GC–FID determination of tetramethylpyrazine and acetoin in vinegars and quantifying the dependence of tetramethylpyrazine on acetoin and ammonium

Extraction of phenolic acids and tetramethylpyrazine in Shanxi aged vinegar base on vortex-assisted liquid-liquid microextraction-hydrophobic deep eutectic solvent: COSMO-RS calculations and ANN-GA optimization

In this study, vortex-assisted liquid-liquid microextraction (VA-LLME) based on hydrophobic deep eutectic solvents (HDES) was used to efficiently and sustainably extract five phenolic acids and tetramethylpyrazine (TMP) from Shanxi aged vinegar (SAV). The VA-LLME technique was employed to investigate the extraction mechanism of HDES with the best extraction performance for the target compounds using a conductor-like screening model for real solvents (COSMO-RS). An artificial neural network combined with a genetic algorithm (ANN-GA) was developed to optimize the extraction conditions based on single-factor and response surface methodology, while also analyzing the interactive effects on the phenolic acids and TMP in the extracted solution during the extraction phase. The optimized conditions were determined, and the greenness of the procedure was evaluated using an analytical greenness metric, indicating that this technique can serve as a green alternative for the determination of phenolic acids and TMP in SAV.

A Ratiometric Fluorescent Probe Dye-Functionalized MOFs Integrated with Logic Gate Operation for Efficient Detection of Acetaldehyde

Volatile organic compounds (VOCs) are a class of hazardous gases that are widely present in the atmosphere and cause great harm to human health. In this paper, a ratiometric fluorescent probe (Dye@Eu-MOFs) based on a dye-functionalized metal-organic framework was designed to detect VOCs, which showed high sensitivity and specificity for acetaldehyde solution and vapor. A linear correlation between the integrated fluorescence intensity (I510/I616) and the concentration of acetaldehyde was investigated, enabling a quantitative analysis of acetaldehyde in the ranges of 1 × 10-4~10-5 μL/mL, with a low detection limit of 8.12 × 10-4 mg/L. The selective recognition of acetaldehyde could be clearly distinguished by the naked eye under the excitation of UV light. The potential sensing mechanism was also discussed. Significantly, a molecular logic gate was constructed based on the whole system, and finally, a molecular logic network system for acetaldehyde detection connecting basic and integrated logic operations was realized. This strategy provided an effective guiding method for constructing a molecular-level logic gate for acetaldehyde detection on a simple platform.

Improved liquid-liquid extraction followed by HPLC-UV for accurate and eco-friendly determination of tetramethylpyrazine in vinegar products

Tetramethylpyrazine (TMP) is an important bioactive compound in vinegars, contributing to their health-enhancing attributes. It serves as a crucial benchmark for the assessment of vinegar quality. Unfortunately, inaccuracies have arisen due to incomplete extraction techniques and the use of an inappropriate standard substance. These challenges have significantly curtailed comprehensive exploration into the underlying TMP formation mechanisms, impeding advancements within prevailing benchmarks and methodologies governing vinegar products. To address these challenges, several critical parameters, encompassing pH, solvent type, centrifugal force, extraction times and reference materials were investigated and optimized. The TMP content was determined by adjusting the pH to 9 using a sodium hydroxide solution, followed by extraction with ethyl acetate and subsequent re-extraction of the ethyl acetate layer with 0.2 mol/L HCl. A high-performance liquid chromatography method with an ultraviolet detector (UV) was developed and validated. This method demonstrated superior sensitivity compared to existing methods, with a limit of detection (LOD) of 0.0237 μg/g, limit of quantification (LOQ) of 0.0829 μg/g, method limit of detection (MLOD) of 0.10 μg/g and method limit of quantitation (MLOQ) of 0.25 μg/g. The modified method exhibited excellent linearity for TMP in the range of 0.1-118.4 μg/mL, with a good correlation coefficient (R2 > 0.999). The recovery rate of TMP in vinegar products ranged from 82.4 to 96.2%. Consequently, the proposed method exhibits substantial promise for systematic inquiry into TMP formation mechanisms and for ensuring consistent quality control during the production of premium-grade vinegars.

