Effect of nitrate and nitrite on Listeria and selected spoilage bacteria inoculated in dry-cured ham

Dual-mode SERS/colorimetric sensing of nitrite in meat products based on multifunctional au NPs@COF composite

The presence of nitrite in food products has generated significant public concern. A simple and rapid dual-mode surface-enhanced Raman spectroscopy (SERS)/colorimetric detection of nitrite is proposed based on a diazo reaction and multifunctional gold nanoparticle-doped covalent organic framework (Au@COF) composite. Under acidic conditions, the reaction between toluidine blue and nitrite yielded a colorless diazo salt, simultaneously attenuating its characteristic absorption peak and Raman signal. The multifunctional Au@COF materials enhanced the Raman signal and ensured good reproducibility. Additionally, the reaction rates improved, and the sensitivity was enhanced due to the excellent adsorption capacity of the COF. The proposed method demonstrated high sensitivity and excellent recovery rates for nitrite detection in food samples. This approach shows potential for precisely detecting nitrite content in real-world food samples by integrating the simplicity of colorimetric analysis with the enhanced sensitivity of SERS.

A New, Rapid, Colorimetric Chemodosimeter, 4-(Pyrrol-1-yl)pyridine, for Nitrite Detection in Aqueous Solution

With increasing concerns over environmental impact and overall health of both the environment and its people, a need to quantify contaminants is of the utmost importance. Chemosensors with low detection limits and a relative ease of application can address this challenge. Nitrite ions are known to be detrimental to both the environment and human health. A new colorimetric chemodosimeter has been prepared from the homolytic photochemical cleavage of a reaction between pyrrole and pyridine. The product, 4-(pyrrol-1-yl)pyridine, yields a limit of detection of 0.330 (±0.09) ppm for the detection of nitrite in aqueous solution, employing a colorimetric change from yellow to pink. It is also highly selective for nitrite when various competitive anions such as SO3 2-, NO3 -, PO4 3-, SO4 -2, Cl-, F-, I-, Br-, AcO-, and CN- are present in great excess. The molecule's especially high sensitivity to nitrite is apparently the result of a complex supramolecular mechanism, characterized by both dynamic light scattering of the aggregate and the Tyndall effect. Consequently, this new sensor provides a simple, low-cost way to rapidly detect nitrite anions in aqueous solution.

Microbiological and physicochemical profile of Italian steak tartare and predicting growth potential of Listeria monocytogenes

In the present study, growth potential of Listeria monocytogenes in steak tartare samples taken at retail and belonging to 13 brands marketed in Northern Italy was investigated. The samples were submitted to microbiological and chemical-physical characterization. The data obtained were used as inputs for the application of the predictive microbiology software FSSP that allows the estimation of the growth of L. monocytogenes during the shelf-life. Lactic acid bacteria, the main component of the microflora, gave variable counts among the brands (from 3.38 to 6.24 log CFU/g). pH and aw values were always higher than 5.3 and 0.96, respectively, thus they could not be considered as single efficient hurdles to prevent the growth of L. monocytogenes according to the EC Reg. 2073/2005; the same was observed for salt content (constantly <2 %) and nitrites (not quantifiable in all the samples, even if declared in some labels). Nevertheless, the combination of all the hurdles, evaluated by predictive microbiology using critical development factors, resulted in an estimated growth <0.5 log CFU/g throughout the shelf life; this output allowed us to consider all the steak tartare analysed as unfavourable substrate for L. monocytogenes growth. The information obtained could be useful for tartare producers as well as for competent authority to evaluate the effective risk concerning these typology of products.

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.

Assessment of dietary exposure to food additives used in Polish processed meat products

Dietary exposure assessments have been performed for nitrites, phosphates, erythorbic acid, and sodium erythorbate in processed meat in Poland. The exposure has been estimated based on the maximum level of use of additives contained in Regulation - tier 2 and the concentration of additives in processed meat - tier 3, additionally for nitrites. Daily intake was estimated using 24-h recall, repeated three times. Exposure analyses were correlated with the frequency of occurrence of food additives based on label analysis (tiers 2a and 3a). The mean nitrite intake from processed meat at tier 2 was 0.1 mg/kg bw (143% ADI), 0.08 mg/kg bw (118% - ADI) at tier 2a, 0.03 mg/kg bw (43% - ADI) at tier 3, and 0.026 mg/kg bw (37% - ADI) at tier 3a. The mean intakes of phosphate and erythorbic acid/sodium erythorbate from processed meat were 3.26 and 0.54 mg/kg bw (8.2% and 9% - ADI), respectively at tier 2. None of the respondents exceeded the ADIs for phosphates or erythorbic acid/sodium erythorbate. In contrast, nitrite consumption is of great concern because of significant ADI exceedances, particularly among young children.

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.

