Hydrolysis of oxidized phosphatidylcholines by crude enzymes from chicken, pork and beef muscles

Flavour enhancement of dry fermented sausages by nitrite-degrading Levilactobacillus brevis CHOL1: Combining flavouromics and lipidomics to elucidate the mechanism of aroma formation

Levilactobacillus brevis CHOL1, exhibiting a nitrite degradation rate of 99.03 %, was added to dry fermented sausages to evaluate its effects on product quality, sensory and aroma properties. Lipidomics analysis was performed to explore the mechanism of aroma formation after inoculation. Results showed that Lev. brevis CHOL1 reduced the sausages' pH, water activity, and nitrite residues. Inoculation also imparted desirable texture and sensory characteristics to the sausages. Furthermore, significant increases in alcohol, acid and ester contents were observed, which enhanced the aroma of the sausages. Correlation analysis revealed that Lev. brevis CHOL1 promoted the hydrolysis of PC 36:2 and PC 35:2, thereby facilitating the production of key aroma compounds such as heptanol, hexanol and octanol. These components improved the aroma profile of the sausages. These findings indicate that Lev. brevis CHOL1 inoculation is a promising method to reduce the content of nitrite residues and improve the flavour of dry fermented sausages.

TMT-labelled quantitative proteomics reveals the mechanism of Rhodotorula mucilaginosa on proteolysis of dry-cured ham: Structural protein degradation, amino acid release and taste improvement

To investigate the mechanism of Rhodotorula mucilaginosa on structural protein degradation and taste development of Jinhua ham, the effects of Rhodotorula mucilaginosa and Pichia kudriavzevii on proteolytic enzyme activities, surface hydrophobicity, myofibril microstructure, protein degradation, free amino acids and sensory attributes were investigated during the dry-ripening of Jinhua ham. The inoculation of Rhodotorula mucilaginosa EIODSF019 (RE) and Rhodotorula mucilaginosa XZY63-3 (RX) consistently exhibited higher proteolytic enzyme activities compared with Pichia kudriavzevii XS-5 (PK). The decrease of α-helix exposing more internal hydrophobic groups of myofibrillar proteins, contributed to higher surface hydrophobicity of RE compared with PK and RX. RE showed the highest proteolysis index among all groups, which could be attributed to more degradation of myosin, actin and troponin; the changes were confirmed by the intense breakdown of myofibrils observed by atomic force microscopy and transmission electron microscopy. 36 down-regulated proteins mainly derived from myofibrils and catalysis-related enzymes were identified in RE by TMT-labeled quantitative proteomics analysis. The degradation of myosin, actin and troponin showed the most intense response to the accumulation of glutamic acid, lysine and alanine. Partial least square regression analysis and correlation analysis revealed that the breakdown of MYH14, MYH3, TNNI1 and TNNTI was highly correlated with improvement of umami, richness and aftertaste.

Correlation of lipid hydrolysis, oxidation, and molecular transformation with volatile compound revolution in pork during postmortem wet-aging process

Lipid hydrolysis and oxidation properties, lipid metabolites, and volatile flavors were investigated to elucidate the wet-aging process (1 h to 10 d) on lipid molecule transformation and volatile flavor evolution in pork. Phospholipase A2 (PLA2) activity increased at 12 h, with lipoxygenase (LOX) increasing from 1 h to 7 d (P < 0.05). A total of 546 differential lipids from 997 lipids and 19 aroma-active compounds out of 43 volatiles were identified, with most fatty aldehydes reaching the highest at 10 d. Acyl carnitine (18:2) and hexadecanal are potential markers to predict the wet-aging progress of pork. Correlation analysis indicated that phospholipid molecule hydrolysis by PLA2 and lipid enzymatic oxidation mediated by LOX rather than reactive oxygen species contributed to volatile aldehyde evolution, while phosphatidylcholine (16:2e/22:6) may be the key lipid molecule. These results offer insights into the lipid transformation and aroma evolution in pork during the wet-aging process.

