Increasing the essential oil yield from Shorea roxburghii inflorescences using an eco-friendly solvent-free microwave extraction method for fragrance applications

Highlights

• Solvent-free microwave extraction was optimized to increase essential oil yield.

• Response surface methodology was used to model the extraction process.

• The extraction conditions were validated to achieve reliable performance.

• The resulting oil odor was similar to that of fresh flowers.

• The irritation properties of the oils were evaluated for fragrance applications.

Abstract

The short bloom period of Shorea roxburghii G.Don is a technical challenge in the development of a fast and efficient process for recovering essential oils. This study aimed to optimize the conditions for the isolation of essential oil and the determination of the resulting oil's possible bioactivities for fragrance applications. Solvent-free microwave extraction (SFME) coupled with response surface methodology (RSM) was applied to study essential oil from fresh inflorescences. The microwave power and irradiation time were chosen as crucial independent variables, while essential oil yield was the response variable. The physicochemical, antioxidant, olfactory, cytotoxic, and irritant properties of the resulting oil were evaluated. SFME yielded essential oil with a unique and pleasant scent, similar to that of fresh flowers. Increased microwave power and irradiation time increased the oil yield. The proportions of oxygenated compounds with high antioxidant properties were notably higher after SFME than after hydrodistillation. The optimal conditions for maximizing the oil yield were 800 W and 35 min. Among 51 volatile substances, germacrene B, kaur-16-ene, β-caryophyllene, and (E)-linalool oxide (furanoid) were the oil's main components. Low toxicity to primary human dermal fibroblast cells was defined at an oil concentration < 50 μg/mL. Moreover, the application of the extracted volatile oil to hen’s egg-chorioallantoic membrane resulted in a low degree of irritation. This research establishes optimal extraction conditions for the isolation of essential oil with potential for fragrance applications.

Introduction

Fragrances affect human olfactory nerves; thus, their ingredients play a crucial role in people’s happiness and confidence (Vijaya et al., 2020). As a result, fragrant volatiles have been used in a wide variety of products, including decorative cosmetics, perfumes, toiletries, detergents, and other scented household products (Bom et al., 2019; Chisvert et al., 2018; Vijaya et al., 2020). The global market for flavors and fragrances is expected to reach $28.37 billion in 2023, with $4.3 billion for the natural fragrance market in 2019–2024 (Research and markets, 2019). Additionally, consumers and producers continue to search for natural fragrance alternatives to synthetic substances associated with an increased risk of allergies. Consequently, discovering new fragrances from natural sources is an important direction for the cosmetic and perfumery industries (Bom et al., 2019).

In tropical Asia, Shorea is a dominant genus with 196 species and the most economically viable plant in the Dipterocarpaceae family (Khan et al., 2016). Of the 196 species, Shorea roxburghii G.Don, a deciduous tree, is medium to large in size. It is widely distributed from East India to Southeast Asia (Greene et al., 2020; Khan et al., 2016; Patcharamun et al., 2011). The flowers formed in the terminal panicle are white, have a peculiar scent and usually appear during a short period in January. During the blossoming period, S. roxburghii flowers emit a characteristic floral fragrance that is widely used in the ethnoperfumery industry and that boosts people’s moods without reported toxicity. The extensive traditional use of its flowers suggests that this plant’s essential oil would be useful as a fragrant ingredient in cosmetics and perfumes. This can also be considered a sustainable source because the aromatic components can be separated from the flowers without cutting down the tree. In addition, sufficient inflorescences are produced by S. roxburghii during the bloom period, so this plant has attracted interest among scientists exploring essential oils as potential aromatic additives. However, the flowering time for S. roxburghii is short, between two and three weeks per year, so efficient extraction is essential to make this plant used as a practical fragrance. Therefore, a faster approach to obtain volatile oil is desired.

To date, research on essential oils from S. roxburghii and the characterization of odor-active constituents and their biological activities have been limited. Some closely related species, such as S. robusta and S. accuminata, were reported to produce volatile compounds. Hydrodistillation of essential oils from the resin and heartwood of S. robusta identified germacrene D as the main constituent (Kaur et al., 2001), while the predominant compounds in bast (cambium and secondary phloem portion of the tree) were τ-cadinol, α-cadinol and globulol (Kaur et al., 2003). In the case of S. accuminata, various volatiles were identified, and germacrene D was the predominant constituent in the stems. In contrast, caryophyllene oxide and β-caryophyllene were the major components in the leaf oil (Muhammad et al., 2011). The essential oil of S. accuminata has also been used as a fixative in heavy perfumes (Shiva and Jantan, 1998).

Hydrodistillation and steam distillation are conventional techniques used to extract essential oil from plant matrices in the modern perfumery industry because they incur low costs and are easy to industrialize (Garcez et al., 2020; Meziane et al., 2019; Paulus et al., 2019). The issue most commonly cited in the literature for these methods is the degradation of some thermolabile components at high temperatures over a long extraction time (Liu et al., 2019). Another method used to isolate essential oils is solvent extraction, as residual solvents can cause unpleasant odors and skin irritation. Solvent-free microwave extraction (SFME) is an emerging technology in which fresh plant materials or predried samples are used as raw materials to retrieve essential oil by microwave heating at atmospheric pressure (Liu et al., 2018). SFME is a technology that is simple, efficient, solvent free, cost effective, and ecofriendly, all of which have advantages over conventional techniques. The use of SFME to extract essential oils from several aromatic plants has been successfully demonstrated (Yingngam and Brantner, 2018). Several research groups have reported the fundamental mechanism of essential oil extraction from aromatic plants. The combination of this extraction technique and response surface methodology (RSM) has produced relatively predictable results even with small sample sizes (Garcez et al., 2020; Köprü et al., 2020; Yingngam and Brantner, 2018). However, there are no standard operating procedures for the extraction of aromatic plants. The extraction method should therefore be optimized for each plant scent. This challenging work is currently being carried out by many researchers.

This research aimed to optimize the processing conditions of the SFME technique to extract the essential oil from S. roxburghii blossoms. SFME was combined with the RSM to optimize the extraction conditions, analyze the interaction among test variables, and minimize the testing limitations. Samples extracted by HD served as a reference for comparison. Chemical components in the oil were examined using gas chromatography coupled with mass spectrometry (GC−MS). The method conditions were optimized primarily on the basis of the recovery of essential oils, odor quality, and aromatic substances typically found in HD-derived oils. The cytotoxicity of the isolated essential oil was also tested on primary human dermal fibroblast (HDFn) cells, while its irritation potential was examined in hen’s egg–chorioallantoic membrane (HET-CAM).