Rapid determination of nine N-nitrosamines in dry-cured mackerel (Scomberomorus niphonius) using salting out homogeneous phase extraction with acetonitrile followed by GC-MS/MS

Method validation for analysis of advanced glycation end products in mouse muscle tissue using liquid chromatography-tandem mass spectrometry

Advanced glycation end products (AGEs) in food and biological samples have been analyzed using several chromatographic and immunological methods, but no studies have quantitatively analyzed the major AGEs, Nε-carboxy-methyl-lysine (CML) and Nε-carboxy-ethyl-lysine (CEL), in muscle tissue. In this study, a quantitative profiling method using ultra-performance liquid chromatography-tandem mass spectrometry in mouse muscle tissue was developed and validated. For extraction, acid hydrolysis and solid-phase extraction were performed. The CML and CEL were well separated and analyzed within 5 min in multiple reaction monitoring mode. The method was validated against ICH guidelines to evaluate the linearity, limits of detection and quantification, matrix effects, recovery, accuracy, and precision, and the validated approach was applied to muscle tissue from aged mice to establish a baseline for the typical range of CML and CEL. This quantitative profiling method has the potential to be applied in the study of diseases influenced by AGEs.

Extraction and analytical approaches for the determination of post-food processing major carcinogens: A comprehensive review towards healthier processed food

Different food processing methods, e.g. fermentation, grilling, frying, etc., to improve food sensory attributes or shelf-stability are typically employed in different cuisines worldwide. These methods may illicit in-situ health-hazardous chemicals via thermal or enzymatic-mediated processes or chemical interactions with food preservatives. This review provides a comparative overview of the occurrence, extraction, and determination of the major food carcinogens such as nitrosamines (NAs), biogenic amines (BAs), heterocyclic aromatic amines (HAAs), polycyclic aromatic hydrocarbons (PAHs), ethyl carbamate (EC), and malondialdehyde (MDA). Their carcinogenicity levels vary from group 1 (carcinogenic to humans) e.g. benzo[a]pyrene, group 2A (probably carcinogenic to humans) e.g. N-nitrosodiethylamine, group 2B (possibly carcinogenic to humans) e.g. chrysene or group 3 (non-classifiable as carcinogenic to humans) e.g. MDA. Chromatography-based methods are the most predominant techniques used for their analysis. LC-MS is widely used for both volatile/non-volatile NAs, HAAs, BAs, and EC, whereas GC-MS is applied more for volatile NAs, PAHs and MDA.

Reduction of N-nitrosamine in cured ham using atmospheric cold plasma-treated cauliflower powder

The effects of cauliflower treated with atmospheric cold plasma (ACP), as a natural nitrite source, on the curing of ground ham and nitrosamine formation were investigated. Ground ham was prepared using sodium nitrite and ACP-treated cauliflower powder (PTCP) to achieve initial nitrite concentrations of 60 and 100 mg/kg, respectively. ACP treatment generated nitrite in cauliflower but significantly reduced the antioxidant activity (P < 0.05). As a nitrite source, PTCP had similar effects as sodium nitrite in the development of cured color in ground ham, with a comparable residual nitrite content (P ≥ 0.05). Three nitrosamines, N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), and N-nitrosopyrrolidine (NPYR), were detected in ground ham. NPYR formation was significantly lower in ground ham treated with PTCP at an initial nitrite concentration of 100 mg/kg (P < 0.05). Therefore, the use of a natural nitrite source manufactured through ACP treatment can prospectively achieve suitable curing efficiency while simultaneously suppressing nitrosamine formation.

Effects of different curing concentrations and drying times on the microbial community structure and metabolites of dried Spanish mackerel

Cured Spanish mackerel has a promising market owing to its nutritious nature as well as ease of transportation and preservation. However, the nutritional and flavor formation mechanism of Spanish mackerel after curing and drying is unclear. To overcome this problem, the effects of different processing conditions on the free amino acid, microbial community, and flavor of Spanish mackerel were explored. Staphylococcus and Cobetia are the main microorganisms in cured mackerel and are closely associated with the formation of their quality. Compared with fresh mackerel, cured mackerel contains increased levels of protein, fat, and chloride, contributing to its distinctive flavor. The contents of free amino acids in the BA64 group were substantially higher than those in other groups, particularly the contents of threonine, glycine, and tyrosine. These findings will contribute to the development of high-quality cured Spanish mackerel products and cured aquatic products.

