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Oat bran (OB) may be regarded as food industry by-product, with a high perspective as a bioresource in the production of high-value polyphenolic substances. On this basis, the investigation presented herein aimed at (i) using 1- and 2-propanol organosolv treatment and studying the effect of an alkali (sodium hydroxide) catalyst on releasing bound polyphenols, (ii) establishing models of polyphenol recovery by employing severity and response surface methodology, and (iii) investigating the polyphenolic profile of the extracts produced. Yield in total polyphenols as a function of treatment severity was satisfactorily described by linear models, indicating that for both 1- and 2-propanol treatments, temperature and time could be used interchangeably to adjust severity. Furthermore, the 1-propanol process was found to be more efficient at lower severity compared to the 2-propanol process. The optimization using response surface methodology revealed that, under identical condition settings (t = 300 min, T = 90 °C), the 1-propanol treatment afforded a total polyphenol yield of 17.15 ± 0.51 mg ferulic acid equivalents per g−1 dry mass, whereas the 2-propanol treatment gave a yield of 14.78 ± 1.11 mg ferulic acid equivalents per g−1 dry mass. Liquid chromatography–tandem mass spectrometry analyses showed that the extract produced from the 1-propanol treatment was significantly more enriched in ferulic acid and p-coumaric acid compared to the extract generated with the 2-propanol treatment. Moreover, the antioxidant activity of the extracts was in concurrence with the polyphenolic composition. Based on the evidence, the alkali-catalyzed, 1-propanol organosolv treatment of OB is proposed as a sustainable and efficient methodology to recover multipurpose natural antioxidants.

The encapsulation of clove essential oil (CEO) in hydroxypropyl-β-cyclodextrin (HP-β-CD) and the subsequent incorporation of the inclusion complex in an elastic chitosan film in order to achieve a controlled release profile of the volatile CEO are herein presented. Freshly distilled CEO was found to contain eugenol in concentrations higher than 70%. The kneading method was implemented for the preparation of a CEO-HP-β-CD inclusion complex, resulting in a 50% inclusion efficiency of the essential oil in particles sized 214.40 nm with ζ-potential −27.5 mV. Free CEO and CEO-HP-β-CD inclusion complex were tested for their ability to scavenge the 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical, and it was found that the CEO-HP-β-CD complex presented enhanced antioxidant activity (88%) compared to the free CEO (71%). Choline chloride-containing chitosan (CS) films were prepared, incorporating either the pure CEO or the CEO-HP-β-CD inclusion complex, and their mechanical properties were determined. The study of the release profile in different pH values demonstrated the capacity of the CS-HP-β-CD system to provide sustained release of CEO, noting its potential use in food processing as smart packaging.

The aim of the present study was the encapsulation of cedar (Juniperus phoenicea) essential oil (CEO) of Greek origin in β-cyclodextrin (β-CD) through the formation of inclusion complexes (ICs) using the co-precipitation method with different β-CD-to-CEO weight ratios (90:10, 85:15, 80:20, 70:30 (w/w)). The encapsulation of CEO in β-CD through host–guest interactions was confirmed by Nuclear Magnetic Resonance (NMR) spectroscopy, FT-IR spectroscopy, Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). The obtained ICs exhibited nanoscale size (315.9 nm to 769.6 nm),Polydispersity Index from 0.326 to 0.604 and satisfactory stability in suspension (−37.0 mV to −17.0 mV). The process yield was satisfactory, ranging between 65% and 78%, while the inclusion efficiency ranged from 10% to 27%. The in vitro release study conducted for the IC with the optimal characteristics (β-CD:CEO 80:20 (w/w)) exhibited a sustained release profile, with an initial burst effect in the first 5 h. The release profile could be well expressed by the Higuchi equation: Q = 18.893 t1/2 + 9.5919, R2 = 0.8491. The cedar EO presented significant acetylcholinesterase inhibition (IC50 37 μg/mL), which was prolonged by its encapsulation into the β-CD cavity.

