Effect of Curing Agents on the Oxidative and Nitrosative Damage to Meat Proteins during Processing of Fermented Sausages

A Comprehensive Review of Cured Meat Products in the Irish Market: Opportunities for Reformulation and Processing

Cured meat products constitute one of the meat categories commonly consumed in Ireland and has been part of the Irish cuisine and diet for many years. Ham, gammon, and bacon are some of the products that involve curing as part of the traditional processing methods. Common among these products are high levels of salt and the addition of nitrites. These products undergo processing treatments to create variety, preserve shelf-life, and develop their unique quality and safety characteristics. However, consumers are becoming more conscious of the level of processing involved in these products, and the effects of some components and ingredients might be perceived as unhealthy. Meat product developers have been exploring ways to reduce the amount of ingredients such as salt, saturated fat, and chemical preservatives (e.g., nitrites), which are linked to health concerns. This is a challenging task as these ingredients play an important techno-functional role in the products' quality, safety, and identity. While innovative processing techniques are being introduced and progress has been made in reformulation and packaging technologies, much is still unknown, especially regarding the applicability of many of the proposed interventions to a wide range of meat products and their sustainability at the industrial scale.

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.

Impact of nitrite-embedded packaging film on quality and sensory attributes of alternatively-cured and nitrite-free bologna

The objectives were to determine the effects of post-thermal processing nitrite-embedded film (NEF) packaging on the quality attributes of alternatively-cured (nitrite from celery juice powder (AC)) and nitrite-free bologna. Attributes evaluated included lipid oxidation, instrumental color, pigment concentration, and sensory properties such as cured meat flavor, aroma, and color. Three bologna formulations, each packaged with two packaging films were produced. A conventionally-cured control formulation (with nitrite from sodium nitrite; CON), a nitrite-free formulation (UCC), and an alternatively cured formulation (nitrite from cultured celery juice powder; AC) were packaged in conventional (CF) or nitrite-embedded (NEF) film. Instrumental a* values (measured during both light and dark storage at intervals of 7 or 14 days over 126 days of storage) and cured pigment concentration (measured at 14-day intervals over 84 days of storage) were significantly greater (P < 0.05) for the UCC-NEF treatment compared to its conventional film counterpart, UCC-CF. No significant differences (P > 0.05) for lipid oxidation (TBARS values) were observed with NEF. Trained sensory panelists, who evaluated samples at 14-day intervals over 70 days of storage, found significantly greater (P < 0.05) cured aroma, cured flavor, pink color and less off-flavor for uncured bologna packaged in NEF compared to conventional film. For the uncured bologna formulation, NEF packaging provided cured meat attributes comparable to the control formulation that included nitrite. This is the first time that cured aroma and flavor have been observed when nitrite from packaging film is added to a cooked meat product under anaerobic conditions.

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.

Influence of Common Reducing Agents on Technological Parameters of Dry-Fermented Sausages with Low Fat Content

The production of dry-fermented sausages currently presents several challenges to be addressed: nutrition, health, sensory traits and technology are among the main issues that concern consumers and the meat industry. The objective of this study was to evaluate the effect of different reducing agents commonly used in the manufacture of dry-fermented sausages (salchichon type) with low fat content on the technological characteristics of the product. Four different reducing agents (ascorbic acid, a starter culture, sodium ascorbate and glucono-delta-lactone) were added to the meat batter to assess their impact on the physico-chemical traits, instrumental color, residual nitrates and nitrites and lipid oxidation of this meat product. High nitrate values were observed during both ripening and storage periods. All batches presented lipid oxidation values below the threshold that indicates meat rancidity. Adjustments of the original lean:fat proportion must be carried out on this low fat content sausage to obtain profitable results. Starter culture and sodium ascorbate have shown the best reducing and antioxidant activities among the additives studied. Once we have the technical design of the product, the next step will be oriented to identify the sensory characteristics in order to find a gap in the market.

