Microwave‐assisted extraction in goji berries: effect on composition and bioactivity,evaluated through conventional and nonconventional methodologies

This study aimed to evaluate the effect of microwave‐assisted extraction (MAE) parameters on the composition and bioactivity of goji (Lycium barbarum) extracts. Extracts were obtained under a central composite design combination of experimental conditions, and characterised through HPLC‐DAD; their bioactive capacity was ascertained for antimicrobial and antioxidant capacity, the later by spectrophotometric [2,2‐azinobis (3‐ ethylbenzothiazoline‐6‐sulfonic acid) diammonium salt‐radical scavenging activity assay – 413–748 mg ascorbic acid equivalents/100 g DW and oxygen radical absorbance capacity – 1901–2292 mg trolox equivalents/100 g DW] and electrochemical (DNA‐based sensor – 3571–6602 mg ascorbic acid/100 g DW) methods. The quantitative profile of phenolic compounds was strongly dependent on MAE conditions. Significant correlations were found between the presence of several flavonoids and solvent composition, as well as between phenolic acids with methoxy group and the response to DNA‐based sensor. Results may improve targeted extractions for specific compounds, leading to the achievement of extracts richer in antioxidant capacity, as well as in the tailoring of the biosensor response sensitivity to the composition of the extracts under analysis.     

Optimisation of microwave‐assisted extraction of prune (Prunus domestica) antioxidants by response surface methodology

Optimal conditions for microwave‐assisted extraction (MAE) of total phenols (TP), epicatechin gallate and antioxidant activity from prune (Prunus domestica), rejected in transformation process of plum to prune, were determined by response surface methodology. The central composite design was used to study the effects of three independent variables: microwave power, irradiation time and solvent polarity on the TP, epicatechin gallate and antioxidant activity. Epicatechin gallate was identified as a major phenolic compound in prune extract by RP‐HPLC. Microwave power and irradiation time significantly affected all responses (P < 0.01). The highest TP (598.89 mg GAE/100 g prune) was obtained using water as an extraction solvent at 500 W, during 115 s. However, the optimal conditions for epicatechin gallate extraction were ethanol 80%, 435 W and 120 s. MAE is more efficient than conventional extraction method to obtain TP from prune. The experimental values were reasonably close to the predicted values confirming the validity of the predicted models.     

Ultrasound‐assisted extraction of polyphenols from potato peels: profiling and kinetic modelling

Ultrasound‐assisted extraction (UAE) at 33 and 42 kHz has been investigated in the extraction of polyphenols from peels of two potato varieties, cream‐skinned Lady Claire (LC) and pink‐skinned Lady Rosetta (LR), commonly used in snack food production. Extraction efficacy between the UAE‐untreated (control) and the UAE‐treated extracts was assessed on the total phenolic content and antioxidant capacities (DPPH and FRAP). Application of UAE showed significantly higher recovery of phenolic compounds compared to solid–liquid extraction process alone. Lower ultrasonic frequency (33 kHz) was more effective in recovering polyphenols compared to 42 kHz ultrasonic treatment. The liquid chromatography‐tandem mass spectrometry revealed that chlorogenic acid and caffeic acid were the most prevalent phenolics in LR peels, whereas caffeic acid was dominant in LC peels. Peleg's equation showed a good correlation (R² > 0.92) between the experimental values and the predicted values on the kinetics of UAE of phenolic compounds.     

Green method for determination of phenolic compounds in mung bean (Vigna radiata L.) based on near‐infrared spectroscopy and chemometrics

Mung bean grains exhibit high level of antioxidant activity due the presence of phenolic compounds. Near‐infrared spectroscopy (NIRS), in conjunction with chemometrics, was used to develop a rapid, nondestructive, chemical free and easy‐to‐use method to determine these compounds in sixty genotypes of mung bean. NIRS calibration curve with high‐performance liquid chromatography (HPLC) as reference method was used to determine phenolic compounds (catechin, chlorogenic acid, caffeic acid, p‐coumaric acid, t‐ferulic acid, vitexin, isovitexin, myricetin, quercetin and kaempferol). It was observed that partial least square regression (PLSR) model in the wavelength range of 1600–2500 nm with standard normal variate (SNV) and linear baseline correction (LBC) as preprocessing techniques can measure phenolic compound accurately (R² > 0.987) with root‐mean‐square error less than 1.82%. This study shows that NIRS along with chemometrics is an accurate method to estimate the phenolic compounds rapidly and nondestructively.     

