Detection and Quantification of 4(5)‐Methylimidazole in Cooked Meat

4(5)‐Methylimidazole (4‐MeI) is a nitrogen‐containing heterocyclic compound found in class III and IV ammoniated caramel colors, a group of additives widely used in the food industry. A suspected carcinogen and neurotoxin and efforts are underway to limit its presence in foods. Several methods have been developed to detect and quantitate 4‐MeI in different food matrices, including roasted coffee, beer, soft drinks, and soy sauce; however, no methods are available to measure 4‐MeI in cooked meat and meat products containing lipids and high levels of interfering nitrogen compounds, such as amino acids and peptides. A rapid method using 0.1 M sodium acetate buffer (pH 5) as an extraction solvent followed by derivatization with isobutylchloroformate and gas chromatograph mass‐spectrometry was developed to quantify 4‐MeI in cooked meat products with added caramel colors containing 4‐MeI. Selected ion monitoring mode was used to monitor 4‐MeI ions fragments. In the 8 commercial meat products tested, 4‐MeI levels ranged from 0.041 to 1.015 mg/kg, with recovery of 94.76% to 103.94%. In addition, a matrix‐matched calibration performed by analyzing a spiked cooked meat sample indicated no significant difference (P > 0.05), which means the meat matrix had no effect on the developed method. This method proved useful in analyzing 4‐MeI in meat products with added caramel color containing 4‐MeI.     

Effect of Various Food Additives on the Levels of 4(5)‐Methylimidazole in a Soy Sauce Model System

In this study, the effect of food additives such as iron sulfate, magnesium sulfate, zinc sulfate, citric acid, gallic acid, and ascorbic acid on the reduction of 4(5)‐methylimidazole (4(5)‐MI) was investigated using a soy sauce model system. The concentration of 4(5)‐MI in the soy sauce model system with 5% (v/v) caramel colorant III was 1404.13 μg/L. The reduction rate of 4(5)‐MI level with the addition of 0.1M additives followed in order: iron sulfate (81%) > zinc sulfate (61%) > citric acid (40%) > gallic acid (38%) > ascorbic acid (24%) > magnesium sulfate (13%). Correlations between 4(5)‐MI levels and the physicochemical properties of soy sauce, including the amount of caramel colorant, pH value, and color differences, were determined. The highest correlations were found between 4(5)‐MI levels and the amount of caramel colorant and pH values (r² = 0.9712, r² = 0.9378). The concentration of caramel colorants in 8 commercial soy sauces were estimated, and ranged from 0.01 to 1.34% (v/v).     

Amino Acids Inhibitory Effects and Mechanism on 2‐Amino‐1‐Methyl‐6‐Phenylimidazo [4,5‐b]Pyridine (PhIP) Formation in the Maillard Reaction Model Systems

This study was to investigate the inhibitory effects of amino acids (AAs) on the formation of 2‐amino‐1‐methyl‐6‐phenylimidazo [4,5‐b]pyridine (PhIP) and to evaluate the inhibition mechanism of PhIP in Maillard model systems. Different AAs were individually added into model systems heat‐treated at 180 °C/1 h. The PhIP, phenylacetaldehyde (PheAce), and pyrazines derivatives were determined using HPLC and GC‐MS. AAs significantly reduced (P < 0.05) PhIP levels in a dose‐dependent response, ranking as: Trp = Lys > Pro > Leu > Met > Val > Ile > Thr > Phe > Asp, at the highest molar ratio. The PheAce content was gradually reduced with increasing AAs levels, suggesting that AAs may inhibit PhIP formation through scavenging the available PheAce. A correlation between PhIP inhibition and PheAce‐scavenging activity of AAs was observed when PheAce and AAs were heated. The variety and quantity of pyrazines formed are highly depending on the type of AAs.     

Color Development in a Model System During Frying: Role of Individual Amino Acids and Sugars

The color of fried potato products is limited by reducing sugars, but can be affected by free amino acids. Filter paper discs saturated with solutions of amino acids in combination with glucose, fructose and sucrose were fried in oil to investigate color formation. Four phases of color development were identified; equilibrium, lag, rapid and slow phase, corresponding to the water content of the system. Lysine, 7-aminobutyric acid and glycine produced most color and glutamic acid least. Fry color of glucose and fructose systems was very similar, but sucrose systems produced less color. Glucose and fructose systems were not affected by pH changes, but there was a slight effect on sucrose systems.     

