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Abstract: Nowadays, free radical chemistry is a field that has gained the wider attention of researchers. Our body generates free radicals’ reactive nitrogen and oxygen species through subjection to several pathological states, endogenous systems, and physicochemical conditions. For the physiological state to occur, it is compulsory to propel a balance between antioxidants and free radicals. Oxidative stress will set in when free radicals can no longer be regulated in the body system. Moreover, free radicals negatively affect DNA, protein, and lipids and cause many diseases in the human body. Thus, natural-sourced antioxidants can be used to manage this oxidative stress. Currently, it has been revealed that some synthetic antioxidants, including butylated hydroxyanisole and butylated hydroxytoluene, are hazardous to human health. Therefore, many efforts have been made in search of natural, non-toxic, and effective compounds that possess anti-oxidative properties. Hence, this review comprehensively presents the roles of plant-based antioxidants in resolving the challenging issues associated with free radical diseases in human beings. It further reviews the characteristics and occurrences of free radicals in the human body, the formation and mechanism of free radicals, some of the physiological impacts of free radicals on human health, sources of free radicals, and plant-sourced antioxidants as a frontier in managing free radicals.

Phenolic compounds are parts of secondary metabolites mostly found in plant species with enormous structural diversities. They can exist as glycosides or aglycones; matrix or free-bound compounds; and comprising mostly polymerized or monomer structures. Additionally, these compounds are not universally dispensed within plants with varied stability. This has contributed to challenging extraction processes; implying that employing a single step or inappropriate extraction technique might change the recovery of phenolic components from the plant samples. Hence, it is important to select an appropriate extraction method so as to recover the targeted phenolic compounds. This is will helps to recover substantial yields from the sample matrix. Therefore, this review mainly focuses on the phenolic compounds and several methods of extraction that are used to obtaining them from plant materials. These extraction methods includes both conventional and unconventional techniques., Graphical abstract Image 1, Highlights • Phenolic compounds from natural sources. • Methods of extracting phenolic compounds. • Selection of an appropriate extraction method to recover the targeted phenolic compounds from plant materials.

Phenolic compounds are essential for growth, pigmentation, resistance to pathogens, reproduction, and among others. This study focused on the optimization of microwave-assisted extraction process variables, i.e., solvent/sample ratio (X1), irradiation time (X2) and microwave power (X3), based on the yields of total phenolic content (TPC) and total flavonoid content (TFC) from Ocimum gratissimum leaf using Box Behnken Design. Furthermore, the chemical compounds in the extract under optimized MAE conditions were identified using LC–ESI–MS/MS analysis; its antioxidant and antibacterial properties were evaluated as well, and optimal MAE conditions, i.e., X1 = 10:1 mL/g, X2 = 3 min and X3 = 553 W, were obtained with TPC and TFC yields of 184.99 ± 3.05 (mg GAE/g extract) and 68.78 ± 2.07 (mg QE/g extract), respectively. The results indicated that the leaf extract of O. gratissimum possesses antioxidant and antibacterial properties. Aside from these, the LC–ESI–MS/MS analysis provided tentative identification of 131 phenolic and other phytochemical compounds in the leaf extract at optimized conditions. The extract showed higher inhibitory activities against all the considered bacteria organisms (at least the concentration of 15 mg/mL). Thus, O. gratissimum leaf can be employed as an industrial crop with potential usage in the nutraceutical and food products.

Vernonia amygdalina leaves are mostly consumed in Asia and Africa, due to its potential as a good source of antioxidants. In this study, a two-level factorial design was used to evaluate the significant extraction parameters in achieving higher recovery yield of extract, total phenolic content, total flavonoid content, and antioxidants from Vernonia amygdalina leaf. Microwave-assisted extraction technique was employed using aqueous ethanol. The independent parameters were irradiation time (1–5 min), microwave power level (500–700 W), temperature (60–80 °C), feed-to-solvent ratio (1:8–1:12 g/ml), and ethanol concentration (40–80%). Amongst the examined parameters, ethanol concentration, irradiation time, microwave power level, and feed-to-solvent ratio were significant (p