In this study, the chemical content of the threatened Cretan endemic Chaerophyllum creticum Boiss. & Heldr. was investigated by High Performance Liquid chromatography-Photodiode Array-Mass Spectrom...

In a previous study, it was demonstrated that a novel deep eutectic solvent (DES), composed of lactic acid and sodium citrate dibasic at a molar ratio of 15:1 (LA-SCDB15), was a high-performing system with regard to polyphenol extraction from the medicinal plant Salvia fruticosa Mill. (Greek or Cretan sage). However, an issue of particular importance that should be addressed is the stability of the extract in this novel liquid since the information available to-date on extract stability in DES is rather limited and inconclusive. In this frame, this study was undertaken to generate extracts of S. fruticosa with LA-SCDB15 (a 77/23 w/w mixture of DES with water) and examine their stability in this solvent. S. fruticosa extracts exhibited remarkable stability under both accelerated and long-term conditions, and the antiradical activity and the ferric-reducing power of the extracts were shown to suffer virtually trivial modifications. Further analytical examination with liquid chromatography-diode array-tandem mass spectrometry assured that the major polyphenolic phytochemicals occurring in Salvia fruticosa extracts underwent non-significant changes and remained practically intact. It was concluded that the neoteric DES LA-SCDB15 may provide outstanding stability in polyphenol-containing extracts and its testing on other plant extracts is proposed as a further step towards revealing its stabilizing potential.

Polyphenols are commonly retrieved from plant material with solid-liquid extraction, the optimization of which requires fundamental laboratory-scale investigation, to clearly identify variables and...

The aim of this study was the examination of the effect of ultrasonication pretreatment and thermal treatment of soft wheat bran (SWB) with a novel acidic, tertiary deep eutectic solvent, composed of glycerol/citric acid/glycine, on the polyphenol extraction yield and antioxidant activity. This was achieved by sequentially deploying ultrasonication pretreatment and prolonged thermal treatment (extraction). Ultrasonication prior to stirred-tank extraction was shown to afford significantly higher total polyphenol yield compared to aqueous control solvents. Furthermore, thermal treatment had a striking effect on SWB polyphenol extraction, which increased from 6.31 ± 0.06 mg ferulic acid equivalents (FAE) g− 1 dry mass (dm) (50 °C, 2.5 h) to 57.12 ± 1.14 mg FAE g− 1 dm (90 °C, 24 h). Combination of ultrasonication pretreatment and thermal treatment boosted even more extraction yield at 94.62 mg FAE g− 1 dm. Comparison of glycerol/citric acid/glycine with other common deep eutectic solvents demonstrated that this particular solvent was an exceptionally high-performing system. Liquid chromatography-tandem mass spectrometry analyses showed that the SWB extract produced with glycerol/citric acid/glycine deep eutectic solvent was dominated by polar compound(s), as opposed to acid and alkaline hydrolyzates, which contained virtually only ferulic acid. It was concluded that this investigation could be expanded by designing and screening task-specific deep eutectic solvents (DES) for improved extraction efficiency under less severe thermal treatment conditions. This would contribute towards the establishment of less energy-demanding processes for wheat bran polyphenol recovery.

Olive leaves (OLL) are an agri-food waste that may be regarded as a bioresource rich in bioactive polyphenolic metabolites. In this examination, simultaneous organosolv treatment/extraction of OLL polyphenols at elevated temperatures (>110 °C) has been optimized using glycerol, but also two glycerol-based deep eutectic solvents (DES). The assessment of the processes was based on the severity factor and the extraction efficiency factor. In any case, the treatment/extraction with a DES composed of glycerol and citric acid (GL-CA) was found to be the less severe and the most effective in recovering polyphenols from OLL, giving a yield of 69.35 mg gallic acid equivalents per g dry mass. On the other hand, liquid chromatography-mass spectrometry investigation revealed that extraction with either DES used provided extracts with differentiated polyphenolic profile than that obtained when water or 60% (v/v) aqueous ethanol was used as solvents. On the ground of these analysis, evidence emerged regarding hydrolysis of flavone glucosides when the treatment was performed with an alkaline DES composed of glycerol and sodium citrate. The extracts produced also exhibited diversified antioxidant activity, a fact putatively attributed to the different polyphenolic profiles. It was concluded that organosolv treatment/extraction of OLL for polyphenol recovery opens new endeavors in the valorization of this particular waste, but metabolite stability is an issue that merits profounder study.