Simple and Fast Sample Preparation Followed by Gas Chromatography‐Tandem Mass Spectrometry (GC‐MS/MS) for the Analysis of 2‐ and 4‐Methylimidazole in Cola and Dark Beer

We have developed a simple and fast sample preparation technique in combination with a gas chromatography‐tandem mass spectrometry (GC‐MS/MS) for the quantification of 2‐methylimidazole (2‐MeI) and 4‐methylimidazole (4‐MeI) in colas and dark beers. Conventional sample preparation technique for GC‐MS requires laborious and time‐consuming steps consisting of sample concentration, pH adjustment, ion pair extraction, centrifugation, back‐extraction, centrifugation, derivatization, and extraction. Our sample preparation technique consists of only 2 steps (in situ derivation and extraction) which requires less than 3 min. This method provided high linearity, low limit of detection and limit of quantification, high recovery, and high intra‐ and interday repeatability. It was found that internal standard method with diluted stable isotope (4‐MeI‐d₆) and 2‐ethylimidazole (2‐EI) could not correctly compensate the matrix effects. Thus, standard addition technique was used for the quantification of 2‐ and 4‐MeI. The established method was successfully applied to colas and dark beers for the determination of 2‐MeI and 4‐MeI. The 4‐MeI contents in colas and dark beers ranged from 8 to 319 μg/L and from trace to 417 μg/L, respectively. Small quantity (0 to 8 μg/L) of 2‐MeI was found only in dark beers. The contents of 4‐MeI (22 μg/L) in colas obtained from fast food restaurants were significantly lower than those (177 μg/L) in canned or bottled colas.     

Reversible Regulation of Gelatinization of Potato Starch with Poly(ε‐lysine) and Amino Acids

Poly(ε‐lysine) (PL), lysine (Lys), monosodium glutamate (GluNa), glycine (Gly), alanine (Ala), and leucine (Leu) were used to regulate the characteristic gelatinization behavior of potato starch. As determined by differential scanning calorimetry, PL, Lys, and GluNa with positive or negative net charge elevated the gelatinization temperature with increasing amount added as compared with the small effect of Gly, Ala, and Leu with zero net charge. The peak viscosity evaluated by a Rapid Viscoanalyser was markedly decreased by adding PL, Lys, and GluNa, whereas Gly and Ala had no effect on the peak viscosity. The swelling was also decreased by added PL, Lys, and GluNa, whereas it was unchanged by added Gly, Ala, and Leu. Potato starch immersed in PL or amino acid solution released most of the retained PL and amino acids by the subsequent washing with water. The increased gelatinization temperature of the PL‐treat­ed potato starch returned to the original value by washing with water. It is thus considered that the regulatory effects of PL and amino acids on the gelatinization behavior of potato starch were substantially reversible.     

Degradation of N‐(1‐Deoxy‐d‐xylulos‐1‐yl)glycine and N‐(1‐Deoxy‐d‐xylulos‐1‐yl)proline using thermal treatment

The formation and degradation of N‐(1‐Deoxy‐d ‐xylulos‐1‐yl)glycine and N‐(1‐Deoxy‐d ‐xylulos‐1‐yl)proline, derived from the secondary amine Maillard reaction in xylose‐amino acid model solutions, were detailed in this study. The identification and quantitative analysis of N‐(1‐Deoxy‐d‐ xylulos‐1‐yl)glycine and N‐(1‐Deoxy‐d‐ xylulos‐1‐yl)proline were carried out using high‐performance anion‐exchange chromatography and high‐performance liquid chromatography. The formation of intermediate and advanced products derived from N‐(1‐Deoxy‐d‐ xylulos‐1‐yl)glycine and N‐(1‐Deoxy‐d‐ xylulos‐1‐yl)proline was also tested using an UV‐Vis spectrophotometer to gain a better comparing of the degradation process of the two important Maillard reaction products using thermal treatment. Results showed that the degradation of N‐(1‐Deoxy‐d‐ xylulos‐1‐yl)glycine was more significant than N‐(1‐Deoxy‐d‐ xylulos‐1‐yl)proline. Moreover, xylose was tested in the degradation products of both N‐(1‐Deoxy‐d‐ xylulos‐1‐yl)glycine and N‐(1‐Deoxy‐d‐ xylulos‐1‐yl)proline, which indicated that the degradation of N‐substituted 1‐amino‐1‐deoxyketoses was a reversible reaction to form reducing sugar.     

