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Microwave hydrodiffusion and gravity: a new technique for extraction of essential oils A new process design and operation for the extraction of essential oils was developed. Microwave hydrodiff usion and gravity (MHG) is a combination of microwaves for hydrodiff usion of essential oils from the inside to the exterior of biological material and earth gravity to collect and separate. MHG is performed at atmospheric pressure without adding any solvent or water. MHG has been compared with a conventional technique, hydrodistillation (HD), for the extraction of essential oil from two aromatic herbs: spearmint (Mentha spicata L.) and pennyroyal (Mentha pulegium L.) belonging to the Labiatae family. The essential oils extracted by MHG for 15 min were quantitatively (yield) and qualitatively (aromatic profi le) similar to those obtained by conventional hydrodistillation for 90 min. MHG also prevents pollution through potential 90% of energy saved which can lead to greenhouse gas emission benefits. Journal of Chromatography A 1190 (2008) 14-17 Comparison of two isolation methods for essential oil from rosemary leaves: hydrodistillation and microwave hydrodiffusion and gravity Traditional Hydrodistillation (HD) and innovative Microwave Hydrodiff usion and Gravity (MHG) methods have been compared and evaluated for their eff ectiveness in the isolation of essential oil from fresh Rosmarinus offi cinalis leaves. The microwave method off ers important advantages over traditional alternatives, namely: shorter isolation times (15 minutes against 3 h for hydrodistillation), environmental impact (energy cost is fairly higher to perform HD than that required for rapid MHG isolation), cleaner features (as no residue generation and no water or solvent used), increases antioxidant activity and provides a more valuable essential oil (with high amount of oxygenated compounds). It off ers also the possibility for a better reproduction of natural aroma of the essential oil from rosemary leaves than the HD essential oil. Moreover, microwave procedure yielded essential oils that could be analysed or used without any clean-up, solvent exchange or centrifugation steps. Scanning electron microscopy shows important structural changes for MHG extraction in contrast to those obtained by HD. Food Chemistry 114 (2009) 355-362 A new process for extraction of essential oil from Citrus peels: microwave hydrodiffusion and gravity. The process uses the hydrodiffusion phenomenon generated by microwaves to extract essential oil from the inside of the biological material and gravity to collect and separate them. The present apparatus permits fast and effi cient extraction, reduces waste, avoids water and solvent consumption, and allows substantial energy savings. A microwave irradiation power of 500 W for 500 g of plant material was chosen as an optimum and permits in only 15 minutes to extract the essential oil completely. MHG is clearly quicker than conventional HD, an extraction time of 15 min with MHG provides yields comparable to those obtained after 180 min by means of HD, which is the one of the reference methods in essential oil extraction. The overall yield of essential oil obtained from lime peels was 1.0 +/- 0.1% and 1.1 +/- 0.1% by MHG and HD, respectively. The essential oils of lime peels extracted either by MHG, HD or CP are rather similar in their composition and contains the same dominant components. Journal of Food Engineering 90 (2009) 409-413 Clean recovery of antioxidant fl avonoids from onions: optimising solvent free microwave extraction method A solvent free microwave hydrodiff usion and gravity extraction (MHG) of fl avonol content from onion (Allium cepa L.) was studied. Eff ectiveness of this innovative method in extraction of onion total phenolic content, total quercetin (TQ), quercetin aglycon (QA), quercetin-3,4’- diglucoside (QDG), quercetin-4’-monoglucoside (Q4G), quercetin-3-monoglucoside (Q3G), kaempferol (KMF) and myricetin (MRT) have been evaluated and compared with conventional solvent extraction. Microwave extraction off ers important advantages like shorter extraction time (23 min), cleaner feature (no solvent or water used) and extraction of valuable onion crude juice retaining fresh organoleptic properties with higher phenolic content (58.29 mg GAE/ gDW) at optimized power (500 W). Microwave extraction resulted signifi cant yield (81.5%) with 41.9% of fl avonol contents, with better retain of remaining fl avonoids (55.9%) in residues of onions. Journal of Chromatography A 1216 (2009) 7700-7707 Additonal Papers on Open Vessel Microwave Extraction
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