Correlation of volatile and nonvolatile components with the total antioxidant capacity of tartary buckwheat vinegar: Influence of the thermal processing

Analysis of characteristic aromas of buckwheat with different germplasm using gas chromatography-mass spectrometry combined with chemometrics and multivariate statistical analysis

In this study, the volatile components in 40 samples of Tartary buckwheat and common buckwheat from 6 major producing areas in China were analyzed. A total of 77 volatile substances were identified, among which aldehydes and hydrocarbons were the main volatile components. Odor activity value analysis revealed 26 aromatic compounds, with aldehydes making a significant contribution to the aroma of buckwheat. Seven key compounds that could be used to distinguish Tartary buckwheat from common buckwheat were identified. The orthogonal partial least squares-discriminant analysis was effectively used to classify Tartary buckwheat and common buckwheat from different producing areas. This study provides valuable information for evaluating buckwheat quality, breeding high-quality varieties, and enhancing rational resource development.

Investigation of bioactive compounds and their correlation with the antioxidant capacity in different functional vinegars

There are complex and diverse substances in traditional vinegars, some of which have been identified as biologically active factors, but the variety of functional compounds is currently restricted. In this study, it was aimed to determine the bioactive compounds in 10 typical functional vinegars. The findings shown that total flavonoids (0.21-7.19 mg rutin equivalent/mL), total phenolics (0.36-3.20 mg gallic acid equivalent/mL), and antioxidant activities (DPPH: 3.17-47.63 mmol trolox equivalent/L, ABTS: 6.85-178.29 mmol trolox equivalent/L) varied among different functional vinegars. In addition, the concentrations of the polysaccharides (1.17-44.87 mg glucose equivalent/mL) and total saponins (0.67-12.46 mg oleanic acid equivalent/mL) were determined, which might play key role for the function of tested vinegars. A total of 8 organic acids, 7 polyphenol compounds and 124 volatile compounds were measured and tentatively identified. The protocatechuic acid (4.81-485.72 mg/L), chlorogenic acid (2.69-7.52 mg/L), and epicatechin (1.18-97.42 mg/L) were important polyphenol compounds in the functional vinegars. Redundancy analysis indicated that tartaric acid, oxalic acid and chlorogenic acid were significantly positively correlated with antioxidant capacity. Various physiologically active ingredients including cyclo (Pro-Leu), cyclo (Phe-Pro), cyclo (Phe-Val), cyclo (Pro-Val), 1-monopalmitin and 1-eicosanol were firstly detected in functional vinegars. Principle component analysis revealed that volatiles profile of bergamot Monascus aromatic vinegar and Hengshun honey vinegar exhibited distinctive differences from other eight vinegar samples. Moreover, the partial least squares regression analysis demonstrated that 11 volatile compounds were positively correlated with the antioxidant activity of vinegars, which suggested these compounds might be important functional substances in tested vinegars. This study explored several new functionally active compounds in different functional vinegars, which could widen the knowledge of bioactive factor in vinegars and provide new ideas for further development of functional vinegar beverages.

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.

Melanoidins present in traditional fermented foods and beverages

Traditional fermented foods and beverages (TFFB) are an important dietary component consumed in large quantities worldwide. Currently, much attention has been focused on the health benefits of TFFB. Melanoidins, a class of bioactive substance produced in the final stage of the Maillard reaction, not only have a significant impact on sensory properties of TFFB but also contribute to the health effects. Melanoidins formed in the fermentation system with a long reaction time at low temperature could be different from those obtained from high-temperature, short-duration roasted systems due to the multiple formative stages and involvement of microorganisms and enzymes. In this paper, the current state of knowledge regarding the formation, distribution, extraction and purification, physicochemical properties, structure characteristics, and biological activities of TFFB melanoidins are comprehensively reviewed, with predominant focus on TFFB that are typically brown like douchi, miso, cheonggukjang, soy sauce, huangjiu (Chinese rice wine), beer, vinegar, and sweet wine. The current challenges and prospective recommendations for the research of melanoidins in fermented systems are also presented. In future, people should pay more attention to the basic research on TFFB melanoidins, especially purification methods and formation mechanisms, further substantiation of health properties of TFFB melanoidins in vivo, and development of specific melanoidins to fulfill technological, productive, or health needs of consumers.

