Improved sample preparation and rapid UHPLC analysis of SO2 binding carbonyls in wine by derivatisation to 2,4-dinitrophenylhydrazine

Simple and sensitive determination of sulfites in Chinese herbal teas by ultrahigh-performance liquid chromatography tandem mass spectrometry

Sulfites are used widely in food and beverage production to prevent browning or oxidation. However, the overingestion of sulfites is harmful to human health and may cause medical complications. Chinese herbal teas have been widely consumed for centuries. However, sulfite levels in Chinese herbal teas are rarely investigated and reported. Here, we present a simple, sensitive, and quantitative method to determine sulfites in Chinese herbal teas using ultrahigh-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) coupled with dispersive solid phase extraction. The method utilized a SeQuant ZIC-HILIC column for separation, and the optimal gradient eluents consisted of acetonitrile and aqueous solution with 0.1% acetic acid and 10 mM ammonium acetate. Porous chitosan/partially reduced graphene oxide/diatomite (CS/prGO/DM) composites were used as efficient dispersive solid phase extraction adsorbents for sample preparation. Several parameters were investigated during the extraction process, including sample-to-extraction solvent volume ratios, the extraction procedure and dosage of the adsorbent. Under the optimum conditions, the developed method gave a good determination coefficient (r² > 0.99), low detection limits (0.51-12.1 μg kg^-1) and high recoveries in the range of 83.8-102.7% at different spiked levels. The method has the great advantages of being time saving, good reproducibility and much lower detection limits when compared to titration methods. The method was further applied to analyze real herbal tea samples collected from the local market, demonstrating that our developed method is robust and useful for determining sulfites in practical application.

Changes in Red Wine Composition during Bottle Aging: Impacts of Grape Variety, Vineyard Location, Maturity, and Oxygen Availability during Aging

This work investigated the influence of grape variety, vineyard location, and grape harvest maturity, combined with different oxygen availability treatments, on red wine composition during bottle aging. Chemometric analysis of wine compositional data (i.e., wine color parameters, SO₂, metals, and volatile compounds) demonstrated that the wine samples could be differentiated according to the different viticultural or bottle-aging factors. Grape variety, vineyard location, and grape maturity showed greater influence on wine composition than bottle-aging conditions. For most measured wine compositional variables, the evolution patterns adopted from the viticultural factors were not altered by oxygen availability treatment. However, contrasting evolution patterns for some variables were observed according to specific viticultural factors, with examples including dimethyl sulfide, phenylacetaldehyde, maltol, and β-damascenone for vineyard locations, 2-methylbutanal, 1,4-cineole, and linalool for grape variety, and methanethiol, methional, and homofuraneol for grape maturity.

Establishing a method of HPLC involving precolumn derivatization by 2,2'-dithiobis (5-nitropyridine) to determine the sulfites in shrimps in comparison with ion chromatography

Although sulfites are widely used in shrimp processing, the contents of residual sulfite need to be strictly controlled due to their potential toxicity. In this paper, a novel method was developed for determination of the free and total sulfites in shrimps. Major procedures of the method includes separation of free and total sulfites with ultrasound-assisted extraction and pH adjustment for 20 min, then a precolumn derivatization was conducted by 2,2'-Dithiobis (5-nitropyridine) and verified by LC-MS, and finally HPLC coupled with an ultraviolet (UV) detector was carried out. Results indicated that the UV absorption wavelength shifted from 213 (sulfites) to 320 nm (new disulfide compounds), significantly reducing the interference of natural occurring compounds and solvents in the matrix. The standard curves exhibited a good linear range of 3.2-51.2 mg/L (R 2 = 0.9996). The limit of detection (LOD) and limit of quantification (LOQ) were 0.3 and 1.0 mg/L, respectively. The contents of free and total sulfite in frozen shrimps were 26.58 ± 0.48 and 31.44 ± 0.83 mg/kg calculated by SO2, respectively. These were similar (p > 0.05) to the data obtained by the method of ion chromatography. In conclusion, the new developed method has been proved to be a reliable and economic method for effective determination of free and total sulfites in the shrimps, and the method could be expanded in determination of the sulfites in other food products.

