Technological aspects and analytical determination of biogenic amines in cheese

The Microbial Diversity on the Surface of Smear-Ripened Cheeses and Its Impact on Cheese Quality and Safety

Smear-ripened cheeses are characterized by a viscous, red-orange surface smear on their rind. It is the complex surface microbiota on the cheese rind that is responsible for the characteristic appearance of this cheese type, but also for the wide range of flavors and textures of the many varieties of smear-ripened cheeses. The surface smear microbiota also represents an important line of defense against the colonization with undesirable microorganisms through various types of interaction, such as competitive exclusion or production of antimicrobial substances. Predominant members of the surface smear microbiota are salt-tolerant yeast and bacteria of the phyla Actinobacteria, Firmicutes, and Proteobacteria. In the past, classical culture-based approaches already shed light on the composition and succession of microorganisms and their individual contribution to the typicity of this cheese type. However, during the last decade, the introduction and application of novel molecular approaches with high-resolution power provided further in-depth analysis and, thus, a much more detailed view of the composition, structure, and diversity of the cheese smear microbiota. This led to abundant novel knowledge, such as the identification of so far unknown community members. Hence, this review is summarizing the current knowledge of the diversity of the surface smear microbiota and its contribution to the quality and safety of smear-ripened cheese. If the succession or composition of the surface-smear microbiota is disturbed, cheese smear defects might occur, which may promote food safety issues. Hence, the discussion of cheese smear defects in the context of an increased understanding of the intricate surface smear ecosystem in this review may not only help in troubleshooting and quality control but also paves the way for innovations that can lead to safer, more consistent, and higher-quality smear-ripened cheeses.

Application of Electrochemical Biosensors for Determination of Food Spoilage

Food security is significantly affected by the mass production of agricultural produce and goods, the growing number of imported foods, and new eating and consumption habits. These changed circumstances bring food safety issues arising from food spoilage to the fore, making food safety control essential. Simple and fast screening methods have been developed to detect pathogens and biomarkers indicating the freshness of food for safety. In addition to the traditional, sequential, chemical analytical and microbiological methods, fast, highly sensitive, automated methods suitable for serial tests have appeared. At the same time, biosensor research is also developing dynamically worldwide, both in terms of the analytes to be determined and the technical toolkit. Consequently, the rapid development of biosensors, including electrochemical-based biosensors, has led to significant advantages in the quantitative detection and screening of food contaminants. These techniques show great specificity for the biomarkers tested and provide adequate analytical accuracy even in complex food matrices. In our review article, we summarize, in separate chapters, the electrochemical biosensors developed for the most important food groups and the food safety issues they can ensure, with particular respect to meat and fish products, milk and dairy products, as well as alcoholic and non-alcoholic beverages.

Eu(III) Functionalized Crystalline Polyimide Hydrogel Film as a Multifunctional Platform for Consecutive Sensing of Spermine and Copper Ions

In this study, a novel Eu(III) functionalized crystalline polyimide hydrogel film (Eu-1) is fabricated by incorporating highly stable polyimide (PI) into a sodium alginate (SA) matrix, followed by cross-linking reaction with Eu³⁺ ions. Based on different fluorescence responses, Eu-1 is used for the consecutive detection of spermine (Spm) and copper ions (Cu²⁺). Eu-1 can be employed as a sensor for polyamine, especially for Spm with significant fluorescence enhancement based on the "turn on" mode. The fluorescent sensor Eu-1@Spm constructed by the Eu-1 and Spm can be further used as a "turn off" sensor to quantitatively monitor Cu²⁺. The good selectivity combined with the low detection limit of the sensor meets the requirements for monitoring Cu²⁺. The possible luminescence response mechanisms to Spm and Cu²⁺ have been studied through experimental data and theoretical calculations. In addition, a back-propagation neural network (BPNN) model based on an Eu-1@Spm sensor is constructed, which can accurately distinguish Cu²⁺ concentrations by deep machine learning (ML). This work not only puts forward a facile method to prepare a novel Eu-functionalized PI-based hybrid film but also demonstrates the potential of PI-based film materials for fluorescence detection.

