Dimitris P. Makris

Implementation of response surface methodology to assess the antiradical behaviour in mixtures of ascorbic acid and α-tocopherol with grape (Vitis vinifera) stem extracts

The efficiency of grape stem extracts to express antiradical activity was assessed using two different approaches and DPPH as the radical probe. In addition, the mixture effects when the extracts were combined with ascorbic acid (AA) and α-tocopherol (α-Tcp) were also evaluated. The approaches included a simple linear regression analysis between the response (antiradical activity) and concentration, but also a response surface methodology, which permitted the monitoring of the response upon simultaneous variation of both the concentration of the total polyphenols of the extracts and either of the antioxidants (AA and α-Tcp). The deployment of linear regression poses important constraints with regard to concentration ranges, whereas response surface methodology might be a valuable statistical tool for similar assessments and credible modelling of binary mixtures of antioxidants. In all combinations tested it was found that an antagonism was manifested, presumably as a result of AA and α-Tcp regeneration by the extract polyphenols, at the expense of the latter.

Kinetics of Ultrasound-Assisted Polyphenol Extraction from Spent Filter Coffee Using Aqueous Glycerol

Culinary filter coffee residues were utilized as raw material, with the aim of recovering functional polyphenolic components. The extraction was performed under ultrasonication using aqueous glycerol, and for this reason, the process was initially optimized with regard to glycerol concentration (Cgl) and extraction time (t), by implementing response surface methodology via a central composite (Box-Behnken) experimental design. The optimized conditions determined were Cgl = 3.6% (w/v) and t = 175 min. The comparative assessment, based on a kinetic assay, illustrated that the progression of the extraction was slower in aqueous glycerol than in water, yet aqueous glycerol was proven a more efficient extraction medium, providing 7.4% higher total polyphenol yield. Liquid chromatography-diode array-mass spectrometry analysis revealed that the major antioxidant phytochemicals in the aqueous glycerol extract were chlorogenic acids (caffeic acid derivatives), accompanied by some other polyphenolic metabolites.

Optimisation of organic solvent-free polyphenol extraction from Hypericum triquetrifolium Turra using Box–Behnken experimental design and kinetics

Hypericum triquetrifolium Turra is a plant rich in biologically functional polyphenolic phytochemicals. The efficient recovery of polyphenols from this material has not been previously investigated in depth, in terms of establishing an environmentally benign and cost-effective process that would aim at producing extracts enriched in polyphenolic compounds. The objective of the present study was the examination of the efficiency of water/glycerol mixtures in extracting polyphenols from dried aerial parts of H. triquetrifolium Turra and its critical comparison with water. Extraction temperature and time were optimised using response surface methodology, while comparative assessment of the extraction efficiency between water/glycerol and water was carried out using kinetics. The results showed that 10xa0% (w/v) aqueous glycerol at 70xa0°C provided very satisfactory extraction yield in total polyphenols (54.83xa0mg gallic acid equivalents per g of dry weight), which was significantly higher than that attained with water (17.3xa0%). Similar results were drawn for the reducing power, in concurrence with the polyphenolic concentration. Liquid chromatography–mass spectrometry analysis showed that the polyphenolic profile of water/glycerol extract was composed by polar substances, such as chlorogenic acids and quercetin glycosides.

Optimization of a green extraction method for the recovery of polyphenols from olive leaf using cyclodextrins and glycerin as co-solvents

Olive leaf, an agricultural by-product, was studied for the valorization of its biophenols using green extraction techniques; i.e. non-toxic and eco-friendly extraction solvents were used, involving water and glycerol. 2-hydroxypropyl-β-cyclodextrin (CD), was also employed as an enhancer of the extraction, since cyclodextrins (CD’s) are known to improve the extractability of olive leaf polyphenols by forming water soluble inclusion complexes. The process was optimized by implementing a central composite (Box-Behnken) experimental design and response surface methodology, taking into consideration the following independent variables: glycerol concentration (Cgl), CD concentration (CCD) and temperature (T). The evaluation of the extraction model was based on two responses: the total polyphenol yield (YTP) and the antiradical activity (AAR). Optimum values for the extraction process were obtained at 60% (w/v) glycerol content, Txa0=xa060xa0°C and 7% (w/v) CD content. LC–MS analysis was also applied in order to characterize the polyphenolic composition of extracts containing cyclodextrins. The main polyphenols present were oleuropein and oleuropein derivatives. Olive leaf aqueous extracts containing glycerol and cyclodextrins may be used as raw materials/ingredients for several end-users in the food, cosmetic and pharmaceutical industries.

Ultrasound-Assisted Green Extraction of Eggplant Peel (Solanum melongena) Polyphenols Using Aqueous Mixtures of Glycerol and Ethanol: Optimisation and Kinetics

Eggplant peels were used to evaluate glycerol and ethanol for their ability to recover polyphenolic antioxidants. The evaluation was based on optimisation by a Box-Behnken experimental design and kinetics. The results showed that extraction with water/ethanol and water/glycerol mixtures, under optimised conditions, afforded virtually equal yield in total polyphenols, which was 13.40 and 13.51xa0mg caffeic acid equivalents per g dry weight, respectively. The extraction kinetics revealed that diffusion of phenolics in water/glycerol mixtures was slower (0.85u2009×u200910−12 m2 s−1) compared with the one attained with water/ethanol (2.23u2009×u200910−12 m2 s−1), yet the ability of both systems to recover essentially the same levels of total polyphenols was confirmed. The determination of total chlorogenates, total flavonoids and total pigments indicated that water/glycerol might be a more effective solvent system, but controversies were observed with regard to the antiradical activity and reducing power. The analytical polyphenolic profile of both extracts was dominated by chlorogenic acid and no major differences were recorded, a finding indicating that none of the solvent systems displayed selectivity. The results suggested that glycerol may be an ideal candidate for use in eco-friendly extraction processes.