This investigation had as objective to study the effective recovery of olive leaf (OLL) polyphenols using a blend of an L-lactic acid/ammonium acetate deep eutectic solvent (DES) with β-cyclodextrin (β-CD). Following an initial DES screening, the extraction process was optimised with response surface methodology by implementing Box-Behnken design. The optimised extraction conditions thus determined were stirring speed 300 rpm, DES concentration 56.4% (w/w), liquid-to-solid ratio 100 mL g−1 and β-CD concentration 0.7% (w/v). Maximum extraction yield (113.66 mg caffeic acid equivalents g−1 dry mass) was achieved at 80 °C, without compromising antioxidant activity. Comparative assessment of the extraction medium DES/β-CD with other green solvents showed that it was a high-performing system providing polyphenol-enriched extract with improved antioxidant characteristics. Stability test of the extract obtained under optimal conditions performed over a period of 30 days at ambient conditions revealed that, while ferric-reducing power fluctuated within narrow limits, the antiradical activity was enormously enhanced by 100%. These changes in the antioxidant activity were not associated with the decline of major polyphenols in the OLL extract. However, the overall polyphenolic profile remained largely unchanged. It is suggested that the DES/β-CD is an efficient green solvent that may confer the OLL polyphenol extract satisfactory stability.

The objective of the study presented herein was the optimisation of onion solid waste (OSW) polyphenol extraction, using sodium propionate-based deep eutectic solvents (DESs) and process variables optimised through response surface methodology. Initial screening of several novel DESs composed of either L-lactic acid or glycerol as hydrogen bond donors, and sodium propionate as the hydrogen bond acceptor, showed that the DES with glycerol/sodium propionate at a molar ratio 8:1 was the highest-performing system. Extraction optimisation showed that theoretical optimal settings were 85% (w/w) aqueous DES, 100 mL g−1 liquid-to-solid ratio and a stirring speed of 900 rpm. Under these conditions, the temperature assay demonstrated that extraction may be performed at 80 °C, without compromising total polyphenol yield and antioxidant activity. Comparison with other green solvents showed that the DES tested could provide extracts with high flavonoid concentration and superior ferric-reducing power. The stability test performed over a period of 30 days suggested that OSW extract may suffer no significant alterations in the polyphenolic profile, but the antiradical activity may be enhanced. Changes in the antioxidant behaviour were not correlated with changes in the two major OSW constituents, quercetin 4′-O-glucoside and quercetin.

This study aimed at investigating the effect of L-cysteine on the Cu2+-induced oxidation of quercetin, within a pH range varying from 6.7 to 8.3 and temperatures varying from 53 to 87 °C. Initial e...

Quercetin (Qt) is a natural flavonoid of high biological significance, and it occurs in a wide variety of plant foods. Although its oxidation by various means has been extensively studied, its behavior with regard to thermal treatments remains a challenge. The study described herein aimed at investigating Qt thermal decomposition, by proposing an empirical sigmoidal model for tracing degradation kinetics. This model was employed to examine the effect of addition of antioxidants on Qt thermal degradation, including ascorbic acid, L-cysteine, and sulfite. Furthermore, degradation pathways were proposed by performing liquid chromatography-tandem mass spectrometry analyses. Upon addition of any antioxidant used, the sigmoidal course of Qt thermal degradation was pronounced, evidencing the validity of the empirical model used in the study of similar cases. The antioxidants retarded Qt degradation in a manner that appeared to depend on Qt/antioxidant molar ratio. No major differentiation in the degradation mechanism was observed in response to the addition of various antioxidants, and in all cases protocatechuic acid and phloroglucinol carboxylic acid were typical degradation products identified. Furthermore, in all cases tested the solutions resulted after thermal treatment possessed inferior antioxidant properties compared to the initial Qt solutions, and this demonstrated the detrimental effects of heating on Qt. The empirical model proposed could be of assistance in interpreting the degradation behavior of other polyphenols, but its validity merits further investigation.