Mechanism of biogenic amine synthesis of Enterococcus faecium isolated from Sanchun ham

Sanchuan ham, produced in Yunnan, China, is food with ethnic characteristics favored by consumers. However, it can contain biogenic amines such as tyramine that are harmful to health, and the synthesis mechanism of biogenic amines in Sanchuan ham is not clear. This study focuses on the regulation of biogenic amine synthesis by quorum sensing. We used high‐performance liquid chromatography to detect the content of biogenic amine in different kinds of ham and found that the content of biogenic amine in Sanchuan ham was higher than that in others. Tyramine‐producing strain isolated from Sanchuan ham was identified as Enterococcus faecium. By monitoring the growth and tyramine synthesis of Enterococcus faecium under cultured conditions, the results found that high temperature and low salt increased tyramine production by E. faecium. After seven exogenous amino acids were applied to E. faecium, only tyrosine could promote the production of tyramine in E. faecium, and tyramine could not be synthesized in E. faecium until a certain amount was reached, indicating the presence of microbial quorum sensing signal molecules in the synthesis of tyramine in E. faecium. Untargeted metabolomics analysis of the differential metabolites produced by E. faecium showed that the contents of some peptides, especially alanyl‐leucine, were significantly increased. Further experiments with synthetic alanyl‐leucine illustrated that alanyl‐leucine activated the expression of tyrosine decarboxylase (tyrDC), thereby regulating the synthesis of tyramine by E. faecium. Alanyl‐leucine acted as quorum sensing signal molecules for biogenic amine synthesis by E. faecium, which provided a theoretical basis for reducing biogenic amine accumulation in ham. It is beneficial to control the content of biogenic amines in ham in the future.

Detection of Potential Microbial Contaminants and Their Toxins in Fermented Dairy Products: a Comprehensive Review

Fermented dairy products are dominant constituents of daily diets around the world due to their desired organoleptic properties, long shelf life, and high nutritional value. Probiotics are often incorporated into these products for their health and technological benefits. However, the safety and possible contamination of fermented dairy products during the manufacturing process could have significant deleterious health and economic impacts. Pathogenic microorganisms and toxins from different sources in fermented dairy products contribute to outbreaks and toxicity cases. Although the health and nutritional benefits of fermented dairy products have been extensively investigated, safety hazards due to contamination are relatively less explored. As a preventive measure, it is crucial to accurately identify and determine the associated microbiota or their toxins. It is noteworthy to highlight the importance of detecting not only the pathogenic microbiota but also their toxic metabolites so that putative outbreaks can thereby be prevented or detected even before they cause harmful effects to human health. In this context, this review focuses on describing techniques designed to detect potential contaminants; also, the advantages and disadvantages of these techniques were summarized. Moreover, this review compiles the most recent and efficient analytical methods for detecting microbial hazards and toxins in different fermented dairy products of different origins. Causative agents behind contamination incidences are also discussed briefly to aid in future prevention measures, as well as detection approaches and technologies employed. Such approach enables the elucidation of the best strategies to control contamination in fermented dairy product manufacturing processes.

Possible inhibitory effect of microbial transglutaminase on the formation of biogenic amines during Trappist cheese ripening

Trappist cheese (semi-hard, rennet-coagulated cheese with round eyes) was manufactured and matured for 4 weeks at 12 ± 1°C, 85% relative humidity (RH). The effect of microbial transglutaminase (MTGase) was followed by measuring the levels of free amino acids (FAAs) and biogenic amines (BAs) every 2 weeks during 4 weeks of cheese ripening. Results show that MTGase can decrease the cadaverine production by 30%, but only at the initial stage of ripening. Application of MTGase results in 49% less putrescine, 12% less tyramine production at the end of 4 weeks ripening time, and can decrease histamine levels by 8% after 2 weeks of ripening time in the examined semi-hard cheese type.

Culture media based on effluent derived from soy protein concentrate production for Lacticaseibacillus paracasei 90 biomass production: statistical optimisation, mineral characterization, and metabolic activities

The waste and by-products of the soybean industry could be an economic source of nutrients to satisfy the high nutritional demands for the cultivation of lactic acid bacteria. The aims of this work were to maximize the biomass production of Lacticaseibacillus paracasei 90 (L90) in three culture media formulated from an effluent derived from soy protein concentrate production and to assess the effects these media have on the enzymatic activity of L90, together with their influence on its fermentation profile in milk. The presence of essential minerals and fermentable carbohydrates (sucrose, raffinose, and stachyose) in the effluent was verified. L90 reached high levels of microbiological counts (∼ 9 log cfu mL^-1) and dry weight (> 1 g L^-1) on the three optimized media. Enzymatic activities (lactate dehydrogenase and β-galactosidase) of L90, and its metabolism of lactose and citric acid, as well as lactic acid and pyruvic acid production in milk, were modified depending on the growth media. The ability of the L90 to produce the key flavour compounds (diacetyl and acetoin) was maintained or improved by growing in the optimized media in comparison with MRS.