Alterations of meat quality, lipid composition and flavor in breast meat of laying hens with fatty liver hemorrhagic syndrome

Fatty liver hemorrhagic syndrome (FLHS) has a high incidence rate in laying hens, and lots of FLHS-affected meat products enter the market every year. At the same time, the meat of laying hens is an important component of the human diet. However, the impact of FLHS on meat of laying hens is unknown, which could have a negative impact on consumers. To explore the effects of FLHS on chicken breast meat, a total of 36 twenty-five-wk-old Jingfen laying hens were used in the experiment. The hens were randomly divided into Control group and Model group, with 6 replicates per group and 3 hens per replicate. All chickens were raised in double-story step cages with individual pens. After a 3-wk acclimation period, the formal experiment began at 28 wk of age and lasted for 8 wk. Blood, liver, and breast meat samples were collected for the study of FLHS effects on breast meat. The impact of FLHS on meat quality was assessed by measuring indicators such as water-holding capacity and tenderness of the breast meat. Absolute quantitative lipidomics was employed to reveal the impact of FLHS on the lipid composition of chicken breast meat, and then validated by using RT-qPCR. Moreover, the volatilomics was utilized to detect changes in volatile organic compounds (VOCs) in chicken breast meat and to elucidate the resulting flavor changes. This research results showed that the meat quality of chicken breast meat decreased under FLHS, mainly manifested as reduced water holding capacity and decreased tenderness. The lipid content in the breast meat of FLHS-affected hens was significantly increased (P < 0.05). Among the affected lipids, 38 triglycerides exhibited notable elevation, possibly linked to heightened gene expression, such as lysophosphatidylcholine acyltransferase 3. The breast meat of laying hens with FLHS demonstrated an increased presence of VOCs, with 20 differential VOCs identified. Notably, 14 VOCs, particularly in 2-Undecenal, trans-Geranylacetone and ethyl nonanoate, exhibited substantial increases. These 3 VOCs had been identified as playing an important role in the formation of flavor in the breast meat of FLHS-affected laying hens. Correlation analysis suggested that the increase in these 3 VOCs might be related to the increase in lipid molecules such as phosphatidylethanolamine (38;3e) and acyl carnitine (10:3). In summary, FLHS reduced the breast meat quality of laying hens, altered its lipid profiles, and enhanced its flavor. These findings underscore the profound impact of FLHS on lipid and VOC profiles in chicken breast meat, offering valuable insights for chicken meat quality affected by FLHS.

Untargeted metabolomics reveals the alteration of metabolites during the stewing process of Lueyang black-bone chicken meat

Introduction

Black-bone chicken meat is rich in nutritional substances and bioactive compounds. Stewing is a traditional and healthy cooking style for black-bone chicken meat. However, the alteration of metabolites in chicken meat during stewing is still unknown.

Methods

A comprehensive analysis of Lueyang black-bone chicken meat metabolites was performed in fresh chicken meat (FM), short-term heat-pretreated meat (PM), fully cooked meat (CM) and chicken soup (CS) via untargeted metabolomics.

Results

By comparison, 200, 992 and 891 significantly differentially metabolites (DMs) were identified in the PM vs. FM, CM vs. FM and CS vs. FM comparisons, respectively. These DMs mainly included amino acids, peptides, carbohydrates and lipids. During the heating process, the abundances of Ser, Ala, Tyr, niacinamide, galactose, guanosine 3'-monophosphate and inosine 5'-monophosphate in chicken meat significantly decreased and were partially dissolved in the soup. Due to the hydrolysis of phospholipids, the relative contents of unsaturated lipids, especially a range of lysophosphatidylcholines, lysophosphatidylethanolamines, arachidonic acid and derivatives, increased in fully cooked meat.

Discussion

Pretreatment had little impact on the changes in metabolites in chicken meat. During stewing, the dissolved amino acids, carbohydrates and nucleic acids could enhance the taste quality of chicken soup, and the high abundance of unsaturated lipids could promote the nutritional quality of black-bone chicken meat. In summary, these data provide helpful information for nutritional quality studies on the metabolite profiles of black-bone chicken meat.

