Abstract
Resveratrol is the most important biopotential phytoalexin of the stilbene group (natural polyphenolic secondary metabolites), synthesized naturally by the action of biotic and abiotic factors on the plant. The yield of individual bioactive compounds isolated from grapevine components, products and by-products is directly dependent on the conditions of the synthesis, extraction and identification techniques used. Modern methods of synthesis and extraction, as well as identification techniques, are centred on the use of non-toxic solvents that have the advantages of the realisation of rapid extractions, maintenance of optimal parameters, and low energy consumption; this is a challenge with promising results for various industrial applications. Actionable advances in identifying and analysing stilbenes consist of techniques for coupling synthesis/extraction/identification methods that have proven accurate, reproducible and efficient. The main challenge remains to keep resveratrol compositionally unaltered while increasing its microbiome solubility and stability as a nutraceutical in the food industry.
1. Introduction
Originating from grape skins, resveratrol is a phytoalexin, a compound produced by grapevine components that acts similarly to an antibiotic in response to the attack of stressors such as the fungus Botrytis cinerea [1,2]. Cis- and trans-isomer resveratrol occurs both in grapevine components and in products and by-products resulting from applied technologies, with considerable attention in the biomedical literature being given to the trans-resveratrol isomer (3,4,5′trihydroxyl-trans-stilbene)—tR. Many publications attest to the existence of resveratrol in grape berries, skin, seeds, pulp, stems, stalks, leaves, vine shoots or roots. Resveratrol is also present in products resulting from the various technologies applied to grapes: wine and juice, grape skin powder, raisins and by-products of the vine: grape pomace, grape canes, wine less and various extracts. Recent studies show that the content of resveratrol is higher in the cut grape pomace than in other produscts (wine, grapes, raisins, etc.) and varies depending on numerous internal and externalfactors, since the applied synthesis and extraction methods have a major role in its quantity and stability [3,4].
Early research such as [5] showed how the concentration of resveratrol during alcoholic fermentation increases in the must and decreases in the skins of black grapes while remaining constant in the seeds. The study shows that after malolactic fermentation, the amount of resveratrol is about twice the amount measured at the end of alcoholic fermentation, indicating a resveratrol amount probably in the form of glucosides or oligomeric form from which the enzymatic activity of malolactic bacteria could release free resveratrol. In recent years, resveratrol is considered a qualitative, integral part of wine due to its several beneficial effects on human health [6]. The identification of resveratrol in grapevine [7] makes this plant of particular importance for industrial, medical and food research [8], and the demand for products based on resveratrol extracted from grapevine components, products and by-products has increased. Numerous types of research prove its beneficial role for health, tackling diseases with an increased incidence: anticancer activity [9], cardioprotection [10], neuroprotection via upregulation of endogenous antioxidant expression and activity [11], protection against diabetes [12] or reducing degenerative effects of neurological diseases such as Alzheimer’s or Parkinson’s [13,14], antioxidant activity [15,16,17], inhibition of platelet aggregation [18] of anti-inflammatory activity [19], etc. (Figure 1).
In recent years, understanding the “French Paradox” has stimulated a new research interest, revealing that the resveratrol synthesized in grapes and contained in wine plays a beneficial role in certain cardiovascular regulatory mechanisms [20,21]. Research in the food industry is interested in using resveratrol in products to increase their functionality [22,23]. Also, maintaining stability after extraction represents a particular interest of current research. The progress that researchers have made so far in the techniques for extraction and identification of resveratrol and, in particular, tR is evident.
Thus, research in the last decade has focused on the modernization of synthesis and extraction methods in order to create premises in which the use of low-toxicity substances can prove its efficacy, decreasing the extraction time by increasing the efficiency of extraction methods with reduced energy consumption; however, the challenge of keeping intact the bioactivity of resveratrol is still topical due to its instability. This study presents the most important methods of synthesis and extraction, the progress made by researchers in terms of identification techniques and aspects regarding the use of simultaneous several methods simultaneously (coupling of methods) so that the obtained results can lead to the accurate determination of resveratrol under the most natural conditions, taking into account its current usage trends.
2. Methods of Synthesis and Extraction
The methods for synthesizing and extracting resveratrol from grapevine components and products are diverse (chemical, natural, biotechnological), utilizing high-performance technology and high-purity gradients. Recently, alternative solvents (deep eutectic solvents—DESs) have significantly increased the concentration of extracted polyphenols, and the ultrasound-assisted extraction method (UAE), provide higher yields than classical methods. Recent studies show is focused on the use of combined synthesis and extraction methods (chemical, natural and biotechnological) which have proven the efficiency of the process. The current priority criteria in terms of innovative extraction are represented by the preservation of the bioactivity of compounds in natural products through the use of environmentally friendly, efficient nanotechnologies, with the obtaining of extracts with high purity, stable, while preserving the condition of an unaltered environment [24].