Vinegar Production from Corinthian Currants Finishing Side-Stream: Development and Comparison of Methods Based on Immobilized Acetic Acid Bacteria

Fruit wastes and side-streams can be used for vinegar production to create added value for the agri-food sector and enhance farmer incomes and local economies. In this study, methods for vinegar production by wild and selected acetic acid bacteria (the quick starter Acetobacter aceti and the acid-resistant Komagataeibacter europaeus), free (FC) and immobilized (IC) on a natural cellulosic carrier, are proposed using sweet wine made from the industrial finishing side-stream (FSS) of Corinthian currants as raw material. The results showed all cultures can produce vinegar with 46.65 ± 5.43 g/L acidity, from sweet FSS wine containing 5.08 ± 1.19% alcohol. The effect of immobilization was more obvious in the case of the selected culture, presenting better acetification efficiency, both fresh and after cold storage for 2 months. The vinegars had an antioxidant capacity of 263.5 ± 8.4 and 277.1 ± 6.7 mg/L (as ascorbic acid) and phenolic content 333.1 ± 12.0 and 222.2 ± 2.9 mg/L (as gallic acid) (for FC and IC, respectively). They also had a rich volatilome (140 compounds identified by SPME GC-MS), with higher percentages of esters identified in vinegars made by IC. The results are encouraging for vinegar production with IC of a mixed A. aceti and K. europaeus culture.

Phenolic and Volatile Compounds in the Production of Sugarcane Vinegar

This study aimed to explore the dynamic variations in the phenolic and volatile organic compounds of sugarcane vinegar subjected to different production processes. The determination of phenolic and volatile organic compounds was performed by UPLC-MS and solid phase micro extraction (SPME) coupled with gas chromatography combined with mass spectrometry (GC-MS). The complete fermentation process of sugarcane lasted nine days, and production of vinegar of up to 3.04% (w/v), total acids, and 4.1° alcoholicity was accomplished. Various phenolic compounds of sugarcane juice (non-sterilized) and those of alcoholic and acetic acid fermentation were obtained after nine days of fermentation. These were benzoic acid (2.024, 1.002, and 1.027 mg L-1), ferulic acid (0.060, 0.205, and 1.124 mg L-1), quinic acid (0.019, 0.074, and 0.031 mg L-1), chlorogenic acid (0.349, 1.635, and 1.217 mg L-1), apigenin (0.002, 0.099, and 0.004 mg L-1), kaempferol (0.003, 0.336, and 0.003 mg L-1), caffeic acid (-, 0.005, and 0.005 mg L-1), luteolin (0.003, 0.323, and 0.005 mg L-1), and p-coumaric acid (0.018, 0.015, and 0.027 mg L-1). Forty-five volatile organic compounds were also identified. The sugarcane juice can be commercialized as an alternative to wine as it presents characteristics of an alcoholic fermented beverage.

Present status and future perspectives of breeding for buckwheat quality

Buckwheat is an important crop globally. It has been processed into cereal grain, noodles, confectionery, bread, and fermented foods for many years. Buckwheat production and processing has supported local economies and is deeply related to the culture of some regions. Buckwheat has many unique traits as a food, with a good flavor and color. In addition, buckwheat is also a healthy food because it contains bioactive compounds that have anti-oxidative, anti-hypertensive, and anti-obesity properties. Therefore, breeding of buckwheat for quality is an important issue to be addressed. Compared to other crops, there is still a lack of basic information on quality, including bioactive compounds generation and enhancement. However, some mechanisms for modifying and improving the quality of buckwheat varieties have recently been identified. Further, some varieties with improved quality have recently been developed. In this review, we summarize the issues around buckwheat quality and review the present status and future potential of buckwheat breeding for quality.

Changes of Physicochemical, Bioactive Compounds and Antioxidant Capacity during the Brewing Process of Zhenjiang Aromatic Vinegar

Zhenjiang aromatic vinegar (ZAV) is a kind of traditional fermented food worldwide. In this study, the changes of physicochemical properties, total phenolic content (TPC), total flavonoid content (TFC), and total antioxidant activity (TAA) were evaluated during the brewing process of ZAV. In addition, the correlation between phenolic compound contents and antioxidant activities was investigated during the aging process (AP) of ZAV. The results showed that total acids, non-volatile acids, and amino nitrogen increased gradually during the brewing process. Reducing sugar decreased sharply at the early fermentation stage and then increased during the AP. Meanwhile, TPC, TFC, and TAA kept a very low level at the stage of alcohol fermentation (AF), and increased to the highest level at the sixth year of the AP. TAA has a high positive correlation with TPC and TFC during the brewing process of ZAV. In addition, the contents of p-hydroxybenzoic acid, vanillic acid, and catechin were higher than other phenolic compounds and reached the highest level at the sixth year of the AP, and were the main composition of phenolic compounds during the AP. Moreover, gallic acid, ferulic acid, and sinapic acid had the higher contribution at the early stage of the AP, and then declined to a lower level. Catechin, vanillic acid, and syringic acid had a higher contribution during the AP. These findings would be helpful in controlling the quality of vinegar and improving its functional properties.