Microwave irradiation enhances the in vitro antifungal activity of citrus by‐product aqueous extracts against Alternaria alternata

The effect of two lemon by‐product aqueous extracts at different concentrations (14, 7, 3.5 and 1 mg mL^?1) was tested against the in vitro growth of Alternaria alternata. Prior to extraction, one batch of by‐product was dehydrated by freeze‐drying (untreated by‐product), while the other batch was treated by microwave irradiation in conjunction with freeze‐drying (microwave‐treated by‐product). High‐performance liquid chromatography (HPLC) was employed for the identification of individual phenolic compounds with potent antifungal activities. Both lemon by‐product aqueous extracts inhibited the mycelial growth and suppressed the spore germination of the fungus in a concentration‐dependent manner. In general, the extracts obtained from the microwave‐treated lemon by‐product displayed enhanced antifungal activity than those obtained from the untreated one. Scanning electron microscopy (SEM) revealed that both lemon by‐product extracts affected the hyphal morphology of the fungus. The antifungal activity of the extracts was attributed to their phenolic acid and ascorbic acid contents.     

Characterisation of black cumin,pomegranate and flaxseed meals as sources of phenolic acids

The article focuses on the extraction of ten phenolic acids from black cumin (Nigella sativa L.), pomegranate (Punica granatum L.) and flax (Linum usitatissimum L.) seed meals. The extracts have been fractionated as free, esterified and insoluble‐bound phenolic compounds and quantitatively determined by HPLC–PDA. The analysed meals can be utilised for obtaining valuable phenolic acids. However, the distribution of phenolic compounds varies depending on the meal source. The insoluble‐bound fraction has been the richest for the black cumin meal, both qualitatively and quantitatively, containing all ten analysed phenolics. In the pomegranate meal, the main phenolic has been gallic acid, accounting for nearly 48% in free form. The esterified form of the flaxseed meal has been abundant with ferulic (1025.44 ± 3.99 mg kg^?1 dry weight), caffeic and p‐coumaric acids. The total amount of phenolic acids would be underestimated if only free fractions would be taken into account, while neglecting esterified (for the pomegranate and flax meals) and insoluble‐bound fractions (for the black cumin and pomegranate meals).     

The Phenolic Compounds,Metabolites, and Antioxidant Activity of Propolis Extracted by Ultrasound‐Assisted Method

The influences of ultrasound‐assisted, pharmacopeia, and supercritical fluid extraction methods on bioactive compounds and biological activities of propolis were evaluated. Results showed that propolis extracted by ultrasound‐assisted method contained more phenolic compounds, and showed the highest total phenolic content (245.84 ± 6.41 mg GAE/g DW), total flavonoids content (198.82 ± 5.74 mg RE/g DW), and stronger in vitro antioxidant activity (DPPH·: 1.03 ± 0.04 mmol Trolox/g DW, ABTS+·: 2.19 ± 0.05 mmol Trolox/g DW, and FRAP: 1.48 ± 0.12 mmol FeSO₄/g DW) than those of pharmacopoeia and supercritical fluid methods. A total of 36 phenolic compounds were identified in propolis. Among them, quercetin, quercetin‐3‐methyl‐ether, kaempferol, isorhamnetin, luteolin‐methyl‐ether, and quercetin‐7‐methyl‐ether could only be found in ultrasound‐assisted and pharmacopoeia methods. Moreover, the phenolic compounds had the similar metabolic pathways in rats and were mainly metabolized by sulfation and glucuronidation pathways. Additionally, ultrasonic‐treated propolis have good in vivo antioxidant activity and could repair D‐galactose‐induced oxidative damage in rats. Therefore, ultrasound‐assisted method could replace pharmacopeia method to be considered as bioactive compounds extraction from propolis, taking into consideration of yield, short extraction time, and high antioxidant activity.     