Direct minimally invasive enzymatic determination of tyramine in cheese using digital imaging

An enzymatic method for the direct (without pretreatment) minimally invasive tyramine determination in cheese is proposed. Colorimetric test strips containing tyramine oxidase (TAO), peroxidase and 3,3',5,5'-tetramethylbenzidine (Q-TAO), allow tyramine determination through the RGB chromatic coordinates of the observed blue colour (LOD = 2.6·10^-6 M, LOQ = 8.7·10^-6 M, RSD% (n = 5; 1.8·10^-4 M) = 3.2%). The strips are inserted in the sample for 2 min and then the RGB coordinates are measured using a smartphone. Previously, these Q-TAO strips have been also optimized for tyramine determination in cheese extract. To do that, a spectrophotometric method in solution for tyramine determination in cheese extracts has been developed, which included an in-depth study of the indicating reaction; this study has allowed to gain new information about the spectroscopic properties of different TMB species and, which it is more important, to detect cross-reactions between TAO and TMB species. A mathematical model has also been developed which relate the RGB signals obtained with the tyramine concentrations, the instrumental characteristics of the smartphone and the spectroscopic properties of the absorbing product of the enzymatic reaction.

Determination of ammonium and biogenic amines by ion chromatography. A review

The amount and type of chemical compounds found in food products and the environment, which are and should be controlled, is increasing. This is associated with toxicological knowledge, resulting regulations, rapid development of analytical methods and techniques, and sample preparation methods for analysis. These include, among others, ammonia derivatives such as ammonium, and amines, including biogenic amines. Their occurrence in the environment and food is related to their widespread use in many areas of life and their formation as a result of various physical and chemical changes. Analysts use various methods both classical and instrumental to theirs quantify in different matrices such as food, medicinal and environmental samples. Nevertheless, there is still a need for analytical methods with increased matrix-tolerance, selectivity, specificity, and higher sensitivity. While in the determination of ammonium, ion chromatography is a reference method. In the case of biogenic amines, its use for these purposes is not yet so common. However, given ion chromatography its advantages and rapid development, its importance can be expected to increase in the near future, especially at the expense of gas chromatography methods. This paper is a summary of the advantages and limitations of ion chromatography in this important analytical field and a literature review of the past 15 years.

Effect of somatic cells count in cow milk on the formation of biogenic amines in cheese

Comparative studies on physicochemical characteristics of milk with different somatic cells count (SCC) (L-low < 400,000 cells/ml, M-medium between 500,000 and 600,000 cells/ml and H-high > 1,000,000 cells/ml) and obtained cheeses, were conducted. No significant differences between samples were found. The H SCC milk was characterized by the highest total viable count. Higher levels of proteolysis were established in cheeses made from milk with SCC exceeding 500,000 cells/ml. After 10 months of ripening and cold storage the water-soluble nitrogen in total nitrogen (WSN/TN), noncasein nitrogen in total nitrogen (NCN/TN), nonprotein nitrogen in total nitrogen (NPN/TN) and free amino groups values of the sample with the highest SCC reached 28.4 ± 0.8%, 24.8 ± 0.9%, 18.3 ± 0.9% and 83.6 ± 0.3 mg/kg respectively. The biogenic amine concentration in the cheese samples from the L and M batches remained below 10 mg/kg throughout the ripening and cold storage period. The present study established an increase in the biogenic amine content during the ripening period and the cold storage of the cheeses made from milks with high SCC (batch H). The main amines accumulated at the end of the storage period (10th month) were tyramine (31.7 ± 0.3 mg/kg), putrescine (20.5 ± 0.2 mg/kg) and cadaverine (14.6 ± 0.2 mg/kg). Histamine was not found in any of the studied cheese samples.