Chemical Composition and Antioxidant Characteristic of Traditional and Industrial Zhenjiang Aromatic Vinegars during the Aging Process

Zhenjiang aromatic vinegar (ZAV) is one of the well-known fermented condiments in China, which is produced by solid-state fermentation. It can be classified into traditional Zhenjiang aromatic vinegar (TZAV) and industrial Zhenjiang aromatic vinegar (IZAV) because of different production methods. The purpose of the study was to evaluate the variations and differences on chemical compositions and antioxidant activities of TZAV and IZAV during the aging process. The proximate composition, organic acids content, total phenolic content (TPC), total flavonoid content (TFC), total antioxidant activity (TAA) and phenolic compounds composition of TZAV and IZAV were detected during the aging process. Organic acids contents, TPC, TFC, TAA and phenolic compounds contents in ZAV were increased during the aging process. Acetic acid, lactic acid and pyroglutamic acid in ZAV were major organic acids. With the extension of aging time, TZAV and IZAV had similar proximate compositions and organic acids content. The values of TPC, TFC and TAA were higher in TZAV than in IZAV when aging is more than 3 years. Rutin and p-coumaric acid were detected in TZAV but not in IZAV. In principal component analysis (PCA), TZAV and IZAV can be divided into two groups according to their phenolic compounds composition. These findings provide references for evaluating TZAV and IZAV on the basis of their characterizations.

Comparative Analysis of the Antioxidant Capacities and Phenolic Compounds of Oat and Buckwheat Vinegars During Production Processes

This study aimed to explore the dynamic changes in the antioxidant activities and phenolic acid profiles of oat and buckwheat vinegars during different production stages. The results showed that both oat and buckwheat vinegar products comparably attenuated D-galactose-induced oxidative damage in mice serum and liver, indicating no obvious dose dependence within the tested concentrations. However, oat vinegar product revealed more favorable in vitro antioxidant activities than those in buckwheat vinegar product as evaluated by 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical scavenging abilities. Moreover, the alcoholic fermentation, acetic acid fermentation and fumigating induced successive increase in DPPH radical scavenging abilities and phenolic acid contents of the fermentation substrates of oat and buckwheat vinegars. Importantly, the different fermentation processes of oat and buckwheat vinegars were accompanied by the dynamic migration and transformation of specific phenolic acids across bound, esterified and free fractions. Thus, the antioxidant activities of oat and buckwheat vinegars could be improved through targeted modulation of the generation of specific phenolic acid fractions during production processes.

PRACTICAL APPLICATION

We had evaluated the in vitro and in vivo antioxidant activities and phenolic acid contents of oat and buckwheat vinegars, and further explored the dynamic changes of bound, esterified and free phenolic acid fractions during successive fermentation processes of oat and buckwheat vinegars. This study provided the theoretical guidance for obtaining minor grain vinegar with the optimal antioxidant activities through targeted modulation of fermentation processes.

Phenolics extracted from tartary (Fagopyrum tartaricum L. Gaerth) buckwheat bran exhibit antioxidant activity, and an antiproliferative effect on human breast cancer MDA-MB-231 cells through the p38/MAP kinase pathway

Phenolics extracted from tartary buckwheat (Fagopyrum tartaricum L. Gaerth) bran were analyzed quantitatively and qualitatively. The bioactivity of the phenolic extracts was evaluated, such as the antioxidant activity, and the inhibition capacity on the growth of cancer cells. The molecular mechanism for the inhibitive effect on cancer cells was explored. Results indicated that tartary buckwheat bran phenolics mainly exist in a free form, and free phenolics were twice as abundant as bound phenolics. Free caffeic acid (119.75 μg per 100 mg DW) and bound rutin (51.66 μg per 100 mg DW) represented the main free and bound phenolic compounds, respectively. The free phenolic extract contributed to the major (>90%) antioxidant activities including the oxygen radical antioxidant capacity (ORAC) and cellular antioxidant activity (CAA). The free phenolic extract exhibited anticancer activity for human breast cancer MDA-MB-231 cells in a dose-dependent manner. This significant inhibition effect was achieved through the p38/MAP kinase pathway by inducing cell apoptosis (up-regulating p-p38 and p-ASK1 expressions and down-regulating TRAF2 and p-p53 expressions), and negatively regulating the progression of the cell cycle from the G1 to S phase (increased expression of p21 and suppressed expressions of PCNA, cyclin D1 and CDK4). All these results indicated that tartary buckwheat bran could be a rich resource of natural antioxidants and inhibitors for the growth of MDA-MB-231 cells.

