Oil extraction from spent coffee grounds assisted by non-thermal plasma

Coffee is one of the most popular beverages in the world and around 50% of the processed coffee beans becomes waste as spent coffee grounds (SCG). These SCG contain up to 20% of oil, which can be recovered and used in many different processes, such as biodiesel production, cosmetics and pharmaceuticals. The extracted oil contains large amounts of antioxidants, anti-inflammatory agents and immunomodulators, in addition to fatty acids that have excellent emollient and moisturizing properties. It is therefore of interest to improve the oil extraction technique, to enhance the efficiency, reduce the extraction time and improve the quality of the oil extracted. Thus, in this study, a new technique for SCG oil extraction, using a non-thermal plasma technology as a pre-extraction procedure prior to Soxhlet extraction, was investigated, aiming to improve the extraction efficiency and oil quality. For comparison purposes, experiments were also carried out using an ultrasound pre-extraction procedure prior to Soxhlet extraction. It was observed that the use of pre-extraction with the plasma more than double the extraction yield compared with the Soxhlet extraction alone. Also, it increased the yield by around 30% compared with the use of ultrasound as the pre-extraction procedure. Analysis of the oil extracted by GC-MS showed that the quality of the oil composition was maintained. Also shows an increase in the antioxidant potential, which can prevent the harmful effects of ultraviolet (UV) radiation on the skin, due to their antioxidant, anti-inflammatory and immunomodulatory properties. The SEM images showed significant changes in the walls of the polyhedral cells of the spent coffee grounds after non-thermal plasma pre-treatment.