Efficient one pot extraction and depolymerization of grape (Vitis vinifera) pomace procyanidins for the preparation of antioxidant thio-conjugates

Synthesis and Isolation of Phenol- and Thiol-Derived Epicatechin Adducts Prepared from Avocado Peel Procyanidins Using Centrifugal Partition Chromatography and the Evaluation of Their Antimicrobial and Antioxidant Activity

Polyphenols from agro-food waste represent a valuable source of bioactive molecules that can be recovered to be used for their functional properties. Another option is to use them as starting material to generate molecules with new and better properties through semi-synthesis. A proanthocyanidin-rich (PACs) extract from avocado peels was used to prepare several semi-synthetic derivatives of epicatechin by acid cleavage in the presence of phenol and thiol nucleophiles. The adducts formed by this reaction were successfully purified using one-step centrifugal partition chromatography (CPC) and identified by chromatographic and spectroscopic methods. The nine derivatives showed a concentration-dependent free radical scavenging activity in the DPPH assay. All compounds were also tested against a panel of pathogenic bacterial strains formed by Listeria monocytogenes (ATCC 7644 and 19115), Staphylococcus aureus (ATCC 9144), Escherichia coli (ATCC 11775 and 25922), and Salmonella enterica (ATCC 13076). In addition, adducts were tested against two no-pathogenic strains, Limosilactobacillus fermentum UCO-979C and Lacticaseibacillus rhamnosus UCO-25A. Overall, thiol-derived adducts displayed antimicrobial properties and, in some specific cases, inhibited biofilm formation, particularly in Listeria monocytogenes (ATCC 7644). Interestingly, phenolic adducts were inactive against all the strains and could not inhibit its biofilm formation. Moreover, depending on the structure, in specific cases, biofilm formation was strongly promoted. These findings contribute to demonstrating that CPC is a powerful tool to isolate new semi-synthetic molecules using avocado peels as starting material for PACc extraction. These compounds represent new lead molecules with antioxidant and antimicrobial activity.

Novel Antihypertensive Prodrug from Grape Seed Proanthocyanidin Extract via Acid-Mediated Depolymerization in the Presence of Captopril: Synthesis, Process Optimization, and Metabolism in Rats

Grape seed extract contains a high content of proanthocyanidins that can be depolymerized into C-4-substituted (epi)catechin derivatives in the presence of nucleophiles. However, the biological and medicinal values of depolymerization products have been rarely investigated. Recently, we developed a novel depolymerization product (-)-epicatechin-4β- S-captopril methyl ester (ECC) derived from the reaction of grape seed proanthocyanidin extract with captopril in the presence of acidified methanol. A central composite design was employed to select the most appropriate depolymerization temperature and time to obtain the target product ECC with a high yield. A total of 16 metabolites of ECC in rat urine, feces, and plasma were identified using liquid chromatography quadrupole time-of-flight tandem mass spectrometry. The in vivo results suggested that ECC could release captopril methyl ester and epicatechin, followed by the generation of further metabolites captopril and epicatechin sulfate conjugates. Therefore, ECC may be used as a potential prodrug with synergistic or additive hypotensive effects.

Foodomics platform for the assay of thiols in wines with fluorescence derivatization and ultra performance liquid chromatography mass spectrometry using multivariate statistical analysis

The presence of specific volatile and aminothiols in wine is associated with quality, worth, price, and taste. The identification of specific thiol-containing compounds in various wines has been reported in many valuable and interesting works. In this study, a novel foodomics assay of thiol-containing compounds, such as free aminothiols and related conjugates, was developed using ultra performance liquid chromatography (UPLC) with fluorescence (FL) and electrospray (ESI) time-of-flight mass spectrometric (TOF/MS) detections. FL specific derivatization was applied along with multivariate statistical analysis. First, the optimal experimental conditions were studied using representative thiols, such as l-cysteine, N-acetyl-l-cysteine, cysteamine, and l-glutathione, and then the UPLC-FL derivatization and separation steps were fixed for the subsequent screening of unknown thiol-containing compounds. The screening assay consisted of monitoring the UPLC-TOF/MS peaks of unknown thiols, which decreased due to the derivatization as compared to the nonderivatized thiols. The principal component analysis of the UPLC-TOF/MS data could be well-differentiated and categorized into two groups. The orthogonal signal correction partial least-squares discriminant analysis, the so-called S-plot, showed that the quality differentiation is directly related to the decrease of native thiols and increase of derivatized thiols. With this strategy, the mass difference from the derivatization reagent (+m/z 198) could be utilized for the identification of these thiols using the FL peaks retention time and metabolomics-databases. The presence of l-glutathione in rice wine was for the first time reported on the basis of the available metabolomics-databases and standard matching. This novel concept based on foodomics could be applied in food analysis for the ready screening of specific functional compounds by exploiting the various derivatization modes available.

