Nanoemulsion is a delivery system used to enhance bioavailability of plant-based compounds across the stratum corneum. Elaeis guineensis leaves are rich source of polyphenolic antioxidants, viz. gallic acid and catechin. The optimal E. guineensis leaves extract water-in-oil nanoemulsion was stable against coalescence, but it was under significant influence of Ostwald ripening over 90 days at 25 °C. The in-vitro permeability revealed a controlled and sustained release of the total phenolic compounds (TPC) of EgLE with a cumulative amount of 1935.0 ± 45.7 µgcm−2 after 8 h. The steady-state flux and permeation coefficient values were 241.9 ± 5.7 µgcm−2 h−1 and 1.15 ± 0.03 cm.h−1, respectively. The kinetic release mechanism for TPC of EgLE was best described by the Korsmeyer–Peppas model due to the highest linearity of R2 = 0.9961, indicating super case II transport mechanism. The in-silico molecular modelling predicted that the aquaporin-3 protein in the stratum corneum bonded preferably to catechin over gallic acid through hydrogen bonds due to the lowest binding energies of − 57.514 kcal/mol and − 8.553 kcal/mol, respectively. Thus, the in-silico study further verified that catechin could improve skin hydration. Therefore, the optimal nanoemulsion could be used topically as moisturizer to enhance skin hydration based on the in-silico prediction.

The essential oils obtained from the fresh rhizome, leaf, and pseudostem of Alpinia aquatica Roscoe. were hydrodistillated and analyzed using capillary gas chromatography (GC) and gas chromatography-mass spectroscopy (GC-MS). β-Pinene (11.7%), α-humulene (8.9%), aromadendrene (8.7%), and sabinene (7.7%) were the major components in the rhizome oil. The most abundant components of the leaf oil were germacrene D (21.3%), β-pinene (15.6%) and sabinene (12.1%), while α-humulene (19.8%), germacrene D (15.2%) and β-caryophyllene (8.7%) were the main constituents in the pseudostem oil. Antityrosinase assay revealed that all the three essential oils exhibited weak tyrosinase inhibition activities. The rhizome oil showed the highest inhibition activity with the value of 9.5% for the L-DOPA oxidation.

As the largest organ in the human body, the skin should be protected from various harmful chemicals and pollutants from the surrounding environment and ultraviolet (UVA/UVB) radiation emitted from sunlight. This has prompted formulation scientists to embark on new technology to formulate cosmetics free of synthetic chemicals using natural plant-based extracts as the replacement. Natural phytoanti-oxidants, viz. catechin, quercetin and gallic acid, are polyphenols whose therapeutic values (antioxidative, antityrosinase, antiviral and antimicrobial) are underutilized. Plant-based nanoemulsions offer an efficient and safe topical delivery system for improving the skin and regenerative treatment. The bioavailability of the phytoanti-oxidants for molecular-level skin repair is enhanced by better permeation of the nanoemulsions' nano-sized particles through the stratum corneum. This review highlights several phytoconstituent-containing nanoemulsions and their bioactivities for cosmetic applications. The mechanisms of skin improvement for anti-aging skin are also presented in detail. In short, nanoemulsion technology is a powerful tool for an effective topical delivery system of potent skin-protecting and rejuvenating plant-based extracts. With increasing demand from consumers worldwide for nano-formulated phytohormones or phytoextractives, nanoemulsions will see a new dimension with better future prospects.

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The present study highlighted the statistical modeling of an ultrasonic-aided extraction (UAE) of Elaeis guineensis leaves extract for maximal extraction yield (EY) and total phenolic content (TPC). A Box-Behnken design investigated the effects of ethanol concentration (X1: 0−100%), extraction time (X2: 5−55 min), the solvent-to-solid ratio (X3: 15:1−35:1 mL/g) and sonification amplitude (X4: 20−100 %). Under optimized conditions, the highest EY of 14.38% was attained using 50% (v/v) ethanol:water ratio, 55 min, 35 mL/g solvent-to-solid ratio, 60% sonication amplitude, whereas maximum TPC was 209.70 mg gallic acid equivalent (GAE)/g [50% (v/v) ethanol:water ratio, 30 min, 25 mL/g solvent-to-solid ratio, 60% sonication amplitude]. Second-order polynomial models of EY and TPC showed the R2 value corresponding to 0.9303 and 0.9500, respectively, indicating their significance (p < 0.05) to predict the responses. HPLC chromatograms revealed gallic acid and catechin were present in the UAE extracts. UAE technique afforded better EY (14.38%) and TPC (209.70 mg GAE/g) than maceration (3.73%, 85.23 mg GAE/g) and Soxhlet (6.86%, 102.13 mg GAE/g) extractions, as based on scanning electron micrographs of untreated, UAE, macerated and Soxhlet treated samples. Cell walls of ultrasonic-treated E. guineensis leaves were visibly disrupted to facilitate the higher release of bioactive plant materials, thus justifying the higher EY and TPC. The application of ultrasound appeared to remarkably increase the extraction efficiency of E. guineensis leaves to extract as compared to the conventional methods.