Accurate quantification, naked eyes detection and bioimaging of nitrite using a colorimetric and near-infrared fluorescent probe in food samples and Escherichia coli

Nitrite (NO₂^-) is an inorganic contaminant that exists widely in the environment including water and food products, excessive amounts of NO₂^- would threaten humans and aquatic life. Developing a rapid and convenient sensing method for NO₂^- remains a great challenge. Herein, a colorimetric and near-infrared fluorescent probe (TBM) was synthesized and applied for sensitively and selectively detecting NO₂^- in water, food samples and Escherichia coli (E. coli). With the addition of NO₂^-, the probe TBM solution has a distinct visual color changed from red to colorless and fluorescence intensity at 620 nm quickly decreased. The probe TBM could detect NO₂^- quantitatively with a detection limit of 85 nM based on a 3σ/slope. Under optimum conditions, TBM has been successfully used to detect NO₂^- in real-world environmental and dietary samples, with positive results. Besides, paper strips loaded with TBM have been used to visually determine NO₂^- levels. Most importantly, TBM has also been proven to be able to discriminate from different concentrations of NO₂^- in E. coli by fluorescence imaging. In summary, the probe TBM was successfully developed for the accurate quantification, naked eyes detection and bioimaging of NO₂^- in water, food samples and E. coli, which provides a useful tool to better guarantee the quality and safety of daily life and food industry.

Easy Nitrite Analysis of Processed Meat with Colorimetric Polymer Sensors and a Smartphone App

We have developed an in situ methodology for determining nitrite concentration in processed meats that can also be used by unskilled personnel. It is based on a colorimetric film-shaped sensory polymer that changes its color upon contacting the meat and a mobile app that automatically calculates the manufacturing and residual nitrite concentration by only taking digital photographs of sensory films and analyzing digital color parameters. The film-shaped polymer sensor detects nitrite anions by an azo-coupling reaction, since they activate this reaction between two of the four monomers that the copolymer is based on. The sensory polymer is complemented with an app, which analyzes the color in two different digital color spaces (RGB and HSV) and performs a set of 32 data fittings representing the concentration of nitrite versus eight different variables, finally providing the nitrite concentration of the test samples using the best fitting curve. The calculated concentration of nitrite correlates with a validated method (ISO 2918: 1975) usually used to determine nitrite, and no statistically significant difference between these methods and our proposed one has been found in our study (26 meat samples, 8 prepared, and 18 commercial). Our method represents a great advance in terms of analysis time, simplicity, and orientation to use by average citizens.

Antimicrobial activity of essential oils and natural plant extracts against Listeria monocytogenes in a dry-cured ham-based model

BACKGROUND

Listeria monocytogenes is a widespread common contaminant in food production facilities during preparation, storage, and distribution, and minimally processed ready-to-eat products are considered at high risk of contamination by this bacterium. Increased antibiotic resistance has led researchers to search for plant-based natural alternatives to control pathogenic microorganisms. Among these products, essential oils and plant extracts have previously shown antimicrobial activity and are possible alternatives to manage food pathogens. In this study, commercial essential oils (cinnamon, clove, oregano, ginger, and thyme) and plant extracts (pomegranate, acorn, olive, strawberry tree, and dog rose) were tested against L. monocytogenes in a dry-cured ham-based model.

RESULTS

Essential oils and plant extracts were screened by agar diffusion and minimum inhibitory concentration for anti-L. monocytogenes activity. Cinnamon, pomegranate, and strawberry trees returned the strongest results and were therefore evaluated in a dry-cured ham-based medium assay with water activity of 0.93 or 0.95. The 10% essential oil of cinnamon was capable of completely inhibiting bacterial growth, while strawberry tree and pomegranate extract also showed antilisterial activity (P > 0.05). Water activity influenced the bacterial count of L. monocytogenes in a dry-cured ham-based medium.

CONCLUSIONS

There was a reduction in L. monocytogenes with the application of cinnamon essential oil but, because of the negative sensory impact of this particular compound in meat products, we suggest the use of pomegranate or strawberry tree for the biocontrol of Listeria in ready-to-eat products. © 2021 Society of Chemical Industry.

Strategies for Nitrite Replacement in Fermented Sausages and Effect of High Pressure Processing against Salmonella spp. and Listeria innocua

The development of nitrite-free meat products is a current industrial concern. Many efforts have been attempted to replace the nitrite effect in cured meats colour formation and pathogens control. Our previous work evidenced that lactic acid and a cold ripening were the best hurdle technologies for nitrite-free fermented sausages from metabolomics. In the first part of this work, we investigated the effect of lactic acid compared with both two alternative additives (glucono-D-lactone and a mix of sodium di-acetate/sodium lactate) and with low-nitrite sausages, all of them following either cold or traditional ripening. For this purpose, microbiological analysis, pH, water activity (aw), and a sensory study were performed. All nitrite-free sausages (cold or traditional ripened) showed quality and safety traits similar to low-nitrite traditionally ripened ones used as control. In addition, sensory study revealed that sausages with lactic acid were the most preferred cold ripened samples, supporting that this is an optimal strategy for the production of nitrite-free sausages. We selected this product for further studies. Indeed, in the second part, we evaluated the impact of ripening, and other hurdle technologies as High Pressure Processing (HPP) and under-vacuum storage against Listeria innocua and Salmonella spp. by a challenge test. Maximal declines were obtained for ripening along with HPP (i.e., 4.74 and 3.83 log CFU/g for L. innocua and Salmonella spp., respectively), suggesting that HPP might guarantee nitrite-free sausages safety. Although the quality of raw materials remains essential, these hurdle strategies largely contributed to nitrite-free sausages safety, offering a promising tool for the meat industry.