Quantitative Analysis of Biogenic Amines in Different Cheese Varieties Obtained from the Korean Domestic and Retail Markets

To evaluate the safety and risk assessment of cheese consumption in the Republic of Korea, sixty cheese samples purchased from the farmstead and retails markets (imported) were analyzed for their biogenic amine (BA) contents. The BA profiles and quantities of eight amines (tryptamine, 2-phenylethylamine, putrescine, cadaverine, histamine, tyramine, spermidine, and spermine) were determined using high-performance liquid chromatography (HPLC). Spermine was the only amine detectable in all the samples. The BAs of fresh cheeses from both farmstead and retail markets were mostly undetectable, and comparatively at lower levels (<125 mg/kg) than ripened samples. Putrescine was undetectable in all the domestic ripened cheeses. The sum of BA levels in the imported ripened cheeses of Pecorino Romano (1889.75 mg/kg) and Grana Padano (1237.80 mg/kg) exceeds >1000 mg/kg, of which histamine accounts nearly 86 and 77% of the total levels, respectively. The tolerable limits of the potential toxic amines, histamine and tyramine surpassed in four and three imported ripened samples, respectively. Furthermore, the presence of potentiators (putrescine and cadaverine) together in samples even with a lower level of toxic amines alarms the risk in consumption. Therefore, adoption of strict hygienic practices during the entire chain of cheese production, along with obligatory monitoring and regulation of BA in cheeses seems to be mandatory to ensure the safety of the consumers.

Exploring the Capability of Yeasts Isolated from Colombian Fermented Cocoa Beans to Form and Degrade Biogenic Amines in a Lab-Scale Model System for Cocoa Fermentation

Yeast starters for cocoa fermentation are usually tested according to their enzymatic activities in terms of mucilage degradation and flavor improvement, disregarding their influence on the production or elimination of toxic compounds as biogenic amines (BAs), important for human health. In this work, we tested 145 strains belonging to 12 different yeast species and isolated from the Colombian fermented cocoa beans (CB) for their capability of producing BAs in vitro. Sixty-five strains were able to decarboxylate at least one of the amino acids tested. Pichia kudriavzevii ECA33 (Pk) and Saccharomyces cerevisiae 4 (Sc) were selected to evaluate their potential to modulate BAs, organic acids, and volatile organic compounds (VOCs) accumulation during a simulated cocoa fermentation. The growth of Sc or Pk in the presence of CB caused a significant reduction (p < 0.05) of 2-phenylethylamine (84% and 37%) and cadaverine (58% and 51%), and a significant increase of tryptamine and putrescine with a strong influence of temperature in BA formation and degradation. In addition, our findings pointed out that Pk induced a major production of fatty acid- and amino acid-derived VOCs, while Sc induced more VOCs derived from fatty acids metabolism. Our results suggest the importance of considering BA production in the choice of yeast starters for cocoa fermentation.

The Role of Enterococcus faecium as a Key Producer and Fermentation Condition as an Influencing Factor in Tyramine Accumulation in Cheonggukjang

The study evaluated the role of Enterococcus faecium in tyramine production and its response to fermentation temperature in a traditional Korean fermented soybean paste, Cheonggukjang. Tyramine content was detected in retail Cheonggukjang products at high concentrations exceeding the recommended limit up to a factor of 14. All retail Cheonggukjang products contained Enterococcus spp. at concentrations of at least 6 Log CFU/g. Upon isolation of Enterococcus strains, approximately 93% (157 strains) produced tyramine at over 100 µg/mL. The strains that produced the highest concentrations of tyramine (301.14–315.29 μg/mL) were identified as E. faecium through 16S rRNA sequencing. The results indicate that E. faecium is one of the major contributing factors to high tyramine content in Cheonggukjang. During fermentation, tyramine content in Cheonggukjang groups co-inoculated with E. faecium strains was highest at 45 °C, followed by 37 °C and 25 °C. The tyramine content of most Cheonggukjang groups continually increased as fermentation progressed, except groups fermented at 25 °C. At 45 °C, the tyramine content occasionally exceeded the recommended limit within 3 days of fermentation. The results suggest that lowering fermentation temperature and shortening duration may reduce the tyramine content of Cheonggukjang, thereby reducing the safety risks that may arise when consuming food with high tyramine concentrations.