The extracts from Vernonia amygdalina leaves dried using different modes of drying were examined for their antioxidant activities. The component identification was carried out on extract with the highest antioxidant property using GC–MS analysis. Using DPPH, ABTS+ and H2O2 radical scavenging assays, the shade, the sun, oven at 40, 50, and 60 °C dried sample extracts were screened. The obtained scavenging activities were in the order: shade drying > sun drying > oven drying at 40 °C > oven drying at 50 °C > oven drying at 60 °C. The extract from shade-dried sample exhibited the highest activity by scavenging 63.21–92.25% of DPPH, 75.32–93.15% of ABTS+, and 82.53–95.78% of H2O2 radicals, which were higher than those of ascorbic and gallic acid scavenging activities. In addition, the effects of drying methods and extract concentrations on the antioxidant activity of V. amygdalina leaf were significant (p < 0.05). A total number of 11 major compounds were identified from the shade-dried extract viz: phytol (43.69%), (z,z,z)-methyl ester-9,12,15-octadecatrienoic acid (17.60%), 2-methyl-3-hexanol (6.83%), ethyl ester-9,12-octadecadienoic acid (6.07%), ethyl ester linoleic acid (5.19%), ethyl ester hexadecanoic acid (5.06), heneicosane (4.15%), heptacosane (3.25%), and others are less than 3%. Therefore, it can be deduced that an increase in drying temperature may deteriorate the antioxidant activity of Vernonia amygdalina leaf.

The nutraceutical potential of black and white pepper has drawn the attention of many researchers to unravel their pharmaceutical and nutritional properties. These properties could be attributed to the presence of some essential bioactive compounds and mineral elements. This study, therefore, investigated the phenolic and mineral element composition in their oleoresin extracts, using a set of physicochemical and characterization protocols. The result obtained at optimum condition gave a total of 17 and 20 phenolic compounds in black and white pepper extracts, respectively. Moreover, four essential mineral elements (Na, Mg, K, and Ca) were detected. The presence of hazardous elements such as Ar, Se, Pb, and Cr, below the detection limit (BDL) indicated the edibility of the oleoresin extracts. The total phenolic content (TPC) in both extracts was evaluated using Folin-Ciocalteu assay. The result showed that the white pepper extract exhibited higher total phenol content (63.40 ± 0.096 mg GAE/g d.w) than black pepper extract (51.95 ± 0.025 mg GAE/g d.w). The combined action of the mineral elements, total phenolic content and the phytochemical profiles confirmed the potential of oleoresin extracts as natural antioxidants in food and pharmaceutical industries.

Fenugreek (Trigonella-Foenum Graecum) is known as one of the traditional and most promising medicinal herbs belongs to the leguminous family. The seeds of fenugreek have been extensively studied for the treatment of inflammation, cancer and diabetes. In this study, fenugreek seed oil was extracted and evaluated for its chemical compositions and bonding through gas chromatography coupled to mass spectrometry (GC-MS) and Fourier transform infrared spectroscopy (FT-IR) analysis, respectively. The antioxidant activity against 2,2-diphenyl-picrylhydrazyl (DPPH) and 2,2′-Azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS+•) radicals, total phenolic content (TPC) and total flavonoid content (TFC) of the oil were also studied. The capacity of antioxidants detected by ABTS was stronger than that by DPPH. A total number of 23 chemical compounds were detected and identified in fenugreek seed oil comprising of 99% of the total oil through GC-MS analysis. The major compounds of the extracted oil were linoleic acid (54.13%), palmitic acid (16.21%), pinene (4.56%), 4-Pentyl-1-(4-propylcyclohexyl)-1-cyclohexene (3.87%) and linoleic acid methyl ester (3.19%). FTIR analysis confirmed the presence of carboxyl group in the oil which were more dominated by unsaturated essential fatty acids. Moreover, the oil of fenugreek seed indicated a strong antioxidant radical scavenging activity against both DPPH and ABTS assays with an IC50 of 172.6 ± 3.1 and 161.3 ± 2.21, respectively. The TPC and TFC of the oil were 38.97 ± 0.34 mg GAE/g. oil and 14.417 ± 0.23 mg QE/g.oil. Thus, this study suggests that the fenugreek seed oil could be used for pharmaceutical purposes. Keywords: Fenugreek seed oil, Gas chromatography-mass spectrometry, Unsaturated essential fatty acid, Antioxidant, Total phenolic content, DPPH, ABTS