Insights into the molecular mechanisms of lipid transformation in sturgeon fillets: Interplay between specific spoilage and dominant bacteria

This study investigates spoilage bacteria's impact on lipid metabolism in sturgeon fillets using UHPLC-Q-Orbitrap-MS/MS-based untargeted lipidomic analysis. A total of 4041 lipid molecules across five classes and 42 subclasses were identified, including glycerophospholipids (GPs, 50.88%), glycerolipids (GLs, 36.08%), sphingolipids (SPs, 10.47%), fatty acyls (FAs, 2.45%), and sterol lipids (STs, 0.12%). Aeromonas sobria, a specific spoilage bacterium, reduced GPs and FAs while increasing GLs, SPs, and STs via extracellular lipases and esterases. Acinetobacter albensis, the dominant bacterium, mainly elevated SPs and FAs. Their interaction promoted lipid metabolism and oxidation while producing volatile organic compounds (VOCs). Ethyl isobutyrate, ethyl propionate, isobutyl formate, pentan-2-one, propan-2-one, 2-butanone, 3-methyl-3-buten-1-ol, and dimethyl sulfide were mainly associated with Acinetobacter albensis, while 1-hexanol, 1-pentanol, 1-penten-3-ol, 1-hydroxypropan-2-one, 3-methyl-1-butanol, 2-methylbutanal, 3-hydroxy-2-butanone, and propionaldehyde were mainly related to Aeromonas sobria. This work unveils the mechanism of lipid transformation in sturgeon fillets during refrigerated storage, offering insights for aquatic products quality control.

A study on the catalytic domain of pork phospholipase A2: Enzymatic properties and hydrolysis characteristics of phosphatidylcholine and its hydroperoxide

Endogenous phospholipase A2 (PLA2) plays an important role in phospholipids degradation during cured meat products manufacturing. The present study was undertaken to reveal more information about the endogenous PLA2 in muscles and its role in degradation of intramuscular phospholipids. With the catalytic domain of pork calcium-independent PLA2 (iPLA2cd), impacts of physic-chemical factors on the activity were investigated and substrate specificity of the enzyme were tested respectively. The optimum temperature and pH of pork iPLA2cd were 40 °C and 7.5, respectively. The iPLA2cd could be stimulated by adequate contents of NaCl and ATP, and inhibited by CaCl2 and NaNO2. For native phospholipids, the iPLA2cd was of a little higher affinity towards phosphatidylcholine (PC) than phosphatidylethanolamine (PE), phosphoserine (PS) and phosphatidylinositol (PI). The iPLA2cd could preferentially hydrolyze peroxidized PC over the native PC. The results would help better understand the degradation of phospholipids and the role played by endogenous enzymes during meat products manufacturing.

Exploring potential lipid precursors for aroma formation in non-smoked bacon during hot air drying via untargeted lipidomics and oxidation model

The effect of drying on the lipid profiles of the lean (LN) and fat (FT) portions of non-smoked bacon was investigated based on a lipidomic approach. The study identified 989 lipids belonging to 26 subclasses in bacon, with triglyceride and phosphatidylethanolamine being the most abundant. Triglycerides, phosphatidylcholines, and phosphatidylethanolamines were significantly decreased, whereas diglycerides, free fatty acids, and lysophospholipids were increased after drying. TG (16:1/18:1/18:2) and TG (16:0/18:1/18:1) were the primary lipids responsible for the binding of volatiles. Based on VIP > 1 and P < 0.05, 355 and 444 differential lipids were observed in the FT and LN portions, respectively. In total, 26 lipids were screened as key precursors for the production of key aroma compounds of bacon in the FT portion, while 127 were screened in the LN portion. PE (18:0/18:2) is believed to be the primary lipid molecule precursors responsible for the development of aroma in both lean and fat portions. This research has enhanced the comprehension of the generation of key aroma compounds derived from lipid oxidation.