Novel insight into the evolution of volatile compounds during dynamic freeze-drying of Ziziphus jujuba cv. Huizao based on GC-MS combined with multivariate data analysis

To understand the evolution of aroma in jujubes during dynamic freeze drying (FD), the relationship between aroma compounds, precursors, and related enzyme activities were analyzed. Fifty-three volatiles were identified during FD processing. After FD, the total aroma contents were increased from 11,004 to 14,603 μg/kg, ketones content was significantly decreased by 54.11 %, resulted in the loss of creamy note in freeze-dried jujube (FDJ). Through the network analysis, serine, glycine, proline, valine, cysteine, arginine, glutamic acid, lysine and leucine had the significant correlation with pyrazines, dominated the roasty note of FDJ. Linoleic acid, α-linolenic acid and oleic acid with lipoxygenase had important effects on the increase of esters (from 412 to 9,486 μg/kg), contributed fruity and sweet notes of FDJ. Besides, through the Mantel test, the influence degree of factors on the formation of FDJ aroma was ranked as temperature > enzyme activity > fatty acids > amino acids.

Production of Tetramethylpyrazine from Cane Molasses by Bacillus sp. TTMP20

2,3,5,6-Tetramethylpyrazine (TTMP) is an active ingredient of Ligusticum wallichii Franch. It can be used in medicine and food fields. In this study, Bacillus sp. TTMP20 was applied to produce TTMP using cane molasses as a carbon source. After pretreatment with phosphoric acid, 170 mL/L treated molasses, combined with 10 g/L yeast powder, 30 g/L tryptone and 30 g/L (NH4)2HPO4 were used for fermentation. After 36 h, TTMP output reached the highest value of 208.8 mg/L. The yield of TTMP using phosphoric acid-treated molasses as carbon source was 145.59% higher than control. Under the sulfuric acid treatment process of molasses (150 g), the maximum yield of TTMP was 895.13 mg/L, which was 183.18% higher than that of untreated molasses (316.1 mg/L). This study demonstrated that molasses is a high-quality and inexpensive carbon source for the manufacture of TTMP, laying the groundwork for the future industrial production of TTMP.

A Green Route for High-Yield Production of Tetramethylpyrazine From Non-Food Raw Materials

2,3,5,6-Tetramethylpyrazine (TMP) is an active pharmaceutical ingredient originally isolated from Ligusticum wallichii for curing cardiovascular and cerebrovascular diseases and is widely used as a popular flavoring additive in the food industry. Hence, there is a great interest in developing new strategies to produce this high-value compound in an ecological and economical way. Herein, a cost-competitive combinational approach was proposed to accomplish green and high-efficiency production of TMP. First, microbial cell factories were constructed to produce acetoin (3-hydroxy-2-butanone, AC), an endogenous precursor of TMP, by introducing a biosynthesis pathway coupled with an intracellular NAD+ regeneration system to the wild-type Escherichia coli. To further improve the production of (R)-AC, the metabolic pathways of by-products were impaired or blocked stepwise by gene manipulation, resulting in 40.84 g/L (R)-AC with a high optical purity of 99.42% in shake flasks. Thereafter, an optimal strain designated GXASR11 was used to convert the hydrolysates of inexpensive feedstocks into (R)-AC and achieved a titer of 86.04 g/L within 48 h in a 5-L fermenter under optimized fermentation conditions. To the best of our knowledge, this is the highest (R)-AC production with high optical purity (≥98%) produced from non-food raw materials using recombinant E. coli. The supernatant of fermentation broth was mixed with diammonium phosphate (DAP) to make a total volume of 20 ml and transferred to a high-pressure microreactor. Finally, 56.72 g/L TMP was obtained in 3 h via the condensation reaction with a high conversion rate (85.30%) under optimal reaction conditions. These results demonstrated a green and sustainable approach to efficiently produce high-valued TMP, which realized value addition of low-cost renewables.

LF-NMR as a tool for predicting the 3D printability of surimi-starch systems

In this study, surimi from golden pompanos was mixed with starch to form a surimi-starch system. The water properties, rheological properties, and three-dimensional (3D) printability of the surimi-starch were measured. Cluster analysis results showed that the 3D printability was closely related to the type and addition content of starch, and the water and rheological properties. The low-field nuclear magnetic resonance (LF-NMR) parameters were used to predict 3D printability using polynomial regression models. The correlation coefficients (R²) for 3D printing accuracy and stability were 0.88 and 0.93, and the root mean square error (RMSE) values were 0.20% and 4.59%, respectively. In the verification test, the R² for the two models were 0.85 and 0.89, and the RMSE values were 0.20% and 1.06%, respectively. The nonlinear surface regression fitting exhibited superior predictive performance. Therefore, LF-NMR is a good non-destructive tool for quickly and accurately predicting the 3D printability of the surimi-starch systems.