Biogenic amines content in Fiore Sardo cheese in relation to free amino acids and physicochemical characteristics

Fiore Sardo is a Protected Designation of Origin (PDO) cheese produced in Sardinia (Italy) from raw sheep's milk, presenting risk factors due to an accumulation of Biogenic Amines (BA). A total of 37 Fiore Sardo cheese samples produced in 19 dairy farms were collected from local retail stores to evaluate BA content and its relationship with free amino acids (FAA) and composition. The following were determined for each sample: pH, water activity, composition (moisture, dry matter, NaCl, protein and fat content). FAA and BA, after extraction, were determined by HPLC-FL. The total BA content in Fiore Sardo PDO cheese samples was 127±87 mg 100 g-1, ranging between 6 and 366 mg 100 g-1. Tyramine showed the highest concentration (82±51 mg 100 g-1), followed by putrescine (21±26 mg 100 g-1). Moreover, cadaverine, histamine, β-phenylethylamine and tryptamine were detected at concentrations lower than 10 mg 100 g-1. Overall 54% of the samples analysed exceeded the threshold of 90 mg 100 g-1 for total BA content, posing a potential risk for consumers. BA, total FAA (2233±764 mg 100 g-1) and pH were positively correlated (P≤0.01) between themselves, whereas BA content was not correlated with aw, humidity and percentage of NaCl. The hierarchical cluster analysis results, considering 37 samples and 6 variables, detected four different groups. Samples with BA ≥200 mg 100 g-1 were distributed in two groups characterized by a higher proteolysis indicator levels (FAA, pH) but significantly different for aw, humidity and NaCl concentration. The results showed that high levels of BA were detectable in some samples of Fiore Sardo PDO cheese, suggesting that effective technological conditions at production should be adopted.

Fermentation for tailoring the technological and health related functionality of food products

Fermented foods are experiencing a resurgence due to the consumers' growing interest in foods that are natural and health promoting. Microbial fermentation is a biotechnological process which transforms food raw materials into palatable, nutritious and healthy food products. Fermentation imparts unique aroma, flavor and texture to food, improves digestibility, degrades anti-nutritional factors, toxins and allergens, converts phytochemicals such as polyphenols into more bioactive and bioavailable forms, and enriches the nutritional quality of food. Fermentation also modifies the physical functional properties of food materials, rendering them differentiated ingredients for use in formulated foods. The science of fermentation and the technological and health functionality of fermented foods is reviewed considering the growing interest worldwide in fermented foods and beverages and the huge potential of the technology for reducing food loss and improving nutritional food security.

Biogenic amines in smear ripened cheeses

Cheeses belong to high protein foods in which enzymatic and microbial activities form amino acids, which are then converted into biogenic amines (BAs) by the activity of bacterial decarboxylases. The most important conditions for BA formation include the presence of microorganisms, the availability of substrate, temperature and storage period, water activity, salt concentration, and the hygiene of the manufacturing process. Tyramine, histamine, 2-phenylethylamine, tryptamine, cadaverine, putrescine, spermidine and spermine were detected in smear ripened cheeses stored in different temperature regimes. The highest (p < 0.05) total BA content was found when storing the cheeses at the end of BBD (best before date) after 35 days in storage regime (A) or (C). During storage in regime (B), the total BA content (p < 0.05) after 49 days of storage was higher than on the production date (B/0). During storage, the tyramine content in regime (B) did not change (p > 0.05), while in the temperature regimes (A) and (C), the highest levels of tyramine and putrescine content were recorded in cheeses at the end of BBD after 35 days ripening. The content of polyamines in cheeses was higher (p < 0.05) at the end of storage than at the beginning, in all temperature regimes.

Liquid chromatography-tandem mass spectrometry method for the analysis of N-(3-aminopropyl)-N-dodecylpropane-1,3-diamine, a biocidal disinfectant, in dairy products

A novel and reliable method to quantify residual levels of N-(3-aminopropyl)-N-dodecylpropane-1,3-diamine in dairy products using ion-pairing reversed-phase liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed and fully validated. Sample extraction was done with salting-out technique using acetonitrile and sodium chloride. For LC-MS/MS, the analyte was detected using positive electrospray ionization (ESI+) and two multiple reaction monitoring (MRM) transitions were monitored. The method was validated in the 5-150 µg kg^-1 range using total error approach. Thus, performance criteria of the method were evaluated. Relative standard deviations for trueness and precision were lower than 10%; with the exception of hard pressed cheese at 5 µg kg^-1 for precision. The limit of quantification (LOQ) was around 5-7 µg kg^-1 depending on the matrix of interest. The method was successfully applied to accurately quantify N-(3-aminopropyl)-N-dodecylpropane-1,3-diamine in 146 various dairy products with a maximum contamination level of 225 µg kg^-1 in cheese.