GC-FID测定黄酒中17种游离氨基酸

建立以N-(特丁基二甲基硅烷)-N-甲基三氟乙酰胺(MTBSTFA)为衍生试剂测定黄酒中17种游离氨基酸的气相色谱(GC)方法。比较了衍生温度、时间、及辅助试剂等对衍生效率的影响,确定N,N-二甲基甲酰胺(DMF)为辅助衍生试剂,衍生温度80℃,衍生时间60 min,可以定量检测黄酒中主要的游离氨基酸。各氨基酸在50～500 mg/L内线性良好(相关系数均大于0.99)。对黄酒样品的测定结果与高效液相色谱测定结果相比皮尔逊相关系数为0.998,样品的平均加标回收率为87.11%～119.47%。结果表明:GC-FID方法操作简便、准确、重现性好,适用于黄酒中17种游离氨基酸的分离检测。该测定方法将为开发气相-燃烧-同位素比率质谱(GC-C-IRMS)测定黄酒中氨基酸13C稳定同位素丰度以及分析黄酒酿造过程中的代谢实验提供研究基础。     

Inhibition of 2‐Amino‐1‐methyl‐6‐phenylimidazo [4,5‐b]pyridine (PhIP) Formation by Alkoxy Radical Scavenging of Flavonoids and Their Quantitative Structure–Activity Relationship in a Model System

The inhibitory effect of 10 flavonoids on the formation of 2‐amino‐1‐methyl‐6‐phenylimidazo[4,5‐b]pyridine (PhIP) in a creatinine–phenylalanine model system was investigated through electronic spin resonance and a quantitative structure–activity relationship. Alkoxy radicals were observed during the heating process, providing evidence for a radical pathway in the formation of PhIP. The alkoxy radical scavenging capability of the flavonoids was proportional to their inhibition of PhIP formation (IC₅₀). We deduced that flavonoid inhibition of PhIP generation occurs via scavenging of alkoxy radicals during the heating process. Multiple linear regression and partial least squares models were used to elucidate the relationship between PhIP inhibition activity and structure characteristics of the flavonoids. The lipo–hydro partition coefficient and molecular fractional polar surface area of the flavonoids were found to be predictive of the inhibition effect.     

Dietary Amino Acids and the Gut‐Microbiome‐Immune Axis: Physiological Metabolism and Therapeutic Prospects

Dietary amino acids (AAs) are not only absorbed and metabolized by enterocytes but also available to the microbiota in the gut in mammals. In addition to serving as the materials for protein synthesis, AAs can act as precursors for numerous metabolic end products in reactions involving the intestinal mucosa and microbiota. After penetrating the epithelial barrier, microbial metabolites can enter and accumulate in the host circulatory system, where they are sensed by immune cells and then elicit a wide range of biological functions via different receptors and mechanisms. Some intestinal bacteria can also synthesize certain AAs, implying that the exchange of AAs between hosts and microorganisms is bidirectional. Changes in AA composition and abundance can affect AA‐metabolizing bacterial communities and modulate macrophages and dendritic cells via toll‐like receptors (TLRs), autoinducer‐2 (AI‐2), and NOD‐like receptors (NLRs), and also regulate the gut‐microbiome‐immune axis via aryl hydrocarbon receptor (AhR), serotonin/5‐hydroxytryptamine (5‐HT), and other signaling pathways, all of which play critical roles in regulating the intestinal mucosal immunity and microbiota directly or indirectly, contributing to intestinal homeostasis. Therefore, the current findings of the effects of certain functional AAs on the gut‐microbiome‐immune axis are reviewed, illustrating signaling pathways of tryptophan (Trp), glutamine (Gln), methionine (Met), and branched‐chain AAs (BCAAs) in the intestinal barrier and regarding immunity via crosstalk with their receptors or ligands. These findings have shed light on the clinical applications of dietary AAs in improving gut microbiota and mucosal immunity, therefore benefiting the gut as well as local and systemic health.     

Formation of 4‐hydroxynonenal (4‐HNE) in frozen mackerel (Scomber scombrus) in the presence and absence of green tea

BACKGROUND: Aldehydes are secondary lipid oxidation products formed during processing and storage of food. 4‐Hydroxynonenal (4‐HNE) is a major toxic lipid peroxidation product which has been extensively investigated in the clinical field but less so in food products. The aim of the present study was to investigate the formation of aldehydes in stored frozen fish (Atlantic mackerel, Scomber scombrus) with and without antioxidant (green tea). RESULTS: The presence of 4‐HNE in frozen fish was detected for the first time. 4‐HNE was extracted from frozen fish and identified using high‐performance liquid chromatography and liquid chromatography/mass spectrometry. The amount of 4‐HNE increased throughout storage for 26 weeks at ? 10 °C in the absence of antioxidant. A significant decrease was observed in fish samples stored at ?10 °C with green tea. Minimal amounts of 4‐HNE were formed in fish stored at ?80 °C. A similar increase in 4‐HNE was found for methyl linoleate and extracted fish oil exposed to UV irradiation. CONCLUSION: The toxic aldehyde 4‐HNE can be formed in badly stored frozen mackerel and is an indicator of reduced texture quality and nutritional value of fish. Addition of instant whole green tea as an antioxidant can provide a cheap and effective way of enhancing safety, especially in developing countries. Copyright © 2008 Society of Chemical Industry     

