Protein oxidation and protein nitration influenced by sodium nitrite in two different meat model systems

The improvement effects of Lentinus edodes powder marination on sous vide cooked chicken patties: Physicochemical attributes, oxidative properties and flavor characteristics

The improvement effects of Lentinus edodes powder (LEP) marination with different concentrations (0, 6-14 %) on physicochemical, oxidative and flavor quality of chicken patties were evaluated. Greater pH, redness, yellowness, water holding capacity and their strong correlations were observed in LEP-marinated samples. Changed water distribution, inhibited lipid oxidation and enhanced protein oxidation occurred through LEP marination. The highest gel strength and resilience and the lowest hardness and chewiness were obtained in 10 % LEP-marinated sample. Meanwhile, taste activity values of amino acids and saltiness peaked and umami rose in this sample. 124 volatiles were detected and 16 compounds were simultaneously detected by gas chromatography-ion mobility spectrometry and gas chromatography-mass spectrometry. Hexanal, 1,2,4-trithiolane and 1-hexanol were considered as the key differential aroma-active compounds according to odor activity values and chemometric analysis. This study confirmed LEP as a prospective ingredient to improve the quality of meat products.

The effects of using sheep tail fat and cooking time on carboxymethyl-lysine formation and some quality characteristics of heat-treated sucuk

The study's aim was to determine the effect of using sheep tail fat (STF) on carboxymethyl-lysine (CML) content and other properties of heat-treated sucuk (HTS), a type of semi-dry fermented sausage. Three mixtures were prepared: 100% beef fat (BF), 50% BF + 50% STF, and 100% STF. After production (fermentation, heat treatment, and drying), the samples were cooked at 180°C for 0, 1, 3, and 5 min to determine the effect of cooking time on CML, thiobarbituric acid reactive substance (TBARS), total sulfhydryl, and carbonyl contents. The lowest pH value (5.50) was observed in the presence of STF. The most oleic acid (46.02%) was observed in the 100% STF group. The score of taste and general acceptability decreased with increasing STF. Using STF had no significant effect on TBARS, total sulfhydryl, carbonyl, or CML content. These parameters were affected by cooking time. The mean CML content increased from 55.77 to 72.90 μg/g after 5 min of cooking. CML correlated more strongly with TBARS than sulfhydryl or carbonyl.

Effects of Edible Organic Acid Soaking on Color, Protein Physicochemical, and Digestion Characteristics of Ready-to-Eat Shrimp upon Processing and Sterilization

Soft-packed ready-to-eat (RTE) shrimp has gradually become popular with consumers due to its portability and deliciousness. However, the browning caused by high-temperature sterilization is a non-negligible disadvantage affecting sensory quality. RTE shrimp is processed through "boiling + vacuum soft packing + high temperature and pressure sterilization". Ultraviolet-visible (UV) spectroscopy with CIELAB color measurement showed that phytic acid (PA) + lactic acid (LA), PA + citric acid (CA), and PA + LA + CA soaking before cooking alleviated browning, as well as UVabsorbance and the browning index (BI). Meanwhile, UV spectroscopy and fluorescence spectroscopy showed that organic acid soaking reduced the content of carbonyl, dityrosine, disulfide bonds, surface hydrophobicity, and protein solubility, but promoted the content of free sulfhydryl and protein aggregation. However, in vitro digestion simulations showed that organic acid soaking unexpectedly inhibited the degree of hydrolysis and protein digestibility. This study provides the basis for the application of organic acids as color protectors for RTE aquatic muscle product.

Assessing the Impact of Pomegranate Peel Extract Active Packaging and High Hydrostatic Pressure Processing on Color and Oxidative Stability in Sliced Nitrate/Nitrite-Reduced Iberian Dry-Cured Loins

Our study aimed to assess the impact of active packaging with pomegranate peel extract (0.06 mg gallic acid eq./cm2) and/or high-pressure treatment (600 MPa, 7 min) on the instrumental color, lipid, and protein oxidation of Iberian dry loins formulated with reduced nitrate/nitrite levels (0, 37.5, and 150 mg/kg) during 100-day refrigerated storage (4 °C). CIE L*a*b* coordinates were measured, and malondialdehyde, carbonyls, and free thiol contents served as markers for lipid and protein oxidation. Active packaging lowered CIE L* (35.4 vs. 34.1) and a* (15.5 vs. 14.5) and increased yellowness (15.6 vs. 16.3) and hue (45.2 vs. 48.4), while pressurization increased CIE L* (33.1 vs. 36.3) and diminished a* values (16.1 vs. 13.9). Ongoing nitrate/nitrite amounts significantly influenced lipid peroxidation, protein carbonyl formation, and free thiol loss. Active packaging and high-pressure processing had varying effects on carbonyl and thiol contents. Neither pressurization nor active packaging impacted malondialdehyde formation. Pressurization enhanced the formation of 4-HNE (503 vs. 697 pg/g). Protein oxidation proved more sensitive to changes, with active packaging offering protection against protein carbonylation (15.4 vs. 14.7 nmol carbonyls/mg protein), while pressurization induced thiol loss (34.3 vs. 28.0 nmol Cys eq./mg protein). This comprehensive understanding provides essential insights for the meat industry, emphasizing the necessity for customized processing conditions to enhance color stability, lipid preservation, and protein integrity in dry-cured loin slices.

Effects of muscle-specific oxidative stress on protein phosphorylation and its relationship with mitochondrial dysfunction, muscle oxidation, and apoptosis

This study aimed to investigate the effects of muscle-specific oxidative stress on phosphorylation and its relationship with mitochondrial dysfunction, muscle oxidation, and apoptosis of porcine PM (psoas major) and LL (longissimus lumborum) during the first 24 h postmortem. The global phosphorylation level decreased and the mitochondrial dysfunction, oxidation level, and apoptosis increased significantly at 12 h postmortem compared with 2 h postmortem, suggesting that lower phosphorylation level was related to more mitochondrial dysfunction and apoptosis during the early postmortem, regardless of muscle type. PM exhibited a higher global phosphorylation level but showed greater mitochondrial dysfunction, oxidation level, and apoptosis than LL, regardless of aging time. The increased mitochondrial dysfunction and oxidative stress accelerated apoptosis, but their relationship with phosphorylation was different in various muscle types at different aging times. These findings provide insight regarding the roles of coordinated regulation of phosphorylation and apoptosis in development of quality of different muscles.