In this study, the chemical content of the threatened Cretan endemic

The aim of the present study is to quantify hydrogen peroxide, generated from various types of honey produced in Crete, as a potent antimicrobial agent, and establish any correlation with their physicochemical parameters. The basic physicochemical parameters (diastase activity, HMF content, moisture, electrical conductivity, color, and sugars) of 30 authentic honey samples were determined. The concentration of hydrogen peroxide in all samples was found to be within the range 0.010–0.092 mM. The known correlation between the electrical conductivity and the color of honey was confirmed in this study. Univariate and multivariate statistics applied to the results indicate that the results can be used to discriminate honey sample groups of different botanical origins.

A series of citrate salts were tested as hydrogen bond acceptors to synthesize deep eutectic solvents (DES) based on lactic acid and glycerol, used as hydrogen bond donors. The DES produced were then screened to identify the highest performing system for the effective extraction of polyphenolic phytochemicals from the medicinal plant Salvia fruticosa Mill. (Greek sage). The most efficacious DES was the one composed of lactic acid and sodium citrate dibasic, at a molar ratio of 15:1 (LA-SCDB15). Furthermore, for the first time there has been evidence concerning DES pH and extraction efficiency. Using this solvent, a batch, stirred-tank extraction process was developed, by employing ultrasonication pretreatment and response surface methodology. The optimal settings determined were stirring speed 900 rpm, proportion of DES/water 77% (w/v), and ultrasonication pretreatment time 15 min. By adjusting these optimal settings, the predicted maximum total polyphenol yield was calculated to be 79.93 &plusmn, 1.92 mg gallic acid equivalents g&minus, 1 dry mass. The examination of temperature effects demonstrated that the batch, stirred-tank extraction stage was very energy-efficient, with a barrier of 7.64 kJ mol&minus, 1. Comparison of the extraction of Salvia fruticosa polyphenols with other green processes previously developed, illustrated the high extraction capacity of LA-SCDB15. The major polyphenols identified in the extracts produced under optimized settings were chlorogenic acid, luteolin 7-O-glucuronide and rosmarinic acid.

Salvia fruticosa Miller, also known as Cretan or Greek sage, is a medicinal plant with significant biological properties, which are largely ascribed to its polyphenolic composition, but there is to-date a scarcity of green and sustainable processes for efficient polyphenol extraction from this plant. The objective of this study was the implementation of an extraction process that would combine a green solvent based on glycerol, a biodiesel industry by-product, and ultrasonication pretreatment. Ultrasonication for 40 min followed by stirred-tank extraction was shown to provide significantly higher total polyphenol yield than mere stirred-tank extraction, while kinetics indicated 50 &deg, C as the most favorable temperature, with the yield being 92 mg gallic acid equivalents (GAE) per g dry mass. Comparison of this method with a previously developed one that used methyl &beta, cyclodextrin revealed that the extracts obtained had similar antioxidant activity, and yield in major polyphenols including luteolin 7-O-glucuronide and rosmarinic acid was virtually equal. The current process is proposed as a sustainable and effective methodology for the generation of polyphenol-enriched extracts from S. fruticosa, which could be used as effective food antioxidants/antimicrobials and/or cosmetic constituents.