枸杞子水浸液中氨基酸和微量元素含量的测定

研究不同试验条件对枸杞子水浸液中氨基酸和微量元素含量的影响。采用正交试验,研究水温、浸泡时间、固液比对枸杞子水浸液中氨基酸及微量元素含量的影响。结果显示:水温、浸泡时间、固液比对氨基酸及微量元素浸出率的影响依次减弱。较高水温及较长时间的浸泡利于枸杞子中氨基酸及微量元素的浸出。     

Analysis and risk assessment of 4(5)-methylimidazole in brown colored foods and beverages

In this study, the 4(5)-methylimidazole (4(5)-MI) levels in various 144 brown coloured foods and beverages were determined. The brown coloured foods and beverages were 62 processed sauces, 40 coffee, 9 caramel syrups, 18 red ginseng juice and 15 Japanese apricot fruit juice. The amount of 4(5)-MI in brewed coffee (1821.3 ng/g) was the highest level among the samples. The 4(5)-MI concentration in processed sauce (47.6 ng/g) was the lowest level among the samples. The levels of 4(5)-MI in various samples were found as follows: 47.6–1748.5 ng/g in processed sauces, 64.1–1821.3 ng/g in commercial coffee, 115.5–491.9 ng/g in caramel syrups, 91.0–854.1 ng/g in red ginseng juice and 137.6–587.4 ng/g in Japanese apricot fruit juice. Based on the 4(5)-MI levels, the estimated daily intake (EDI) and chronic daily intake (CDI) were calculated. EDI and CDI of red ginseng juice was the highest among all samples, and they were 1618.6 and 1256.8 ng/kg bw/day, respectively.     

Simultaneous Analysis of Nε‐(Carboxymethyl)Lysine and Nε‐(Carboxyethyl)Lysine in Foods by Ultra‐Performance Liquid Chromatography‐Mass Spectrometry with Derivatization by 9‐Fluorenylmethyl Chloroformate

Isotope dilution ultra‐performance liquid chromatography–electrospray tandem mass spectrometry with derivatization by 9‐fluorenylmethyl chloroformate was successfully applied to quantify N^ε‐(carboxymethyl)lysine (CML) and N^ε‐(carboxyethyl)lysine (CEL) in processed foods. We demonstrate that this analytical method is well validated for the determination of CML and CEL contents in processed foods. Relative standard deviations (RSD) indicate repeatability (RSD < 6% for CML and CEL) and reproducibility (RSD < 6% for CML and < 7% for CEL) in this method. Percent recovery is also good. We obtain recoveries of 102% to 112% for CML and 86% to 114% for CEL. CML levels detected in the samples vary from 2.29 to 480 mg/kg food, whereas CEL is detected in significantly lower concentrations ranging from 0.56 to 107 mg/kg food. These data could help consumers make better food choices by monitoring intake of advanced glycation end‐products, which may pose a risk to human health.     

以三聚氯化氰为脱水剂合成饱和5（4H）—恶唑酮反应的研究

从N酰基氨基酸出发，以三聚氯为氰为脱水剂，合成出8种2（取代苯基）5恶唑酮。通过熔点测定，红外光谱测定，核磁测定对产品进行了表征。     

Effects of oxidised linoleic acid on the formation of Nε‐carboxymethyl‐lysine and Nε‐carboxyethyl‐lysine in Maillard reaction system

This study investigated the effects of oxidised linoleic acid (18:2) on N^ε‐carboxymethyl‐lysine (CML) and N^ε‐carboxyethyl‐lysine (CEL) formation in Maillard reaction systems. Model systems of lysine/glucose (L/G), lysine/18:2 (L/18:2), lysine/18:2/glucose (L/18:2/G), myofibrillar protein/glucose (MFP/G), MFP/18:2 and MFP/18:2/G were maintained at 37 °C for 6 weeks. The results showed that CML/CEL contents in L/G (6.99 and 0.96 mmol mol^?1 lysine, respectively) were significantly higher than those in L/18:2/G (1.43 and 0.41 mmol mol^?1 lysine, respectively), and there is a small amount of CML/CEL generation in L/18:2. However, the CML/CEL levels in MFP/G (197.2 and 83.8 ng mg^?1 protein, respectively) were markedly lower than those in MFP/18:2/G (283.2 and 118.5 ng mg^?1 protein, respectively). 18:2 favours the formation of CML/CEL in MFP/18:2/G, not in L/18:2/G. All these findings indicated that the role of 18:2 on CML/CEL formation in Maillard reaction system was complex, and depended on CML/CEL formation rate and substrate types (lysine or lysine residue in protein).     

固体硫酸铁催化合成不饱和5（4H）-噁唑酮反应的研究

首次采用固体硫酸铁作催化剂，用饱和噁唑酮与醛酮反应，合成了10种不饱和噁唑酮。并通过m．p测定，IR测定，IR测定等，对产物进行了表征。