2.3.4 Effect of Contact Surface Area and Water Content
Not only the parameters already discussed but the characteristics of the sample also affect the MAE process. It is known that in a higher contact surface area the extraction efficiency increases. Also, fi ner particles allow improved or much deeper penetration of the microwave [ 49 ] . On the other hand, very fi ne particles may pose some technical problems; consequently, centrifugation or fi ltration is applied to prepare the matrix [ 13, 29 ] . In the preparation step the sample is grinded and homogenized to increase the contact area between the matrix and the solvent. The particle sizes are usually in the range of 100 m m to 2 mm [ 8 ] . In some cases soaking of the dried plant material in the extracting solvent before MAE has resulted in improved yield. This procedure is called pre-leaching extraction [ 13 ] .