(177i) Grape Residue Anthocyanin Extraction Using Ultrasound

During the processing of fruits and vegetables there is a large amount of waste generated, being discarded in the environment or used as low value-added products. It is estimated that the utilization of plant raw materials does not exceed 80% to 85% during processing. Extraction techniques have been investigated to obtain valuable natural components of plants for commercialization. However, traditionally used methods, such as Soxhlet, require relatively high amounts of solvent, and are a long-lasting process. Thus, there is a growing demand for new extraction techniques that can overcome these problems and among them, there is the ultrasonic-assisted extraction. Ultrasound-assisted extraction is a technique that is not costly, simple and an efficient alternative to conventional techniques. The greatest benefits of using this technique in solid-liquid extraction include increased extraction rate and rapid kinetics. Ultrasound can also reduce the operating temperature, allowing the extraction of thermolabile components. Compared with other innovative techniques, such as microwave-assisted extraction, ultrasonic equipment has a lower cost and simpler operation. Furthermore, ultrasonic assisted extraction can be used with various solvents to separate a wide variety of natural components. Thus, the present work had the objective of evaluating the use of ultrasound for the extraction of anthocyanins from grape agroindustrial residue, which also had its antioxidant capacity evaluated. The grapes of the Isabel (Vitis labrusca L.) variety were processed in a local industry (Recife, Brazil), and the residue was obtained, mainly containing bark and seeds. The residues were dried (50 °C) in a oven until reaching 9% moisture. With the dried residue, grinding was performed with a knife mill until the flour passed through a 20 mesh sieve. The obtained flour was packed under vacuum and stored at -5 ° C and kept under refrigeration until use. An aqueous solution of 50% ethanol at the concentration of 1:18 (grape residue: solvent) was used for the ultrasonic assisted extraction (probe type) of the grape residue anthocyanins. For the optimization of the process, the effect of ultrasound application on anthocyanin content and antioxidant capacity was evaluated by means of a complete factorial (2²) experimental design, including the central points (level 0) and the axial points (± α levels) . This experimental design generated a quadratic model, where the value of the dependent variables Y (total anthocyanins content and antioxidant capacity) were a function of the independent variables (intensity of ultrasound power and time). The regression coefficients, analysis of variance and generation of response surfaces were obtained with the aid of Statistica 7.0. The samples were evaluated without light to avoid photo-oxidation. After the extraction process, the extract obtained was centrifuged, the supernatant was evaporated using an evaporator route to remove the residual ethanol. The final volume was standardized in approximately 50 mL. The extracts were quantified for the anthocyanin content and the antioxidant capacity was evaluated. In relation to the anthocyanins, the results were adjusted by a second-degree polynomial and with this the response surface was obtained. It was observed that the anthocyanins content presented a linear behavior, since the quadratic terms of power intensity and time were not significant (95% confidence level). The higher the ultrasound power and the longer the exposure time of the extracts, the higher the anthocyanin content of the samples. For the antioxidant capacity, the obtained model was also considered predictive and the response surface was generated. It was observed that intermediate bands of power intensity, regardless of the time of application of the ultrasound, resulted in higher values of this parameter. Thus, from the results presented, it could be observed that the ultrasound is shown as an efficient technique in the extraction of anthocyanins from the grape residue. The extracts obtained from these compounds were rich in the component and the extraction by ultrasound could be performed in reduced time compared to the existing conventional techniques. For the tests performed, high ultrasound intensity and longer exposure times resulted in better anthocyanin extraction efficiency and higher antioxidant capacity values.