Enantioselctive syntheses of sulfur analogues of flavan-3-Ols

The first enantioselective syntheses of sulfur flavan-3-ol analogues 1–8 have been accomplished, whereby the oxygen atom of the pyran ring has been replaced by a sulfur atom. The key steps were: (a) Pd(0) catalyzed introduction of –S t-butyl group, (b) Sharpless enantioselective dihydroxylation of the alkene, (c) acid catalyzed ring closure to produce the thiopyran ring, and (d) removal of benzyl groups using N,N-dimethylaniline and AlCl₃. The compounds were isolated in high chemical and optical purity.

Influence of postharvest processing and storage on the content of phenolic acids and flavonoids in foods

The review is based on the evaluation of electronically collated data published between 2002 to June 2006. It is based on 325 references dealing with the following subclasses of phenolic compounds: hydroxycinnamic and hydroxybenzoic acids, chalcones, flavanones, flavones, flavonols, monomeric flavanols and anthocyanins. Only publications dealing directly with the effects of storage and postharvest processing on the phenolic acid and flavonoid contents of foods were considered. The expectation that the structural diversity even within each subgroup, and the number of different procedures and of different parameters would make finding homogenous tendencies unlikely, has, in most instances, been confirmed. By adding a database Excel table combined with a focused and unified evaluation, specific additional information was rendered accessible and concise. It holds true for most of the subclasses in question that the effect of storage and food processing on the polyphenol content is negligible in comparison to the differences between different varieties of plants. Variety dependence must always be considered, for all classes of compounds.

Biological and medicinal properties of grapes and their bioactive constituents: an update

The grape is one of the most valued conventional fruits, worldwide. Although most of the parts of the grapevine are useful, primarily, the grape is considered as a source of unique natural products not only for the development of valuable medicines against a number of diseases, but also for manufacturing various industrial products. Over the last few decades, apart from the chemistry of grape compounds, considerable progress has been made towards exploring the biological activities of various grape-derived constituents. Today, it is well established that in addition to serving as food, the grape is a major source of several phytochemicals. The main biologically active and well-characterized constituent from the grape is resveratrol, which is known for various medicinal properties in human diseases. This review discusses the roles of various grape-derived phytochemicals in relation to various diseases.

Determination of ochratoxin A in grapes, dried vine fruits, and winery byproducts by high-performance liquid chromatography with fluorometric detection (HPLC-FLD) and immunoaffinity cleanup

A liquid chromatographic method for the determination of ochratoxin A in grapes, dried vine fruits, and winery byproducts was developed. A mixture of either acetonitrile/water or acetonitrile/water/methanol was used as an extraction solvent mixture. After immunoaffinity column cleanup, the final extract was analyzed by high-performance liquid chromatography (HPLC) with a fluorometric detector (FLD). Mean recoveries from grapes, grape pomace, and lees samples spiked in the range of 1-200 microg/kg were 78, 86, and 88%, respectively, with a detection limit of 0.1 microg/kg and within-laboratory repeatability ranging from 6 to 15%. Tested on naturally contaminated samples of grapes, grape pomace, and sultanas, the method showed better performances as compared to two other methods also based on immunoaffinity cleanup and HPLC/FLD determination. Ochratoxin A was detected in samples of grape pomace (levels ranging from 34.2 to 456.8 microg/kg) and lees (levels ranging from 48.3 to 602.5 microg/kg) derived from the wine making of red grapes of 2004 and 2005 vintages in southern Italy. After distillation of contaminated grape pomace in a pilot-scale equipment to produce grappa, the toxin remained unchanged in the exhausted pomace and was not detected in any of the distilled fractions (detection limit of 0.02 microg/L).

Antioxidant activity of commonly consumed plant foods of India: contribution of their phenolic content

Antioxidants are important in protection against hypertension, diabetes, cardiovascular diseases and cancer. Polyphenols are potent antioxidants in plant foods, but their contribution to such protective effects is yet to be established. This study attempted to generate a database on the antioxidant activity (AOA) and phenolic content (PC) of some plant foods commonly consumed in India and to assess the contribution of the PC to their AOA. Plant foods belonging to different food groups such as cereals, legumes, oil seeds, oils, green leafy vegetables, other vegetables, spices, roots and tubers were analysed for AOA and PC. AOA was the highest in black pepper (0.43 mg food required for 50% inhibition of the coupled auto-oxidation of beta-carotene and linoleic acid in a mixture in vitro) and it had the highest PC (191 mg gallic acid equivalent/100 g food). The AOA (18.4 mg) as well as the PC (not detectable) were the lowest in sunflower oil. PC in oil seeds was higher than that in the oil, which could be due to the hydrophilic nature of phenolics and suggests the need for greater use of oil seeds than oils. A significant correlation was observed between the AOA and PC of the plant foods studied in general (r=-0.465), but the coefficient of correlation and determination were high only in spices (r=-0.86 and r2 =74%, respectively) and dehusked legumes (r=-0.65 and r2 = 42.2%, respectively). The results suggest that phenolics may contribute significantly to the AOA of some plant foods, such as spices and dehusked legumes.