Pomegranate peel as a source of antioxidants for the control of lipid and protein oxidation during the ripening of Iberian dry uncured sausages

This study aimed to evaluate a pomegranate peel extract (PPE), selected for its level of phytochemical compounds and antioxidant activities, as a nitrite substitute in dry sausages, as well as its effect on lipid and protein oxidative changes and instrumental colour during the drying period (28 days). Of the extraction solvents screened, water: acetone 3:7 (v/v) was the most effective extraction solvent, yielding extracts with the highest content of phenolic compounds, flavonoids and condensed tannins and antioxidant activities (ABTS, DPPH and FRAP). Four batches of dry sausages were produced with different incoming amounts of sodium nitrite (NaNO₂) and PPE: 1) 150 ppm NaNO₂; 2) 0 ppm NaNO₂; 3) 0 ppm NaNO₂ + 1% PPE (v/w) and 4) 0 ppm NaNO₂ + 2% PPE (v/w). Nitrite removal increased lipid oxidation in uncured dry sausages, while nitrite and PPE caused lower TBA-RS values in cured and PPE treated sausages. During drying, both nitrite and PPE addition significantly decreased carbonyl and thiol contents compared to the uncured dry sausages. A dose-response was found for PPE, with lower carbonyl and thiol concentrations, the higher the level of PPE added. PPE significantly modified instrumental colour coordinates L*a*b* producing significant total colour changes compared to cured dry sausages.

Research Progress of Nitrite Metabolism in Fermented Meat Products

Nitrite is a common color and flavor enhancer in fermented meat products, but its secondary amines may transfer to the carcinogen N-nitrosamines. This review focuses on the sources, degradation, limitations, and alteration techniques of nitrite. The transition among NO3− and NO2−, NH4+, and N2 constitutes the balance of nitrogen. Exogenous addition is the most common source of nitrite in fermented meat products, but it can also be produced by contamination and endogenous microbial synthesis. While nitrite is degraded by acids, enzymes, and other metabolites produced by lactic acid bacteria (LAB), four nitrite reductase enzymes play a leading role. At a deeper level, nitrite metabolism is primarily regulated by the genes found in these bacteria. By incorporating antioxidants, chromogenic agents, bacteriostats, LAB, or non-thermal plasma sterilization, the amount of nitrite supplied can be decreased, or even eliminated. Finally, the aim of producing low-nitrite fermented meat products is expected to be achieved.

Incorporation of betel leaf extract provides oxidative stability and improves phytochemical, textural, sensory and antimicrobial activities of buffalo meat sausages

The antioxidant effect of betel leaf extract (BLE) on lipid and protein oxidation, microbial count and physicochemical attributes was investigated in meat sausages during refrigerated storage at 4 ± 1 °C. Buffalo meat sausages were developed after incorporating 0, 250, 500 and 750 mg kg^-1 of BLE (BLE0, BLE1, BLE2 and BLE3) respectively. The sausages showed no changes in proximate composition due to BLE inclusion, but there was an improvement in microbial quality, color score, textural properties and lipid and protein oxidative stability. Further, higher sensory scores were observed for the BLE-incorporated samples. The images from scanning electron microscopy (SEM) revealed a reduction in surface roughness and unevenness showing microstructure modification in BLE treated sausages compared to the control sausages. Hence, to improve the storage stability and impede the rate of lipid oxidation in sausages, BLE incorporation proved to be an effective strategy.

Effect of Nitric Oxide and Its Induced Protein S-Nitrosylation on the Structures and In Vitro Digestion Properties of Beef Myofibrillar Protein

This study aimed to investigate the effects of nitric oxide (NO) and its induced protein S-nitrosylation on the structures and digestion properties of beef myofibrillar protein (MP). The MP was treated with 0, 50, 250, 500, and 1000 μM concentrations of NO-donor S-nitrosoglutathione (GSNO) for 30 min at 37 °C. The results indicated that GSNO treatment significantly decreased the sulfhydryl contents whereas the carbonyl contents increased. Meanwhile, compared with the control group, the surface hydrophobicity, the intrinsic fluorescence intensity, and the α-helix content of proteins were decreased significantly with the enhancement of GSNO concentrations. In addition, 250 μM GSNO treatment increased the gastric digestibility of MP, while the gastrointestinal digestibility and the release of peptides were both inhibited by 500 and 1000 μM GSNO treatments. These data demonstrate that protein S-nitrosylation can affect the in vitro digestion properties of proteins by altering the physicochemical properties and structure of MP.

Ellagic Acid Triggers the Necrosis of Differentiated Human Enterocytes Exposed to 3-Nitro-Tyrosine: An MS-Based Proteomic Study

To study the molecular basis of the toxicological effect of a dietary nitrosated amino acid, namely, 3-nitrotyrosine (3-NT), differentiated human enterocytes were exposed to dietary concentrations of this species (200 μM) and analyzed for flow cytometry, protein oxidation markers and MS-based proteomics. The possible protective role of a dietary phytochemical, ellagic acid (EA) (200 μM), was also tested. The results revealed that cell viability was significantly affected by exposure to 3-NT, with a concomitant significant increase in necrosis (p < 0.05). 3-NT affected several biological processes, such as histocompatibility complex class II (MHC class II), and pathways related to type 3 metabotropic glutamate receptors binding. Addition of EA to 3-NT-treated cells stimulated the toxicological effects of the latter by reducing the abundance of proteins involved in mitochondrial conformation. These results emphasize the impact of dietary nitrosated amino acids in intestinal cell physiology and warn about the potential negative effects of ellagic acid when combined with noxious metabolites.

Scavengome of an antioxidant

The term "scavengome" refers to the chemical space of all the metabolites that may be formed from an antioxidant upon scavenging reactive oxygen or nitrogen species (ROS/RNS). This chemical space covers a wide variety of free radical metabolites with drug discovery potential. It is very rich in structures representing an increased chemical complexity as compared to the parent antioxidant: a wide range of unusual heterocyclic structures, new CC bonds, etc. may be formed. Further, in a biological environment, this increased chemical complexity is directly translated from the localized conditions of oxidative stress that determines the amounts and types of ROS/RNS present. Biomimetic oxidative chemistry provides an excellent tool to model chemical reactions between antioxidants and ROS/RNS. In this chapter, we provide an overview on the known metabolites obtained by biomimetic oxidation of a few selected natural antioxidants, i.e., a stilbene (resveratrol), a pair of hydroxycinnamates (caffeic acid and methyl caffeate), and a flavonol (quercetin), and discuss the drug discovery perspectives of the related chemical space.