Intake of tobacco nitrosamines of smokers in various provinces of China and their cancer risk: A meta-analysis

Nitrosamines are a class of carcinogens which have been detected widely in food, water, some pharmaceuticals as well as tobacco. The objectives of this paper include reviewing the basic information on tobacco consumption and nitrosamine contents, and assessing the health risks of tobacco nitrosamines exposure to Chinese smokers. We searched the publications in English from "Web of Science" and those in Chinese from the "China National Knowledge Infrastructure" in 2022 and collected 151 literatures with valid information. The content of main nitrosamines in tobacco, including 4-(methylnitrosoamino)-1-(3-pyridyl)-1-butanone (NNK), N-nitrosonornicotine (NNN), N-nitrosoanatabine (NAT), N-nitrosoanabasine (NAB), total tobacco-specific nitrosamines (TSNA), and N-nitrosodimethylamine (NDMA) were summarized. The information of daily tobacco consumption of smokers in 30 provinces of China was also collected. Then, the intakes of NNN, NNK, NAT, NAB, TSNAs, and NDMA via tobacco smoke were estimated as 1534 ng/day, 591 ng/day, 685 ng/day, 81 ng/day, 2543 ng/day, and 484 ng/day by adult smokers in 30 provinces, respectively. The cancer risk (CR) values for NNN and NNK inhalation intake were further calculated as 1.44 × 10-5 and 1.95 × 10-4. The CR value for NDMA intake via tobacco smoke (inhalation: 1.66 × 10-4) indicates that NDMA is similarly dangerous in tobacco smoke when compared with the TSNAs. In China, the CR values caused by average nitrosamines intake via various exposures and their order can be estimated as the following: smoke (3.75 × 10-4) > food (1.74 × 10-4) > drinking water (1.38 × 10-5). Smokers in China averagely suffer 200% of extra cancer risk caused by nitrosamines in tobacco when compared with non-smokers.

Occurrence of N-nitrosodimethylamine in roasted Alaska pollock fillets during processing and storage and preliminary cancer risk assessment

BACKGROUND

Dried and salt-fermented fish products are important sources of N-nitrosodimethylamine (NDMA) exposure for human. As a potent carcinogen, NDMA was frequently detected in roasted Alaska pollock fillet products (RPFs), which is among the most common fish products in China. Until now, the occurrence and development of NDMA and its precursors (nitrites, nitrates and dimethylamine) in RPFs during processing and storage were not well elucidated, and safety evaluation of this fish product is also urgently needed.

RESULTS

The presence of precursors in the raw material was verified and significant increase of nitrates and nitrites during processing was observed. NDMA was found generated during pre-drying (3.7 μg kg-1 dry basis) and roasting (14.6 μg kg-1 dry basis) process. Continuous increase in NDMA content can also be found during storage, especially at higher storage temperature. The 95th percentile of Monte Carlo simulated cancer risk (3.73 × 10-5 ) surpassed the WHO threshold (1.00 × 10-5 ) and sensitivity analysis implies the risk was mainly attributable to NDMA level in RPFs.

CONCLUSION

The occurrence of NDMA in RFPs was mainly a result of endogenous factors originating in Alaska pollock during processing and storage rather than exogenous contamination, and temperature played a pivotal role. The preliminary risk assessment results suggest that long-term consumption of RPFs would impose potential health risks for consumers. © 2023 Society of Chemical Industry.

The roles of lipoxygenases and autoxidation during mackerel (Scomberomorus niphonius) dry-cured processing

The roles of enzymatic (Lipoxygenases, LOX) oxidation and autoxidation in the dry-cured processing of mackerel were investigated by adding exogenous substances in this study. Four groups, namely control, chlorogenic acid (inhibiting LOX activity), EDTA-2Na (inhibiting autoxidation), and exogenous LOX (adding eLOX), were assigned. The results showed that lipid oxidation of mackerel was reduced by inhibiting LOX activity and autoxidation, while adding eLOX promoted lipid oxidation. Inhibition of LOX activity and autoxidation suppressed fatty acid accumulation mainly in the air-drying and curing stage, respectively. The total contents of key flavors in the mackerel during dry-cured processing were decreased by inhibiting LOX activity and autoxidation, and the former inhibitory effect was stronger than autoxidation, while it was corresponding increased through adding eLOX, of particular in the later stage of air-drying. Collectively, LOX could promote the flavor formation of the mackerel in the dry-cured processing, which could be applied in the flavor adjustment of aquatic products or some similar fields.