S. fruticosa, collectively known as Cretan sage, is a medicinal plant to which a number of bioactivities have been attributed. In spite of its importance in nutrition and pharmacy, reports on the extraction of major polyphenols using sustainable processes are particularly limited. In this study, three common cyclodextrins, namely, methyl &beta, cyclodextrin (m-&beta, CD), hydroxypropyl &beta, cyclodextrin (HP-&beta, CD), and &beta, cyclodextrin (&beta, CD), were tested as green boosters of aqueous extraction of polyphenols from aerial parts of S. fruticosa. To examine simultaneously important extraction parameters, including the concentration of cyclodextrins (CCD), pH, and liquid-to-solid ratio (RL/S), a Box&ndash, Behnken design was chosen, with three central points. Temperature effects on the extraction yield were also considered, by carrying out kinetics. The results showed that m-&beta, CD was the most effective extraction booster, providing total polyphenols yields that amounted to 98.39 mg gallic acid equivalents g&minus, 1 dry mass. The kinetic assay demonstrated that extraction was highly effective at 80 &deg, C, increasing significantly polyphenol yield, as well as the ferric-reducing power and antiradical activity of the extracts. It was also proven that extraction with m-&beta, CD was the least energy-demanding process. Liquid chromatography-tandem mass spectrometry examination revealed that m-&beta, CD might possess higher affinity for luteolin 7-O-glucuronide extraction, but &beta, CD for rosmarinic acid extraction.

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 ch...

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.

Polyphenol-containing extracts from olive (Olea europaea) leaves (OLL) were obtained using a glycerol-based deep eutectic solvent (DES) and a combination of DES with methyl β-cyclodextrin (m-β-CD). The extracts were stored at various temperatures for a period of 20 days and the reducing power (PR) was monitored to trace changes in the antioxidant potency of the extracts. Over the examination period and at every temperature tested, PR displayed a constant decline, which followed pseudo zero-order kinetics. The determination of the decay constants indicated that the presence of m-β-CD acted protectively, slowing down the progression of the PR decline. Examination of the polyphenolic profiles using liquid chromatography–diode array–mass spectrometry showed that after storage for 20 days at 50 °C, some major polyphenols occurring in OLL suffered extended degradation. The formation of a yellow pigment in the extracts stored in DES but not in aqueous ethanol suggested that polyphenol oxidation did occur during storage. It was concluded that the oxidation of some OLL components was rather responsible for the PR decline observed.

A novel LTTM composed of glycerol and sodium acetate was used to assess the effect of 2-hydroxypropyl β-cyclodextrin (CD) on the effectiveness of polyphenol extraction from M. oleifera leaves (MoL). The extraction process was based on a 23-full factorial design and response surface methodology, to evaluate simultaneously the effect of CD concentration (CCD), liquid-to-solid ratio (RL/S) and temperature (T). By employing optimized conditions (CCD = 1%, RL/S = 40 mL g−1, T = 40 °C), the yield in total polyphenols (YTP) was 67.18 ± 5.04 mg gallic acid equivalents per g dry weight. This yield was significantly higher than that achieved with the extraction performed with LTTM alone or 80% aqueous ethanol. The extraction kinetics suggested that the extraction rate was slowed down in the presence of CD, without compromising the higher extraction capacity of the LTTM/CD. Extract characterization by means of liquid chromatography-mass spectrometry showed that there was no selective extraction of any particular polyphenol, indicating that CD acted only as an extraction booster.

Medicinal and aromatic plants (MAPs) have always been a source of a vast variety of secondary metabolites with high biological potency. There is to-date an enormous ongoing research on the development of sophisticated methodologies for the production of bioactive MAP extracts, which may be applied in a spectrum of products, such as foods, pharmaceuticals and cosmetics. A great concern in implementing an extraction protocol is the use of appropriate conditions to achieve maximum efficiency with minimum cost, energy, and environmental aggravation. Although several parameters may affect the effectiveness of an extraction process, time and temperature are of utmost importance, and largely define both operating cost and quality of the final extract. Thus, there is a need for a simple tool of assessing an extraction method and allow for sound comparisons. In such a frame, this study introduces for the first time the concept of “extraction efficiency factor” (FEE). The purpose was to combine time (t) and temperature (T) in a single factor for evaluating extraction processes in general, and to enable easy and sound comparison of results obtained by solid-liquid extractions of MAPs. Such an approach could facilitate process control and would permit trading time and temperature of a treatment such that equivalent final effects are obtained.

