Abstract
<p>Comparison between conventional and microwave-assisted hydrodistillation at different power levels has been applied for the extraction of essential oil from <i>Zingiber officinale</i> Rosc. rhizome. In addition to the collected essential oils, as the main products, hydrolats were also collected, as valuable by-products from both extraction techniques. A comparison of two applied techniques was done in terms of extraction time, extraction yield, the chemical composition of essential oils and hydrolats, and environmental impact. Microwave-assisted hydrodistillation achieved a higher extraction yield (1.70, 1.70, and 1.85 % for power levels of 180, 360, and 600 W, respectively) compared to hydrodistillation (1.50 %). Furthermore, distillation time related to the energy consumption has been reduced from 144 min and 1.44 kWh for conventional hydrodistillation to 37, 32, 27 min and 0.11, 0.19, 0.27 kWh for power levels of 180, 360, and 600 W, respectively. Content of α-zingiberene in essential oil and hydrolat obtained by hydrodistillation was 29.89 and 6.87 %, while content of α-zingiberene in essential oils and hydrolats obtained by microwave-assisted hydrodistillation was higher yielding the amounts of 34.12, 34.43, and 42.00 % and 18.70, 22.60, and 32.92 % for power levels of 180, 360, and 600 W, respectively. Microwave-assisted hydrodistillation has proven to be promising technique for the isolation of ginger’s essential oil regarding improved yield, reduced time and energy requirements, as well CO2 emissions while maintains oil quality.</p> <p><br /> </p>
Highlights
Ginger (Zingiber officinale Rosc., Zingiberaceae) is a perennial plant species whose tuberous rhizome is widely used as a very popular spice, for food and beverages flavoring and as a medicinal raw material
Yield of ginger rhizome essential oil improvement was achieved using microwave-assisted hydrodistillation (MAHD) extraction method, with no significant differences in the chemical composition comparing with conventional HD
Extraction time was significantly reduced in the case of MAHD (27-37 min compared to 144 min)
Summary
Ginger (Zingiber officinale Rosc., Zingiberaceae) is a perennial plant species whose tuberous rhizome is widely used as a very popular spice, for food and beverages flavoring and as a medicinal raw material. Whole or cut, dried ginger rhizomes (Zingiberis rhizoma) with a minimum essential oil content of 1.5 % (v/w) are official herbal drug according to the European Pharmacopoeia 10.0 (Ph.Eur. 10.0., 2019). The main ingredients of the essential oil are sesquiterpene hydrocarbons α-zingiberene, β-sesquiphellandrene, βbisabolene, α-farnesene, ar-curcumene, and lower content of the monoterpene hydrocarbons and oxygenated monoterpenes (camphene, geraniol, citral, cineol, β-phellandrene) (Kamaliroosta et al, 2013; Talebi et al, 2021). Conventional hydrodistillation (HD) and steam distillation are still the most commonly used technique for essential oil isolation at both laboratory and industrial levels (Drinicet al., 2020). The main limitations of these traditional distillation techniques are the thermal and/or hydrolytic degradation of esters and polyunsaturated ingredients during prolonged exposure to elevated
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