ULTRASONICALLY ASSISTED EXTRACTION OF PHENOLIC COMPOUNDS FROM AROMATIC PLANTS: COMPARISON WITH CONVENTIONAL EXTRACTION TECHNICS

Extracts of aromatic plants contain bioactive substances such as phenolic compounds, which could be used as natural antioxidants. Conventional, as well as ultrasonically assisted extractions (UAEs ) of phenolic compounds from aromatic plants using different solvents, have been studied. Reversed phase high performance liquid chromatography (RP‐HPLC ) with ultraviolet detection was employed for the analysis of phenolic compounds. Total phenolic compounds were determined by the Folin–Ciocalteu assay. The amount of extractable phenolic substances for this method decreased with decreasing polarity of the solvent in the order water, 60% methanol, 60% acetone, and ethyl acetate/water (60:30, v/v). The HPLC results indicate that UAE is a more effective technic compared to the conventional method but was dependent on the solvent and the temperature employed. Increasing the temperature of sonication, the efficiency of extraction of phenolic compounds for all solvents is enhanced. However, water extraction was found to give reduced amounts of phenolic compounds when compared with the conventional method.     

Comparative evaluation of microwave‐assisted extraction and preheated solvent extraction of bioactive compounds from a plant material: a case study with cabbages

Preheated solvent extraction (PSE) was evaluated via the analysis of the extraction kinetics, microstructure of extracted samples and energy consumption as alternative to microwave‐assisted extraction (MAE). Cabbage outer leaves and ethanol were used as test material and extraction solvent, respectively. MAE was first optimised in terms of glucosinolates and phenolics yields; total antioxidant activity of the extracts was also assessed. MAE at a specific absorbed power of 0.37 W g^?1 for 9 min was selected as optimum condition to extract glucosinolates and phenolics, while PSE was optimised at 6 min of the extraction. The highest normalised total glucosinolates and phenolic contents as well as antioxidant activities of the extracts obtained via MAE were not significantly different from those obtained via PSE. Confocal laser scanning microscopy revealed no significant differences in cabbage cell damages rendered by MAE and PSE. PSE nevertheless exhibited slightly higher specific energy consumption than MAE.     

Influence of ethanol/water ratio in ultrasound and high‐pressure/high‐temperature phenolic compound extraction from agri‐food waste

The valorisation and management of agri‐food waste are currently hot investigation topics which probe the recovery of valuable compounds, such as polyphenols. In this study, high‐pressure/high‐temperature extraction (HPTE) and ultrasound‐assisted extraction (UAE) have been used to study the recovery of phenolic compounds from grape marc and olive pomace in hydroalcoholic solutions. The main phenolic compounds in both extracts were identified by HPLC‐DAD. Besides extraction yield (total polyphenol and flavonoid content) and the antiradical power, polyphenol degradation under HPTE and UAE has also been studied. HPTE with ethanol 75% gave higher phenolic extraction yields: 73.8 ± 1.4 mg of gallic acid equivalents per gram of dried matter and 60.0 mg of caffeic acid equivalents per gram of dried matter for grape marc and olive pomace, respectively. In this study, the efficient combination of ethanol/water mixture with HPTE or UAE has been used to enhance the recovery of phenolic compounds from grape marc and olive pomace. HPLC‐DAD showed that UAE prevents phenolic species degradation damage because of its milder operative conditions.     

Extraction,identification and enzymatic synthesis of acylated derivatives of anthocyanins from jaboticaba (Myrciaria cauliflora) fruits

Polyphenols were extracted from the skin of jabuticaba fruits (Myrciaria cauliflora). Their total concentration and in vitro antioxidant activity were analysed by the DPPH and ABTS methods. The corresponding results (dry basis) were 1290 mg gallic acid equivalent (GAE)?(100 g)^?1, 98% of DPPH radical inhibition and 120 μm TEAC?g^?1 (ABTS method). All these values are at least as higher as average values reported in the literature for other fruits. A more specific analysis of the fractions of phenolic compounds was also performed by HPLC‐MS. Ellagic acid, quercetin, rutin, delphinidin‐3‐glucoside and cyanidin‐3‐glucoside were the main compounds detected; the latter two were the most abundant. The crude extract was subjected to enzymatic acylation assays in order to synthesise new esters with new potential techno‐functionalities. Palmitic acid was used as acyl donor and lipase B of Candida antactica (CALB) as biocatalyst. HPLC‐MS evidenced the formation of palmitic monoesters in connection with the delphinidin‐3‐glucoside and cyanidin‐3‐glucoside fractions.     