The aim of the present study was the encapsulation of Rosmarinus officinalis essential oil (REO) in β-cyclοdextrin (β-CD) and two chemically modified β-CD matrices and the evaluation of the antibacterial activity of the prepared inclusion complexes against Staphylococcus aureus. The inclusion complexes possessed nanoscale size ranging from 395.7 ± 13.7 to 594.9 ± 18.8 nm, good size dispersion (0.366 ± 0.009 to 0.482 ± 0.043) and satisfactory stability in suspension (ζ-potential, −24.3 ± 4.2 to −31.5 ± 4.9 mV), while the inclusion efficiency ranged from 65% to 78%. The in vitro release profiles of the inclusion complexes revealed an initial burst effect, with the release kinetics being better fitted on the Higuchi model following quasi-Fickian diffusion. The antibacterial activity of the inclusion complexes of REO in β-CD, HP-β-CD and Me-β-CD against S. aureus was evaluated for 3 days and it was observed that both β-CD and HP-β-CD exhibited prolonged activity in comparison to the pure REO.

The medicinal plant Satureja thymbra (pink savory) has been chosen to study the capacity of three newly designed glycerol-based, natural low-transition temperature mixtures (LTTMs) to extract polyphenolic antioxidants. First, it was assessed the effect of water concentration ( C W ) and the liquid-to-solid ratio (R L/S ), by deploying response surface methodology (Box-Behnken design). As a further step, kinetics was investigated to examine the effect of temperature. It was found that the optimum C W varied from 54.8 to 63.8% (v/v) and R L/S from 29.5 to 36.2 mL g −1 . Under optimised conditions, all three LTTMs displayed apparent anti-Arrhenius kinetics over a temperature ranging from 40 to 80 °C, evidencing peculiar extraction behaviour. The investigation of the polyphenolic composition of the extracts obtained by liquid chromatography-diode array-mass spectrometry showed that the major constituents were apigenin, luteolin, quercetin and rosmarinic acid derivatives, but none of the LTTMs exhibited notable selectivity. However, significant differences were seen with regard to the antiradical activity and reducing power of the extracts, as extract obtained with LTTM1 displayed consistently strong effects, whereas the extract obtained with LTTM3 had rather questionable efficiency.

A novel deep eutectic solvent (DES) with optimised composition was used to evaluate the effect of methyl β-cyclodextrin (CD) on the efficiency of polyphenol extraction from Olea europaea leaves (OLLs). The process developed was based on a 23 full-factorial design and response surface methodology to assess the simultaneous effect of CD concentration (C CD), liquid-to-solid ratio (R L/S ) and temperature (T). Under optimised conditions (C CD = 9%, R L/S = 40 mL g−1, T = 51 °C), the yield in total polyphenols (Y TP) was 116.65 ± 3.60 mg gallic acid equivalents per g dry weight. This value was significantly higher than that determined for the extraction performed with 60% aqueous ethanol. The extraction kinetics also showed that the extraction rate was slowed down in the presence of CD, yet the higher extraction capacity of the DES/CD medium was confirmed. Characterisation of the extracts obtained with DES/CD and DES by means of liquid chromatography-mass spectrometry demonstrated that there was no selective extraction of any particular polyphenol, suggesting that CD acted merely as an extraction booster.