A reassessment of the safety profile of monoamine oxidase inhibitors: elucidating tired old tyramine myths

This review appraises over 150 recent original papers reporting data that demonstrate the greatly reduced tyramine content of modern-day 'foods', about which the medical literature has a paucity of information. It discusses the cardiovascular pharmacology of tyramine and the characteristics, extent, risks, and treatment of the blood pressure increases that sometimes result from tyramine ingestion (the pressor response). In past decades, cheese was the only food associated with documented fatalities resulting from hypertension. Today, few foods contain problematically high tyramine levels, which is a result of changes in international food production techniques (especially the use of starter cultures), and hygiene regulations. Nowadays, even 'matured' cheeses are usually safe in healthy-sized portions. The mechanism by which tyramine may be produced in foods (by certain micro-organisms) is explained and hundreds of recent estimations of cheeses are reviewed. Numerous other previously inadequately documented foods are reviewed, including fish and soy sauces, salami-type sausages, dried meats, beers, wines, and various condiments. Evidence that the risk of harm from the pressor response has previously been overstated is reviewed, and the iatrogenic harms from hasty and aggressive treatment of hypertensive urgency are re-evaluated. Evidence now suggests that MAOIs are of comparable safety to many newer drugs and are straightforward to use. Previously held concerns about MAOIs are misplaced and some are of over-estimated consequence. The variability of pressor sensitivity to tyramine between individuals means that the knowledge and judgement of doctors, and some care, are still required.

Direct solid phase microextraction combined with gas chromatography - Mass spectrometry for the determination of biogenic amines in wine

A direct method based on immersion solid phase microextraction (DI-SPME) gas chromatography mass-spectrometry (GC-MS) was optimized and validated for the determination of 16 biogenic amines in Polish wines. In the analysis two internal standards were used: 1,7-diaminoheptane and bis-3-aminopropylamine. The method allows for simultaneous extraction and derivatization, providing a simple and fast mode of extraction and enrichment. Different parameters which affect the extraction procedure were studied and optimized including ionic strength (0-25%), fiber materials (PDMS/DVB, PDMS/DVD + OC, Polyacrylate, Carboxen/PDMS and DVB/CAR/PDMS) and timings of the extraction, derivatization and desorption processes. Validation studies confirmed the linearity, sensitivity, precision and accuracy of the method. The method was successfully applied to the analysis of 44 wine samples originating from several regions of Poland and 3 wine samples from other countries. Analysis showed that many of the samples contained all examined biogenic amines. The method, assessed using an Eco-Scale tool with satisfactory results, was found to be green in terms of hazardous chemicals and solvents usage, energy consumption and production of waste. Therefore the proposed method can be safely used in the wine industry for routine analysis of BAs in wine samples with a minimal detrimental impact on human health and the environment.

Electrochemical enzyme biosensors based on calcium phosphate materials for tyramine detection in food samples

Electrochemical tyrosinase biosensors for tyramine determination were developed by the immobilization of the enzyme in calcium phosphate materials (CaPs) followed by cross-linking with glutaraldehyde. Tyramine was detected by the electrochemical reduction at -0.1V of the o- enzymatically-formed dopaquinone. Three different CaPs were explored as immobilization systems, monetite, brushite and brushite cement. Biosensors based on brushite matrices provide better analytical properties than the monetite one. Compared to brushite, a 10-fold increase of sensitivity was obtained with the brushite cement-based biosensor, which highlights the effect of brushite crystal formation in the presence of the enzyme in the biosensor performance. Several variables involved in the enzyme immobilization method such as glutaraldehyde cross-linking time, PPO/brushite ratio and thickness of the brushite-enzyme film were investigated. Furthermore, the effects of pH and temperature on biosensor performance were also optimized. Brushite cement-PPO-GA biosensor resulted in a reliable, highly sensitive, fast, inexpensive and easy analytical method for tyramine detection. Under optimal conditions (time of 15min, a ratio of 1.0 and 50μg of the brushite-enzyme mixture, 20°C and pH 6,0), a linear range of 5.8 × 10^-7 to 1.6 × 10^-5, sensitivity 1.50 × 10³mAM^-1 cm^-2, detection limit, 4.85 × 10^-8M and a response time, 6s were obtained. The suitability of the proposed biosensor to determine the tyramine content in cheese samples has been explored. The mean analytical recovery of added tyramine in gouda and brie cheeses were found to be 95.5±5.8 and 96.9±7.5 respectively. A study of the tyramine content evolution over the course of a week under inadequate storage showed the importance of monitoring the degradation of certain foods.