Protective Effects of Four Natural Antioxidants on Hydroxyl-Radical-Induced Lipid and Protein Oxidation in Yak Meat

The impacts of natural antioxidants, including ferulic acid, diallyl sulfide, α-tocopherol, and rutin, at a level of 0.2 g/kg on lipid and protein oxidation of minced yak meat in a hydroxyl-radical-generating system were investigated, and the effectiveness was compared with synthetic antioxidant 2,6-di-tert-butyl-4-methylphenol (BHT). The exposure of yak meat to oxidative stress from 12 h to 24 h elevated lipid and protein oxidation. Treatments with antioxidants resulted in significantly lower peroxides, conjugated dienes, and thiobarbituric acid-reactive substances, and were also effective in retarding the formation of carbonyl groups, reducing the loss of sulfhydryl groups and protecting α-helix contents, of which ferulic acid and rutin were the most effective. Myosin heavy chain underwent lower degradation in the samples treated with ferulic acid or rutin compared with the oxidized control and other antioxidant treatments, while that of the BHT treatment showed a similar intensity with oxidized control at 24 h of oxidation. The physical stability of myofibrillar proteins in samples with antioxidants from high to low was rutin, ferulic acid, α-tocopherol, and BHT~diallyl sulfide. These results indicate that rutin and ferulic acid may be promising antioxidants in inhibiting the oxidative reactions during the processing of yak meat.

Combined effect of beet powder and lentil flour as a partial nitrite substitute on physicochemical, texture and sensory characteristics, color, and oxidative stability of pork bologna

The combined effect of beet powder (BP; 0.1%, 0.3%, and 0.5%) and 6% lentil flour (LF) as a partial nitrite substitute on quality attributes of pork bologna incorporated with 7.5% mechanically separated pork during 12 weeks of cold storage was evaluated. A randomized block experimental design with nine treatments and five storage times (0, 3, 6, 9, and 12 weeks) was used for pH, thiobarbituric acid reactive substance, protein oxidation (carbonyl and sulfhydryl), and color parameters. Bologna preparation at a pilot plant scale was replicated three times. LF addition resulted (p < 0.05) in higher viscosity, emulsion stability, and lower expressible drip. Together BP and LF decreased protein oxidation during storage but were not as effective as nitrite with respect to lipid oxidation. Bologna with BP addition showed lower lightness and higher redness, whereas LF increased lightness and decreased redness. A consumer panel rated color acceptability of bologna lower with LF addition, whereas BP raised color acceptability. However, addition of the highest BP level alone to the bologna was negatively perceived as a result of the low acceptability of purge color of the vacuum-packaged bologna slices. Consequently, the combination of BP and LF could be used to improve eating quality and stability attributes when used as a potential nitrite substitute.

The effect of a polystyrene nanoplastic on the intestinal microbes and oxidative stress defense of the freshwater crayfish, Procambarus clarkii

The widespread generation and accumulation of plastic waste has become a globally recognized problem. However, there are limited reports on the adverse effects of nanomaterials on freshwater crustaceans. This study tested the acute effects of different concentrations (0, 5, 10, and 20 mg/L) after 48 h exposure of 75 nm polystyrene nanoplastic on intestinal microbes, and oxidative stress parameters of freshwater crayfish, Procambarus clarkii. High-throughput sequencing analysis revealed the richness, diversity, and composition of intestinal microbiota in P. clarkii exposed to polystyrene nanoplastic. At the genus level, abundances of Lactobacillus, Faecalibaculum, Niveibacterium, and Candidatus Bacilloplasma were significantly different. The reduced abundance of Lactobacillus could affect the balance of intestinal microbes through quantitative disadvantage, which may lead to reduced immunity of P. clarkii. Streptococcus salivarius, Clostridium butyricum and Lachnospiraceae bacterium10-1 in intestinal tract reached maximum abundance at a polystyrene concentration of 20 mg/L. The increase in the number of some pathogenic bacteria may upset the balance of intestinal microorganisms through the number of dominance, and the decrease in the relative abundance of lactic acid bacteria. Probiotics, such as Lactobacillus salivarius, Lactobacillus murinus, Lactobacillus gasseri, Lactobacillus reuteri, Lactobacillus iners AB-1, and Lactobacillus crispatus in the intestinal tract reached the lowest value at a concentration of 10 mg/L. The reduced abundance of Lactobacillus can affect the balance of intestinal microbes through quantitative disadvantage, which may lead to reduced immunity in P. clarkii. At nanoplastic 10 mg/L, the relative abundance of intestinal pathogens increased, while the relative abundance of lactic acid bacteria and other probiotics decreased. With increases in nanoplastic concentrations, the values of glutathione (GSH), superoxide dismutase (SOD), acid phosphatase (ACP), lysozyme (LZM), alkaline phosphatase (AKP), peroxidase (POD), glutathione peroxidase (GPX), and protein carbonylation were significantly changed. Our data suggested that Lactobacillus may play an adjunctive role in the treatment of oxidative stress in P. clarkii exposed to 75 nm polystyrene. This study represents an important step towards a better understanding of the toxic effects of nanoplastics on aquatic crustaceans.

Effects of nitrite concentrations on the quality and protein oxidation of salted meat

The objective of this study was to investigate the effects of different concentrations of sodium nitrite on the quality and protein oxidation of salted meat during 21 days of curing. The salted meat was treated with sodium nitrite at 50, 100, and 150 mg/kg for curing, and salted meat without sodium nitrite was used as a control. The results showed that in salted meat added with sodium nitrite, the carbonyl group, disulfide bond, dityrosine, surface hydrophobicity, and the transformation rate from α-helix to β-sheet were all significantly reduced, whereas the sulfhydryl group content of myofibrillar proteins was significantly increased compared to the control. Meanwhile, the total volatile basic nitrogen and aerobic plate content were significantly decreased, while both the pH and a* value were significantly increased with an increase in nitrite concentration compared to the control group. Importantly, this phenomenon was also observed in salted meat treated with low doses of sodium nitrite (50 mg/kg). In conclusion, the quality of salted beef can be improved by adding low-dose sodium nitrite to inhibit protein oxidation during the curing process. PRACTICAL APPLICATION: A low dose of sodium nitrite inhibited the rate of α-helix to β-sheet transformation of myofibrillar proteins in salted meat, reducing the exposure of hydrophobic groups and decreasing the production of protein oxidation products and TVB-N to improve the quality of salted meat. These results provided a theoretical basis and technical guidance for the application of low-dose sodium nitrite in meat processing enterprises.

