be used as biomarkers to detect long-term stored duck meat deterioration. KEGG enrichment analysis showed that protein catabolism, nucleotide catabolism, fat decomposition and oxidation, and carbohydrate decomposition were the main metabolic processes of meat deterioration during the long-term storage of duck meat. In addition, Non-target metabolome technology is a powerful tool to reveal the meat deterioration process during long-term storage systematically. This study provided a reference for optimizing domestic poultry meat storage methods and ensuring food safety.

Sensory Properties and Main Differential Metabolites Influencing the Taste Quality of Dry-Cured Beef during Processing

This study adopted widely targeted high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) metabolomics and multivariate data analysis methods to evaluate the correlation between changes in metabolites and their taste formation in dry-cured beef during processing. The physicochemical profile changed significantly in the maturity period (RG), especially due to the continuous hydrolysis and oxidation of proteins. The sensory characteristic of dry-cured beef was highest in saltiness, umami, overall taste, and after-taste in RG. Overall, 400 metabolites were mainly identified, including amino acids, peptides, organic acids, and their derivatives, nucleotides, and their metabolites, as well as carbohydrates. Cysteine and succinic acid were significantly up-regulated during the process of dry-curing beef compared to the control group (CG). Moreover, glutamine and glutathione were significantly down-regulated in the fermentation period (FG) and in RG. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed that glyoxylate and dicarboxylate metabolism, glutathione metabolism, alanine, aspartate, and glutamate metabolism, arginine biosynthesis, taurine, and hypotaurine metabolism were the main metabolic pathways influencing the taste of dry-cured beef during processing. Results of correlation analysis revealed that umami is positively correlated with salty, L-cysteine, L-arginine, inosine, creatinine, and succinic acid. Our study results provide a better understanding of the changes in taste substances and will contribute to quality evaluation of dry-cured beef.

1H NMR-based water-soluble lower molecule characterization and fatty acid composition of Chinese native chickens and commercial broiler

The aim of this study was to compare the water-soluble low molecular weight (WLMW) compounds and fatty acids (FAs) in raw meat and chicken soup between the two Chinese native chickens (Wuding chicken and Yanjin silky fowl chicken) and one typical commercial broiler (Cobb chicken). The WLMW compounds of chicken meat was studied using ¹H nuclear magnetic resonance spectroscopy (¹H NMR) and the FAs were identified and quantified using gas chromatography-mass spectrometry (GC-MS). Compared with typical commercial broiler, the main flavor substances (WLMW compounds and FAs) content were significantly higher in the breast and leg meat of the two Chinese native chickens (P < 0.05). Instead, the content of main flavor compounds was significantly higher in chicken soup of typical commercial broiler (P < 0.05). These results contribute to a further understanding the distinction of the flavor compounds between the typical commercial broiler and Chinese native chickens, which could be used to help assess the meat quality of different local broilers.

Evaluation by electronic tongue and headspace-GC-IMS analyses of the flavor compounds in dry-cured pork with different salt content

Traditional dry-cured pork, a meat product with a unique flavor and good chewability, occupies an important place in the Chinese market. However, the salt content of dry-cured pork is on the high side and long-term consumption of high-salt meat products is not good for human health. This study determined the role of salt in volatile organic substances and non-volatile taste components of dry-cured pork. Dry-cured pork samples with different salt content (0%, 1%, 3%, 5%, and 7%) were analyzed by electronic tongue for moisture content, pH, salt (NaCl) value, taste activity value, free amino acids, and taste components and by headspace-gas chromatography-ion mobility spectrometry for volatile organic components. The results showed that the moisture content of the tested samples decreased while the salt content increased. The highest amounts of free amino acids were found in dry-cured pork with 3% salt content (P < 0.05). The highest peak area of volatile organic compounds and the maximal taste indexes were found in dry-cured pork with 3% and 5% salt content.

Microbiological properties and volatile compounds of salted-dried goose

Salted-dried goose is a traditional Turkish product with specific flavor that is produced by dry salting, post-salting, and subsequently air-drying of the goose carcass. In this study, the leg and breast parts of salted-dried goose carcasses were analyzed in terms of microbiological properties and volatile compounds. Lactic acid bacteria and Micrococcus-Staphylococcus bacteria constituted a significant part of microbiota in both leg and breast samples. The Enterobacteriaceae count was below the detectable level (<2 log cfu g^-1) in 60% of the leg samples and in 47% of the breast samples. The yeast-mold count was less than 5 log cfu g^-1 in 80% of both leg and breast samples. Many volatile compounds belonging to different chemical groups, including aldehydes, aliphatic and aromatic hydrocarbons, esters, alcohols, terpenes, ketones, sulfur compounds, and furans, were identified from samples. The breast samples showed a higher mean amount of hexanal than the leg samples. No significant difference was found between the breast and leg samples in terms of ketones and sulfur compounds. It was also determined that a considerable part of volatile compounds is formed by lipid oxidation.

Effect of different time of ultrasound treatment on physicochemical, thermal, and antioxidant properties of chicken plasma protein

The aim of present study was to investigate the effect of different times (5 min (UCPP-5), 10 min (UCPP-10), 20 min (UCPP-20), and 30 min (UCPP-30)) of ultrasound treatment on physicochemical, thermal, and antioxidant properties of chicken plasma protein (CPP). UCPP-20 had the highest fluorescence intensity and the lowest particle size. However, no major changes in the subunit compositions and the secondary structure of UCPPs were presented in SDS-PAGE and circular dichroism. The surface hydrophobicity and sulfhydryl content of UCPPs increased significantly (P < 0.05) as compared to those of CPP. With the increasing time of ultrasound treatment, there were more and deeper holes on the protein surfaces. Furthermore, protein modification by ultrasound could improve the thermal properties of UCPPs. Additionally, UCPPs showed a significant increase in antioxidant properties over CPP, especially UCPP-20. These observations indicated that ultrasound treatment was necessary for modification of CPP to meet the requirements for food processing.

