Influence of sea buckthorn pomace pre-treatment and drying conditions on the drying kinetics, quantity and quality of seed oil

Sea buckthorn (Hippophae rhamnoides L.) pomace was pre-treated by sonication or freezing and a thin layer of pre-treated or untreated pomace was dried under various conditions. The seeds separated from dried pomace were ground and subjected to batch extraction using hexane as a solvent. Effects of process factors, i.e. drying temperature (40 degrees C and 50 degrees C), pomace layer thickness (3 mm and 10 mm), ultrasound amplitude (0 % and 20 %) and pre-treatment temperature (-20 degrees C and 20 degrees C), on the drying kinetics, quantity and quality of seed oil were evaluated. Performance of air drying and oil extraction were correlated with the process factors by multiple regression equations, which highlighted a significant effect of pomace layer thickness. A thicker layer led to higher levels of effective diffusivity ((0.141-1.484) x 10(-9) m(2).s(-1)), oil yield (13.1-14.5 %) and extraction efficiency (90.5-93.5 %) as well as to lower values of mean drying rate (0.144-0.354 kg.kg(-1).h(-1)). Mean mass percentages of fatty acids found in the oils extracted from the seeds separated from the pomace dried at 50 degrees C, i.e. 26.8 % alpha-linolenic, 38.9 % linoleic, 22.7 % oleic, 0.9 % palmitoleic, 7.9 % palmitic and 2.8 % stearic acid, were almost invariant with the process factors.