Determination of rheological property and its effect on key aroma release of Shanxi aged vinegar

The rheological property of Shanxi aged vinegar (SAV) was determined by rheometer, and its effects on release in eight key aroma components of SAV was investigated by SPME-GC-MS. In order to simulate the change of rheological property of SAV, a modified SAV system was developed from a finished SAV using carboxymethylcellulose, pectin, glucose, fructose, sodium chloride and tannic acid at indicate levels. The consistency coefficients (K) of SAV ranged from 1.09e-5 to 0.0137, which was correlated to glucose, polyphenol, acids and oBx. SAV changed from shear-thickening to Newtonian fluid during long-time ageing. In the modified SAV system, the K values increased significantly, and two modified vinegar became quasi-Newtonian fluids too. Furthermore, release of the eight key aroma compounds decreased significantly and decreased was pronounced, for acetic acid, furfural and tetramethylpyrazine. The results demonstrated rheological property correlated to the concentrate of sugar, salt, polyphenol, acids and macromolecule, which significantly affected the release of major aroma compounds.

Chemical composition and health effects of Tartary buckwheat

Tartary buckwheat (Fagopyrum tataricum) contains a range of nutrients including bioactive carbohydrates and proteins, polyphenols, phytosterols, vitamins, carotenoids, and minerals. The unique composition of Tartary buckwheat contributes to their various health benefits such as anti-oxidative, anti-cancer, anti-hypertension, anti-diabetic, cholesterol-lowering, and cognition-improving. Compared with the more widely cultivated and utilised common buckwheat (F. esculentum), Tartary buckwheat tends to contain higher amounts of certain bioactive components such as rutin, therefore, showing higher efficiency in preventing/treating various disorders. This review summarises the current knowledge of the chemical composition of Tartary buckwheat, and their bio-functions as studied by both in vitro and in vivo models. Tartary buckwheat can be further developed as a sustainable crop for functional food production to improve human health.

Development of a SPME-GC-MS method for the determination of volatile compounds in Shanxi aged vinegar and its analytical characterization by aroma wheel

A solid-phase microextraction followed by gas chromatography-mass spectrometry method was developed to determine the volatile compounds in Shanxi aged vinegar. The optimal extraction conditions were: 50 °C for 20 min with a PDMS/DVB fiber. This analytical method was validated and showed satisfactory repeatability (0.5 %<RSD<12 %), reproducibility (2.5 %<RSD<15.6 %), accuracy and linearity in analysis of volatile compounds. According to the calculation of odor activity value, 19 volatile compounds were identified as aroma-active compounds. Among them, propanoic acid, acetic acid, trimethyl-oxazole, butanoic acid, acetoin, 3-methylbutanoic acid and furfural were the most powerful odorants. The aroma wheel of Shanxi aged vinegar showed that the classes of sensory descriptors are first fatty and roasty, next woody and nutty and minor fruity and floral. Principal component analysis enabled us to investigate dissimilarity/similarity of Shanxi aged vinegar sample of different raw material and ageing time.

Assessment of flavonoids and volatile compounds in tea infusions of water lily flowers and their antioxidant activities

Water lily, a member of the Nymphaeaceae family, can be made into tea on the basis of outstanding fragrance characteristics and health care functions. In this study, 16 flavonoids were identified and quantified in tea infusions prepared from the petals of 33 water lily cultivars using HPLC-DAD and HPLC-ESI-MS/MS. The infusions were analyzed with HS-SPME coupled with GC-MS; 29 volatile compounds were detected, of which nine were found to be scent components. The cultivars were clustered into three clusters characterized according to scent components. The 'Conqueror' and 'Virginia' cultivars had the highest antioxidant activities. The concentrations of polyphenols and flavonoids showed significant positive correlations with antioxidant activity as measured by DPPH, ABTS(+), and FRAP assays. This study is valuable for a fuller understanding of this important tea and can also be used for the development of water lily.

Possible antioxidant mechanism of melanoidins extract from Shanxi aged vinegar in mitophagy-dependent and mitophagy-independent pathways

Melanoidins are widely reported to have antioxidant activity; however, their mechanism has not been frequently studied. In this study, we found that melanoidins from Shanxi aged vinegar induced mitopahgy, the specific autophagic elimination of mitochondria, as assessed by up-regulation of the autophagy markers LC3-II and Beclin1 as well as degradation of the autophagy substrate p62 and mitochondrial proteins. Melanoidins reduced reactive oxygen species (ROS) in normal human liver cells and mouse livers through a mitophagy-dependent pathway, by the observation that the reducing ROS effect of melanoidins was partially lost when mitophagy was inhibited by chloroquine. Impaired Akt signaling was found in cells treated with melanoidins, which might explain the activation of autophagy induced by melanoidins. These results suggest that in addition to direct free radical scavenging activity, melanoidins decreased ROS levels through mitophagy in which damaged mitochondria, the source of ROS, were degraded.