Cancer management is associated with serious side-effects due to the harmful nature of radiation and chemotherapy on the body cells. These side-effects have necessitated the need for diversifying the alternative or complementary sources of cancer therapy. Natural products have been on the front line as alternative sources of anticancer agents and have attracted much attention in recent times. In this study, the anticancer activity of Hypsizygus tessellatus (white var.) caps (also known as Bunapi shimeji) extracted with acetone and ethyl acetate was evaluated in vitro against MDA-MB-231 and MCF-7 (breast cancer cell lines) and MCF-10a (Vero or normal breast cells). Likewise, the free radical scavenging and metal reducing activities of the extract were evaluated through in vitro chemical-based methods. Furthermore, the phytochemical compositions of the extracts were determined through LC–MS-QTOF-assisted mass spectroscopy. The results of this study indicated that acetone fraction had better radical scavenging activity against DPPH (IC50 = 0.76 mg/mL) and H2O2 (IC50 = 0.84 mg/mL) than ethyl acetate fraction against DPPH (IC50 = 1.10 mg/mL) and H2O2 (IC50 = 1.26 mg/mL) (p

The study investigated the effects of extraction parameters on the yield, antioxidant activities, morphological and functional group characteristics of black and white pepper oleoresin extracts. Optimized oleoresin yields of 5.64 and 8.72 w/w% were obtained as black and white pepper extracts, respectively. Moreover, from the antioxidant assay, the concentration of black and white pepper extracts required to scavenge half of stable DPPH radicals were 94.92 and 107.57 µg/ml, respectively. From the complementary antioxidant assay; the concentration of black and white pepper extracts required to scavenge half of the stable ABTS free radicals were 82.36 and 94.71 µg/ml, respectively. This indicated that extracts from white pepper exhibited higher antioxidant capacity than the black pepper extracts. The results from the untargeted compositional GC-MS analysis identified a total of 23 and 31 bioactive compounds in black and white oleoresin extracts, respectively. This study, therefore, revealed the potential of microwave extraction in obtaining high-quality extracts.

Mushrooms are rich in pharmacologically-important phytochemicals with reported medicinal values. In this study, the antibacterial activity of Flammulina velutipes (Enoki), Hypsizygus tessellatus (brown (Buna shimeji) and white (Bunapi shimeji) variants) stem extracts prepared with different solvents (water, methanol, acetone, and ethyl acetate) was investigated against Escherichia coli (E. coli ATCC 25922), Serratia marscenscens (S. marscenscens ATCC14756), Bacillus subtilis (B. subtilis ATCC 23857), and Staphylococcus aureus (S. aureus ATCC 25923). Their antioxidant activities were evaluated using radical scavenging assays of 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydrogen peroxide (H2O2) and ferric reducing power (FRP). The water extracts of Enoki, Buna shimeji, and Bunapi shimeji showed bacterial growth inhibition in a concentration-dependent manner. From the obtained results, all the Enoki extracts showed a significant inhibition of the gram positive bacterial species (E. coli and S. marcescens > 68%) and a reduced inhibition of the gram negative bacterial species (B. subtilis and S. aureus

In this study, ethanolic microwave-assisted extraction of total phenolic content (TFC), total flavonoid content (TFC) and antioxidant from Vernonia amygdalina leaf was investigated using response surface methodology. Four extraction variables, including irradiation time (1‒5 min), microwave power level (500‒700 W), feed-to-solvent ratio (1:8‒1:12 g/ml), and ethanol concentration (60‒80%) were optimized to obtain optimal yields. The analysis of variance results showed that ethanol concentration, microwave power level and irradiation time mostly affected the TFC, TPC and antioxidant activities significantly (p

In this study, the microwave-assisted extraction (MAE) variables were optimized using a face-centered central composite design of response surface methodology for optimal recoveries of total flavonoid content (TFC) and antioxidant capacities (DPPH and ABTS) of Vernonia amygdalina leaf extract. The independent variables were irradiation time (5–15 min), microwave power level (400–600 W), temperature (90–110 °C), and feed-to-solvent ratio (0.08–0.13 g/ml). The ANOVA results showed that TFC, DPPH and ABTS radical scavenging activities were significantly (p

In this study, the effects of extraction solvents on the yield and total phenolic content of Vernonia amygdalina leaf were examined. The considered solvents were water, 20% v/v ethanol, 40% v/v ethanol, 60% v/v ethanol, 80% v/v ethanol, and 100% v/v ethanol using Soxhlet extraction technique. Highest extraction yield (19.45 ± 0.22% g/g) and total phenolic content (96.25 ± 2.52 mg GAE/g d.w.) were achieved using 60% v/v aqueous ethanol solution. In addition, there exist a significant correlation between total phenolic content and antioxidant activities using DPPH (R2 = 0.9397, p

Black and white peppers are functional crops, used in food industries as spice and in traditional medicine, for the treatment of many degenerative diseases. This study investigated the influence of microwave heating on the extraction yield, energy absorption and dietary elemental composition of oleoresin extracts from black and white pepper. Under the largest donating rule, the maximum extract yield obtained was 48.22 mg/g from black pepper and 79.02 mg/g from white pepper microwave. The study therefore elucidated the energy absorption capacities in microwave heating and itsresultant effects on extraction yield. This clearly showed the potentials of microwave technology in obtaining high quality extracts with properly controlled parameters.

