Optimization of Mechanical Extraction Conditions for Producing Grape Seed Oil

Abstract

Abstract. In the U.S., over 150 thousand metric tons of dried grape seeds containing 13% to 19% oil are produced every year as a byproduct of processing about 5.8 million metric tons of grapes. The health-promoting properties of grape seed oil are due to the presence of many bioactive components, such as unsaturated fatty acids, and antioxidants. The chemical (hexane) extraction method is detrimental to these vital bioactive components and accelerates the oil oxidation process. The objectives of this study were to determine the effects of the grape seed moisture content (MC), particle size, and the mechanical expeller’s screw speed and die diameter on grape seed oil yield and optimize the operating conditions of the expeller for maximum oil yield. Results showed that preheating the screw press with a ring heater to 60°C almost eliminated the initial time lag to extract oil. Reducing the particle size by grinding the seeds did not significantly influence the oil yield and hindered the extraction by clogging the feeding chute. Increasing the screw speed from 36 to 120 rpm increased the filtered oil production rate from 0.20 to 0.57 kg h -1 with a 10 mm die diameter and 5.3% MC seeds without significantly affecting the oil extraction percentage. Increasing the die diameter from 6 to 10 mm increased the oil production rate from 0.15 to 0.43 kg h -1 at 95 rpm for 5.3% MC seeds and decreased the filtered oil extraction percentage from 9.2% to 7.3%. Seed MC in the range of 3.1% to 8.7% did not affect the oil yield; however, above 8.7% MC, oil yield was significantly reduced. Extracting whole grape seeds with 5.3% MC at 120 rpm using a 10 mm die diameter was found to be the optimum condition, which produced a grape seed oil yield of 7.6% at an oil extraction rate of 0.57 kg h -1 and seed residence time of 8.6 s.