Efficient Analysis of 2-Acetyl-1-pyrroline in Foods Using a Novel Derivatization Strategy and LC-MS/MS

Integrative analysis of the multi-omics reveals the stripe rust fungus resistance mechanism of the TaPAL in wheat

Wheat is one of the major food crops in the world. However, stripe rust fungus significantly decreases wheat yield and quality. In the present study, transcriptomic and metabolite analyses were conducted in R88 (resistant line) and CY12 (susceptible cultivar) during Pst-CYR34 infection due to the limited availability of information regarding the underlying mechanisms governing wheat-pathogen interactions. The results revealed that Pst infection promoted the genes and metabolites involved in phenylpropanoid biosynthesis. The key enzyme gene TaPAL to regulate lignin and phenolic synthesis has a positive resistance contribution to Pst in wheat, which was verified by the virus-induced gene silencing (VIGS) technique. The distinctive resistance of R88 is regulated by the selective expression of genes involved in the fine-tuning of wheat-Pst interactions. Furthermore, metabolome analysis suggested that lignin biosynthesis-related metabolite accumulation was significantly affected by Pst. These results help to elucidate the regulatory networks of wheat-Pst interactions and pave the way for durable resistance breeding in wheat, which may ease environmental and food crises around the world.

Effects of Hevea brasiliensis Intercropping on the Volatiles of Pandanus amaryllifolius Leaves

Pandanus amaryllifolius Roxb. is a special tropical spice crop resource with broad development prospects. It is widely cultivated under a Hevea brasiliensis (Willd. ex A. Juss.) Muell. Arg. canopy to improve the comprehensive benefits to Hevea brasiliensis plantations in Hainan Provence, China. However, the effects of intercropping with Hevea brasiliensis on the component number and relative contents of volatile substances in different categories in the Pandanus amaryllifolius leaves are still unknown. Therefore, a Hevea brasiliensis and Pandanus amaryllifolius intercropping experiment was set up to clarify the differences between several cultivated patterns on volatile substances in the Pandanus amaryllifolius leaves, and the key regulatory factors of volatile substances. The results showed that the soil pH was significantly decreased, while soil bulk density, alkali-hydrolyzable nitrogen and available phosphorus contents were significantly increased under the intercropping pattern. The component numbers of esters in volatile substances were increased by 6.20%, while the component numbers of ketones were decreased by 4.26% under the intercropping pattern. Compared with the Pandanus amaryllifolius monoculture, the relative contents of pyrroles, esters and furanones were significantly increased by 8.83%, 2.30% and 8.27%, respectively, while the relative contents of ketones, furans and hydrocarbons were decreased by 1.01%, 10.55% and 9.16% under the intercropping pattern, respectively. The relative contents of pyrroles, esters, furanones, ketones, furans and hydrocarbons were associated with changes in soil pH, soil available phosphorus content and air temperature. The results indicated that the reduction in soil pH and enhancement in soil-available phosphorus may be the main reasons for promoting the relative content of pyrroles and reducing the relative content of hydrocarbons under an intercropping pattern. Overall, Hevea brasiliensis intercropping with Pandanus amaryllifolius could not only improve soil properties, but also significantly increase the relative contents of the main volatile substances in Pandanus amaryllifolius leaves, which could provide a theoretical basis for the application and promotion of high-quality production patterns of Pandanus amaryllifolius.

Determination of 2-Acetyl-1-pyrroline via a Color-Change Reaction Using Chromium Hexacarbonyl

At present, there is no colorimetric method for the quantitation of the aroma compound 2-acetyl-1-pyrroline (2AP). A novel colorimetric method was developed for the determination of 2AP content using chromium hexacarbonyl (Cr(CO)₆) as a reagent. The reaction of synthetic 2AP with chromium hexacarbonyl reagent solution in the presence of light produced a green product with an absorption maximum (λ_max) at 623 nm. GC–MS was used to confirm the color-change reaction, which showed the loss of 2AP after the addition of Cr(CO)₆. This novel method enables facile and cost-effective determination of 2AP in fragrant rice. A comparative analysis of fragrant and nonfragrant rice grain extracts showed that no color-change reaction occurred with the nonfragrant rice sample. A limit of detection (LOD) of 2.00 mg L⁻¹ was determined by method validation with an effective linear concentration ranging from 5.00 to 60.00 mg L⁻¹ of 2AP. The results obtained using the developed colorimetric method were consistent with those obtained by automated static headspace gas chromatography with nitrogen-phosphorus detection (SHS-GC–NPD).

The determination of monosaccharide in different years Qingzhuan Dark Tea polysaccharide by liquid chromatography-mass spectrometry

AIM

To establish a fast, sensitive and accurate high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method for determining the monosaccharide content of Qingzhuan Dark Tea polysaccharides in different years (2 years, 5 years and 11 years).

