Measuring dielectric properties for microwave-assisted extraction of essential oils using single-mode and multimode reactors

Postharvest Microwave Drying of Basil (Ocimum basilicum L.): The Influence of Treatments on the Quality of Dried Products

Edible herbs are widely used in the human diet due to their pleasant flavors and countless health benefits associated with their components having, mainly, antioxidant and anti-inflammatory therapeutic functions. Since herbs are highly perishable materials because of their high water content, to guarantee products are safe and stable over time, it is necessary that they undergo stabilization operations. The application of microwave-assisted drying, a promising technique in terms of process sustainability, for the stabilization of the aromatic herb, Ocimum basilicum L., was investigated. The activities were carried out by applying different operating conditions in order to evaluate the impact of the time/temperature combination on the final quality of dried basil. The latter was investigated via the chemical characterization of extracted essential oils and tissue damages. Conventional convective processes were also applied to perform comparisons between dried basil products both under production and the quality preservation points of view. Results showed that microwave heating is suitable as a drying method, as expected, due to the well-known interaction between vegetable tissue (rich in water) and the electromagnetic field; and that drying methods have a different influence on the chemical composition of the essential oils extracted from dried products, in terms of the number (ranging from 41 to 18 components in different dried samples) and percentage (until 67% in linalool and 21% in α-trans-bergamotene in different dried samples) of its’ constituents.

Impact of drying methods on the yield and chemistry of Origanum vulgare L. essential oil

Oregano (Origanum vulgare L.) is mainly cultivated, both as fresh and dried herb, for several purposes, such as ailments, drugs, and spices. To evaluate the influence of some drying methods on the chemical composition of the essential oil of oregano, its aerial parts were dehydrated by convective drying techniques (shade, static oven), microwave-assisted heating (three different treatments) and osmotic treatment. The oils were analyzed by GC-FID and GC-MS. The highest essential oil yield was achieved from microwave and shade drying methods. In total, 39 components were found, with carvacrol (ranging from 56.2 to 81.4%) being the main constituent; other compounds present in lower amounts were p-cymene (1.6-17.7%), γ-terpinene (0.8-14.2%), α-pinene (0.1-2.1%), thymol methyl ether (0.4-1.8%) and thimoquinone (0.5-3.5%). The essential oil yields varied among the different treatments as well as the relative compositions. The percentages of p-cymene, γ-terpinene and α-pinene decreased significantly in the dried sample compared with the fresh sample; on the other hand, carvacrol, isoborneol and linalool increased significantly in the dried materials. The choice of the drying method for obtaining the essential oil therefore appears crucial not only in relation to the higher yield but also and above all in reference to the percentage presence of components that can direct the essential oil toward an appropriate use.

Microwave-assisted Natural Deep Eutectic Solvents Pretreatment Followed by Hydrodistillation Coupled with GC-MS for Analysis of Essential Oil from Turmeric (Curcuma longa L.)

In the past decade, natural deep eutectic solvents (NADESs) as green and sustainable extraction solvents with great potential for the efficient extraction of bioactive compounds from the plants are emerging. In this study, a microwave-assisted technology is used to prepare natural deep eutectic solvents. And natural deep eutectic solvents as pretreatment solvents coupled with microwave-assisted hydrodistillation (MAHD) for isolating essential oil (EO) derived from turmeric (Curcuma longa L.) is investigated. To improve the essential oil yield of turmeric (Curcuma longa L.) as a target, various factors affecting extraction efficiency including the type and amount of natural deep eutectic solvents, pretreatment time, pretreatment temperature and hydrodistillation (HD) time are discussed and optimized through central composite design (CCD) of the response surface methodology (RSM). The optimal conditions are as follows: natural deep eutectic solvent composed of choline chloride and oxalic acid (molar ratio with 1:1) as a pretreatment solvent, an amount of 60 g, a pretreatment time of 5 min, a pretreatment temperature of 84 ºC, a hydrodistillation time of 76 min. Under the optimum conditions, the highest essential oil yield of 0.85% is achieved. Additionally, the essential oil is analyzed by using gas chromatography-mass spectrometry (GC-MS), with a total of 49 compounds being identified. Through combining natural deep eutectic solvents with a microwave-assisted hydrodistillation technique, this work provides an eco-friendly extraction way of isolating essential oil, which boosts development in the monitoring other spice quality field.