Validation of a Fluorescence Sensor Microtiterplate for Biogenic Amines in Meat and Cheese

An optical sensor microtiterplate for quantitative analysis of the total content of biogenic amines (TAC) in meat and cheese was developed and validated for the first time. In the plate, a chameleon dye (Py-1) is embedded in a polymeric cocktail which is deposited on the bottom of the wells in a common microtiterplate. On reaction with biogenic amines (BAs), the fluorescence of Py-1 at 620 nm rapidly delivers a precise TAC. After 10 min incubation at 25 °C the determination of the TAC in various (real) samples is possible in high-throughput with a standard microplate reader. The optimized fluorescence method was validated for linearity, sensitivity, accuracy, precision (intraday and inter day repeatability) and recovery using histamine (HIS) as a representative BA. The sensor microtiterplate was successfully applied to quantitatively analyze the TAC in 10 real samples of cheese and meat obtained from various Egyptian markets. The TAC of these real samples obtained by the sensor microtiterplate was validated against the contents of BAs obtained by GC-MS at various times of storage. The data of the sensor microtiterplate agreed well with those of GC-MS. This demonstrates that the sensor microtiterplate is a reliable screening tool for the degradation status of food samples.

Extraction Efficiency of Different Solvents and LC-UV Determination of Biogenic Amines in Tea Leaves and Infusions

Biogenic amines (BAs), that is, spermine, spermidine, putrescine, histamine, tyramine, β-phenylethylamine, cadaverine, and serotonin, have been determined in several samples of tea leaves, tea infusions, and tea drinks by LC-UV method after derivatization with dansyl chloride. Different extraction solvents have been tested and TCA 5% showed better analytical performances in terms of linearity, recovery percentages, LOD, LOQ, and repeatability than HCl 0.1 M and HClO4 0.1 M and was finally exploited for the quantitative determination of BAs in all samples. In tea leaves total BAs concentration ranged from 2.23 μg g(-1) to 11.24 μg g(-1) and PUT (1.05-2.25 μg g(-1)) and SPD (1.01-1.95 μg g(-1)) were always present, while SER (nd-1.56 μg g(-1)), HIS (nd-2.44 μg g(-1)), and SPM (nd-1.64 μg g(-1)) were detected more rarely. CAD and PHE were determined in few samples at much lower concentrations while none of the samples contained TYR. Tea infusions showed the same trend with total BAs concentrations never exceeding 80.7 μg L(-1). Black teas showed higher amounts of BAs than green teas and organic and decaffeinated samples always contained much lower BAs levels than their conventional counterparts.

Putrescine production by Lactococcus lactis subsp. cremoris CECT 8666 is reduced by NaCl via a decrease in bacterial growth and the repression of the genes involved in putrescine production

The reduction of NaCl in food is a public health priority; high NaCl intakes have been associated with serious health problems. However, it is reported that reducing the NaCl content of cheeses may lead to an increase in the content of biogenic amines (BAs). The present work examines the effect of NaCl on the accumulation of putrescine (one of the BAs often detected at high concentration in cheese) in experimental Cabrales-like cheeses containing Lactococcus lactis subsp. cremoris CECT 8666, a dairy strain that catabolises agmatine to putrescine via the agmatine deiminase (AGDI) pathway. The genes responsible for this pathway are grouped in the AGDI cluster. This comprises a regulatory gene (aguR) (transcribed independently), followed by the catabolic genes that together form an operon (aguBDAC). Reducing the NaCl concentration of the cheese led to increased putrescine accumulation. In contrast, increasing the NaCl concentration of both pH-uncontrolled and pH-controlled (pH 6) cultures of L. lactis subsp. cremoris CECT 8666 significantly inhibited its growth and the production of putrescine. Such production appeared to be inhibited via a reduction in the transcription of the aguBDAC operon; no effect on the transcription of aguR was recorded. The present results suggest that low-sodium cheeses are at risk of accumulating higher concentrations of putrescine.

