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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 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.

Carica papaya is a perennial large herbaceous plant known for diverse biological activities. Different parts of this plant such as seeds, leaves, fruits, peels, roots, and stems have been previously reported to possess nutritional and medicinal values. This plant possesses a nutritional value that is rich in vitamins and natural minerals but low in calories. Moreover, every part of this plant had been used in treating different type of diseases which include wound dressing, antibacterial, anthelminthic effects, traditionally used to control birth, and several other activities. These were born out of the in vitro and in vivo studies conducted on the extracts from parts of C. papaya. Furthermore, the occurrences of different kinds of phytochemicals in the extracts might have been responsible for its diverse pharmacological properties. Thus, this article comprehensively outlines and discusses nutritional values, phytochemistry and pharmacological activities of C. papaya.

Aloe vera is a perennial ethno-medicinal potential plant with a xerophytic characteristic, but not a cactus. It has a famous history owing to its phytopharmaceutical properties and this had made it useful in the pharmaceutical, cosmetic and food industries. Studies had shown the positive effects of its extract against bacteria, organisms. The phytochemical properties of A. vera have fungi, virus and parasitic been exploited for various economic and commercial purposes. This review contributes literature on the bioactive potential composition, processing and the pharmaceutical potential uses, an adverse side-effect that might spring up in case of over dosage and important safety precautions are summarized. More scientific innovations and developments in the aspect of analytical chemistry are on the way to provide more acceptable, purified chemical characterization of A. vera using sophisticated laboratory equipment and machines.

Vernonia cinerea is one of the medicinal plants with several potentials for treating different ailments. In the present study, Microwave-assisted extraction (MAE) was employed in extracting phenolics compounds from this plant. However, different factors that affect this extraction method in the recovery of phenolics compounds abound, these factors need to be screened to determine actual contributing factor in order to minimize cost. Irradiation time (1-5 min), ethanol concentration (20-60% v/v), microwave power (40-80 W), extraction temperature (40-80 oC), and feed/solvent (1:10 - 1:18 g/mL) have been screened using two-factorial design for the recoveries of phenolic compounds from V. cinerea leaves. The results obtained in this study indicated that only microwave power, ethanol concentration, irradiation time and feed/solvent contributed to recoveries of total phenolic content (TPC) and total flavonoid content (TFC) from V. cinerea leaves. Thus, these factors at these ranges can be further optimized to obtain optimal yields of phenolic compounds from V. cinerea leaves.

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.

Phaleria macrocarpa or Mahkota Dewa has been a unique plant because of its antioxidant, anti-inflammatory and anti-cancer properties. The phytochemical studies of this plant have revealed the presence of bioactive compounds: phenolic compound, terpenes (isoprenoids) compounds, alkaloids compounds, and benzophenones compounds. Researches done on its have shown its ability to treat some diseases and serves as herbal medicines. The aim of this review is to summarize and evaluate the existing researches regarding the pharmacological effects, phytochemical properties, and toxicological studies of Phaleria macrocarpa. This review is expected to be useful for researchers working on the potential roles of Phaleria macrocarpa in the treatment of diseases or for product development.