A number of biological activities have been attributed to polyphenolic substances occurring in the leaves of the olive tree (Olea europaea), an olive oil industry waste material, and for this reason several extraction processes have been developed for the efficient recovery of these phytochemicals. The study presented herein describes for the first time the use of an eco-friendly deep eutectic solvent (DES) as a highly effective solvent for the extraction of polyphenols from olive tree leaves. Initially, a central composite design was implemented to optimise solvent composition and liquid-to-solid ratio and then a kinetic assay was performed to investigate diffusivity (D e) and temperature effects. The maximum total polyphenol yield was 106.25 mg gallic acid equivalents per g dry weight, achieved at 70 °C. This value was by 18% higher than that achieved with 60% aqueous methanol. Furthermore, the DES extract exhibited significantly higher antiradical activity and reducing power. Temperature increase up to 70 °C was shown to boost D e and the activation energy determined for the process was 29.55 kJ mol−1. Characterisation of the extract by means of liquid chromatography–diode array–mass spectrometry showed oleuropein and certain flavone glycosides to be the major polyphenolic constituents.

In this study, the extraction of polyphenols from Moringa oleifera leaves was investigated, using a biomolecule-based low-transition temperature mixture (LTTM), composed of glycerol and sodium acetate. The first step was to optimise LTTM concentration (C LTTM) and the molar ratio (R mol) of glycerol-to-sodium acetate, by employing a Box–Behnken experimental design. Following this, a kinetic assay was undertaken to assess the effect of temperature. A maximum yield in total polyphenols (Y TP = 53.80 mg gallic acid equivalents per g lyophilised material) was achieved using a C LTTM = 80% (w/v) and a R mol = 6. The extraction followed a second-order model, requiring activation energy (E a) of 55.71 kJ mol−1. Comparative evaluation using 80% ethanol showed that the LTTM used was significantly more efficient in extracting polyphenols and flavonoids, yielding extracts with higher reducing power. However, results concerning the antiradical activity were contradictory. Liquid chromatography–diode array–mass spectrometry examination of both the LTTM and the hydroalcoholic extracts revealed some qualitative differences, which might indicate selectivity of the LTTM towards relatively polar substances.

The current investigation was undertaken to examine saffron processing waste (SPW) as a bioresource, which could be valorized to produce extracts rich in antioxidant polyphenols, using a green, natural deep eutectic solvent (DES). Initially, there was an appraisal of the molar ratio of hydrogen bond donor/hydrogen bond acceptor in order to come up with the most efficient DES composed of L-lactic acid/glycine (5:1). The following step was the optimization of the extraction process using response surface methodology. The optimal conditions thus determined were a DES concentration of 55% (w/v), a liquid-to-solid ratio of 60 mL g&minus, 1, and a stirring speed of 800 rounds per minute. Under these conditions, the extraction yield in total polyphenols achieved was 132.43 &plusmn, 10.63 mg gallic acid equivalents per g of dry mass. The temperature assay performed within a range of 23 to 80 &deg, C, suggested that extracts displayed maximum yield and antioxidant activity at 50&ndash, 60 &deg, C. Liquid chromatography-mass spectrometry analysis of the SPW extract obtained under optimal conditions showed that the predominant flavonol was kaempferol 3-O-sophoroside and the major anthocyanin delphinidin 3,5-di-O-glucoside. The results indicated that SPW extraction with the DES used is a green and efficient methodology and may afford extracts rich flavonols and anthocyanins, which are considered to be powerful antioxidants.

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 134.54 mg gallic acid equivalents per g of dry weight and a total pigment yield of 3.32 mg 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.

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.

A novel natural low transition temperature mixture (LTTM), composed of glycerol and ammonium acetate (molar ratio 3:1), was tested for its efficacy as a solvent in recovering phenolics from chlorogenate-rich agri-food solid wastes, including potato peels (PPs), eggplant peels (EPPs), and spent filter coffee (SFC). The efficacy of this solvent was compared with other eco-friendly solvents, including aqueous glycerol, aqueous ethanol, and water. The LTTM was demonstrated to be by far the most efficient in extracting chlorogenates and superior or equally efficient with the other solvents in recovering flavonoids. LTTM extracts produced from waste were also more potent radical scavengers, but results on the reducing power were inconclusive. Liquid chromatography-diode array-mass spectrometry analysis showed that the polyphenolic profiles of all waste extracts obtained with the LTTM were rich in caffeoylquinic and p-coumaroylquinic acid conjugates.