Microwave-Assisted Extraction of Phenolic Compounds and Antioxidants for Cosmetic Applications Using Polyol-Based Technology

Nowadays, there is a global trend towards environmental awareness in the beauty industry, leading manufacturers to focus on green technology for extracting plant components using sustainable alternatives¹. Typically, traditional solvents such as ethanol, methanol, and hexane are used to extract plant phenolic components and natural antioxidants². Nevertheless, the presence of solvent residues within plant extracts poses a potential risk to human health, inducing skin and eye irritation³, particularly concerning their intended application in cosmetics. Consequently, it is challenging to eliminate such solvent residues from the extracts, a process that demands considerable investment in time, energy, and human resources⁴. Recently, superheated water, ionic liquids, deep eutectic solvents, and bio-derived solvents have emerged as promising approaches for green solvent extraction⁵. However, their use is still limited by product separation in aqueous-based processes. To address these challenges, the development of ready-to-use extracts emerges as a viable solution⁶.

Polyols are often used in cosmetic formulations as humectants because of their good polarity and ability to retain moisture from the environment⁷. In addition, polyols such as glycerin, propylene glycol, butylene glycol, methylpropanediol, isopentyldiol, pentylene glycol, 1,2-hexanediol, and hexylene glycol can be utilized for plant extractions. They are considered non-toxic, biodegradable, environmentally friendly, non-reactive, and safe solvents for use in plant extraction⁸. Additionally, polyols can withstand the heat generated during microwave-assisted extraction (MAE) due to their elevated boiling points and polarity⁹. These polyols are generally recognized as safe (GRAS) chemicals by the United States Food and Drug Administration (FDA). Unlike conventional solvents such as ethanol or methanol, which may require rigorous removal from the extract due to their potentially harmful effects, polyols offer the advantage of minimizing the energy, time, and costs associated with solvent removal processes¹⁰. This not only streamlines the extraction process but also enhances the overall efficiency and sustainability of the extraction method. Previous investigations have employed polyols such as propylene glycol and butylene glycol as solvents in the extraction of bioactive compounds from Camellia sinensis flowers¹⁰ and coffee pulp¹¹, revealing significant potential for their role as sustainable alternative solvents in the plant extraction process. Thus, the continued development and optimization of a polyols-water solvent system holds the potential for significant advancements in green chemistry and sustainable industrial practices.

Generally, bioactive compounds found in plants are synthesized as secondary metabolites. These compounds can be categorized into three primary groups: terpenes and terpenoids, alkaloids, and phenolic compounds¹². Various extraction methods are utilized under different conditions to isolate specific bioactive compounds from plants. Bioactive compounds from plant materials can be extracted using either conventional or non-conventional techniques. Traditional methods include maceration, reflux extraction, and hydro-distillation, while non-conventional methods consist of ultrasound-assisted extraction, enzyme-assisted extraction, microwave-assisted extraction (MAE), pulsed electric field-assisted extraction, supercritical fluid extraction, and pressurized liquid extraction¹³. These non-conventional methods are designed to enhance safety by utilizing safer solvents and auxiliaries, improving energy efficiency, preventing degradation of the bioactive components, and reducing environmental pollution¹⁴.

Furthermore, MAE is among the sophisticated green technologies for extracting bioactive compounds from plants. Conventional extraction procedures require significant amounts of time, energy, and high temperatures, which over time might degrade heat-sensitive bioactive compounds¹³. In contrast to conventional thermal extractions, MAE facilitates the extraction of bioactive compounds by generating localized heating within the sample, disrupting cell structures, and enhancing mass transfer, thereby increasing the efficiency of compound extraction. Heat is transferred from inside the plant cells by microwaves, which operate on the water molecules within the plant components¹³. Moreover, MAE has advanced to improve the extraction and separation of active compounds, increasing product yield, enhancing extraction efficiency, requiring fewer chemicals, and saving time and energy while preventing the destruction of bioactive compounds¹⁵.

This research focuses on the extraction of plant phenolic compounds and natural antioxidants through microwave-assisted extraction (MAE) using different types of polyols as solvents. The total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activities (DPPH, ABTS, and FRAP) of polyol-based MAE extracts are determined. Additionally, polyol-based MAE is compared with MAE using conventional solvents such as water and ethanol. This research is expected to contribute to the development of environmentally sustainable extraction technology for natural components, promoting sustainability by reducing reliance on hazardous chemicals, shortening processing times, and minimizing energy consumption in raw material production for potential applications within the cosmetics industry.