Microwave assisted hydro-distillation of essential oils from wet citrus peel waste

Over 30% of the total citrus fruits grown all over the World are processed, generating large quantities of peel waste from which essential citrus oils are often extracted by traditional methods demanding high energy costs, long extraction times and additional reagents. In this research an alternative technique based on microwave-assisted hydro-distillation (MAHD) has been studied to successfully extract the essential oil present in wet citrus peel waste whilst reducing costs, avoiding the use of additives and improving the effectiveness of the process. To achieve this goal factors affecting the scalability of the process to develop a new bio-refinery model to be used at industrial scale were considered. Optimal conditions for the essential oil MAHD involved the irradiation of a waste orange peel:water mixture (1:1.5) over two subsequent steps using different irradiation powers for a total extraction time of 20 min (keeping a constant pressure of 300 mbar through all the process). The essential oil yield obtained in Navel Navelate oranges using MAHD accounted for 1.8± 0.1% (dry basis; n = 3) and was comparable to that obtained by conventional hydro-distillation (1.7± 0.1%; dry basis; n = 3). The applicability of the suggested methodology was successfully tested in other varieties of orange and citrus fruits leading to the potential to apply MAHD of essential oils from other waste feedstocks and offering an attractive process for future extraction processes at industrial scale.