Covalent organic framework-based magnetic solid-phase extraction coupled with gas chromatography-tandem mass spectrometry for the determination of trace phthalate esters in liquid foods

Covalent organic framework-coated magnetite particles (Fe3O4@COF) were synthesized and applied as the adsorbent to the selective capture of phthalate esters (PAEs) in liquid foods. Combined with the magnetic solid-phase extraction (MSPE) technology, a gas chromatography-tandem mass spectrometry (GC-MS/MS) method was employed for the separation and quantification of PAEs. Following optimization of the magnetic extraction and elution parameters, the developed analytical method offered a satisfactory linear range (0.1-5 μg L-1) with determination coefficients ranging from 0.9934 to 0.9975 for the five different PAEs studied. The limits of detection (LOD) were in the range 1.9-12.8 ng L-1. The recoveries ranged from 70.0 to 119.8% with a relative standard deviation (RSD) less than 9.7%. Density functional theory (DFT) calculations established that the dominant adsorption mechanism used by the COF to bind PAEs involved π-π stacking interactions. Results encourage the wider use of COF-based adsorbents and MSPE methods in the analytical determination of PAEs in foods.

Characteristics and health risk assessment of volatile N-nitrosamines in the plasma of adults in Guangdong Province, China

N-nitrosamines are strong carcinogens that are widely present in the environment. This study developed a method, and analyzed the concentrations of volatile N-nitrosamines (VNAs) in the plasma of adults in Guangdong Province, China. Finally, the health risks to adults in Guangdong Province, China, with dietary exposure to VNAs were assessed. Gas chromatography/mass spectrometry (GC/MS) in electron impact (EI) ionization source mode was used to quantitatively analyze VNAs, and to perform accurate mass determination. The lower limit of detection (LOD) of nine nitrosamines are ranged from 0.01 to 2.14 ng/mL. The recovery rate ranged from 83 % to 116 %, and the relative standard deviation (RSD) was < 10 %. The method developed is simple, rapid, and provides good reproducibility and high sensitivity. N-nitrosodimethylamine (NDMA), N-nitrosomethylethylamine (NMEA), N-nitrosodinbutylamine (NDBA), N-nitrosopiperidine (NPIP), N-nitrosopyrrolidine (NPYR), N-nitrosomorpholine (NMOR) and N-nitrosodiphenylamine (NDPhA) were detected in 92 adult plasma samples. NDMA and NMEA were detected in 56.5 % and 44.6 % of the samples, followed by NPIP (34.8 %). NDMA had the highest median concentration (43.7 ng/mL) in the total samples. There were gender-related differences found in the concentrations of NDBA and NDPhA. The exposure risk assessment results showed that the two highest daily dietary intakes of VNAs were N-nitrosodi-n-propylamine (NDPA) and NDMA, and aquatic products and pickled vegetables contributed the most total nitrosamine intake. The lifetime cancer risk of adults ranged from 2.88 × 10^-10 to 7.46 × 10^-5, and the risk associated with NDMA, NDPA, N-nitrosodiethylamine (NDEA), NMEA and NPIP are important and should attract more attention. This study aimed to explore the exposure levels of VNAs in the plasma of adults in Guangdong Province, China, and to assess the health risks of dietary intake of VNAs, which provides a basis of the effect of VNAs exposure on human health.