Characterization and Regulation of the Acetolactate Synthase Genes Involved in Acetoin Biosynthesis in Acetobacter pasteurianus

Acetoin is an important aroma-active chemical in cereal vinegars. Acetobacter pasteurianus was reported to make a significant contribution to acetoin generation in cereal vinegars. However, the related acetoin biosynthesis mechanism was largely unknown. Two annotated acetolactate synthase (ALS) genes of A. pasteurianus were investigated in this study to analyze their functions and regulatory mechanisms. Heterologous expression in Escherichia coli revealed that only AlsS1 exhibited ALS activity and had the optimal activity at 55 °C and pH 6.5. Two alsS-defective mutants of A. pasteurianus CICC 22518 were constructed, and their acetoin yields were both reduced, suggesting that two alsS genes participated in acetoin biosynthesis. A total 79.1% decrease in acetoin yield in the alsS1-defective mutant revealed that alsS1 took a major role. The regulator gene alsR disruptant was constructed to analyze the regulation effect. The decline of the acetoin yield and down-regulation of the alsD and alsS1 gene transcriptions were detected, but the alsS2 gene transcription was not affected. Acetoin was an important metabolite of lactate catabolism in A. pasteurianus. The coexistence of two alsS genes can help strains rapidly and securely assimilate lactate to deal with the lactate pressure in a vinegar brewing environment, which represented a new genetic mode of acetoin production in bacteria.

Vinegar from Anacardium othonianum Rizzini using submerged fermentation

BACKGROUND

Anacardium othonianum Rizzini is a native Cerrado fruit, recently described in the literature. Its use is restricted to its native region and there is a lack of studies regarding production of vinegar from the pulp. This work aims to investigate the production of A. othonianum Rizzini vinegar using submerged fermentation.

RESULTS

The density, alcohol content, proximal composition, pH, color coordinates, and chromatographic profile of the volatile compounds were analyzed in the slurry, fermented juice, and vinegar produced from the corpulent parts of A. othonianum Rizz. Sensory acceptance and willingness to pay were also assessed with vinegar at 4% and 6% of total acidity. The results indicated compliance with European legislation and the presence of volatile compounds such as carbon dioxide, acetic acid, ethanol, and acetaldehyde in the analyzed vinegars. Our results indicate the potential of vinegar production from A. othonianum, with 74% and 86% willingness to pay.

CONCLUSIONS

The process of transformation of the fruit pulp into new products can contribute to fruit valorization and consequent preservation of the plant in the Cerrado biome. To the best of our knowledge, this is the first report of volatile compounds and minerals in A. othonianum Rizz. slurry. Our observations can be used as a basis for future studies regarding the preparation of vinegars from this species and for investigating their application in cooking and guiding consumer perception. © 2020 Society of Chemical Industry.

Vinegar/Tetramethylpyrazine Induces Nutritional Preconditioning Protecting the Myocardium Mediated by VDAC1

Vinegar is good for health. Tetramethylpyrazine (TMP) is the main component of its flavor, quality, and function. We hypothesized that vinegar/TMP pretreatment could induce myocardial protection of "nutritional preconditioning (NPC)" by low-dose, long-term supplementation and alleviate the myocardial injury caused by anoxia/reoxygenation (A/R). To test this hypothesis, TMP content in vinegar was detected by HPLC; A/R injury model was prepared by an isolated mouse heart and rat cardiomyocyte to evaluate the myocardial protection and mechanism of vinegar/TMP pretreatment by many enzymatic or functional, or cellular and molecular biological indexes. Our results showed that vinegar contained TMP, and its content was in direct proportion to storage time. Vinegar/TMP pretreatment could improve hemodynamic parameters, decrease lactate dehydrogenase (LDH) and creatine phosphokinase activities, and reduce infarct size and apoptosis in the isolated hearts of mice with A/R injury. Similarly, vinegar/TMP pretreatment could increase cell viability, decrease LDH activity, and decrease apoptosis against A/R injury of cardiomyocytes. Vinegar/TMP pretreatment could also maintain the mitochondrial function of A/R-injured cardiomyocytes, including improving oxygen consumption rate and extracellular acidification rate, reducing reactive oxygen species generation, mitochondrial membrane potential loss, mitochondrial permeability transition pore openness, and cytochrome c releasing. However, the protective effects of vinegar/TMP pretreatment were accompanied by the downregulation of VDAC1 expression in the myocardium and reversed by pAD/VDAC1, an adenovirus that upregulates VDAC1 expression. In conclusion, this study is the first to demonstrate that vinegar/TMP pretreatment could induce myocardial protection of NPC due to downregulating VDAC1 expression, inhibiting oxidative stress, and preventing mitochondrial dysfunction; that is, VDAC1 is their target, and the mitochondria are their target organelles. TMP is one of the most important myocardial protective substances in vinegar.