High performance liquid chromatographic analysis of phenolic compounds and their antioxidant activities in rice varieties

The analytical method for the determination of phenolic compounds in rice varieties was developed. The method consisted of extraction of phenolic compounds from rice before analysis by high performance liquid chromatography (HPLC). Reversed phase HPLC equipped with photodiode array detection was used and the separation condition was optimized. Under the optimum condition, twelve phenolic compounds were separated within 24 min. Pressurized liquid extraction (PLE) was used to extract free phenolic compounds from rice with the optimum extraction condition of 70% methanol and extraction time of 15 min. While, bound phenolic compounds were extracted using alkaline hydrolysis for 15 min. Six varieties of Thai rice including pigment and non-pigment rice in their brown and polished forms were investigated. All of 12 phenolic compounds were detected as free phenolic compounds in all samples. Ferulic acid was the most abundant free phenolic compounds in all samples, while ferulic acid and p-coumaric acid were found as bound phenolic compounds in some samples. The content of phenolic compounds, total flavonoid and antioxidant activity detected in pigment rice and brown form were higher than non-pigment rice and polished form.     

Recovery of phenolic compounds from peach pomace using conventional solvent extraction and different emerging techniques

The study compared high-pressure, microwave, ultrasonic, and traditional extraction techniques. The following extraction conditions were implemented: microwave-assisted extraction (MAE) at 900 W power for durations of 30, 60, and 90 s; ultrasonic-assisted extraction (UAE) at 100% amplitude for periods of 5, 10, and 15 min; and high-pressure processing (HPP) at pressures of 400 and 500 MPa for durations of 1, 5, and 10 min. The highest yield in terms of total phenolic content (PC) was obtained in UAE with a value of 45.13 ± 1.09 mg gallic acid equivalent (GAE)/100 g fresh weight (FW). The highest PC content was determined using HPP-500 MPa for 10 min, resulting in 40 mg GAE/100 g, and MAE for 90 s, yielding 34.40 mg GAE/100 g FW. The highest value of antioxidant activity (AA) was obtained by UAE in 51.9% ± 0.71%. The PCs were identified through the utilization of Fourier transform infrared (FTIR) spectroscopy and high-performance liquid chromatography (HPLC). Utilizing multivariate analysis, the construction of chemometric models were executed to predict AA or total PC of the extracts, leveraging the information from IR spectra. The FTIR spectrum revealed bands associated with apigenin, and the application of HPP resulted in concentrations of 5.41 ± 0.25 mg/100 g FW for apigenin and 1.30 ± 0.15 mg/100 g FW for protocatechuic acid. Furthermore, HPLC analysis detected the presence of protocatechuic acid, caffeic acid, p-coumaric acid, and apigenin in both green extraction methods and the classical method. Apigenin emerged as the predominant phenolic compound in peach extracts. The highest concentrations of apigenin, p-coumaric acid, and protocatechuic acid were observed under HPP treatment, measuring 5.41 ± 0.25, 0.21 ± 0.04, and 1.30 ± 0.15 mg/kg FW, respectively.     

Microwave‐assisted extraction optimised with response surface methodology and antioxidant activity of polyphenols from hawthorn (Crataegus pinnatifida Bge.) fruit

Microwave‐assisted extraction (MAE) of polyphenols from hawthorn (Crataegus pinnatifida Bge.) fruit was investigated, and the best combination of extraction parameters was obtained using response surface methodology (RSM). The optimised procedure was achieved by soaking the sample powder with 83% ethanol for 90 min at solid–liquid ratio of 1–20, and then microwave irradiation for 13 min at power of 440 W. Under this condition, an extraction yield of 23.5% was obtained and the percentage of phenolic compounds in the extract reached 41.2%. The total content of polyphenols in hawthorn fruit was 96.9 ± 4.3 mg gallic acid equivalents per gram of dry weight measured by Folin‐Ciocalteu reagent method, and the main phenolic compounds were determined as procyanidin B₂, epicatechin, chlorogenic acid, procyanidin C₁ and rutin. Biological studies showed that the extract possessed a strong inhibitory effect against DPPH, hydroxyl radicals and lipid peroxidation, as well as strong reducing power.     