Alteration of Mitochondrial Lipidome and Its Potential Effect on Apoptosis, Mitochondrial Reactive Oxygen Species Production, and Muscle Oxidation in Beef during Early Postmortem

Lipid molecules are important participants in mitochondria-mediated apoptosis. This study explored the effect of mitochondrial lipids on mitochondria-mediated apoptosis, mitochondrial reactive oxygen species (ROS) production, and muscle oxidation of beef longissimus lumborum (LL, n = 6) and psoas major (PM, n = 6) during 24 h postmortem. A total of 432 lipid species matched with 21 lipid classes were identified. Remarkably, at 12 h postmortem, the levels of cardiolipin and phosphatidylserine in PM and ceramide, cardiolipin, phosphatidylserine, and sphingosine in LL increased significantly compared with 1 h postmortem, indicating that mitochondria-mediated apoptosis in beef muscle was accelerated during early postmortem. Moreover, PM had higher levels of cardiolipin and phosphatidylserine than LL, also suggesting a higher degree of apoptosis in PM during postmortem. Lipid molecules may assist the production of mitochondrial ROS and decrease the mitochondrial membrane potential (MMP) during postmortem apoptosis, resulting in muscle oxidation and the damage of antioxidant system. Notably, compared with LL, PM had higher abundance of apoptosis-related lipid molecules, a higher amount of ROS, faster diminishment in MMP, and then a higher degree of apoptosis. These findings provided new insights into the apoptosis and muscle biochemistry in beef during early postmortem.

Impact of Various Dry-Aging Methods on Meat Quality and Palatability Attributes of Beef Loins (M. longissimus lumborum) from Cull Cow

The objective of this study was to determine the effect of various dry-aging methods on meat quality and palatability attributes of cull cow beef loins. Paired bone-in loins (m. longissimus lumborum) from 13 cull cow carcasses (Holstein, 42þ mo) were obtained at 5 d postmortem, divided into 4 equal sections, and randomly assigned into 4 aging methods (wet-aging [WA], conventional dry-aging [DA], dry-aging in water-permeable bag [DWA], and ultraviolet light dry-aging [UDA]). The beef sections were aged for 28 d at 2°C, 65% relative humidity, and 0.8 m/s airflow. Following aging, surface crusts and bones were removed, and loin samples were collected for the meat quality, microbiological, and sensory analyses. Results indicated that all dry-aged loins had greater moisture and trimming loss compared with WA (P &lt; 0.05), while DWA had lower loss than DA and UDA (P &lt; 0.05). No differences in shear force, cook loss, or both lipid and protein oxidation across all treatments were observed (P &gt; 0.05). Among all treatments, DWA exhibited the least color stability indicated by rapid discoloration observed in the sample, while UDA had color attributes comparable with WA throughout the whole display. Microbial analysis indicated that UDA had lower microbial concentration on the surface than the other samples (P &lt; 0.05). The consumer panel analysis found that all loins were acceptable, and the trained panel analysis indicated that DA loins decreased sourness and animal fat flavor (P &lt; 0.05) and had a trend of decreasing oxidized flavor (P = 0.07). The results indicate that dry-aging can potentially be utilized as an effective natural process by nullifying some of well-known off-flavor attributes associated with cull cow beef while not compromising other meat quality attrib- utes or microbiological shelf life.

Exacerbated Protein Oxidation and Tyrosine Nitration through Nitrite-Enhanced Fenton Chemistry

Nitrite is a common additive used during meat curing to prevent microbial contamination and retain an attractive red color in the product. However, the effects of nitrite on Fenton reactions catalyzed by free iron in meat products are not well understood, although such processes can induce protein oxidation and nitration, affecting the nutritional and aesthetic quality of meat products. This contribution reveals the mechanism through which nitrite affects Fenton reactions that generate reactive nitrogen and oxygen species by increasing the availability of Fe³⁺, facilitating its reduction and stabilizing Fe²⁺, and accelerating Fe³⁺/Fe²⁺ cycling, leading to exacerbated oxidative and nitrosative stress on proteins, with implications not only for meat processing but also in many biological and environmental processes due to the ubiquitous presence of iron, hydrogen peroxide, and nitrite in nature.

Formation of Lipid and Protein Oxidation Products during In Vitro Gastrointestinal Digestion of Dry-Cured Loins with Different Contents of Nitrate/Nitrite Added

The effect of nitrate/nitrite (0, 37.5, 75, and 150 mg/kg) in the dry-cured loin formulation on the formation of lipid and protein oxidation products during in vitro digestion was evaluated. Dry-cured loins formulated with nitrate/nitrite resulted in significantly less lipid and protein oxidation than uncured loins before and after simulated digestion. Compared to loins added with 0 mg/kg nitrate/nitrite, dry-cured loins with 37.5, 75, and 150 mg/kg contained a significantly lower content of conjugated dienes, malondialdehyde, carbonyls, and non-heme iron, and higher amounts of nitrosylmioglobin and thiols. During in vitro digestion, the content of conjugated dienes, malondialdehyde, and carbonyls increased, while thiol content decreased, indicating the development of lipid and protein oxidative processes. At the end of the intestinal phase, the 75 mg/kg digests had a significantly higher content of conjugated dienes, while no differences were found among the other digests. During the in vitro intestinal phase (180 and 240 min), nitrate/nitrite curing resulted in significantly lower malondialdehyde concentrations in the 37.5, 75, and 150 mg/kg loin digests than in the uncured loin digests. No significant differences were observed at the end of the intestinal digestion phase between the cured loin digests. Digests of dried loins without nitrate/nitrite addition showed higher carbonyl contents than the nitrate/nitrite cured counterparts. The loss of thiols was significantly higher in loin digests without added nitrate/nitrite than in loin digests with different amounts of curing salts. The addition of 37.5 mg/kg nitrate/nitrite in the cured loin formulation prevents the formation of lipid peroxidation products and carbonyls from protein oxidation and thiol loss during digestion.

Critical overview of the use of plant antioxidants in the meat industry: Opportunities, innovative applications and future perspectives

The number of articles devoted to study the effect of "natural antioxidants" on meat systems has remarkably increased in the last 10 years. Yet, a critical review of literature reveals recurrent flaws in regards to the rationale of the application, the experimental design, the characterisation of the plant sources, the discussion of the molecular mechanisms and of the potential benefits. The selection of the appropriate source of these antioxidants and the identification of their bioactive constituents, are essential to understand their mode of action and set effective and safe doses. The methodological approach should also be planned with care as the recorded effects and main conclusions largely depend on the accuracy and specificity of the methods. This article aims to critically review the recent advances in the application of plant antioxidants in meat and meat products and briefly covers current trends of innovative application and future trends.

Effect of Pig Breed and Processing Stage on the Physicochemical Properties of Dry-Cured Loin

This study investigated the effect of pig breeds on the quality characteristics of dry-cured loins according to the processing stage. Physicochemical properties of 20 dry-cured processed loins with the different pig breeds [Berkshire vs Landrace×Yorkshire× Duroc (LYD; n=10)] and different processing stages (raw, curing, dry-ripened 15 day and 30 day) were analyzed. The pig breed influenced moisture content and pH with values of 59% and 53%, and 6.17 and 5.94, for Berkshire and LYD, respectively, on day 30. Dry-cured loins made with Berkshire showed higher hardness and lower cohesiveness than that of the LYD (p<0.05). Redness and yellowness were higher for Berkshire than LYD (p<0.05). Lipid oxidation and lightness did not affect by pig breed during processing stages (p>0.05). However, sulfhydryl content was significantly higher in Berkshire compared to the LYD after dry-ripened for 15 days (p<0.05). The concentration of total free amino acids and fatty acids was higher for Berkshire during all processing stages (p<0.05). Berkshire may be better quality due to its high moisture content and pH compared to the LYD.