Increasing Yield of 2,3,5,6-Tetramethylpyrazine in Baijiu Through Saccharomyces cerevisiae Metabolic Engineering

Baijiu is a traditional distilled beverage in China with a rich variety of aroma substances. 2,3,5,6-tetramethylpyrazine (TTMP) is an important component in Baijiu and has the function of promoting cardiovascular and cerebrovascular health. During the brewing of Baijiu, the microorganisms in jiuqu produce acetoin and then synthesize TTMP, but the yield of TTMP is very low. In this work, 2,3-butanediol dehydrogenase (BDH) coding gene BDH1 and another BDH2 gene were deleted or overexpressed to evaluate the effect on the content of acetoin and TTMP in Saccharomyces cerevisiae. The results showed that the acetoin synthesis of strain α5-D1B2 was significantly enhanced by disrupting BDH1 and overexpressing BDH2, leading to a 2.6-fold increase of TTMP production up to 10.55 mg/L. To further improve the production level of TTMP, the α-acetolactate synthase (ALS) of the pyruvate decomposition pathway was overexpressed to enhance the synthesis of diacetyl. However, replacing the promoter of the ILV2 gene with a strong promoter (PGK1p) to increase the expression level of the ILV2 gene did not result in further increased diacetyl, acetoin and TTMP production. Based on these evidences, we constructed the diploid strains AY-SB1 (ΔBDH1:loxP/ΔBDH1:loxP) and AY-SD1B2 (ΔBDH1:loxP-PGK1p-BDH2-PGK1t/ΔBDH1:loxP-PGK1p-BDH2-PGK1t) to ensure the fermentation performance of the strain is more stable in Baijiu brewing. The concentration of TTMP in AY-SB1 and AY-SD1B2 was 7.58 and 9.47 mg/L, respectively, which represented a 2.3- and 2.87-fold increase compared to the parental strain. This work provides an example for increasing TTMP production in S. cerevisiae by genetic engineering, and highlight a novel method to improve the quality and beneficial health attributes of Baijiu.

Metabolic network of ammonium in cereal vinegar solid-state fermentation and its response to acid stress

Shanxi aged vinegar (SAV), a Chinese traditional vinegar, is produced by various microorganisms. Ammonium is an important nitrogen source for microorganisms and a key intermediate for the utilization of non-ammonium nitrogen sources. In this work, an ammonium metabolic network during SAV fermentation was constructed through the meta-transcriptomic analysis of in situ samples, and the potential mechanism of acid affecting ammonium metabolism was revealed. The results showed that ammonium was enriched as the acidity increased. Meta-transcriptomic analysis showed that the conversion of glutamine to ammonia is the key pathway of ammonium metabolism in vinegar and that Lactobacillus and Acetobacter are the dominant genera. The construction and analysis of the metabolic network showed that amino acid metabolism, nucleic acid metabolism, pentose phosphate pathway and energy metabolism were enhanced to resist acid damage to the intracellular environment and cell structures. The enhancement of nitrogen assimilation provides nitrogen for metabolic pathways that resist acid cytotoxicity. In addition, the concentration gradient allows ammonium to diffuse outside the cell, which causes ammonium to accumulate during fermentation.