Biogenic amines and volatile N-nitrosamines in Chinese smoked-cured bacon (Larou) from industrial and artisanal origins

This study aimed to compare biogenic amines (BAs), volatile N-nitrosamines (VNAs) and chemical properties of Chinese smoked-cured bacon (Larou) from industrial and artisanal sources. The results indicated that nitrite residues were low in artisanal Larou, whereas the salt content was relatively high in all samples. The family-made Larou accumulated high levels of BAs and probably present a health risk. Additionally, phenylethylamine exceeded 30 mg/kg in 4 out of 5 industrial Larou samples, whereas, 9 VNAs concentrations were low and unlikely to induce adverse health effects on consumers. Principal component analysis revealed that the industrial Larou products had similar safety properties in terms of BAs and VNAs content when compared to the family-made samples. Correlation analysis indicated that BAs and VNAs were significantly correlated with free amino acids, a_w, pH and NaCl, respectively. This study suggests that the quality of Larou needs to be further improved by reducing salt and BAs content.

Risk assessment of N-nitrosamines in food

EFSA was asked for a scientific opinion on the risks to public health related to the presence of N-nitrosamines (N-NAs) in food. The risk assessment was confined to those 10 carcinogenic N-NAs occurring in food (TCNAs), i.e. NDMA, NMEA, NDEA, NDPA, NDBA, NMA, NSAR, NMOR, NPIP and NPYR. N-NAs are genotoxic and induce liver tumours in rodents. The in vivo data available to derive potency factors are limited, and therefore, equal potency of TCNAs was assumed. The lower confidence limit of the benchmark dose at 10% (BMDL10) was 10 μg/kg body weight (bw) per day, derived from the incidence of rat liver tumours (benign and malignant) induced by NDEA and used in a margin of exposure (MOE) approach. Analytical results on the occurrence of N-NAs were extracted from the EFSA occurrence database (n = 2,817) and the literature (n = 4,003). Occurrence data were available for five food categories across TCNAs. Dietary exposure was assessed for two scenarios, excluding (scenario 1) and including (scenario 2) cooked unprocessed meat and fish. TCNAs exposure ranged from 0 to 208.9 ng/kg bw per day across surveys, age groups and scenarios. 'Meat and meat products' is the main food category contributing to TCNA exposure. MOEs ranged from 3,337 to 48 at the P95 exposure excluding some infant surveys with P95 exposure equal to zero. Two major uncertainties were (i) the high number of left censored data and (ii) the lack of data on important food categories. The CONTAM Panel concluded that the MOE for TCNAs at the P95 exposure is highly likely (98-100% certain) to be less than 10,000 for all age groups, which raises a health concern.

Development of a fully automated analytical platform based on static headspace-gas chromatography-tandem mass spectrometry for the analysis of five N-nitrosamines in dried aquatic products of animal origin

BACKGROUND

The development of rapid and sensitive monitoring methods for trace N-nitrosamines (NAs) in foodstuffs is essential for mitigating the potential health risks to consumers. In the present study, an analytical platform based on one step fully automated static headspace sampling and gas chromatography-tandem mass spectrometry (GC-MS/MS) was developed and validated for the analysis of N-nitrosamines in dried aquatic products of animal origin. The samples and sodium chloride solution mixture were incubated in a heated headspace vial for analyte evaporation, coupled to automatic sampling and online GC-MS/MS analysis. The proposed method requires minimal sample preparation and organic solvent consumption. Five N-nitrosamines including N-nitroso dimethylamine, N-nitroso methyl ethylamine, N-nitroso pyrolidine, N-nitroso piperidine and N-nitroso diphenylamine were selected as model compounds to optimize the significant factors by a using Box-Behnken design.

RESULTS

The optimum conditions achieved limits of detections in the range 0.08-0.29 μg kg^-1 , with correlation coefficient over 0.998. Relative recoveries in dried aquatic product sample were in the range 76.9-92.4%, with relative SDs of 1.9-7.2%.

CONCLUSION

These results confirm the reliability of the developed method for further application in trace level monitoring of the target analytes in foodstuffs. © 2022 Society of Chemical Industry.