Antioxidant activity of purslane extract and its inhibitory effect on the lipid and protein oxidation of rabbit meat patties during chilled storage

BACKGROUND

Currently, synthetic antioxidants have been widely used to retard lipid and protein oxidation in the meat industry. However, consumers have concerns about these synthetic antioxidants because of their potential toxicological effects. Accordingly, natural antioxidants can be used as a result of their health safety compared to synthetic antioxidants. The present research aimed to assess the protective effects of purslane (Portulaca oleracea L.) extract (PE) against lipid and protein oxidation under chilled storage for 12 days. Rabbit meat patties were divided into five experimental groups: control (without extract), butylated hydroxytoluene BHT (with 0.02% BHT, w/w) and the different concentrations of PE (0.1%, 0.3% and 0.5%, w/w) added to rabbit meat patty labeled as 0.1% PE, 0.3% PE and 0.5% PE groups, respectively. 1,1-Diphenyl-2-picrylhydrazyl (DPPH), 2,2'-azinobis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging activity, lipid oxidation and protein oxidation were determined, and kinetic models were employed.

RESULTS

PE showed the strongest DPPH and ABTS radical scavenging activity, and the half maximal inhibitory concentrations (i.e. IC₅₀ ) of DPPH and ABTS radicals were 5.112 ± 0.384 and 12.607 ± 2.130 μg mL^-1 , respectively. Samples that were treated with PE showed low lipid and protein oxidation. Furthermore, the results of kinetic models indicated that PE could reduce the rates of lipid and protein oxidation.

CONCLUSION

PE showed a preservative effect with respect exerting a protective effect against lipid and protein oxidation under chilled storage conditions. Our findings demonstrate the strong potential of PE as a natural antioxidant in meat and meat products. © 2020 Society of Chemical Industry.

Utilizing Pork Exudate Metabolomics to Reveal the Impact of Aging on Meat Quality

This study was performed to assess the changes in meat quality and metabolome profiles of meat exudate during postmortem aging. At 24 h postmortem, longissimus lumborum muscles were collected from 10 pork carcasses, cut into three sections, and randomly assigned to three aging period groups (2, 9, and 16 d). Meat quality and chemical analyses, along with the metabolomics of meat exudates using ultra-high-performance liquid chromatography coupled with a quadrupole time-of-flight mass spectrometer (UHPLC-QTOF-MS) platform, were conducted. Results indicated a declined (p < 0.05) display color stability, and increased (p < 0.05) purge loss, meat tenderness, and lipid oxidation as aging extended. The principal component analysis and hierarchical clustering analysis exhibited distinct clusters of the exudate metabolome of each aging treatment. A total of 39 significantly changed features were tentatively identified via matching them to METLIN database according to their MS/MS information. Some of those features are associated with adenosine triphosphate metabolism (creatine and hypoxanthine), antioxidation (oxidized glutathione and carnosine), and proteolysis (dipeptides and tripeptides). The findings provide valuable information that reflects the meat quality’s attributes and could be used as a source of potential biomarkers for predicting aging times and meat quality changes.

In vitro and in vivo digestion of red cured cooked meat: oxidation, intestinal microbiota and fecal metabolites

Mechanisms explaining epidemiological associations between red (processed) meat consumption and chronic disease risk are not yet elucidated, but may involve oxidative reactions, microbial composition alterations, inflammation and/or the formation of toxic bacterial metabolites. First, in vitro gastrointestinal digestion of 23 cooked beef-lard minces, to which varying doses of nitrite salt (range 0-40 g/kg) and sodium ascorbate (range 0-2 g/kg) were added, showed that nitrite salt decreased protein carbonylation up to 3-fold, and inhibited lipid oxidation, demonstrated by up to 4-fold lower levels of 'thiobarbituric acid reactive substances', 32-fold lower 4-hydroxynonenal, and 21-fold lower hexanal values. The use of ascorbate increased the antioxidant effect of low nitrite salt levels, whereas it slightly increased protein carbonylation at higher doses of nitrite salt. The addition of a low dose of ascorbate without nitrite salt slightly promoted oxidation during digestion, whereas higher doses had varying antioxidant effects. Second, 40 rats were fed a diet of cooked chicken- or beef-lard minces, either or not cured, for three weeks. Beef, compared to chicken, consumption increased lipid oxidation (2- to 4-fold) during digestion, and gut protein fermentation (cecal iso-butyrate, (iso-)valerate, and fecal indole, cresol), but oxidative stress and inflammation were generally not affected. Cured, compared to fresh, meat consumption significantly increased stomach protein carbonylation (+16%), colonic Ruminococcaceae (2.1-fold) and cecal propionate (+18%), whereas it decreased cecal butyrate (-25%), fecal phenol (-69%) and dimethyl disulfide (-61%) levels. Fecal acetaldehyde and diacetyl levels were increased in beef-fed rats by 2.8-fold and 5.9-fold respectively, and fecal carbon disulfide was 4-fold higher in rats consuming cured beef vs. fresh chicken. Given their known toxicity, the role of acetaldehyde and carbon disulfide in the relation between meat consumption and health should be investigated in future studies.

Elucidating mechanisms involved in flavor generation of dry-aged beef loins using metabolomics approach

The present study was conducted to identify flavor-related chemical compounds and to elucidate beef flavor development in response to dry-aging. Paired grass-fed beef loins (n = 18) were obtained at 7 d postmortem, cut into two sections and assigned to 3 aging methods: conventional dry-aging (DA), vacuum packaged wet-aging (WA) and dry-aging in a bag (DW) for 28 days. Following aging, samples were analyzed for UPLC-MS metabolomics, volatile, fatty acid profiling, and consumer sensory comment analysis. Greater number of proteins and nucleotides derived metabolites were liberated in dry-aged samples compared to WA (P < 0.05). In particular, the liberation of gammaglutmayl peptides and glutamine metabolites through the glutathione metabolism were identified. While fatty acid profile was not affected by treatments (P > 0.05), higher concentrations of volatile compounds were found in the dry-aged (P < 0.05). Dry-aging process decreased the presence of terpenoid and steroid lipid group, which could possibly result in reducing undesirable flavor of grass-fed beef.