Simultaneous Analysis of the Stable Carbon Isotope Ratios of Acetoin and Acetic Acid by GC-C-IRMS for Adulteration Detection in Brewed Rice Vinegar Products

In this study, we developed a method to simultaneously measure the stable carbon isotope ratio for acetic acid (δ 13Cacetic acid) and acetoin (δ13Cacetoin) in rice vinegar by gas chromatography-combustion-isotope ratio mass spectrometry. The method showed good precision and accuracy. With this method, data from 16 brewed rice vinegars and 10 acetic acid samples were used to evaluate the feasibility of adulteration detection. On the basis that all δ13Cacetoin values of brewed rice vinegars are nearly constant, a characteristic pattern of the stable carbon isotope in rice vinegar was built with the 95% confidence intervals for δ13Cacetic acid (-26.97 to -25.38‰), δ13Cacetoin (-28.14 to -27.09‰), and Δδ13C (0.61 to 2.27‰). An adulteration detection curve of Δδ13C was proposed based on the results of vinegar and acetic acid samples and confirmed by vinegar spiked with different amounts of acetic acid. This method could be useful in estimating the blending ratio of adulterated rice vinegar products. Products containing more than 10% of synthetic acetic acid could be possibly identified.

Tetramethylpyrazine from adlay (Coix lacryma-jobi) biotransformation by Bacillus subtilis and its quality characteristics

Adlay, as a traditional Chinese medicine, has been used in nourishing foods, which are rich in a variety of nutrients (special biological compounds). The study was designed to optimize the fermentation parameters of dehulled, polished and broken adlay fermented by Bacillus subtilis BJ3-2 with regard to tetramethylpyrazine (TMP) yield and fibrinolytic enzyme activity. Then the proximate and bioactive components of B. subtilis-fermented adlay were evaluated. Box-Behnken design results showed that the TMP yield was 6.93 mg/g DW (dried weight) of B. subtilis-fermented polished adlay, which was about 136 times higher than that of B. subtilis-fermented soybean (BSB). The fibrinolytic enzyme activity was 2236.17 U/g in B. subtilis-fermented dehulled adlay, and slightly less than in BSB. B. subtilis-fermented adlay contained higher fat, free amino acids and fatty acids contents but lower protein and starch contents than raw adlay. Except for coixol and coixan, the levels of γ-aminobutyric acid, triterpenes, phenolics, flavonoids and coixenolide in B. subtilis-fermented adlay increased by 14.05, 2.02, 2.31 and 1.36 times, respectively. The contents of phenolic acids including caffeic, gallic, catechinic and chlonogenic acids in the free phenolic extracts significantly increased (p < 0.05). The results demonstrated that the biotransformation of high-yield TMP, fibrinolytic enzyme and other bioactive components of B. subtilis-fermented adlay products was realized. B. subtilis-fermented adlay could be a promising value-added food, and that is more suitable for human consumption.

Modulating microbiota metabolism via bioaugmentation with Lactobacillus casei and Acetobacter pasteurianus to enhance acetoin accumulation during cereal vinegar fermentation

Acetoin, giving a creamy yogurt aroma and buttery taste, exists in cereal vinegar as an important flavor substance and is mainly produced by the metabolism of Lactobacillus and Acetobacter during multispecies solid-state acetic acid fermentation. However, the impacts of Lactobacillus-Acetobacter interactions on acetoin accumulation and the microbial metabolism during acetic acid fermentation are not completely clear. Here, six strains isolated from vinegar fermentation culture and associated with acetoin metabolism, namely, Lactobacillus reuteri L-0, L. buchneri F2-6, L. brevis 4-20, L. fermentum M10-7, L. casei M1-6 and Acetobacter pasteurianus G3-2, were selected for microbial growth and metabolism analysis in monoculture and coculture fermentations. Lactobacillus sp. and A. pasteurianus G3-2 respectively utilized glucose and ethanol preferentially. In monocultures, L. casei M1-6 (183.7 mg/L) and A. pasteurianus G3-2 (121.0 mg/L) showed better acetoin-producing capacity than the others. In the bicultures with Lactobacillus sp. and A. pasteurianus G3-2, biomass analysis in the stationary phase demonstrated that significant growth depressions of Lactobacillus sp. occurred compared with monocultures, possibly due to intolerance to acetic acid produced by A. pasteurianus G3-2. Synergistic effect between Lactobacillus sp. and A. pasteurianus G3-2 on enhanced acetoin accumulation was identified, however, cocultures of two Lactobacillus strains could not apparently facilitate acetoin accumulation. Coculture of L. casei M1-6 and A. pasteurianus G3-2 showed the best performance in acetoin production amongst all mono-, bi- and triculture combinations, and the yield of acetoin increased from 1827.7 to 7529.8 mg/L following optimization of culture conditions. Moreover, the interactions of L. casei M1-6 and A. pasteurianus G3-2 regulated the global metabolism of vinegar microbiota during fermentation through performing in situ bioaugmentation, which could accelerate the production of acetic acid, lactic acid, acetoin, ethyl acetate, ethyl lactate, ligustrazine and other important flavoring substances. This work provides a promising strategy for the production of acetoin-rich vinegar through Lactobacillus sp.-A. pasteurianus joint bioaugmentation.