Rapid and selective determination of 9 nitrosamines in biological samples using ultra-high performance liquid chromatography-triple quadrupole linear ion trap mass spectrometry

A sensitive, selective and convenient method for the simultaneous determination of 9 nitrosamines (NAs) in biological samples was developed using isotope dilution ultra-high performance liquid chromatography-triple quadrupole linear ion trap mass spectrometry (UPLC-QTRAP-MS). Multiple reaction monitoring-information dependent acquisition-enhanced product ion (MRM-IDA-EPI) scan mode was performed to eliminate false positive results, and the whole detection procedure was characterized by less time consuming and simple sample preparation. 9 NAs were separated through a T3 column with the gradient elution of acetonitrile and water, and detected by UPLC-QTRAP-MS with an atmospheric pressure chemical ionization (APCI) source in the positive mode. The quantitative analysis was carried out via the isotope internal standard method with a matrix calibration curve. Under the optimized conditions, good linearity for the 9 NAs was achieved in the range of 0.2-20 μg L^-1 with correlation coefficients (r) higher than ≥0.9991, and the limits of detection and limits of quantitation were 0.02-0.1 μg L^-1 (S/N = 3) and 0.06-0.3 μg L^-1 (S/N = 10), respectively. Satisfactory recoveries ranging from 79.4% to 108.0% were obtained, and the precision of the proposed method, indicated by the relative standard deviations (RSDs), was 2.3-12.9%. The matrix effect study showed that NDMA, NMOR and NMEA presented a matrix suppression effect, NDPHA displayed a matrix enhancement effect, and the matrix effects of the other 5 analytes could be ignored. Real application of the developed method in 13 urine and 24 plasma samples demonstrated that NDBA, NPIP and NPYR occurred in both urine and plasma samples with the concentration of 0.038-0.60 μg L^-1, while other NAs were not detected. Such a method was sensitive and selective, and could be applied to the rapid qualitative and quantitative analysis of the 9 NAs in biological samples.

Bacterial Diversity of Sun-Dried Spanish Mackerel in Dalian and Application of Lactobacillus plantarum X23 as a Biopreservative

ABSTRACT

Sun-dried Spanish mackerel is a common food in Dalian and made by adding salt and sun drying, which has special physical, chemical, and microbiological properties. In this study, the physicochemical properties and microbial composition of commercially available sun-dried Spanish mackerel in Dalian were assessed, and some Lactobacillus strains were screened as a biopreservative for sun-dried Spanish mackerel preparation. The results showed that the total volatile base nitrogen content in the traditional sun-dried Spanish mackerel samples from Dalian was within 30 mg/100 g, the histamine content was 7 to 17 mg/kg, and the dominant bacteria at the genus level were Lactobacillus, Psychrobacter, and Ralstonia. A strain with biopreservative potential was isolated from a sun-dried Spanish mackerel sample, identified as L. plantarum species by 16S rDNA sequencing, and assigned as L. plantarum X23. Fresh Spanish mackerel flesh was treated with 16% brine and L. plantarum X23 at a dose of 107 CFU/mL and then dried in the sun. The sun-dried Spanish mackerel flesh treated with 16% brine and L. plantarum X23 showed a decreased histamine and acid value, increased free amino acid content, and a higher sensory score compared with the sun-dried Spanish mackerel without L. plantarum X23 treatment (P < 0.05). In conclusion, the sun-dried Spanish mackerel purchased from the supermarkets in Dalian were safely edible, and L. plantarum X23 can significantly reduce the content of histamine and putrescine in self-made, low-salt, sun-dried Spanish mackerel and has potential as a biopreservative for sun-dried Spanish mackerel preparation.

HIGHLIGHTS

Homogeneous liquid-liquid extraction as an alternative sample preparation technique for biomedical analysis

Liquid-liquid extraction is a widely used technique of sample preparation in biomedical analysis. In spite of the high pre-concentration capacities of liquid-liquid extraction, it suffers from a number of limitations including time and effort consumption, large organic solvent utilization, and poor performance in highly polar analytes. Homogeneous liquid-liquid extraction is an alternative sample preparation technique that overcomes some drawbacks of conventional liquid-liquid extraction, and allows employing greener organic solvents in sample treatment. In homogeneous liquid-liquid extraction, a homogeneous phase is formed between the aqueous sample and the water-miscible extractant, followed by chemically or physically induced phase separation. To form the homogeneous phase, aqueous samples are mixed with water-miscible organic solvents, water-immiscible solvents/cosolvents, surfactants, or smart polymers. Then, phase separation is induced chemically (adding salt, sugar, or buffer) or physically (changing temperature or pH). This mode is rapid, sustainable, and cost-effective in comparison with other sample preparation techniques. Moreover, homogeneous liquid-liquid extraction is more suitable for the extraction of delicate macromolecules such as enzymes, hormones, and proteins and it is more compatible with liquid chromatography with tandem mass spectrometry, which is a vital technique in metabolomics and proteomics. In this review, the principle, types, applications, automation, and technical aspects of homogeneous liquid-liquid extraction are discussed.