Quantitative Determination of Spermidine in 50 German Cheese Samples on a Core-Shell Column by High-Performance Liquid Chromatography with a Photodiode Array Detector Using a Fully Validated Method

In the current study, the spermidine (8) contents of 51 German and 9 international cheese samples (from France, Ireland, Italy, The Netherlands, and Switzerland) were analyzed by a modified and fully validated method using high-performance liquid chromatography with photodiode array detection. After precolumn derivatization of biogenic amines with dansyl chloride (11), the compounds were separated on a Kinetex C18 column and detected at λ = 254 nm. This method for compound 8 analysis in cheese was validated for the first time according to U.S. Food and Drug Administration (FDA) guidelines for bioanalytical method validation with regard to selectivity, precision, accuracy, recovery, linearity, lower limit of detection (LOD), lower limit of quantitation (LOQ), standard solution stability, short- and long-term stability, freeze-thaw stability, and benchtop stability. The detector response was linear from 0.002 to 8 mg/L 8 (R(2) > 0.999). Low LOD and LOQ values of 1 and 2 μg/L, respectively, reflected the high sensitivity of the method. The intra- and interday recoveries of the 8-spiked cheese samples ranged between 87.7 and 102.6%. This validated method was selective, accurate, and precise and was successfully applied for the quantitative analysis of compound 8 in 60 cheese samples. Furthermore, the simultaneous detection of eight additional biogenic amines is possible but not validated.

High-throughput DNA sequencing to survey bacterial histidine and tyrosine decarboxylases in raw milk cheeses

BACKGROUND

The aim of this study was to employ high-throughput DNA sequencing to assess the incidence of bacteria with biogenic amine (BA; histamine and tyramine) producing potential from among 10 different cheeses varieties. To facilitate this, a diagnostic approach using degenerate PCR primer pairs that were previously designed to amplify segments of the histidine (hdc) and tyrosine (tdc) decarboxylase gene clusters were employed. In contrast to previous studies in which the decarboxylase genes of specific isolates were studied, in this instance amplifications were performed using total metagenomic DNA extracts.

RESULTS

Amplicons were initially cloned to facilitate Sanger sequencing of individual gene fragments to ensure that a variety of hdc and tdc genes were present. Once this was established, high throughput DNA sequencing of these amplicons was performed to provide a more in-depth analysis of the histamine- and tyramine-producing bacteria present in the cheeses. High-throughput sequencing resulted in generation of a total of 1,563,764 sequencing reads and revealed that Lactobacillus curvatus, Enterococcus faecium and E. faecalis were the dominant species with tyramine producing potential, while Lb. buchneri was found to be the dominant species harbouring histaminogenic potential. Commonly used cheese starter bacteria, including Streptococcus thermophilus and Lb. delbreueckii, were also identified as having biogenic amine producing potential in the cheese studied. Molecular analysis of bacterial communities was then further complemented with HPLC quantification of histamine and tyramine in the sampled cheeses.

CONCLUSIONS

In this study, high-throughput DNA sequencing successfully identified populations capable of amine production in a variety of cheeses. This approach also gave an insight into the broader hdc and tdc complement within the various cheeses. This approach can be used to detect amine producing communities not only in food matrices but also in the production environment itself.

Microbiota of Minas cheese as influenced by the nisin producer Lactococcus lactis subsp. lactis GLc05

Minas cheese is a popular dairy product in Brazil that is traditionally produced using raw or pasteurized cow milk. This study proposed an alternative production of Minas cheese using raw goat milk added of a nisin producer Lactococcus lactis subsp. lactis GLc05. An in situ investigation was carried on to evaluate the interactions between the L. lactis subsp. lactis GLc05 and the autochthonous microbiota of a Minas cheese during the ripening; production of biogenic amines (BAs) was assessed as a safety aspect. Minas cheese was produced in two treatments (A, by adding L. lactis subsp. lactis GLc05, and B, without adding this strain), in three independent repetitions (R1, R2, and R3). Culture dependent (direct plating) and independent (rep-PCR and PCR-DGGE) methods were employed to characterize the microbiota and to assess the possible interferences caused by L. lactis subsp. lactis GLc05. BA amounts were measured using HPLC. A significant decrease in coagulase-positive cocci was observed in the cheeses produced by adding L. lactis subsp. lactis GLc05 (cheese A). The rep-PCR and PCR-DGGE highlighted the differences in the microbiota of both cheeses, separating them into two different clusters. Lactococcus sp. was found as the main microorganism in both cheeses, and the microbiota of cheese A presented a higher number of species. High concentrations of tyramine were found in both cheeses and, at specific ripening times, the BA amounts in cheese B were significantly higher than in cheese A (p<0.05). The interaction of nisin producer L. lactis subsp. lactis GLc05 was demonstrated in situ, by demonstration of its influence in the complex microbiota naturally present in a raw goat milk cheese and by controlling the growth of coagulase-positive cocci. L. lactis subsp. lactis GLc05 influenced also the production of BA determining that their amounts in the cheeses were maintained at acceptable levels for human consumption.