Protein carbonylation in food and nutrition: a concise update

Protein oxidation is a topic of indisputable scientific interest given the impact of oxidized proteins on food quality and safety. Carbonylation is regarded as one of the most notable post-translational modifications in proteins and yet, this reaction and its consequences are poorly understood. From a mechanistic perspective, primary protein carbonyls (i.e. α-aminoadipic and γ-glutamic semialdehydes) have been linked to radical-mediated oxidative stress, but recent studies emphasize the role alternative carbonylation pathways linked to the Maillard reaction. Secondary protein carbonyls are introduced in proteins via covalent linkage of lipid carbonyls (i.e. protein-bound malondialdehyde). The high reactivity of protein carbonyls in foods and other biological systems indicates the intricate chemistry of these species and urges further research to provide insight into these molecular mechanisms and pathways. In particular, protein carbonyls are involved in the formation of aberrant and dysfunctional protein aggregates, undergo further oxidation to yield carboxylic acids of biological relevance and establish interactions with other biomolecules such as oxidizing lipids and phytochemicals. From a methodological perspective, the routine dinitrophenylhydrazine (DNPH) method is criticized not only for the lack of accuracy and consistency but also authors typically perform a poor interpretation of DNPH results, which leads to misleading conclusions. From a practical perspective, the biological relevance of protein carbonyls in the field of food science and nutrition is still a topic of debate. Though the implication of carbonylation on impaired protein functionality and poor protein digestibility is generally recognized, the underlying mechanism of such connections requires further clarification. From a medical perspective, protein carbonyls are highlighted as markers of protein oxidation, oxidative stress and disease. Yet, the specific role of specific protein carbonyls in the onset of particular biological impairments needs further investigations. Recent studies indicates that regardless of the origin (in vivo or dietary) protein carbonyls may act as signalling molecules which activate not only the endogenous antioxidant defences but also implicate the immune system. The present paper concisely reviews the most recent advances in this topic to identify, when applicable, potential fields of interest for future studies.

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.

A comprehensive review of the role of microorganisms on texture change, flavor and biogenic amines formation in fermented meat with their action mechanisms and safety

Meat fermentation ensures its preservation, improved safety and quality. This prominently used traditional process has survived for ages, creating physical, biochemical, and microbial changes, and to significantly affect the functionality, organoleptic property, and nutrition of the fermented products. In some process, the growth of various pathogenic and spoilage microorganisms is inhibited. The production of fermented meat relies on naturally occurring enzymes (in the muscle or the intestinal tract) as well as microbial metabolic activities. In this review, fermented meat types and their health benefits were firstly introduced. This was followed by a description of fermentation conditions vis-à-vis starters, bacterial, yeast and mold cultures, and their role in meat. The review focuses on how microorganisms affect texture change, flavor formation, and biogenic amines (BA) accumulation in fermented meat. In addition, the production conditions and the major biochemical changes in fermented meat products were also introduced to present the best factors influencing the quality of fermented meat. Microorganisms and microbial enzymes in fermented meats were discussed as they could affect organoleptic characteristics of fermented meats. Moreover, safety concerns and prospects for further research of fermented meat were also discussed with emphasis on novel probiotic and starter cultures development; bioinformatics, omics technologies and data modeling to maximize the benefit from fermentation process in meat production.

New Insights into the Chemical Reactivity of Dry-Cured Fermented Sausages: Focus on Nitrosation, Nitrosylation and Oxidation

Nitrite and nitrate are added to cured meat for their bacteriological, technological and sensorial properties. However, they are suspected to be involved in the formation of nitroso compounds (NOCs), such as potentially mutagenic nitrosamines, nitrosylheme and nitrosothiols. Controlling the sanitary and sensorial qualities of cured meat products by reducing these additives requires elucidating the mechanisms involved in the formation of NOCs. To this end, we studied the dose-response relationship of added sodium nitrite and/or sodium nitrate (0/0, 80/80, 0/200, and 120/120 ppm) on the formation of NOCs in dry cured fermented sausages. The results showed a basal heme iron nitrosylation in the absence of NaNO2/NaNO3 due to starter cultures. This reaction was promoted by the addition of NaNO2/NaNO3 in the other conditions. Reducing the dose to 80/80 ppm still limits lipid oxidation without the formation of non-volatile nitrosamines. Conversely, the addition of NO2/NO3 slightly increases protein oxidation through higher carbonyl content. The use of 80/80 ppm could be a means of reducing these additives in dry-cured fermented meat products.