Nitrite reduction in fermented meat products and its impact on aroma

Fermented meat products are important not only for their sensory characteristics, nutrient content and cultural heritage, but also for their stability and convenience. The aroma of fermented meat products is unique and its formation mechanisms are not completely understood; however, the presence of nitrite and nitrate is essential for the development of cured aroma. The use of nitrite and nitrate as curing agents in meat products is based on its preservation activity. Even though their presence has been associated with several risks due to the formation of nitrosamines, their use is guarantee due to their antimicrobial action against Clostridium botulinum. Recent trends and recommendations by international associations are directed to use nitrite but at the minimum concentration necessary to provide the antimicrobial activity against Clostridium botulinum. This chapter discuss the actual limits of nitrite and nitrite content and their role as curing agents in meat products with special impact on dry fermented products. Regulatory considerations, antimicrobial mechanisms and actual trends regarding nitrite reduction and its effect on sensory and aroma properties are also considered.

Alternative Curing Methods

Purpose of Review

Curing—the treatment of meat products with nitrite and nitrate—is controversially discussed by consumers, as increased consumption of cured foods might negatively influence human health.

Recent Findings

However, omitting of curing chemicals might reduce microbiological safety, thereby increasing the risk to consumer health. Also, besides the addition of nitrate/nitrite, meat products are additionally preserved within the hurdle principle by other methods such as chilling, ripening, or heating.

Summary

The present article focuses on the addition of plants/plant extracts or plasma-treated water as nitrate sources and the direct treatment of meat products with plasma for nitrate generation. With regard to color and microbial safety of cured meat products, which are relevant to the consumers, promising results were also obtained with the alternative curing methods. Nonetheless, it is doubtful to what extent these methods are viable alternatives, as the curing chemicals themselves and not their origin are problematic for consumer health.

Effect of nitrite addition on the two-phase anaerobic digestion of waste activated sludge: Optimization of the acidogenic phase and influence mechanisms

To simultaneously achieve biological denitrification and bio-energy recovery from sludge, the effects of nitrite on the two-phase anaerobic digestion (AD) of waste activated sludge were explored. Herein, effects of nitrite on the acidogenic phase are optimized, and the corresponding influence mechanisms are investigated. The experimental results show that the optimal nitrite treatment conditions for improving the acidogenic phase are an initial pH of 8.0, a nitrite addition concentration of 500 mg NO₂^--N·L^-1, and a fermentation time of six days. By comparing the effects of nitrite and nitrate on the acidogenic phase, it was found that it was the nitrite, not the nitrate, that significantly enhanced the sludge organic solubilization, hydrolysis, and acidification, which are primarily attributed to the redox property of nitrite. Based on an analysis of different forms of soluble nitrogen concentrations, there was no obvious accumulation of nitrite or nitrate during the acidogenic phase. An analysis of the methane production and the volatile solid (VS) degradation during the two-phase AD revealed that the nitrite improved the methane production from the methanogenic phase and enhanced the VS degradation of sludge during the entire two-phase AD process. These findings could provide references for simultaneously treating nitrite-rich wastewater and improving anaerobic sludge digestion via two-phase system.

Reduction of nitrate and nitrite in Iberian dry cured loins and its effects during drying process

Four batches of Iberian dry-cured loins were manufactured with reduced ingoing amounts of both nitrate and nitrite: 150 mg/kg, 75 mg/kg, 37.5 mg/kg and 0 mg/kg. The effect of reducing or removing nitrate and nitrite and time of drying on physicochemical parameters (moisture, pH, water activity, chloride and residual nitrate and nitrite contents), instrumental colour and nitrosylmyoglobin content, lipid and protein oxidation and on microbiological counts (L. monocytogenes, aerobic mesophilic bacteria and moulds and yeast counts) were investigated. Lipid oxidation increased during the drying process being higher for non-added NO₃^-/NO₂^-, meanwhile protein oxidation affected also those with 37.5 and 75 mg/kg of NO₃^-/NO₂^- added. The removal of these additives affected instrumental colour coordinates and total colour changes showing that the variation of coloration would be perceptible by the consumer. Nitrosylmyoglobin content was significantly higher for NO₃^-/NO₂^- added loins. Reduced levels of these additives up to 37.5 mg/kg did not show significant effects on their physico-chemical, microbiological and colour.