METHODS

The optimised chromatographic conditions were achieved on a C18 column (5.0 μm, 250 mm × 4.6 mm inner diameter). The mobile phase flow rate was 0.9 mL/min and the column temperature was set to 27°C. The aqueous phase A (5 mM aqueous ammonium acetate) and organic phase B (acetonitrile) were used to elute the target analyses isocratically (0-60 min: 18% B). The mass spectrometer detector was equipped with an electron spray ionisation (ESI)source, and multiple reaction monitoring (MRM) mode was used for the determination of 1-phenyl-3-methyl-5-pyrazolone (PMP) derived monosaccharides.

RESULTS

We carried out a comprehensive methodological validation of PMP derived monosaccharides, including linearity, precision, stability and repeatability. Nine monosaccharides (rhamnose, mannose, ribose, glucose, galacturonic acid, xylose, galactose, fucose and arabinose) of Qingzhuan Dark Tea polysaccharides were identified, in which ribose and fucose were reported for the first time. The results showed the contents of these nine monosaccharides differed significantly among different years.

CONCLUSIONS

The validated method is reliable, accurate, repeatable and can be applied to quality assessment of these monosaccharides.

Benzothiazines as Major Intermediates in Enzymatic Browning Reactions of Catechin and Cysteine

The course of melanin formation is yet not thoroughly resolved on a mechanistic level. With the present study, incubations of catechin (CA)- and cysteine-derived dihydro-1,4-benzothiazine carboxylic acid derivatives were investigated for colored products during enzymatic browning. Analyses by high-performance liquid chromatography (HPLC)-mass spectrometry revealed the formation of two novel decarboxylated dihydro-1,4-benzothiazine derivatives [8-(3,5,7-trihydroxy-3,4-dihydro-2H-chromen-2-yl)-5-hydroxy-3,4-dihydro-2H-benzothiazine and 7-(3,5,7-trihydroxy-3,4-dihydro-2H-chromen-2-yl)-5-hydroxy-3,4-dihydro-2H-benzothiazine] preferentially under acidic conditions. Furthermore, in model reactions under neutral pH, a colored phenazine dimer intermediate was isolated by high-performance countercurrent chromatography and preparative HPLC when conducting the incubations in the presence of o-phenylenediamine (OPD). Mass spectrometry and nuclear magnetic resonance spectroscopy unequivocally verified the structure as (12E)-5,5'-dioxo-11a,11a'-bis(3,5,7-trihydroxy-3,4-dihydro-2H-chromen-2-yl)-3,3',4,4',5a,5a',6,6',11,11',11a,11a'-dodecahydro-2H,2'H,5H,5'H-12,12'-bi[1,4]thiazino[2,3-b]phenazine-3,3'-dicarboxylic acid. Enzymatically catalyzed incubations under aeration starting from the initial CA-cysteine adducts and their follow-up dihydro-1,4-benzothiazine carboxylic acids, respectively, proved that the unstable colored compound was a trichochrome-like reaction intermediate of the browning reaction cascade which can be trapped by postincubation with OPD, thus verifying their direct mechanistic relationship.

Isotope-Coding Derivatization for Quantitative Profiling of Reactive α-Dicarbonyl Species in Processed Botanicals by Liquid Chromatography-Tandem Mass Spectrometry

α-Dicarbonyls (α-DCs) are key reactive Maillard intermediates with structural diversity and are widely found in foods and in vivo, but little is known regarding the complete molecular profiles of these potentially harmful electrophiles. Herein, we reported a novel isotope-coding derivatization (ICD) strategy for the broad-spectrum, quantitative profiling of (non)target α-DC species in natural foodstuffs. It utilized differential isotope labeling (DIOL) with a reagent pair o-phenylenediamine (OPD)/OPD-d₄ (deuterated) to form stable quinoxalines for class-specific fragmentation-dependent acquisition using liquid chromatography-hybrid quadrupole linear ion trap mass spectrometry (LC-QqLIT). A combination of facile one-pot quantitative labeling and convenient cleanup protocol afforded satisfactory sensitivity, linearity, accuracy (81-116%), and process recovery (86-109% with RSDs < 10%) by matrix-matched ICD-internal standard calibration, without significant matrix interference (-9 to 5%), isotopic effect (<0.5%), and cocktail effect. A more generic DIOL-based LC-QqLIT algorithm integrated double precursor ion and neutral loss scan to trigger enhanced product ions with the unique isobaric doublet tags (4 Da shift), enabling simultaneous screening and relative quantitation of nontarget α-DC analogues in a single analysis. This study has widened the vision on complex α-DC profiles in traditional botanicals, which revealed a wide occurrence of α-DCs in such processed sugar-rich products, yet their abundance varied greatly among different samples.

