Response Surface Methodology for Ultrasound-Assisted Oil Extraction Optimization from Blackberry, Chokeberry, and Raspberry Waste Products

Berry fruit seeds which are considered as a fruit industry waste product can be a source of oil with unique chemical, physical, and nutritional properties. The blackberry, chokeberry, and raspberry seeds can be perceived as an alternative source of oil. However, conventional oil extraction is merged with financial and environmental expanses. Therefore, alternative extraction methods, ultrasound-assisted, for example, are being gradually introduced to the common practice. The aim of the following study was to determine the optimal conditions of ultrasound-assisted extraction of oil from blackberry, chokeberry, and raspberry seeds in order to obtain oil with high yield and improved oxidative stability. The variables of the experiment were extraction time and ultrasound amplitude. Based on the results, the mathematical models were fit, and optimum conditions of time and amplitude were calculated: 8.20 min and 72.98%, 10.11 min and 59.18%, 8.43 min and 95.57% for blackberry, chokeberry, and raspberry seed oils, respectively. Additionally, oils obtained in the optimized conditions were assessed in differential scanning calorimetry study to evaluate their melting and crystallization characteristics. The results showed that ultrasound application affected thermal properties of oils only slightly. The evaluation of oxidation kinetics led to the conclusion that ultrasound may cause an activation energy increase. Also, the profile of fatty acids and their distribution in triacylglycerol molecules were studied. The output values of experiments were comparable between oils obtained from the same berry seeds. All of the oils were characterized with a high share of polyunsaturated fatty acids (over 70%) with predominant content of linoleic acid. Summarized results show that the ultrasound technique can be successfully applied in the oil extraction procedure. The benefits contain improved yield, longer oxidation induction time, and invariance of the specific oil chemical and physical properties.