2.1. Synthesis and Chemical Extraction Methods
The best classical solvents for extracting stilbenes from grapevine cords are alcohols that have a hydroxyl group (MeOH-methanol or C2H5OH-ethanol) [25]. One of the most well-known methods for the chemical extraction of polyphenols is the MeOH method developed by [26]. Thus, dried grape skin samples (approximately 2 g) and dried seed samples (approximately 1 g) were extracted three times with 20 mL MeOH containing 0.1% HCl (skin) and 10 mL MeOH/H2O (80/20) containing 0.1% HCl (seeds). Using the MeOH/H2O mixture (70:30, v/v) as solvent, ref. [27] shows the presence of total polyphenols and RSA in grape seed extracts and grape skin and pulp extracts, with higher potential for seeds.
Also, ref. [28] obtained good results for extracting stilbenes from grapevine compounds using C2H5OH and MeOH and found that the other stilbenes were better extracted in acetone. The optimization of solvent (water, C2H5OH, acetone-C3H6O, MeOH and butanol) extraction on phenolic compounds from grape must based on an experimental design was investigated by [29], who concluded that acetone and C2H5OH facilitate the extraction of phenolic substances from grape must, and C2H5OH is more recommended because it is considered an environmentally friendly solvent. Good extraction was obtained with C2H5OH/H2O (80:20, v/v) by [30], showing that recovery (>96%) and reproducibility (6.83–15.13%) were satisfactory. After extraction, the resveratrol isomers in grape skin were quantified by high-performance liquid chromatography coupled to a visible ultraviolet–visible diode array detector. In order to improve the (endogenous) tR content in grapes harvested at late maturity (LMC), several short anoxic dry nitrogen treatments were applied, and the results allowed the design of an anoxic treatment protocol for grapes prior to the vinification process, which resulted in tR enriched wines [31]. In another study, the skins of red and white grapes were separated from the other GP residues and subjected to extraction with 1:1 C2H5OH–acidic water as an extractant to obtain as many phenolic compounds as possible from this material [32]. Combined methods to improve synthesis and extraction processes are also used by [33], evaluating the effect of pressure (100, 400 bar), temperature (35, 55 °C) and modifier addition (5% C2H5OH, v/v) to identify the optimal extraction of resveratrol from GP obtained as a by-product in winemaking. The remarkable results have been achieved when combining high pressure with low temperature, using 5% C2H5OH, v/v as co-solvent.
2.2. Synthesis and Natural Extraction Methods
Some of the most important extraction methods applied to grapevine products and by-products, in addition to conventional extraction by maceration (MAC), are represented by sustainable extraction techniques, such as microwave-assisted processes (MAEs), UAE, pressurized supercritical fluids and hydrothermal fluids, in order to obtain safe, stable and high-quality extracts. Traditional extraction methods are energy-intensive and use toxic, expensive, environmentally unfriendly solvents. Although they offer satisfactory extraction yields, they cannot maintain the stability of some heat-sensitive compounds (including resveratrol), hence the need for research to find innovative techniques.
2.2.1. Conventional Extraction (Maceration)
Carrying out dynamic MAC with hydroethanol solution on grape seed powder (30 mL to 1 g of powder sample) followed by simple solid–liquid organic extraction yielded good results (45.7 ± 0.2 mg/g total phenolic compounds extract) in the research by [34]. The combination of cold MAC with thermomaceration (heating crushed grapes at 50 °C for 1 h) and enzymatic macerationperformed by [35] increased the total phenolic compounds content (tR increases from 0.09 to 0.23 mg/100 g). The total phenolic compounds and antioxidant capacity were monitored during conventional fermentation (10 days) by [36]. The main conclusion is that compared to conventional heat treatment, the phenolic compound content must be doubled immediately after OH treatment (ohmic heating) at preset parameters (E = 55 V/cm, t = 60–90 s, T = 72 °C).
Testing the use of an alternative maceration technique (nitrogen maceration) instead of carbonic maceration by [37] resulted in increased polyphenols and anthocyanins in macerated wines. In another study, four environmentally friendly extraction methods were tested, obtaining 29 polyphenols, including stilbene, from grapevine stems, involving the use of polyethylene glycol and water (natural solvents), together with advanced techniques such as low pressure, MAC or UAE, two of which had higher efficacy (water + MAE + UAE + atmospheric pressure (1121 ± 4.8 μg/g tR), water + MAE + UAE + reduced pressure (916 ± 1.9 μg/g tR)), the others yielding lower amounts (694 ± 1.0 μg/g tR) [38]. An interesting approach to the impact of prolonged MAC (6 months) on phenolic quality is found in the study by [39], which shows that this quality is maintained for 4 months, after which a decrease is witnessed probably due to precipitation/reabsorption while the extraction of phenols from the seeds occurred during longer maceration periods, with differences from one variety to another.
Download the full article as PDF here:
Methods for Synthesis and Extraction of Resveratrol from Grapevine: Challenges and Advances in Compound Identification and Analysis
or continue reading here
Căpruciu, R.; Gheorghiu, C.N. Methods for Synthesis and Extraction of Resveratrol from Grapevine: Challenges and Advances in Compound Identification and Analysis. Foods 2025, 14, 1091. https://doi.org/10.3390/foods14071091