Chemical Characterization and Sensory Relationships of Beef M. longissimus lumborum and M. gluteus medius Steaks After Retail Display in Various Packaging Environments

Volatile compounds, carbonyls, non-heme iron, and thiobarbituric acid reactive substances (TBARS) were measured in both raw and cooked beef samples to determine the effects of muscle and packaging type on beef flavor development. All paired strip loins and top sirloin butts were packaged under vacuum and aged for 14 d postmortem. After initial aging, all subprimals were fabricated to produce M. gluteus medius (GM) or M. longissimus lumborum (LL) steaks. At 14 d postmortem, steaks were randomly assigned to 1 of 5 package types: high-oxygen modified atmosphere lidded trays (80% O2/20% CO2 [“HIOX”]), carbon monoxide modified atmosphere lidded trays (0.4% CO/30% CO2/69.6% N2 [“CO”]), rollstock (forming and non-forming films [“ROLL”]), vacuum packaging without retail display (“VAC”), and traditional overwrap (“OW”) remained under vacuum prior to retail display. Steaks were stored in darkness an additional 7 d prior to display. At 21 d postmortem, HIOX, OW, CO, and ROLL packages were displayed for 48 h under continuous fluorescent lighting, while VAC steaks remained in dark storage. Packaging and muscle type impacted (P &lt; 0.05) quantities of multiple volatile flavor compounds, including alcohols, n-aldehydes, esters, furans, hydrocarbons, sulfur-containing compounds,and ketones in both raw and cooked samples. Volatile compounds related to lipid oxidation were more (P &lt; 0.05) prominent in HIOX packaging. Package type (P &lt; 0.05) and muscle (P &lt; 0.05) had an impact on raw-steak TBARS, although package type did not influence (P &gt; 0.05) cooked-steak TBARS. The GM possessed greater (P &lt; 0.05) TBARS values than the LL in both raw and cooked samples. Package type had no effect (P &gt; 0.05) on carbonyl and non-heme iron content although these analyses differed among muscles (P &lt; 0.05), with the GM being greater (P &lt; 0.05) than the LL. These results indicate that the development of lipid oxidation that occurs during storage and display was muscle and packaging specific. Therefore, to maintain flavor, quality packaging systems should be selected on a muscle-specific basis.

Assessment of the Stability of Fresh Beef Patties with the Addition of Clove Extract during Frozen Storage

The study assessed the stability for fresh beef patties with the inclusion of clove extract (CE) as a natural antioxidant in comparison to butylated hydroxytoluene (BHT) and ascorbic acid (AA) at frozen storage. Four different patties were made dependent on the added antioxidants: control (added no antioxidants), added with 0.02% BHT, 0.05% AA, and 0.1% CE. Inclusion of BHT, AA, and CE resulted in a significant reduction of thiobarbituric acid reactive substances (TBARS) and hue angle (h°) value and increase of redness (CIE a*) and chroma (C*) values (p<0.05). BHT, AA, and CE were observed effectively to retard lipid oxidation and increase color stability. BHT and AA revealed significantly (p<0.05) higher thiol content than the control and CE. However, the reduction percentage for thiol content in CE treated patties was lower than the control and AA-treated patties from first to last time of storage. Moreover, inclusion of AA and CE led to significantly (p<0.05) increased heme iron content when compared to BHT and the control. In conclusion, CE can replace the application of AA and BHT while improving lipid stability, heme iron content, and color stableness of fresh beef patties throughout frozen storage.

Combined impacts of initial freezing rate of pork leg muscles (M. biceps femoris and M. semitendinosus) and subsequent freezing on quality characteristics of pork patties

The objective of this study was to determine the combined impacts of initial sub-primal freezing with subsequent freezing of manufactured pork patties on quality attributes and oxidative stability. Patties were manufactured (n = 3 batches) from pork leg muscles (M. biceps femoris and M. semitendinosus) frozen at different methods including still-air freezing (SAF), blast freezing (BF), and cryogenic freezing (CF). Then, patties were subjected to additional freezing treatments. Frozen/thawed patties exhibited increased cooking loss, springiness, and chewiness, lipid and protein oxidation, and decreased protein solubility compared to unfrozen counterparts (P < .05). However, patties from CF legs maintained similar protein solubility and lipid/protein oxidation compared to unfrozen controls (P > .05), while significantly minimizing sub-primal thawing loss and oxidation compared to patties from SAF. The results of the present study suggest the importance of initial freezing rate of sub-primals with subsequent freezing on quality characteristics of frozen/thawed meat patties.

Commercial luncheon meat products and their in vitro gastrointestinal digests contain more protein carbonyl compounds but less lipid oxidation products compared to fresh pork

Because of the large diversity in processed meat products and the potential involvement of oxidation processes in the association between red and processed meat consumption and chronic diseases, the concentration of oxidation products after gastrointestinal digestion of commercial luncheon meat products was investigated. A broad spectrum of meat products (n = 24), displaying large variation in macro- and micronutrient composition and processing procedures, was digested in vitro by simulating digestion fluids of the human gastrointestinal tract. Lipid and protein oxidation was assessed in the meat products before digestion and in the corresponding digests by measurement of free malondialdehyde, 4-hydroxy-2-nonenal, hexanal and protein carbonyl compounds. Compared to an unprocessed cooked pork mince, that was included as a reference in the digestion experiment, levels of lipid oxidation products were low in the digests of most meat products. Only the digests of Parma ham had slightly higher or comparable levels as the reference pork. In contrast, protein carbonyl compounds were comparable or up to 6 times higher in the processed meat products compared to the reference pork. Particularly raw-cooked and precooked-cooked meat products and corresponding digests had higher protein carbonyl levels, but also lower protein contents and higher fat to protein ratios. In conclusion, most luncheon meat products and corresponding digests contained lower amounts of free lipid oxidation products, but more protein carbonyl compounds compared to the reference pork.

Functional/physicochemical properties and oxidative stability of ground meat from broilers reared under different photoperiods

Long photoperiods are used in the broiler industry to maximize animal performance, though the impact on meat quality remains poorly understood. The current study evaluated the impact of photoperiod on functional/physicochemical properties and oxidative stability of meat through broiler processing. Ross 308 broilers (n = 432) were randomly assigned to 4 photoperiod treatments (hours in L = light, D = dark): 20L:4D, 18L:6D, 16L:8D, or 12L:12D with 6 pens per treatment. At 42 D of age, 2 broilers per pen (n = 12 per treatment) were harvested under standard conditions. Broiler tenderloin (M. Pectoralis minor) and leg muscles were removed at 1 D postmortem and frozen/stored at -40°C. After 24 h thawing at 2°C, the samples were deboned, ground, and formed into patties in 3 independent batches. Photoperiod had no impact on pH, water-holding capacity, textural profile, meat emulsion activity index, and thiol content (P > 0.05). The patties from 12L:12D and 16L:8D had lower CIE b∗ (yellowness) values than 18L:6D and 20L:4D (P < 0.05), whereas 12L:12D had lower chroma (color intensity) values than other treatments (P < 0.05). The meat from 20L:4D exhibited lower sarcoplasmic protein solubility than other treatments (P < 0.05), whereas both 20L:4D and 18L:6D exhibited lower total protein solubility than 12L:12D (P < 0.05). Higher transmission values (indication of protein denaturation) were observed in 20L:4D than in other treatments (P < 0.05), whereas 12L:12D also maintained lower values than both 18L:6D and 16L:8D (P < 0.05). There was an interaction (P < 0.05) between photoperiod and display storage on 2-thiobarbituric acid reactive substances values, where the patties from 12L:12D maintained less lipid oxidation compared with the patties from other treatments. Results of this study suggest photoperiod has limited impact on meat quality attributes, though rearing broilers with a 12L:12D lighting schedule may be beneficial in reducing protein denaturation and improving lipid stability.