Rapid, High-Throughput Quantitation of Odor-Active 2-Acetyl Azaheterocycles in Food Products by UHPLC-MS/MS

A rapid, high-throughput method for the quantitation of the 2-acetyl azaheterocycles, 2-acetyl-1-pyrroline, 2-acetyl-1,4,5,6-tetrahydropyridine, 2-acetylpyrazine, and 2-acetyl-2-thiazoline, in different food products, by liquid chromatography-tandem mass spectrometry (LC-MS/MS), was developed. The quick extraction by bead beater homogenization, fast derivatization by 3-nitrophenylhydrazine (40 °C, 2 h), and efficient LC separation make this method suitable for high-throughput analysis. As established in this study, the highly precise LC-MS/MS method applies to different food products or beverages without requiring further adjustment. The analysis was performed with sample amounts of 0.2-0.5 g, and limit of quantitation values of 0.6, 0.5, 0.6, and 1.0 μg/kg were obtained for 2-acetyl-1-pyrroline, 2-acetyl-1,4,5,6-tetrahydropyridine, 2-acetylpyrazine, and 2-acetyl-2-thiazoline, respectively. Thus, it was possible to quantitate the analytes in the range of their odor thresholds.

Methylglyoxal binds to amines in honey matrix and 2'-methoxyacetophenone is released in gaseous form into the headspace on the heating of manuka honey

Reports on the thermal stability of manuka honey in terms of food processing have been few. This study investigated changes in nine characteristic chemicals of manuka honey during heating. Among these, methylglyoxal (MGO) and 2'-methoxyacetophenone (MAP) were significantly decreased by heating at 90 °C. To elucidate the mechanism for this decrease, artificial honey was prepared from sugars and water with MAP or MGO and then heated. The decrease of MGO was enhanced with l-proline, lysine, or arginine derivatives, accompanied by formation of 2-acetyl-1-pyrroline, MGO-derived lysine dimer, or argpyrimidine, respectively, suggesting that an amino-carbonyl reaction is one pathway for the loss of MGO. The decrease of MAP in the artificial honey depended on the volume of headspace in a vessel. MAP from heated manuka honey was also detected in the gas phase, indicating that MAP was vaporized. Heating could thus reduce the beneficial and/or signature molecules in honey.

Identification of key odorants in complex mixtures occurring in nature

Covering: up to 2019Soon after the birth of gas chromatography, mass spectrometry and olfactometry were used as detectors, which allowed impressive development to be achieved in the area of odorant determinations. Since the mid-80s, structured methods of gas chromatography-olfactometry have appeared, allowing the determination of which odor constituents play a key role in materials. Progressively, numerous strategies have been proposed for sample preparation from raw materials, the representativeness evaluation of extracts, the identification of odor constituents, their quantification, and subsequently, the recombination of the key odorants to mimic the initial odor. However, the multiplicity of options at each stage of the analysis leads to a confusing landscape in this field, and thus, the present review aims at critically presenting the available options. For each step, the most frequently used alternatives are described, together with their strengths and weaknesses based on theoretical and experimental justifications according to the literature. These techniques are exemplified by many applications in the literature on aromas, fragrances and essential oils, with the initial focus on wine odorants, followed by a short overview on the molecular diversity of key odorants, which illustrates most of the facets and complexities of odor studies, including the issues raised by odorant interactions such as synergies.

Occurrence of 2-Acetyl-1-pyrroline and Its Nonvolatile Precursors in Celtuce (Lactuca sativa L. var. augustana)

Lactuca sativa L. var. augustana has a basmati rice-like odor with a green note in the background. This typical odor is due to the release of 2-acetyl-1-pyrroline (2-AP) after heating, which is confirmed by volatile analysis. Recent metabolomic and genomic studies of different rice varieties highlighted that the presence of 2-AP was linked to the accumulation of γ-aminobutyraldehyde; genome-wide association studies also indicated that acyltransferases were involved. These results prompted us to analyze nonvolatile compound precursors in L. sativa L. var. augustana (celtuce) to search for compound derivatives with a 4,5-dioxohexan alkyl amine-like structure. Hypothetical synthetic compounds were prepared from a reductive amination between 4,5-dioxohexanal and glycine, alanine, aspartic acid, and glutamic acid to give 2-(2-acetylpyrrolidin-1-yl) alkanoic acid. We proved that 2-(2-acetylpyrrolidin-1-yl) propionic acid is present in L. sativa, which, when thermally treated, released 2-AP. Other 2-AP precursors occurring in this plant are discussed.