Microwave in food processing

Abstract

Traditional treatment of thermal food processing has been nowadays overridden by the appearance of more sophisticated methods. Microwaves, accordingly, possess tremendous heating potential, as they can penetrate materials and deposit energy, causing the rapid and uniform heat generation throughout the volume of the material. In the last decade, microwaves have drawn significant research attention in the extraction technology. The extraction step of the most analytical procedures demands incessant progress, considering that still today Soxhlet extraction (developed in 1879) is of use in many routine laboratories. In a compliance with the previously, an effective, rapid and cheap method for obtaining of natural antioxidants from spent coffee has been developed by using of microwave-assisted extraction. Due to the proper impregnation of plant matrix with the solvent, which possess high heating efficiency under the microwave, the generation of strong pressure pushes the cell wall from inside, stretches and ultimately ruptures it, thus facilitating the leaching out of the bioactive constituents. The aqueous ethanol, as a solvent, enabled a high selectivity towards the analyte of interest, excluding unwanted matrix components, due to specific dielectric properties of chemical substances that absorb microwave energy to a certain extent. The maximal antioxidant content, equivalent to total polyphenols, has been produced after 40 s of microwave radiation, using predominantly aqueous ethanol solution. The extract exhibited good bioactive compound stability, considering to high inhibition of DPPH free radical species and featured reducing capacity (expressed by FRAP assay). This procedure provided shortened extraction time, reduced solvent consumption, increased pollution prevention concern and the special care for thermolabile constituents, enhancing overall quality in comparison to the existing techniques. Spent coffee extracts, rich in antioxidants, may be later used in food and pharmaceutical industries to increase the nutritional values or product stability, as well as to develop new healthy products.