Evaluation of effects of ultrasound-assisted curing on the flavor of Chinese bacon

The curing stage is of great importance in flavor formation during Chinese bacon processing. Ultrasound-assisted curing plays an essential role in the Lipid oxidation of meat products. In this study, GC-MS and electronic nose were used to analyze the influence of different power ultrasonic-assisted curing on the flavor formation of Chinese bacon. Through the analysis of phospholipid and lipase, the fundamental precursors of ultrasonic on the flavor of Chinese bacon were determined. It was found that there were differences in the flavor contour description of Chinese bacon between the ultrasonic treatment group, mainly due to the change in the W1W sensor. A total of 28 volatile compounds were detected by GC-MS, and the aldehyde content increased with ultrasonic power. PC and PE are the main flavor precursors in the curing process. This study provides a theoretical basis for improving the curing technology of Chinese bacon.

Paradoxical effects of lipolysis on the lipid oxidation in meat and meat products

Lipolysis in meat and meat products is a phenomenon involving hydrolysis of lipids, notably via enzymatic catalysis that takes place even postmortem. During refrigerated and frozen storage of meat, in particular fish, endogenous lipolytic enzymes actively degrade triacylglycerols and phospholipids resulting in accumulation of free fatty acids and other hydrolytic products. A classical conjecture suggests that lipolysis enhances lipid oxidation which is involved in quality deterioration of fresh meat and, to some degrees, flavor development of certain meat products. Recent studies (<5 years) have shown that under some circumstances, lipolysis of certain lipolytic enzymes can inhibit lipid oxidation in muscle models, which provides more insight in lipid oxidation mechanisms in muscle matrices as well as implies potential strategies for improving meat quality. This review will discuss such paradoxical effects and potential mechanisms of lipolysis on lipid oxidation in meat and meat products.

A Water-Dispersible Carboxylated Carbon Nitride Nanoparticles-Based Electrochemical Platform for Direct Reporting of Hydroxyl Radical in Meat

In this paper, carboxylated carbon nitride nanoparticles (carboxylated-g-C₃N₄ NPs) were prepared through a one-step molten salts method. The synthesized material was characterized by transmission electron microscope (TEM), Fourier transform-infrared spectra (FTIR), and X-ray photoelectron spectroscopy (XPS), etc. An electrochemical sensor based on single-stranded oligonucleotide/carboxylated-g-C₃N₄/chitosan/glassy carbon electrode (ssDNA/carboxylated-g-C₃N₄/chitosan/GCE) was constructed for determination of the hydroxyl radical (^•OH), and methylene blue (MB) was used as a signal molecule. The sensor showed a suitable electrochemical response toward ^•OH from 4.06 to 122.79 fM with a detection limit of 1.35 fM. The selectivity, reproducibility, and stability were also presented. Application of the sensor to real meat samples (i.e., pork, chicken, shrimp, and sausage) was performed, and the results indicated the proposed method could be used to detect ^•OH in practical samples. The proposed sensor holds a great promise to be applied in the fields of food safety.

Process optimization and the relationship between the reaction degree and the antioxidant activity of Maillard reaction products of chicken liver protein hydrolysates

The aim of this study was to optimize the protein hydrolysates from chicken liver with xylose under Maillard reaction (MR) conditions using response surface methodology. The correlation between the browning degree, grafting degree, and the antioxidant activities of the Maillard reaction products (MRPs) was investigated. The optimal reaction conditions were achieved with a reaction temperature of 138.78°C, an initial pH of 7.99, and a reaction time of 93.14 min. The grafting degree (41.98%) and browning degree (2.582) of chicken liver protein hydrolysate MRPs (CLPHM) were notably higher (P < 0.05) than those of protein MRPs (CLPM) and were significantly lower (P < 0.05) than those of sonicated hydrolysate MRPs (SCLPHM). The reducing power, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and hydroxyl radical scavenging of CLPM, CLPHM, and SCLPHM were significantly higher (P < 0.01) than those of the protein or hydrolysate substrates. The grafting degree and browning degree of CLPM, CLPHM, and SCLPHM had positive correlations with DPPH and hydroxyl radical scavenging activity. Hence, this study could enhance the added value of chicken liver by exhibiting the enhancements from ultrasound pretreatment and the MR. MRPs could have an effective and potential application in the food industry.