Translation of a One-Dimensional to a Comprehensive Two-Dimensional Gas Chromatography Method with Dual-Channel Detection for Volatile Organic Compound Measurement in Forensic Applications

After its introduction in the early 1990s, comprehensive two-dimensional gas chromatography (GC×GC) has evolved from a separation science research tool to the central component of many industries. Despite the maturity of the technique, some fields remain reluctant to its use in routine applications. In the case of forensic science, some constraints are the strict requirements enforced in forensic laboratories and the time and effort that must be invested for intralaboratory method validation. Concerns may also arise about whether information could be lost when transitioning to a new technique. This study reports on a method translation from conventional one-dimensional (1D) GC to GC×GC, ensuring the integrity of data as conversion is made. The GC was retrofitted with a reverse fill/flush (RFF) flow modulator and equipped with dual-channel detection using a quadrupole mass spectrometer (qMS) and a flame ionization detector (FID). The parallel use of two detectors, where qMS was applied for qualitative identification and FID for quantification, allowed higher flows and slightly wider peaks to be exploited for the analysis of a volatile organic compound (VOC) reference mixture relevant to forensic VOC profiling. Peak quality assessment and calibration curves using GC-qMS and GC×GC-qMS/FID document the transfer and adaptation of the original method without a loss in data quality. Furthermore, the preprocessing and the data analysis processing steps, including calibration and peak quality assessment for each of the three data sets, are explained in detail. This information provides benchmark data for routine laboratories that want to implement a GC×GC approach into routine workflows.

Tetramethylpyrazine production from edible materials by the probiotic Bacillus coagulans

2,3,5,6-Tetramethylpyrazine (TMP) has health care functions, especially for cardiovascular and cerebrovascular health. In this study, we found that Bacillus coagulans, a well-known probiotic, has the capability to produce acetoin, a precursor of TMP. The culture conditions and medium for the production of TMP by B. coagulans CICC 20138 were optimized. Then, a novel three-step process was successfully performed for the production of TMP from edible materials by B. coagulans. First, in the acetoin enrichment process, 12.61 ± 0.34 g/L acetoin was generated at 36 h. Second, in the spore enrichment process, various factors were optimized to make the bacteria produce more spores to improve the resistance to subsequent high-temperature reactions. Third, in the TMP enrichment process, the final concentration of TMP and B. coagulans spores contained in the product reached 2.54 ± 0.26 g/L and 8.81 × 10⁸ CFU/mL at 46 h, respectively. This is the first report of using a probiotic bacterium to produce TMP. Using edible materials and the probiotic strain, this work provides a novel method for the production of a TMP food additive rich in B. coagulans spores.

Characterization of the key aroma compounds in aged Zhenjiang aromatic vinegar by gas chromatography-olfactometry-mass spectrometry, quantitative measurements, aroma recombination and omission experiments

Zhenjiang aromatic vinegar (ZAV) is one of the most famous traditional Chinese cereal vinegars. The key aroma compounds in aged ZAV were characterized by gas chromatography-olfactometry-mass spectrometry (GC-O-MS), odor activity values (OAVs), aroma recombination and omission experiments. Sensory analysis revealed that higher odor intensity of caramel-like, buttery and overall complexity were observed for aged ZAV compared with fresh ZAV. A total of 68 compounds were quantitated, including 27 odorants with OAVs >1.0 in the aged ZAV. Sotolon was detected for the first time in Chinese cereal vinegars. Furthermore, the levels of 2,3-butanedione, 2-methylpropanal, sotolon, dimethyl trisulfide, 3-hydroxy-2-butanone, 2,4,5-trimethyloxazole and tetramethylpyrazine changed significantly during the aging process. Aroma recombination revealed that the aroma profile of the aged vinegar could be closely simulated. Omission experiments demonstrated the important contributions of seven aroma compounds to the aged ZAV aroma, including 2,3-butanedione, acetic acid, 2-methylpropanal, sotolon, 2,4,5-trimethyloxazole, 3-methylbutanoic acid and tetramethylpyrazine. This study indicates that the aging process substantially contribute to the overall aroma of ZAV.