Investigation of the effect of sodium nitrite on protein oxidation markers in food protein suspensions

The aim of this study is to investigate the effect of sodium nitrite (NaNO₂ ) on protein oxidation and the use of 3-nitrotyrosine (3NT) as a protein oxidation marker in suspensions of the food protein. Food proteins, namely bovine serum albumin, casein, and myofibrillar protein, were suspended in 100 mM sodium phosphate buffer and nitrated with 25 µM iron (III) chloride, 2.5 mM hydrogen peroxide, and 150 mg/kg NaNO₂ at 37°C for a period of 24 hr. The food protein suspensions were analyzed at different sampling periods for the loss of tryptophan (TRY) residues as well as the formation of Schiff bases (SBs), protein carbonyls, 3NT, and dityrosine (DT). It was found that NaNO₂ has pro-oxidant activity in NaNO₂ -added food protein suspensions due to the increased amounts of SBs, protein carbonyls, 3NT, and DT as well as decreased TRY fluorescence. Positive correlations between the 3NT and other protein oxidation markers except for TRY fluorescence were found in NaNO₂ -added food protein suspensions. In conclusion, these findings on the detection of 3NT indicate that it might be a useful tool as a new protein oxidation biomarker in food samples. PRACTICAL APPLICATIONS: Sodium nitrite (NaNO₂ ) supports protein oxidation in different food protein suspension. 3-nitrotyrosine (3NT) was found in food protein suspensions and can be a potential biomarker for protein nitration in food sample due to potential relationship between 3NT and other oxidation markers. The results showed that this study has formed novel insight into interaction between NaNO₂ and food proteins and indicate that it might affect the food quality and its nutritional value. Moreover, the relationship between protein oxidation/nitration and food quality as well as the comprehension of the scientific and technological meaning of these phenomena has been hindered because of the lack of knowledge about the basic chemistry behind the protein oxidation and nitration pathways. For the clarification of these phenomena, further studies are still needed.

Immune Effects of the Nitrated Food Allergen Beta-Lactoglobulin in an Experimental Food Allergy Model

Food proteins may get nitrated by various exogenous or endogenous mechanisms. As individuals might get recurrently exposed to nitrated proteins via daily diet, we aimed to investigate the effect of repeatedly ingested nitrated food proteins on the subsequent immune response in non-allergic and allergic mice using the milk allergen beta-lactoglobulin (BLG) as model food protein in a mouse model. Evaluating the presence of nitrated proteins in food, we could detect 3-nitrotyrosine (3-NT) in extracts of different foods and in stomach content extracts of non-allergic mice under physiological conditions. Chemically nitrated BLG (BLGn) exhibited enhanced susceptibility to degradation in simulated gastric fluid experiments compared to untreated BLG (BLGu). Gavage of BLGn to non-allergic animals increased interferon-γ and interleukin-10 release of stimulated spleen cells and led to the formation of BLG-specific serum IgA. Allergic mice receiving three oral gavages of BLGn had higher levels of mouse mast cell protease-1 (mMCP-1) compared to allergic mice receiving BLGu. Regardless of the preceding immune status, non-allergic or allergic, repeatedly ingested nitrated food proteins seem to considerably influence the subsequent immune response.

Effects of Heating Time and Temperature on Functional Properties of Proteins of Yellow Mealworm Larvae (Tenebrio molitor L.)

Although the yellow mealworm (Tenebrio molitor L.) is a promising alternative protein source, the effects of processing conditions on functional properties are unclear. In this study, a protein extract of yellow mealworm larvae (PEYM) was subjected to different heat temperature (55°C, 75°C, and 95°C) with different time (20, 40, and 60 min) to evaluate the functional properties and protein oxidation. Different heat temperature treatment significantly affected the exposure of surface hydrophobicity of the proteins and protein molecule aggregation, which reached maximum levels at 95°C for 60 min. Protein oxidation was inversely proportional to the temperature. Both the highest carbonyl value (1.49 nmol/mg protein) and lowest thiol value (22.94 nmol/mg protein) were observed at 95°C for 60 min. The heating time-temperature interaction affected several functional properties, including solubility, emulsifying potential, and gel strength (GS). Solubility decreased near the isoelectric point (pH 5 to 6). As the temperature and heating time increased, emulsifying properties decreased and GS increased. The oil absorption capacity and foaming properties decreased and the water absorption capacity increased. These results confirmed that PEYM is a suitable source of proteins for processing and applications in the food industry.

Effect of Different Storage-Temperature Combinations on Longissimus dorsi Quality upon Sous-vide Processing of Frozen/Thawed Pork

This study investigated the effect of storage state (chilled state on sous-vide, CS; frozen state without thawing on sous-vide, FS; and frozen/thawed states on sous-vide, TS) and sous-vide cooking temperature (65°C and 72°C) on the longissimus dorsi muscle quality of pork. FS showed a higher moisture content than that of CS and TS (p<0.001), whereas both FS and CS showed higher expressible moisture loss than that of TS (p<0.001). FS showed a lower cooking loss (p<0.001) than that of CS and TS. FS and TS exhibited significantly higher lipid oxidation than that of CS. Carbonyl and sulfhydryl content were not significantly affected by the storage treatment. FS and TS exhibited lower shear force than that of CS (p<0.001). FS and TS showed higher springiness than that of CS (p<0.001), FS exhibited lower gumminess than that of CS and TS (p<0.01). Sous-vide treatment at 65°C exhibited significantly higher moisture content and lower expressible moisture loss, cooking loss, and total and sarcoplasmic protein than those at 72°C. Shear force and springiness of 65°C-treated groups were lower than those of 72°C-treated groups (p<0.01). Cooking temperature significantly influenced overall acceptability, whereas the storage state did not affect the overall acceptability. These results indicated that meat quality might be improved upon cooking from the frozen or frozen/thawed state using sous-vide when compared with traditional processing.