Optimization of polyphenol extraction from red grape pomace using aqueous glycerol/tartaric acid mixtures and response surface methodology.

ABSTRACT Grape pomace is a food industry waste containing a high burden of antioxidant polyphenols and several methodologies have been developed for their efficient extraction. However, a sustainable and environmentally friendly process should involve recovery means composed of benign, non-toxic solvents, such as tartaric acid and glycerol, which are natural food constituents. In this line, this study examined the extraction of polyphenols using aqueous tartaric acid/glycerol solutions. The aim was to assess the role of acid and glycerol concentration in the extraction yield, employing a Box-Behnken experimental design and response surface methodology. The results showed that solutions containing only glycerol (20%, w/v) are more suitable for retrieving polyphenols, flavonoids, and pigments from grape pomace, while tartaric acid exerted a negative effect in this regard, when tested at concentrations up to 2% (w/v).

Origanum species native to the island of Crete: in vitro antioxidant characteristics and liquid chromatography–mass spectrometry identification of major polyphenolic components

Extracts from three Origanum species, including Origanum microphyllum, Origanum dictamnus and Origanum vulgare subsp. hirtum, native to the island of Crete (southern Greece), were partly fractionated through successive partition with ethyl acetate and n-butanol. All the fractions obtained were profiled with regard to their major polyphenolic constituents, using liquid chromatography-diode array-mass spectrometry. Furthermore, the antioxidant potency of each fraction was assessed by estimating the antiradical activity (AAR) and the hydroxyl free radical scavenging activity (SAHFR). The chromatographic analyses revealed a rich profile mainly for the ethyl acetate fractions, composed principally by flavones, which were accompanied by a limited number of phenylpropanoids, flavanones and dihydroflavonols. The highest values of antioxidant activity were displayed by the ethyl acetate extract of O. dictamnus, which also possessed the richest polyphenolic composition.

Development of a Green Process for the Preparation of Antioxidant and Pigment-Enriched Extracts from Winery Solid Wastes Using Response Surface Methodology and Kinetics

Red grape pomace (RGP), an abundant wine industry solid waste, was used for the recovery of polyphenols and anthocyanin pigments, using ultrasound-assisted extraction and water/glycerol mixtures as the solvent. Glycerol concentration (Cgl) and liquid-to-solid ratio (RL/S) were first optimized by implementing Box−Behnken experimental design and the process was further studied through kinetics. The optimal conditions were found to be Cgl = 90% (w/v) and RL/S = 90 mL g−1, and under these conditions the extraction of total polyphenols (TP) and total pigments (TPm) obeyed first-order kinetics. Maximum diffusivity (De) values were 4.22 × 10−12 and 12.59 × 10−12 m2 s−1, for TP and TPm, respectively, and the corresponding activation energies were (Ea) 13.94 and 8.22 kJ mol−1.

Stability and transformation of major flavonols in onion ( Allium cepa ) solid wastes

Onion solid wastes were analysed using HPLC and LC / MS and the major polyphenols detected were quercetin, quercetin 4′-O-glucoside, accompanied by protocatechuic acid and a benzofuranone derivative. The latter two compounds have been demonstrated as some of the degradation products that might arise as a result of peroxidase-mediated decomposition of quercetin. These four substances, along with two principal enzymes implicated in flavonols breakdown, β-glycosidase and peroxidise, were monitored throughout an examination period of 48xa0h, in ground onion solid waste. The determinations showed that quercetin 4′-O-glucoside content increased by 13.3%, while quercetin, benzofuranone derivative and protocatechuic acid contents increased by 68.6, 37.5 and 58.4%, respectively. β-Glycosidase activity exhibited fluctuations and increased by 38.2%, whereas the POD showed a constant increasing trend, leading in 21.7% higher activity. On such a ground, a hypothesis was set up to explain transformations of flavonols.

Screening of Natural Sodium Acetate-Based Low-Transition Temperature Mixtures (LTTMs) for Enhanced Extraction of Antioxidants and Pigments from Red Vinification Solid Wastes

Low-transition temperature mixtures (LTTMs), also known as deep eutectic solvents, are liquid mixtures of natural substances that possess unique properties, not encountered with conventional solvents. Such liquids represent a state-of-the-art means of extracting bioactive plant constituents, yet the plethora of combinations of various substances that form LTTMs dictates detailed comparative testing, to identify LTTMs with high extraction capacity. In this study, a number of combinations of hydrogen bond donors (HBDs) with sodium acetate serving as the hydrogen bond acceptor (HBA), was attempted. The stable LTTMs formed were then used to extract antioxidant polyphenols and pigments from red grape pomace (RGP). The LTTM composed of L-lactic acid and sodium acetate at a molar ratio of 5:1 was found to be the most efficient solvent, giving a total polyphenol yield of 134.54xa0mg gallic acid equivalents per g of dry weight and a total pigment yield of 3.32xa0mg malvin equivalents per g of dry weight. The extract obtained with this particular LTTM also possessed the strongest antioxidant activity. The principal compounds in this extract were tentatively identified as phenolic acids, anthocyanin pigment derivatives and a flavonol glycoside.