Comparative antioxidant and cytotoxic effect of procyanidin fractions from grape and pine

There is a great interest in characterizing the biological properties of natural compounds obtained from plants, especially polyphenols. We studied the structure-activity-cytotoxicity relationships of polyphenolic fractions obtained from grape pomace and pine bark. These fractions contained similar polymerised flavonoids but different percentages of pyrogallol groups that confer on them different biological properties. The human keratinocyte cell line HaCaT and the mouse fibroblast cell line 3T3 were used to study the cytotoxicity of the different fractions after 24, 48, and 72 h of exposure. Antioxidant activity of the fractions was evaluated by measuring the inhibition of hemolysis mediated by AAPH. Our results demonstrate that the polyphenolic fractions studied show high antioxidant capacity in a concentration range that is not harmful to normal human cells. Pine fractions presented slightly lower antioxidant activity than grape fractions but are less cytotoxic. This data provides useful information to help design safe antioxidant products that act without altering critical cell functions.

Comparative study of the cytotoxicity induced by antioxidant epicatechin conjugates obtained from grape

We studied the cytotoxicity of epicatechin conjugates obtained by depolymerization of grape polymeric flavanols in the presence of cysteamine or cysteine and the resulting conjugates purified by ion exchange and/or reversed-phase high-resolution chromatography and compared it to their antioxidant capacity. The studies were carried out on fibroblast and keratinocyte cell lines. The cytotoxic effects of these products were observed at concentrations 3-7-fold higher than the antioxidant concentration after exposure for 24, 48, and 72 h. The compounds with a gallate group were more toxic than the corresponding products without one. It is interesting to note that the esther ethyl derivative exhibited low cytotoxicity but had the most potent antioxidant activity. The results indicated that effective antioxidant activity can be obtained from these products in a concentration range that is safe for the normal cell. This finding suggests new pharmaceutical applications and may also help us to identify the potential therapeutic dose.

HPLC determination of phenolics adsorbed on yeasts

An analytical HPLC method was developed to determine monomeric anthocyans as catechin (CA), flavonols as rutin (RU) and phenol acids as gallic acid (GA) adsorbed on the cell wall of 23 Saccharomyces cerevisiae strains grown on two media containing high levels of phenolic compounds, from grape seeds and grape skins, and on one control medium. Microbial biomass purification by liquid-liquid extraction of the phenolics is followed by reversed-phase chromatographic separation and CA, RU and GA detection by ultraviolet detector. The method was linear over the studied range of concentrations: GA at 0.12-0.96 microg/ml, CA at 0.25-20.00 microg/ml and RU at 0.02-0.20 microg/ml. The correlation coefficient for each analyte was greater than 0.9983. The recovery was greater than 85% for both GA and RU, and greater than 94% for CA. The detection limits for GA, CA and RU were determined to be 0.015, 0.025 and 0.029 microg/mg of biomass, respectively. The proposed method is highly responsive for the determination of different phenolics, and seems to be useful to evaluate their adsorption profile on yeasts.

Efficient preparation of catechin thio conjugates by one step extraction/depolymerization of pine (Pinus pinaster) bark procyanidins

The skin penetrating antioxidant cysteamine derivative of (-)-epicatechin as well as other thio conjugates were efficiently obtained with high yields from pine (Pinus pinaster) bark by simultaneous one pot extraction and depolymerization using water and cysteamine hydrochloride. The influence of the concentration of bark, acid, and cysteamine, as well as the reaction time on the total conversion, was studied. The total conversion into the epicatechin and catechin conjugates was as high as 47 g/kg pine bark with 1666 g cysteamine/kg bark and 28 g/kg with 166 g cysteamine/kg bark. A fast cleanup step by absorption/desorption on XAD-16 greatly facilitated further purification of the active major component. At a pilot scale, 4beta-(2-aminoethylthio)epicatechin (1) (conversion 263 g, purity 35% by reversed phase high-performance liquid chromatography/weight) was obtained from 17 kg of pine bark after simultaneous extraction/depolymerization followed by cleanup with the polymeric resin in approximately 10 h. The results show that pine (P. pinaster) bark is a suitable source of flavanols for the preparation of active thio derivatives. Conditions are given for the fast and efficient preparation of the conjugates.

Procyanidin fractions from pine (Pinus pinaster) bark: radical scavenging power in solution, antioxidant activity in emulsion, and antiproliferative effect in melanoma cells

Pine (Pinus pinaster) bark is a rich source of procyanidin oligomers. From a total polyphenolic extract, we have generated fractions of different procyanidin composition. The mixtures, devoid of gallate esters, were active as free radical scavengers against ABTS(*+), DPPH, and HNTTM. Pine bark fractions were tested for antioxidant activity in solution (hydrogen donation and electron transfer) and emulsion (inhibition of lipid peroxidation) and compared with their galloylated counterparts from grape origin. While galloylation clearly influenced the free radical scavenging efficiency in solution, it did not seem to play a determinant role in protection against lipid peroxidation in emulsion. The fractions were very mild inhibitors of cell proliferation. Because gallate esters appear to interfere with crucial cell functions, gallate free pine procyanidins may be the innocuous chemopreventative agents of choice for many applications in food and skin protection.