1 H-NMR-based water-soluble low molecular weight compound characterization and fatty acid composition of boiled Wuding chicken during processing

BACKGROUND

Boiled Wuding chicken was produced using whole chicken by washing, boiling 1 h with salt, deep frying, and boiling 2 h. The effect of the process on the water-soluble low molecular weight (WLOM) compound profiles of products was characterized using proton nuclear magnetic resonance spectroscopy, and the fatty acid composition of products was analyzed using gas chromatography-mass spectrometry.

RESULTS

The metabolome was dominated by 49 WLOM compounds, and 22 fatty acid compounds were detected. Principal component (PC)1 and PC2 explained a total of 93.4% and 3% of variance respectively. Compared with the control group, the total WLOM compound and fatty acid contents of the chicken breast were significantly decreased in the other three processing stages (P < 0.05). Comprehensive multivariate data analysis showed significant differences about precursor substance between the different processing including creatine, lactate, creatinine, glucose, taurine, anserine, and acetate (P < 0.05).

CONCLUSION

These results contribute to a more accurate understanding of precursor substance changes of flavor in chicken meat during processing. Boiled, treated chicken had significant effects on fatty acid and WLOM compounds. © 2018 Society of Chemical Industry.

1H NMR-based metabolic characterization of Chinese Wuding chicken meat

The aim of this study was to evaluate the chemical composition of precursor flavor substance of Wuding chicken with the age of 110, 140, 170, 200 and 230 days. The metabolic composition of chicken meat was studied using ¹H nuclear magnetic resonance (NMR) spectroscopy. Compared with 110 days, the total metabolite content was significantly higher in other four periods for the chicken breast and leg meat (P < 0.01). Organic acid and small peptides were the two most metabolites for the chicken breast and leg meat. Comprehensive multivariate data analysis showed significant differences about precursor substance between the chicken samples of 230 days and other four ages including lactate, creatine, IMP, glucose, carnosine, anserine, taurine and glutamine (P < 0.05). These results contribute to a further understanding of changes in chicken meat metabolism as chicken ages, which could be used to help assess the quality of chicken meat.

The effect of cooking temperature on the aggregation and digestion rate of myofibrillar proteins in Jinhua ham

BACKGROUND

In order to evaluate the effect of cooking temperature on the nutrition quality of dry-cured hams, 60 biceps femoris samples from 16 Jinhua hams were divided into four groups (control, 70, 100 and 120 °C) and cooked for 30 min. Carbonyl content, sulfhydryl groups, surface hydrophobicity, microstructure, protein aggregation and digestibility of myofibrillar proteins were investigated.

RESULTS

Cooking promoted carbonylation and decreased sulfhydryl groups in a temperature-dependent way. Scanning electron microscopy and Nile Red revealed that protein aggregation became a main phenomenon at 120 °C; it coincided with surface hydrophobicity. The increased carbonyl content and decreased sulfhydryl groups contributed to the formation of aggregates. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles showed the initial difference in proteolysis rate among four groups. The in vitro digestibility of pepsin and of trypsin and α-chymotrypsin increased from the control to 100 °C and decreased from 100 to 120 °C.

CONCLUSION

The increased digestibility could be attributed to the oxidation of proteins and exposing recognition sites of digestive enzymes, while the decreased digestibility was due to the formation of aggregates. Cooking was a main factor that affected the digestibility of Jinhua ham, and cooking at 100 °C could be an ideal way to gain the highest digestibility of Jinhua ham. © 2018 Society of Chemical Industry.

Characteristic Flavor of Traditional Soup Made by Stewing Chinese Yellow-Feather Chickens

The traditional recipe for Chinese chicken soup creates a popular taste of particular umami and aroma. The present study investigated the effects of stewing time (1, 2, and 3 h) on the principal taste-active and volatile compounds and the overall flavor profile of traditional Chinese chicken soup by measuring the contents of free amino acids (FAAs), 5'-nucleotides, minerals and volatile compounds and by evaluating the taste and aroma profiles using an electronic nose, an electronic tongue and a human panel. Results showed that the major umami-related compounds in the chicken soup were inosine 5'-monophosphate (IMP) and chloride, both of which increased significantly (P < 0.05) during stewing. The taste active values (TAVs) of the equivalent umami concentration (EUC) increased from 4.08 to 9.93 (P < 0.05) after stewing for 3 h. Although the FAA and mineral contents increased significantly (P < 0.05), their TAVs were less than 1. The volatile compounds were mainly hexanal, heptanal, octanal, nonanal, (E)-2-nonanal, (E)-2-decenal, (E,E)-2,4-decadienal, 1-hexanol, and 2-pentyl furan. With the prolonged stewing time, the aldehydes first increased and then decreased significantly (P < 0.05), while 1-hexanol and 2-pentyl furan increased steadily (P < 0.05). The aroma scores of the chicken soup reached the maximum after stewing for 3 h. The discrepancy in overall flavor characteristics tended to stabilize after 2 h of stewing. In general, stewing time has a positive effect on improving the flavor profiles of chicken soup, especially within the first 2 h.