Spyros Grigorakis

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.

Phytochemical analysis and antioxidant activity of Lycium barbarum (Goji) cultivated in Greece

Abstract Context: The fruit of Lycium barbarum L. (Solanaceae), known as goji berry, has been exploited for a long time in traditional Chinese medicine. In recent decades, it has received much attention as one of the trendiest functional foods with a wide array of pharmacological activities in Western diets. Objective: In this study the phenolic profile and potential antioxidant capacity of Lycium barbarum cultivated in Crete (Greece) were investigated. Materials and methods: The berries were defatted with hexane and then extracted with dichloromethane and methanol using a Soxhlet apparatus. Furthermore, the methanol extract was fractionated with ethyl acetate and butanol. All fractions/extracts were tested for their antioxidant activity (DPPH, FRAP, chemiluminescence). Folin–Ciocalteu and LC-DAD-MS analyses were utilized for the identification of the phenolic compounds. Results: The total phenolic content ranged from 14.13 ± 0.40 (water fraction) to 109.72 ± 4.09 (ethyl acetate fraction) mg gallic acid equivalent/g dry extract. Ethyl acetate extract exhibited the highest scavenging activities determined as EC50 (4.73 ± 0.20 mg/mL) and IC50 (0.47 ± 0.001 mg/mL) using DPPH and chemiluminescence assays. Seventeen phenolic compounds, including cinnamoylquinic acids and derivatives, hydrocinnamic acids and flavonoid derivatives, were tentatively identified. To the best of our knowledge, quercetin 3-O-hexose coumaric ester and quercetin 3-O-hexose-O-hexose-O-rhamnose are reported for the first time in goji berry fruits. Discussion and conclusion: The results of this study suggest that consumption of goji berry fruits could serve as a potential source of natural antioxidant compounds and that goji berry phenolic extracts could be exploited for nutritional pharmaceutical purposes.

Implementation of kinetics and response surface methodology reveals contrasting effects of catechin and chlorogenic acid on the development of browning in wine model systems containing either ascorbic acid or sulphite

Wine model systems, containing catechin (Ct) and chlorogenic acid (CGA) as major browning substrates, were used to examine the effect of browning development, upon addition of ascorbic acid (AA) or sulphite. Browning rate was found to obey zero-order kinetics, and the browning rate constant, k, was used as the response to assess the effect of various combinations of Ct/CGA/AA and Ct/CGA/sulphite on browning onset, by deploying factorial design and response surface methodology. The models found suggested that browning rate was higher in model solutions containing AA and lower in those containing sulphite, while the presence of CGA did not affect browning reactions. This fact was confirmed by liquid chromatography–diode array–mass spectrometry analyses, which demonstrated the formation of yellow pigments deriving from Ct.

The effect of 2-hydroxypropyl β-cyclodextrin on the stability of polyphenolic compounds from Moringa oleifera Lam leaf extracts in a natural low-transition temperature mixture

Abstract Polyphenol extracts from Moringa oleifera leaves (MoL) were obtained with a glycerol-based low-transition temperature mixture (LTTM) and a combination of LTTM with 2-hydroxypropyl β-cyclodextrin (HP-β-CD). The extracts were maintained at 4, 22 and 50 °C for 18 days and the antiradical activity (AAR) was recorded to detect modifications in the antioxidant activity of the extracts. AAR displayed a constant decline at every temperature tested, following pseudo first-order kinetics and the decay constants suggested that the presence of HP-β-CD had a protective action, slowing down AAR decline. The analysis of the polyphenolic profiles using liquid chromatography-diode array-mass spectrometry revealed that after storage for 18 days at 50 °C, the major quercetin glycosides occurring in MoL were extensively degraded. Based on the detection of protocatechuic acid in the stored extracts, putative pathways of flavonol glycoside degradation were proposed. It was concluded that the decomposition of these components was mainly responsible for the AAR decline observed.

Characterisation of Polyphenol-Containing Extracts from Stachys mucronata and Evaluation of Their Antiradical Activity

Background: The aromatic plant Stachys mucronata (Lamiaceae) is endemic to the island of Crete (southern Greece), but as opposed to other native Greek members of this family, this species has never been investigated in the past with regard to its polyphenolic composition and antioxidant potency. Methods: Aerial parts of S. mucronata were exhaustively extracted and partly fractionated through partition, using n-butanol and dichloromethane. Results: Following an initial examination, which consisted of estimating the total polyphenol content and the antiradical activity, the n-butanol extract was found to be by far the richest in polyphenols, exhibiting much stronger antiradical activity compared with the dichloromethane counterpart. On this basis, the n-butanol extract was analysed by liquid chromatography-diode array-mass spectrometry, to tentatively characterise the principal polyphenolic components, which were shown to be flavonol but mainly flavone derivatives. Conclusions: The most potent radical-scavenging compounds were detected in the n-butanol fraction of the extracts, suggesting that the most active antioxidants in S. mucronate are relatively polar. The analyses suggested the major constituents to be derivatives of the flavone luteolin, accompanied by apigenin analogues, as well as flavonol glycosides and chlorogenate conjugates.

Natural food colorants derived from onion wastes: Application in a yoghurt product

The valorization of onion (Allium cepa) solid wastes, a 450 000 tonnes/year waste in Europe, by a green extraction method is presented. Polyphenols of onion solid wastes were extracted using eco‐friendly solvents, such as water and glycerol. The 2‐hydroxypropyl‐β‐cyclodextrin was also used as a co‐solvent for the augmentation of the extraction yield. The process has been optimized by implementing a central composite face centered design of experiments, with two replicates in the central point, taking into consideration the following independent variables: glycerol concentration, cyclodextrin concentration and temperature. The assessment of the extraction model was based on two responses: the total pigment yield and the antiradical capacity. LC‐MS analysis was also employed in order to identify polyphenols and colorants of the obtained extracts. The main polyphenols found were quercetin and quercetin derivatives and the main colorant was cyanidin 3‐O‐glucoside. The extract was also tested as a food colorant in a yoghurt matrix. The onion leaf extract was found to be a stable natural colorant and could be utilized as an alternative ingredient to synthetic coloring agents.

Polyphenol extraction from Origanum dictamnus using low-transition temperature mixtures composed of glycerol and organic salts: Effect of organic anion carbon chain length

ABSTRACT Novel low-transition temperature mixtures (LTTMs), composed of glycerol and sodium acetate, sodium propionate, and sodium butyrate, were synthesized with the aim to investigate the organic anion chain length effect on the performance of polyphenol extraction from the medicinal plant Origanum dictamnus. The LTTMs used as hydrogen bond donor:hydrogen bond acceptor molar ratio of 6:1 and after establishing optimal conditions of water content and liquid-to-solid ratio by response surface methodology, kinetics was performed to identify the highest efficient system. The results drawn indicated that the longer the anion chain length, the higher the requirement for water content to achieve optimal total polyphenol yield. Extractions with LTTMs comprising of sodium propionate and sodium butyrate gave virtually equal yields in total polyphenols, yet extraction with the former solvent was significantly less energy-demanding, with the activation energy being 8.77 kJ mol−1. Liquid chromatography-diode array-mass spectrometry analyses revealed that the extract obtained with glycerol/sodium propionate at 70 °C also displayed a richer polyphenolic profile, while the antioxidant activity of the extract was not negatively affected up to this temperature. This novel green solvent is therefore proposed as a highly efficient means of recovering bioactive polyphenols from plant material.