Characterization of a Novel Food Grade Emulsion Stabilized by the By- Product Proteins Extracted From the Head of Giant Freshwater Prawn (Macrobrachium rosenbergii)

The aim of this work was to develop a food-grade emulsion that stabilized by the by-product proteins in the head of giant freshwater prawn. The physicochemical properties of protein particles were characterized, and the stability of proteins-stabilized emulsions under different environmental stresses was evaluated. Results showed that the proteins were relatively hydrophilic and preferentially resided in the aqueous phase to form oil/water emulsions. On this basis, the proteins exhibited superior ability to stabilize the emulsions, and remarkably, the emulsions stabilized by 2% proteins and 3:7 oil/water ratio efficiently resisted the freeze-thaw treatment and the change of pH (3-9), salt addition (NaCl, 50-400 mM), and storage temperatures (4-60°C). Furthermore, the emulsions showed a matched long-term stability with the existing biopolymers-stabilized emulsions. Consequently, this is the first finding of the by-product proteins in the head of giant freshwater prawn as an excellent emulsifier to stabilize emulsions, which help to improve the stability of food-grade emulsions and the added value of aquatic products.

Formation of amino acid-derived volatile compounds in dry-cured mackerel (Scomberomorus niphonius): Metabolic pathways involving microorganisms, precursors, and intermediates

This study focuses on the formation mechanism of amino acid-derived volatile compounds (AAVC) in dry-cured mackerel (Scomberomorus niphonius) (DCM) during the process. Three kind of AAVC (3-methylbutanal, 3-methylbutanol, and phenylacetaldehyde) were detected in DCM. The content of 3-methylbutanal (14.6 mg/kg) was higher than that of phenylacetaldehyde (12.9 mg/kg), and part of which was reduced to 3-methylbutanol (5.15 mg/kg). While the corresponding intermediate, α-ketoisocaproate (156 μg/kg), was lower than that of phenylpyruvic acid (271 μg/kg), indicating its decarboxylation was limited. Five strains (Bacillus, Enterobacter, Staphylococcus, Macrococcus, and Lactobacillus) that can produce the relative transaminases and decarboxylases were involved in the production of AAVC. The most dominant strain, Bacillus (81.9%), was only involved in the production of 3-methylbutanal. The relative abundance of Staphylococcus, the sole phenylpyruvate decarboxylase-producing bacteria, was low, resulting in low product conversion. These results indicated that the production of AAVC is determined by specific microorganisms in the products.

Perchlorate occurrence in foodstuffs and water: Analytical methods and techniques for removal from water - A review

Perchlorate (ClO₄^-), a type of contaminant with high diffusivity and durability, has been widely detected in water and foodstuffs, arousing a global concern. It can interfere with normal function of the human thyroid gland, affecting human health. Therefore, determination of perchlorate in water and foodstuffs, and removal from water are important. This review focuses on the occurrence of perchlorate, mainly in water and foodstuffs, and provides an overview of analytical methods for determination of perchlorate over the last two decades. In addition, merits and drawbacks of the various methods have been considered. This review also highlights the most commonly used approaches for removal of perchlorate from water. Finally, current trends and future perspectives in determination of perchlorate and removal from water are proposed. This review provided a comprehensive understanding of perchlorate occurrence and its removal from water, and had practical significance in reducing the harm of perchlorate to human.

High-throughput quantification of eighteen heterocyclic aromatic amines in roasted and pan-fried meat on the basis of high performance liquid chromatography-quadrupole-orbitrap high resolution mass spectrometry

Triple quadrupole mass spectrometry has been the main technique for HAAs analysis in recent decade, while it requires extensive optimization of compound-dependent parameters. A novel method based on HPLC-Q-Orbitrap-HRMS was developed firstly for simultaneous determination of eighteen HAAs. Extraction and purification conditions were optimized and the developed method was validated in terms of linearity, accuracy and precision. Results indicated eighteen HAAs and two internal standards could be separated in 12 min using a gradient elution program. The full MS/dd-MS² scan was adopted for analysis, which indicated favorable recoveries (71.3-114.8%) along with LODs and LOQs in the ranges of 0.02-0.6 and 0.05-2.0 μg/kg, respectively. Internal standards used for calibration could effectively reduce quantification errors produced by matrix effects. The validated method was successfully applied for HAAs analysis in roasted and pan-fried meat and was confirmed to be an alternative method when triple quadrupole mass spectrometry is absent in lab.