Phaleria macrocarpa locally known as Mahkota Dewa is one of the important medicinal plants that originates from Papua Island, Indonesia and grows in tropical areas. Mangiferin is one of the major bioactive compounds of Phaleria macrocarpa. The effect of extraction time (4–6 h) and extraction temperature (90–110 °C) on the mangiferin yield were investigated using Face Centered Central Composite Design (FCCCD) with five centre points under Response Surface Methodology (RSM). The presence of mangiferin in the extract was confirmed using HPLC-DAD and the functional groups were identified through FTIR analyses. A second order polynomial model was employed in predicting the response. The regression analysis showed that more than 98% of the variation was explained by the models with the optimum of 38.7 mg/g mangiferin yield at 105 °C and 6 h extraction time. The experimental values show good accuracy with those predicted (1.1% deviation), thus indicating the suitability of the model employed and the success of FCCCD in optimizing the extraction conditions.

Hibiscus sabdariffa comprises calyx which is rich in flavonoids and numerous phytochemical compounds. Nevertheless, the extraction parameters can influence the recoveries of these bioactive compounds. It is then important to investigate the contributing effects of the process parameters and optimized their conditions to achieve higher recovery yield. Hence, this study was carried out to examine the contributing effects of microwave‐assisted extraction (MAE) process factors (irradiation time, ethanol concentration, solvent/sample ratio, temperature, and microwave power) on the yield of total flavonoid (TF) contents from H. sabdariffa calyces using one‐variable‐at‐a‐time. The significant MAE process parameters were further optimized using Box Behnken design. At the MAE optimal conditions, the extract was analyzed to identify the flavonoid compounds using liquid chromatography‐mass spectrometry quadrupole time of flight. An optimum TF content of 94.32 mg QE/g extract from H. sabdariffa calyces was obtained at the following MAE conditions: Irradiation time of 4 min; ethanol concentration of 52% vol/vol; microwave power of 450 W and solvent/sample ratio 15:1 ml/g. Moreover, 95 flavonoid compounds were tentatively identified in the extract at optimized MAE conditions. Thus, these flavonoids can be further isolated in future studies to unveil embedded potentials of H. sabdariffa calyx extract. PRACTICAL APPLICATION: The procedure described the microwave‐assisted extraction (MAE) which can serve as a guideline for extracting flavonoids from Hibiscus sabdariffa calyx. Moreover, the liquid chromatography‐mass spectrometry quadrupole time of flight analysis provided the developed conditions for identifying flavonoids from the calyces. The results obtained suggested the exact MAE conditions to achieve an optimum yield of flavonoids from H. sabdariffa calyces. Most importantly, the tentatively identified flavonoids can further be isolated and purified in future studies to unveil the embedded biological potentials.

Background: Black- and white pepper extracts are natural products, which had been extensively used in food industries as a seasoning agent, and in herbal medicine for the treatment of many free radical-related diseases. Owing to the medicinal and nutritive benefits of this functional spice, the need then arises to find a way of extracting its fixed oil at optimum condition. Objectives: The aim of this study was to investigate the effect of extraction parameters on the extraction yield, antioxidant activities, microstructure, functional group characteristics, and elemental composition of fixed oils extracted from the two cultivars. Methods: Extraction of fixed oil was carried out using a heat reflux extraction technique. The dietary elemental composition was conducted using Energy Dispersive Spectroscopy (EDS). The effect of localized heating on the extracts was evaluated to determine the structural changes in the pepper sample using Brunauer-Emmett-Teller (BET) and Scanning Electron Microscopy (SEM). Results: The optimal fixed oil yields under the optimum condition were 10.38 mg/g for the black pepper and 15.27 for the white pepper. The antiradical powers (ARP) of 0.007985 and 0.009046 mL/µg were obtained for black- and white pepper fixed oil, respectively. This suggests that the fixed oil from white pepper exhibited higher antiradical characteristics than black pepper fixed oil. The results of BET-parameters revealed the percentage of deformations related to the black- and white pepper under the localized heating was 21.47% and 29.14%, respectively. Conclusions: The results revealed a greater deformation on the microstructure of white pepper than black pepper. Moreover, rich dietary elements present in the extracts succinctly unveiled the potential of fixed oil extracts in curative applications and preventive traditional medicine.