Effect of static-state fermentation on volatile composition in rapeseed meal

BACKGROUND

Fermented rapeseed meal has been used as an alternative protein source for animal feed, but the volatile compounds and how their contents change during fermentation have not been reported. To clarify the effect of static-state fermentation on its aroma, the volatile compounds of rapeseed meal during different stages of fermentation were analyzed using an electronic nose system and headspace solid-phase microextraction-gas chromatography-mass spectrometry.

RESULTS

The results suggested that the volatile compounds in the raw rapeseed meal, mostly hydrocarbons and some aldehydes, were lost. The levels of the volatile compounds resulting from microbial metabolism, especially pyrazines, greatly increased during fermentation. Nonanal was the dominant volatile measured in the headspace of raw rapeseed meal. However, the volatile compounds found at high concentrations in rapeseed meal after 5 days of fermentation were tetramethylpyrazine, followed by butanoic acid, benzenepropanenitrile, 2-methylbutanoic acid, trimethylamine, 2,3,5-trimethyl-6-ethylpyrazine, and 2,3,5-trimethylpyrazine.

CONCLUSION

The fermentation process could significantly change the composition and content of volatile compounds in rapeseed meal. The results may provide reference data for studies on the choice of fermentation period and formation mechanism of flavor substances in fermented rapeseed meal. © 2020 Society of Chemical Industry.

Fermentative production of chiral acetoin by wild-type Bacillus strains

In recent years, there have been many studies on producing acetoin by microbial fermentation, while only a few studies have focused on chiral acetoin biosynthesis. The weight assignment method was first applied to balance the chiral purity (expressed as the enantiomeric excess value) and the titer of acetoin. Bacillus sp. H-18W, a thermophile, was selected from seven Bacillus strains for chiral acetoin production. To lower the cost of the fermentation medium, soybean meal was used as a feedstock. Four kinds of frequently used commercial proteinases with different active sites were tested for the hydrolyzation of the soybean meal, and the combination of the acidic proteinase and the neutral proteinase showed the best results. In a fermentation medium containing 100 g L-1 glucose and 200 g L-1 hydrolysate, Bacillus sp. H-18W produced 21.84 g L-1 acetoin with an ee value of 96.25% at 60 h. This is the first report of using a thermophilic strain to produce chiral acetoin by microbial fermentation. Thermophilic fermentation can reduce the risk of bacterial contamination and can save cooling water. Using soybean meal hydrolysate and glucose as feedstocks, this work provides an economical and alternative method for the production of chiral pure acetoin.

Dispersive liquid-liquid microextraction for rapid and inexpensive determination of tetramethylpyrazine in vinegar

The concentration of tetramethylpyrazine (TMP) in vinegar is an active indicator of vinegar quality. Dispersive liquid-liquid microextraction (DLLME) was first applied to vinegar as a clean-up pre-treatment for the rapid (5 min) determination of TMP by high-pressure liquid chromatography with ultraviolet detection (HPLC-UV), and may serve as an alternative to solid-phase extraction (SPE) or solid-phase microextraction (SPME). High sensitivity of HPLC for TMP determination was obtained using the DLLME pretreatment, with a limit of detection (LOD) of 0.001 mg L^-1 and limit of quantification (LOQ) of 0.005 mg L^-1. The developed method exhibited excellent linearity in the concentration range of 0.050-80.000 mg L^-1, with a correlation coefficient R² > 0.999. Furthermore, the percentage recovery of TMP in vinegar using the developed method was within the range 97.97-105.24%. Therefore, DLLME coupled with HPLC-UV is a sensitive and promising method for vinegar clean-up and TMP assay.

5-Hydroxy-γ-decalactone production by Bacillus sp. 1s-1 and its complete genome sequence

Lactones are useful flavor compounds and some 5-hydroxy-γ-butyrolactones also have important biological activities. In this study, a newly isolated Bacillus strain 1s-1 was identified to be capable of producing 5-hydroxy-γ-decalactone (HDL) from peanut oil by gas chromatography-mass spectrometry and authentic standards. The complete genome of this strain was sequenced and de novo assembled to a single circular chromosome of 4,166,290 bp with a guanine-cytosine content of 46.3%. The biosynthesis pathway of HDL in strain 1s-1 was postulated and this study provides helpful information for further utilizing Bacillus sp. 1s-1 as a source of valuable hydroxy lactones.