Extraction of phenolic compounds from olive-waste cake using ultrasonic process

Health hazards of artificial antioxidants have motivated use of natural phenolic compounds in food industry. Olive-waste cake, resulted from olive oil extraction, is accounted as a rich resource of phenolic compounds. In this study, extraction of phenolic compounds through sonication process was investigated. In this respect, effects of sample weight to solvent ratio (in three levels of 1: 10, 1: 30 and 1: 50) and sonication time (in three levels of 10, 30 and 50 min) were evaluated on total phenolic content, antioxidant activity and color parameters of L* and a* of the extracts. Results showed that changing the independent variable of sample weight to solvent ratio from 1: 50 to 1: 10 results in a significant increase in total phenolic content and antioxidant activity parameters (P <= 0.01) and a significant reduction of L* color parameter (P <= 0.01) of the extracts. Also, the results of this study demonstrated that prolonging sonication time from 10 to 50 min provides significant increase of L* color parameter (P <= 0.01) and insignificant enhancement of total phenolic content and antioxidant activity (P > 0.05) while it reduces a* color parameter of the extracts, significantly (P <= 0.01). Based on Fourier transform infrared spectra of the treatments, ultrasound waves do not impose any destructive impact on functional groups of the extracts. Moreover, scanning electron microscopy images of the olive-waste cake powders showed higher porosity in the microstructure of the sonicated solid residues, specifically when longer ultrasonic times were applied.