Carica papaya leaf is one of the considered agricultural waste; nevertheless, this leaf has been reported to contain diverse health benefits to humans. In as much as natural-based oils are of higher demands because of their aromatherapy property, this study focused on the extraction of oil from C. papaya leaf using microwave-assisted extraction (MAE) technique. Then, the extracted oil was analysed using gas chromatography-mass spectrometry. The influences of MAE parameters which include time of irradiation, microwave power, volume of solvent, and temperature on the extracted oil were investigated. The considered parameters were time of irradiation (30–180 min), microwave power (400–700 W), volume of the solvent used (distilled water) within the range of 100 to 300 mL, and temperature (40–100 °C). The outcomes from this finding showed that time of irradiation, microwave power and volume of solvent significantly altered the oil yield from C. papaya leaves. At the apex points of the considered parameters (time of irradiation, 120 min; microwave power, 500 W; volume of solvent, 200 mL; and temperature of 100 °C); the major identified compounds were n-Hexadecanoic acid; 9, 12, 15-Octadecatrienoic acid; phytol; 9-Octadecenoic acid; 9, 17-Octadecadienal; Oleic acid; and Octadecanoic acid. Therefore, C. papaya leaf is an embodiment of oil rich in fatty acid which can be employed as aromatherapy agent.

Vernonia amygdalina leaf has a significant importance in food and traditional medicine. It has been reported to possess various pharmacological effects. This study was carried out to investigate the influence of microwave-assisted extraction factors on the extraction from V. amygdalina leaves. The results highlighted that an increase in temperature deteriorated the yields of V. amygdalina leaf. Thus, shade-dried samples gave the highest yields at the irradiation times of 10 and 2 min, microwave power of 500 and 600 W, the temperature of 100 and 80°C, the feed-to-solvent ratio of 1:10, and ethanol concentration of 60% v/v using water and ethanol as the extracting solvents, respectively. Likewise, the antioxidant assay resulted in IC50 values of 260 ± 1.1 µg/mL DPPH and 149.78 ± 0.81 µg/mL ABTS for water and 204 ± 0.92 µg/mL DPPH and 31.17 ± 1.4 µg/mL ABTS for ethanol. Therefore, the synergistic mechanism of mass and heat transfer may be accounted for the accelerated extraction due to microwave energy.

Phaleria macrocarpa, commonly known as Mahkota dewa is a well-known medicinal plant native to Malaysia and Indonesia. P. macrocarpa has been used as traditional medicine for the treatment of many diseases for a long time. In this study, P. macrocarpa peels’ bioactive compounds were extracted using microwave-assisted extraction method. The effects of different process parameters such as irradiation time (0.5, 1, 3, 5, and 10 min), microwave temperatures (60, 70, 80, 90, and 100 °C) and microwave power (200, 300, 400, 500, and 600 W) on the extraction yield were investigated. Moreover, the antioxidant activity and total phenolic (TPC) content of the extract were estimated. The results reflected that the extraction yields, antioxidant activity and total phenolic content increased with increasing levels of process parameters to certain conditions where highest yields were attained. However, the best conditions of processing parameters that resulted to the highest amount of yield (61.25%) were 1 min, 80 °C and 300 W. The highest amount of antioxidant activity and TPC yield were 61.15±0.93% and 102.60±1.17 mg GAE/g d.w, respectively. These illustrated that P. macrocarpa peels can serve as a good source of antioxidant.

Fatty acids are reduced carbon chains mostly found in nature with different usages in the industrial feedstock, pharmaceutical and food industries. Plants are embodiments of substantial amounts of fatty acids. In this study, gas chromatography-mass spectrometry (GC–MS) analysis was employed to identify the chemical compositions of oils from Hibiscus sabdariffa flower, Stigma maydis; Chromolaena odorata leaf extracted through microwave-assisted hydrodistillation method. In addition, the oils from the three plant samples were characterized using Fourier transform infrared spectroscopy (FTIR) analysis to evaluate the fingerprints. A total number of 16, 13 and 13 chemical compounds were identified in the oils from H. sabdariffa flower, S. maydis and C. odorata leaf, respectively. The main identified compounds were fatty acids and esters. Moreover, the FTIR characterization reflected the presence of hydroxyl group, cellulose-fatty acids, methyl carboxylic acid, nucleic acid, and carbohydrate. This finding has fully demonstrated that the oils from H. sabdariffa flower, S. maydis and C. odorata leaf can serve as the potential sources of fatty acids.