Rapid Quantitation of 12 Volatile Aldehyde Compounds in Wine by LC-QQQ-MS: A Combined Measure of Free and Hydrogen-Sulfite-Bound Forms

This work outlines a rapid novel methodology for the direct quantitation of 12 volatile aldehyde compounds related to oxidative off-flavors in wine, by measuring the combined free and hydrogen-sulfite-bound forms of each aldehyde compound, consisting of four general aldehydes, four Strecker aldehydes, and four (E)-2-alkenals. The methodology requires minimal preparation of wine samples: the addition of internal standards and 6 g/L sulfur dioxide, and filtration prior to quantitation by liquid chromatography-triple quadrupole-mass spectrometery. Overall, the limit of detection, limit of quantification, accuracy (recovery, 97-114%), and precision (repeatability and reproducibility, RSD ≤ 10%) were satisfactory to enable routine measurement of the 12 aldehyde compounds in wine. The methodology was applied to 20 commercial white and red wines from various varieties and vintages. A general trend of higher concentrations of the aldehyde compounds in white wines compared to red wines was observed.

Direct Analysis of Free and Sulfite-Bound Carbonyl Compounds in Wine by Two-Dimensional Quantitative Proton and Carbon Nuclear Magnetic Resonance Spectroscopy

Recent developments that have accelerated 2D NMR methods and improved quantitation have made these methods accessible analytical procedures, and the large signal dispersion allows for the analysis of complex samples. Few natural samples are as complex as wine, so the application to challenges in wine analysis look promising. The analysis of carbonyl compounds in wine, key oxidation products, is complicated by a multitude of kinetically reversible adducts, such as acetals and sulfonates, so that sample preparation steps can generate complex interferences. These challenges could be overcome if the compounds could be quantified in situ. Here, two-dimensional ((1)H-(1)H) homonuclear and heteronuclear ((13)C-(1)H) single quantum correlations (correlation spectroscopy, COSY, and heteronuclear single quantum coherence, HSQC) nuclear magnetic resonance spectra of undiluted wine samples were observed at natural abundance. These techniques achieve simultaneous direct identification and quantitation of acetaldehyde, pyruvic acid, acetoin, methylglyoxal, and α-ketoglutaric acid in wine with only a small addition of D2O. It was also possible to observe and sometimes quantify the sulfite, hydrate, and acetal forms of the carbonyl compounds. The accuracy of the method was tested in wine samples by spiking with a mixture of all analytes at different concentrations. The method was applied to 15 wine samples of various vintages and grape varieties. The application of this method could provide a powerful tool to better understand the development, evolution, and perception of wine oxidation and insight into the impact of these sulfite bound carbonyls on antimicrobial and antioxidant action by SO2.

A rapid, one step preparation for measuring selected free plus SO2-bound wine carbonyls by HPLC-DAD/MS

Carbonyl compounds are produced during fermentation and chemical oxidation during wine making and aging, and they are important to wine flavor and color stability. Since wine also contains these compounds as α-hydroxysulfonates as a result of their reaction with sulfur dioxide, an alkaline pre-treatment requiring oxygen exclusion has been used to release these bound carbonyls for analysis. By modifying the method to hydrolyze the hydroxysulfonates with heating and acid in the presence of 2,4-dinitrophenylhydrazine (DNPH), the carbonyl compounds are simultaneously and quickly released and derivatized, resulting in a simpler and more rapid method. In addition, the method avoids air exclusion complications during hydrolysis by the addition of sulfur dioxide. The method was optimized for temperature, reaction time, and the concentrations of DNPH, sulfur dioxide and acid. The hydrazones were shown to be stable for 10 h, adequate time for chromatographic analysis by HPLC-DAD/MS. This method is demonstrated for 2-ketoglutaric acid, pyruvic acid, acetoin and acetaldehyde, wine carbonyls of very different reactivities, and it offers good specificity, high recovery and low limits of detection. This new rapid, simple method is demonstrated for the measurement of carbonyl compounds in a range of wines of different ages and grape varieties.