An high-throughput sequencing approach to the preliminary analysis of bacterial communities associated with changes in amino acid nitrogen, organic acid and reducing sugar contents during soy sauce fermentation

Soy sauce is a traditional fermented soy food for enhancing the umami taste in Asian cuisines. In this study, 16S rRNA gene throughput sequencing analysis showed the bacterial communities and the changes in soy sauce during fermentation. Weissella, Bacillus and Lactococcus were the most abundant at genus level. The uncultured bacterium Weissella and Lactococcus had relatively high abundance at species level. Alpha diversity analysis indicated the bacterial community diversity increased at fermentation initiation, while decreased as fermentation progressed. Based on beta-diversity analysis, four clusters including cluster I (time point A-F), cluster II (G,H), cluster III (I,J) and cluster IV(K) were distinctly separated, indicating the fermentation time significantly affected bacterial community diversity. Also, close associations were found between the bacterial communities in soy sauce and its amino acid nitrogen, organic acid and reducing sugar contents during fermentation. Therefore, it will provide important information for optimization of the soy sauce production process.

The application of L-glutaminase for the synthesis of the immunomodulatory γ-D-glutamyl-L-tryptophan and the kokumi-imparting γ-D-glutamyl peptides

Glutaminase of Bacillus amyloliquefaciens has been used to synthesize the immunomodulatory γ-D-glutamyl-L-tryptophan (γ-D-Glu-L-Trp) and the kokumi-active γ-D-glutamyl peptides. The optimum yield of γ-D-Glu-L-Trp was 55.76 mM in corresponding to a minimum yield of by-product (γ-D-Glu-γ-D-Glu-L-Trp) in the presence of 75 mM D-Gln and 100 mM L-Trp. The glutaminase has a low Km values for the donors (D-Gln and L-Gln:5.53 and 0.98 mM), but high ones for the acceptors (L-Trp, L-Phe, L-Met, L-Val and γ-[D-Glu]( n =1,2,3)-L-Val/L-Phe/L-Met, ranging from 32.51 to 193.05 mM). The highest Km value appearing when n = 2 (γ-[D-Glu]( n =0,1,2)-L-Val/L-Phe/L-Met) suggested the rising difficulty for synthesis when the number of donor increases in the reaction mixtures. The γ-[D-Glu]( n =1,2,3)-L-Val/L-Phe/L-Met at 5 mM can impart the blank chicken broth an enhancing monthfulness, thickness, and umaminess taste.

Key aroma compounds of Chinese dry-cured Spanish mackerel (Scomberomorus niphonius) and their potential metabolic mechanisms

The key aroma compounds of six commercially available dry-cured Spanish mackerel (Scomberomorus niphonius, DCSM) were identified using electronic nose (E-nose), gas chromatography-olfactometry (GC-O), and two-dimensional gas chromatography-time-of-flight mass spectrometry (GC × GC-TOFMS). A total of 38-55 aroma compounds were identified, and 21-26 of them, which presented high flavor dilution factors based on aroma extract dilution analysis, were quantified. Lastly, 9-14 key aroma compounds with high odor-active value, including 3-methyl-1-butanal, octanal, 1-octen-3-ol, nonanal, cis-4-decenal, ethyl caproate, (E)-2-octenal, (Z)-2-nonenal decanal, 3-methyl-1-butanol, 1-heptanol, 3-octanone, 2-octanol, and 6-methyl-5-hepten-2-one, were identified as the key aroma contributors in DCSM. Results also indicated that a longer dry-curing time would promote the generation of aroma compounds. The metabolism analysis implied that the auto-oxidation/oxidation of unsaturated fatty acids, such as oleic and linoleic acid, and the enzymatic degradation of l-leucine might be potential metabolic mechanisms.