Lipid and Protein Oxidation during in Vitro Gastrointestinal Digestion of Pork under Helicobacter pylori Gastritis Conditions

Helicobacter pylori gastritis affects gastric pH and concentrations of ascorbic acid, hydrogen peroxide, hypochlorite, ammonia and urea, pepsin, and mucin. First, the separate effects of each of these altered factors on oxidation of pork were investigated during in vitro gastrointestinal digestion. Lipid and protein oxidation increased (range 23-48%) in duodenal digests of pork previously exposed to elevated (6.1) versus normal acidic stomach pH (2.3 to 3.5) conditions. Salivary nitrite reduced the formation of lipid and protein oxidation products (range 14-20%) under normal acidic but not elevated stomach pH conditions. Higher amounts of hydrogen peroxide and lower amounts of ascorbic acid decreased concentrations of lipid oxidation products in duodenal pork digests, whereas ammonia slightly stimulated protein oxidation during digestion. Second, two H. pylori gastritis-duodenal digestion models were installed using a set of altered compound concentrations at normal acidic or elevated stomach pH. The elevated pH-gastritis-duodenal digestion model increased pork protein oxidation compared with the normal pH-gastritis and the normal digestion model (14.3 ± 2.1 vs 8.2 ± 1.0 nmol DNPH/mg protein, P < 0.001). Compared with the other models, protein oxidation was also increased when nitrite-cured pork was exposed to the elevated pH-gastritis-duodenal digestion model (10.8 ± 1.4 vs 5.9 ± 0.8 nmol DNPH/mg protein, P < 0.001), but no significant effect of the model was observed when the pork was seasoned with herbs. Lipid oxidation was not or was marginally affected by the installed model.

Effect of Allium hookeri Root on Physicochemical, Lipid, and Protein Oxidation of Longissimus Dorsi Muscle Meatball

The antioxidant effects of Allium hookeri root (AHR) were investigated by evaluating lipid and protein oxidation in meatballs during refrigerated storage at 4±1℃. AHR was mixed at concentrations of 0.5% (w/w, T2) and 1% (w/w, T3) with minced longissimus dorsi muscle. Meatballs containing AHR (T2 and T3) were compared to those containing 0.05% (w/w) ascorbic acid (T1) as a reference and without antioxidant as a control. The 2-thiobarbituric acid reactive substances (TBARS) value, disulfide bond formation, carbonyl contents, and volatile basic nitrogen (VBN) value of T2 were lower than those of the control during storage (p<0.05). The pH values of T2 and T3 were higher than that of the control (p<0.05). Texture profile analysis of T2 revealed a lower value compared to the control (p<0.05). Therefore, the VBN value, TBARS value, disulfide bond formation, and carbonyl content in meatball containing AHR were lower than those of the control meatball. These results indicate that AHR improves the quality of meat products and functions as an antioxidant.

Protein oxidation and proteolysis during roasting and in vitro digestion of fish (Acipenser gueldenstaedtii)

BACKGROUND

Roasted fish enjoys great popularity in Asia, but how roasting and subsequent digestion influence the oxidation and proteolysis of fish meat is unknown. This study aimed to investigate the effect of roasting time on lipid and protein oxidation and their evolution and consequence on proteolysis during simulated digestion of fish fillets.

RESULTS

Several oxidation markers (thiobarbituric acid-reactive substances (TBARS), free thiols, total carbonyls and Schiff bases) were employed to assess the oxidation of fish. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and the 2,4,6-trinitrobenzenesulfonic acid (TNBS) assay for free amino groups were used to study the proteolysis during gastrointestinal digestion. The results showed that significant lipid and protein oxidative changes occurring in roasted fish fillets were reinforced after gastric digestion and were much more intense after intestinal digestion. Throughout roasting and digestion, a close interconnection between lipid and protein was also manifested as the levels of total carbonyls and Schiff bases rose while TBARS fell. Furthermore, free amino groups decreased with prolonged roasting time, signifying that protein oxidation before digestion resulted in impaired proteolysis during digestion.

CONCLUSION

This study indicated that the lipid and protein oxidation of fish fillets could be dependent on time of roasting, and the oxidation continued to develop and have an impact on proteolysis during in vitro digestion. © 2018 Society of Chemical Industry.

The Dry-aging and Heating Effects on Protein Characteristics of Beef Longissiumus Dorsi

The aim of this study was to investigate the effects of dry-aging (DA) and the cooking process on the myofibril protein functionalities and in vitro digestibility of proteins in beef loin. Six sirloins from beef were dry-aged for 28 d, and the control group (n=6) was analyzed 2 d postmortem for this study. Dimensional changes (reduction of thickness and surface shrinkage) after cooking were significantly greater in the control group than the DA group, whereas the shear force of the DA group was significantly lower than that of the control. Effect of cooking on aggregation, hydrophobicity, and in vitro digestibility were significantly higher in the DA group than in the control. After cooking, the protein in DA sirloins was more oxidized than in the control samples. According to the sodium dodecyl sulfate-polyacrylamide gel electrophoresis result, the low molecular weight bands (below 17 kDa) increased in the DA group, finding that the protein characteristics of dry-aged beef was affected by cooking.

Inhibition of Epigallocatechin-3-gallate/Protein Interaction by Methyl-β-cyclodextrin in Myofibrillar Protein Emulsion Gels under Oxidative Stress

Nowadays, natural antioxidants abundant in polyphenols have been widely used to substitute synthetic antioxidants in meat products. In general, high doses of natural antioxidants are required to provide comparative antioxidant effects as synthetic antioxidants. Noticeably, the qualities of meat products can be jeopardized due to interactions between polyphenols and myofibrillar proteins (MPs). In this study, methyl-β-cyclodextrin was used to increase the polyphenol loading amount by preventing interactions between polyphenols and proteins. Solubility, electrophoresis, fluorescence spectroscopy, and surface hydrophobicity analyses indicated that methyl-β-cyclodextrin could dose-dependently inhibit epigallocatechin-3-gallate-induced attacks on MPs under oxidative stress. Gel strength, cooking loss, confocal laser scanning microscopy, dynamic rheological testing, and Raman spectrum during gelation were further analyzed to investigate the effects of methyl-β-cyclodextrin on the qualities of epigallocatechin-3-gallate-treated emulsion gel. Methyl-β-cyclodextrin addition prevented modification of the secondary structure of MPs caused by epigallocatechin-3-gallate. In consequence, the gel and emulsifying properties of MPs were significantly improved. Moreover, β-cyclodextrins could partly inhibit oxidative attacks on MPs and thus increase their solubility. These results indicated that methyl-β-cyclodextrin addition effectively enhanced epigallocatechin-3-gallate loading capacity in meat products.