Effect of sugar acylation on the antioxidant properties of Vitis vinifera red grape malvidin‐3‐glucoside

This work aims at studying the influence of sugar acylation on the antioxidant properties of Vitis vinifera red grape malvidin‐3‐glucoside. The antioxidant properties of malvidin‐3‐glucoside, malvidin‐3‐acetylglucoside, malvidin‐3‐coumaroylglucoside and malvidin‐3‐caffeoylglucoside were measured using different techniques. Their antiradical and reducing properties were determined using the DPPH and FRAP method, respectively. Malvidin‐3‐caffeoylglucoside displayed a DPPH value (20.2 μm Trolox eq.) much higher than malvidin‐3‐glucoside (13.6 μm Trolox eq.), but no significant differences were observed from the FRAP assay. Furthermore, the ability of these compounds to inhibit lipid peroxidation in a liposome membrane system was examined by monitoring oxygen consumption and the formation of conjugated dienes. Both assays allowed concluding that malvidin‐3‐caffeoylglucoside and malvidin‐3‐coumaroylglucoside inhibit lipid peroxidation significantly more than malvidin‐3‐glucoside. Altogether, the results reported herein indicate that acylation of malvidin‐3‐glucoside with phenolic acids like caffeic or coumaric acids, but not acetic acid, increases their overall antioxidant properties.     

Copigmentation between malvidin-3-glucoside and some wine constituents and its importance to colour expression in red wine

Thermodynamic parameters for intermolecular copigmentation interactions involving malvidin-3-glucoside were determined by UV/visible spectroscopy at wine pH (pH 3.6). These included association constants, enthalpy and entropy changes, which were measured for chlorogenic acid, caffeic acid, quercetin, quercetin-3-glucoside, (−)-epicatechin, (+)-catechin, procyanidin dimer and seed tannin. Quercetin produced the strongest copigment (K_CP = 2900 ± 1300), whilst the addition of glucose at position 3 (quercetin-3-glucoside) reduced its effect by almost 10-fold. Malvidin-3-glucoside self-association (K_D = 3300 ± 300 mol⁻¹ l) was thermodynamically favoured over intermolecular interaction with any of the copigments tested. No colour enhancement due to self-association was observed for malvidin-3-glucoside-derived pigments that cannot enter hydration reactions. In addition, malvidin-3-(6-O-p-coumaryl)glucoside did not show colour enhancement suggesting that the p-coumaryl group prevents self-association. The malvidin-3-glucoside circular dichroism (CD) spectrum was not affected by indicated changes in malvidin-3-glucoside concentration. These observations demonstrate that self-association of malvidin-3-glucoside is more important than copigmentation in young red wine.     

Anthocyanin content and antioxidant capacity in bran extracts of some Thai black rice varieties

This study investigated both the anthocyanin content and the antioxidant capacity of a set of genetically related glutinous and nonglutinous Thai black rice varieties. The ethanol/water extracts of the brans of these black rice varieties showed relatively potent antioxidant activities compared with those of tocopherol. These antioxidant activities were determined by thiocyanate, H₂O₂‐scavenging chemiluminescence (XYZ), Cu⁺⁺/bathocuproine colorimetry (PAO) and 1,1‐diphenyl‐2‐picrylhydrazyl radical‐scavenging assay. The structural identification and quantification of the black rice anthocyanins performed by high‐performance liquid chromatography coupled with electrospray ionisation and tandem mass spectrometry found cyanidin‐3‐O‐glucoside and peonidin‐3‐O‐glucoside as the major anthocyanins in the ranges of 16.01–34.40 and 2.43–7.36 μg mL^?1, respectively. The comparative study in terms of quantity of these phytochemicals and antioxidant capacity of the black rice bran extracts suggested the contribution of overall phenolic components rather than that of the particular anthocyanin pigments.     

Colorimetric assay for determination of trimethylamine-nitrogen (TMA-N) in fish by combining headspace-single-drop microextraction and microvolume UV–vis spectrophotometry

In this work, headspace-single-drop microextraction has been used in combination with microvolume UV–vis spectrophotometry to enhance the determination of trimethylamine-nitrogen (TMA-N) in fish samples. TMA-N is often used for monitoring fish freshness, but due to the low analytical sensitivity usually achieved, its determination must be performed after certain time of storage in some fish species. The proposed methodology, based on the extraction and subsequent complexation of volatile TMA-N onto a picric acid-containing xylene microdrop exposed to the headspace, involves an important improvement of sensitivity (detection limit 6 × 10⁻⁴ mg TMA-N per 100 g of fish), a miniaturization of the AOAC Official Method (971.14) and a simple approach for routine labs. This method is well suited to determination of TMA-N in different species of frozen and fresh fish samples from markets and to study the evolution of TMA-N concentration in farmed turbot at the earliest stages of deterioration.     

Screening method for identification of adulterate and fake tequilas by using UV–VIS spectroscopy and chemometrics

Based on UV–VIS spectroscopy and chemometric techniques, a screening method is presented with which the studied brands of white and rested tequila can be differentiated among them and on the other hand, adulterate and fake tequilas can be distinguished from the corresponding genuine brands. Eighty bottles of tequila (39 white type and 41 rested type) were studied and purchased at liquor stores; special care was taken to get different batches. Through the use of support vector machine (SVM), principal component analysis (PCA) and linear discriminant analysis (LDA) the studied tequilas were differentiated and classified into 8 sets: 4 sets of white and 4 of rested tequilas; each set corresponded to a specific tequila brand. Seven additional samples with similar labeling than the 80 samples were used to validate the method and it was found that each sample was located within the ellipse of confidence of the corresponding tequila brand. Furthermore, 14 adulterated samples were generated from 2 bottles of tequila, one white and one rested, and they could be distinguishable from the genuine tequila, i.e., they were outside of the corresponding ellipse of confidence. In addition, the screening method here presented was employed to analyze rested tequilas that were purchased on the street market, i.e., fake tequilas, with the same label than 3 of the used brands in this work. These samples were discriminated from the corresponding genuine tequila brand. The results suggested that the reported method could play an important role when a quick, trustworthy and feasible result on site is needed since the test of the spirit takes minutes, affording robustness, reliability and in addition, a skilled worker is not required necessarily to apply the method.     

Survey on the content of vitisin A and hydroxyphenyl-pyranoanthocyanins in Tempranillo wines

Little is known about the content and development of pyranoanthocyanins, pigments mainly formed during red wine ageing, in commercial wines. Some of the major pyranoanthocyanins in a wide selection of 1–10 years-old Spanish Tempranillo wines and also in a 29 years wide-vertical series of Tempranillo wines from an individual cellar have been determined. Great variability in pyranoanthocyanin concentrations was found (range, mg/l): vitisin A, 0–10.76; pinotin A, 0–4.26; and malvidin 3-glucoside-4-vinylphenol, 0.03–1.37. Vitisin A and malvidin 3-glucoside-4-vinylphenol were already present in 1–2 years-old wines, whereas pinotin A was only detectable in a few of the 1 and 2 years-old wines. Vitisin A tended to decrease with wine age, while hydroxyphenyl-pyranoanthocyanins showed the reverse trend. However, the aforementioned trends were interrupted by various temporary maxima, most likely due to some “refreshment” of the oldest wines (i.e., addition of young wine), as suggested by unexpected high concentrations of malvidin 3-glucoside, in contrast to the results found in the wine vertical series. The effects of addition of young wine on aged wine pyranoanthocyanin concentrations were confirmed by wine refreshment experiments.