Nitrated food proteins induce a regulatory immune response associated with allergy prevention after oral exposure in a Balb/c mouse food allergy model

BACKGROUND

Food allergy is associated with a high personal health and economic burden. For immunomodulation toward tolerance, food compounds could be chemically modified, for example, by posttranslational protein nitration, which also occurs via diet-derived nitrating agents in the gastrointestinal tract.

OBJECTIVE

We sought to analyze the effect of pretreatment with nitrated food proteins on the immune response in a mouse food allergy model and on human monocyte-derived dendritic cells (moDCs) and PBMCs.

METHODS

The model allergen ovalbumin (OVA) was nitrated in different nitration degrees, and the secondary structures of proteins were determined by circular dichroism (CD). Allergy-preventive treatment with OVA, nitrated OVA (nOVA), and maximally nitrated OVA (nOVAmax) were performed before mice were immunized with or without gastric acid-suppression medication. Antibody levels, regulatory T-cell (Treg) numbers, and cytokine levels were evaluated. Human moDCs or PBMCs were incubated with proteins and evaluated for expression of surface markers, cytokine production, and proliferation of Th2 as well as Tregs.

RESULTS

In contrast to OVA and nOVA, the conformation of nOVAmax was substantially changed. nOVAmax pretreated mice had decreased IgE as well as IgG1 and IgG2a levels and Treg numbers were significantly elevated, while cytokine levels remained at baseline level. nOVAmax induced a regulatory DC phenotype evidenced by a decrease of the activation marker CD86 and an increase in IL-10 production and was associated with a higher proliferation of memory Tregs.

CONCLUSION

Oral pretreatment with highly nitrated proteins induces a tolerogenic immune response in the food allergy model and in human immune cells.

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.

Salmonella Brandenburg in the pork chain in Italy: Genetic comparison with the human isolates

Salmonella Brandenburg ranked 16th among the serovars responsible for human infections in EU in 2015 and it was found to be associated with swine. In Emilia- Romagna and Lombardy regions of northern Italy, S. Brandenburg was isolated from mesenteric lymph nodes, fecal matter, carcasses and conveyor belts at pig slaughterhouses in 2014 and 2015. In the same area, S. Brandenburg was detected in pork salami in 2015. In the present study, 12 isolates of S. Brandenburg recovered from the pork food-chain were typed by XbaI PFGE and their three profiles were compared to all human S. Brandenburg isolates processed by the Surveillance System of Emilia- Romagna region from 2012 to 2017 (105 isolates). The most frequent pulsotype of porcine origin (6/12) was the second most frequent in humans (16/105). Of the other two pulsotypes of porcine origine (3/12 each), one was the most frequent in humans (41/105), the other was undetected among human isolates.

Effect of sodium ascorbate and sodium nitrite on protein and lipid oxidation in dry fermented sausages

The effects of sodium nitrite and ascorbate on lipid and protein oxidation were studied during the ripening process of dry fermented sausages. Samples were taken at day 0, 2, 8, 14, 21 and 28 of ripening to assess lipid (malondialdehyde) and protein (carbonyls and sulfhydryl groups) oxidation. Sodium ascorbate and nitrite were separately able to reduce the formation of malondialdehyde. Their combined addition resulted in higher amounts of carbonyl compounds compared to their separate addition or the treatment without any of both compounds. Moreover, sodium nitrite limited the formation of γ-glutamic semialdehyde whereas sodium ascorbate showed a pro-oxidant effect. A loss of thiol groups was observed during ripening, which was not affected by the use of sodium ascorbate nor sodium nitrite. In conclusion, sodium nitrite and ascorbate affected protein and lipid oxidation in different manners. The possible pro-oxidant effect of their combined addition on carbonyl formation might influence the technological and sensory properties of these products.