Process optimisation of microwave‐assisted extraction of peony (Paeonia suffruticosa Andr.) seed oil using hexane–ethanol mixture and its characterisation

Ethanol and hexane mixture agent microwave‐assisted extraction (MAE) method was conducted to extract peony (Paeonia suffruticosa Andr.) seed oil (PSO). The aim of the study was to optimise the extraction for both yield and energy consumption in mixture agent MAE. The highest oil yield (34.49%) and lowest unit energy consumption (14 125.4 J g^?1) were obtained under optimum extraction condition: solid‐liquid ratio 0.37 g mL^?1, extraction time 3.72 min, extraction temperature 80.92 °C, ethanol ratio 20.00%. GC–MS results showed that unsaturated fatty acids (UFAs) accounted for 88.60% of total fatty acids in PSO. Moreover, linolenic acid content of 37.35% was the highest UFA and caused PSO to possess good nutrition. PSO in DPPH radical scavenging experiment showed that IC₅₀ value of 28.80 ± 2.13 mg mL^?1 exhibited strong antioxidant property. All experiments proved that mixed solvent MAE is an efficient and promising method to extract PSO. This method can effectively reduce the energy consumption and extraction time.     

Pulsed electric fields- and ultrasound-assisted green extraction of valuable compounds from Origanum vulgare L. and Thymus serpyllum L.

This work compared the effects of pulsed electric fields (PEF) and ultrasound (US) technologies on the extent of cell disintegration of two Mediterranean herb tissues (Origanum vulgare L., Thymus serpyllum L.), as well as on the extractability of phenolic compounds during the subsequent hydroalcoholic extraction (0%–50% ethanol in water, v/v) for up to 4 h. The rate of phenolic compounds extraction decreased with time and was predicted rather satisfactorily (R² = 0.898–0.989) by the Peleg’s model. The application of either PEF or US treatment prior to solid–liquid extraction (SLE) has the potential to reduce duration and concentration of ethanol to achieve the same recovery yield of phenolic compounds. Under optimised PEF (3 kV cm⁻¹, 10 kJ kg⁻¹) and US (400 W, 20 min) treatment conditions, the extracts obtained from either PEF or US pretreated herb samples showed higher total phenolic yield (36% on average) and antioxidant activity (FRAP) (36% on average) as compared to the control extraction, especially when 25% ethanol was used as a solvent. GC/MS analyses revealed no evidence of degradation of individual phenolics due to either PEF or US application.     

Phenolic content,antioxidant and physico‐chemical properties of Sardinian monofloral honeys

In this study, fifty‐one monofloral Sardinian honeys from ten various floral origins were screened for their phenolic content, antioxidant activity, colour and electrical conductivity. The total phenolic amounts have been evaluated by Folin–Ciocalteu method, whereas quantification of several phenolic compounds (phenolic acids and flavonoids) has been carried out by HPLC‐DAD technique. The richest sample in phenolic compounds resulted strawberry tree honey with about 40 mg GAE/100 g, as well FRAP test and DPPH˙ test confirm that antioxidant activity of strawberry tree honey extract exceed both honey extracts and synthetic antioxidants like BHA and BHT. Among the studied phenolic compounds a total of five phenolic acids (ferulic, syringic, trans‐cinnamic, chlorogenic and p‐hydroxycinnamic) and nine flavonoids (catechin, kaempferol, rutin, quercetin, luteolin, apigenin, galangin, pinocembrin and pinobanksin) were identified. Our results show good correlations between total polyphenol amount and antioxidant activity and between colour and electrical conductivity.     

Evaluation of the extraction efficiency for polyphenol extracts from by‐products of green kiwifruit juicing

The health benefits of fruits are attributable in part to their bioactive components such as phenolics and pectic polysaccharides. By‐products derived from kiwifruit processing can be a good source of such bioactive compounds. Extracts were produced using different concentrations of ethanol in water (0%, 30%, 50%, 74% and 96% v/v) from by‐products (skin, residue and pulp) of the green‐fleshed kiwifruit (Actinidia deliciosa‘Hayward’) juicing process. The amounts of phenolic compounds and uronic acid (UA) as well as the phenolic composition in each extract were determined. Results show that different by‐products contained different concentrations of phenolics and pectic polysaccharides. Based on total phenolic contents, 96% v/v ethanol appeared to be the best extraction medium. The 30% or 74% ethanolic dilution was the second best medium for phenolic extraction from skin and pulp/residue, respectively. Water was a good medium for extracting satisfactory quantities of phenolics as well as the highest concentration of pectic polysaccharides. Phenolic profiling by high‐performance liquid chromatography (HPLC) was used to detect individual phenolic compounds in an extract. Results using HPLC showed that alkali pre‐treatment has improved the extraction efficiency of phenolics as a function of alkali concentration, fruit tissue type, extraction media, by‐product preparation method, and class of polyphenols. As a result more efficient methods for both extraction and characterisation of polyphenols could be evaluated.     

Optimisation of ultrasound extraction for flavonoids from semen astragali complanati and its identification by HPLC‐DAD‐MS/MS

The optimisation of ultrasound extraction of semen astragali complanati flavonoids was studied by measuring characteristic absorbance at 266 nm as the response and using response surface methodology (four‐variable, three‐level Box–Behnken design, BBD) in this article. The optimal conditions were obtained as 52 °C, 34 min, 26:1 (mL:g) and 100 mesh (0.120–0.150 mm) for extraction temperature, extraction time, solvent‐to‐sample ratio as well as particle size, respectively. Under these conditions, validation experiments were carried out and the experimental value of A₂₆₆ was 0.9907 ± 0.032 (n = 3), which corresponded to an experimental extraction yield of 7.08%. Compounds in the extracts obtained with the optimum extraction conditions were identified by high‐performance liquid chromatography coupled with diode array and mass spectrometry detectors (HPLC–DAD–MS). Among the 14 compounds that were tentatively identified in the extracts according to their ultraviolet‐visible spectroscopy, mass spectrometry and related literature reports, four were reported for the first time.     

Two Kaempferol Glycosides Separated from Camellia Oleifera Meal by High‐Speed Countercurrent Chromatography and Their Possible Application for Antioxidation

Recently, kaempferol and its glycosides have attracted considerable attention owing to their potentially health‐benefitting properties including protection against chronic diseases. Here, a microwave‐assisted extraction (MAE) method was developed for the extraction of total flavonoid glycosides (FG) from Camellia oleifera meal, a major agrifood waste largely generated as a byproduct from the Camellia oil processing industry. Compared with traditional extraction methods, MAE enables more efficient extraction of FG. High‐speed countercurrent chromatography was then applied to separate FG from MAE extract, and two major compounds were successfully separated with purities above 90.0% as determined by HPLC. These two compounds were further identified by UV, FT‐IR, ESI‐MS, ¹H‐NMR, and ¹³C‐NMR as kaempferol 3‐O‐[α‐L‐rhamnopyranosyl‐(1→6)‐β‐D‐glucopyranosyl]‐7‐O‐β‐D‐glucopyranoside and kaempferol 3‐O‐[β‐D‐glucopyranosyl‐(1→4)‐α‐L‐rhamnopyranosyl]‐7‐O‐α‐L‐rhamnopyranoside, which were for the first time separated from C. oleifera meal. The results of antioxidant activity assay demonstrated that both compounds had excellent scavenging activity for DPPH radical, and exhibited protective effects against H₂O₂‐induced oxidative damage of vascular endothelial cells. The findings of this work suggest the possibility of employing C. oleifera meal as an attractive source of health‐promoting compounds, and at the same time facilitate its high‐value reuse and reduction of environmental burden.