Antioxidant protection of proteins and lipids in processed pork loin chops through feed supplementation with avocado

This study was conducted to analyze the impact of dietary avocado on the oxidative stability of lipids and proteins during pork processing. Loins from control (fed basic diet) and treated pigs (fed on avocado-supplemented diet) were roasted (102 °C/20 min) and subsequently packed in trays wrapped with oxygen-permeable films and chilled at 4 °C for 12 days. At each processing stage (raw, cooked and cooked & chilled), pork samples from both groups were analyzed for the concentration of TBARS, the loss of tryptophan and free thiols, and the formation of protein carbonyls, disulphide bonds and Schiff bases. Processing led to a depletion of tryptophan and sulfur-containing amino acids and an increase of lipid and protein oxidation products. Dietary avocado was not able to protect against the oxidation of tryptophan and thiols but cooked & chilled loins from treated pigs had significantly lower concentration of lipid and protein carbonyls than control counterparts. Likewise, dietary avocado alleviated the formation of Schiff bases during cooking. These results illustrate the benefits of dietary avocado on the oxidative stability of processed pork loins.

Nitration of β-Lactoglobulin but Not of Ovomucoid Enhances Anaphylactic Responses in Food Allergic Mice

Background

We revealed in previous studies that nitration of food proteins reduces the risk of de novo sensitization in a murine food allergy model. In contrast, in situations with preformed specific IgE antibodies, in vitro experiments suggested an increased capacity of effector cell activation by nitrated food proteins.

Objective

The aim of this study was to investigate the influence of protein nitration on the effector phase of food allergy.

Design

BALB/c mice were immunized intraperitoneally (i.p.) with the milk allergen β-lactoglobulin (BLG) or the egg allergen ovomucoid (OVM), followed by intragastric (i.g.) gavages to induce a strong local inflammatory response and allergen-specific antibodies. Subsequently, naïve and allergic mice were intravenously (i.v.) challenged with untreated, sham-nitrated or nitrated BLG or OVM. Anaphylaxis was monitored by measuring core body temperature and determination of mouse mast cell protease-1 (mMCP-1) levels in blood.

Results

A significant drop of body temperature accompanied with significantly elevated concentrations of the anaphylaxis marker mMCP-1 were only observed in BLG allergic animals challenged with nitrated BLG and not in OVM allergic mice challenged with nitrated OVM. SDS-PAGE and circular dichroism analysis of the differentially modified allergens revealed an effect of nitration on the secondary protein structure exclusively for BLG together with enhanced protein aggregation.

Conclusion

Our data suggest that nitration affects differently the food allergens BLG and OVM. In the case of BLG, structural changes favored dimerization possibly explaining the increased anaphylactic reactivity in BLG allergic animals.

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

The effect of NaNO2 on protein oxidation was studied in isolated myofibrillar protein isolates (100 and 1000 mg NaNO2/kg) and in porcine patties (18 and 180 mg NaNO2/kg). In addition, the potential use of 3-nitrotyrosine as a specific marker for reactive nitrogen species mediated nitration was investigated. Overall, no distinct pro- or antioxidant effect of NaNO2 against carbonyl formation was observed in the isolates or in the patties. However, in the isolates, higher protein carbonyl concentrations were found in the NaNO2-treated samples compared to the treatment without added nitrite immediately after the addition of oxidants and NaNO2. Addition of 180 mg NaNO2/kg to patties resulted in significantly lower thiol concentrations at 4 and 7 days of illuminated chilled display compared to the treatments with 0 and 18 mg/kg NaNO2, whereas no effect was observed in the isolates. No effect of NaNO2 was found on the protein solubility of either meat model. 3-Nitrotyrosine was present in all samples, but no clear effect of NaNO2 addition or oxidation time was observed.