Ethanolic extraction of Rosa rubiginosa soluble substances: Oil solubility equilibria and kinetic studies

The kinetics of extractable substances from rosehip seeds (Rosa rubiginosa) with ethanol as solvent was studied. The influence of temperature and water content on the oil solubility was also analyzed, because oil represents about 80% of soluble substances. The experimental extraction data led us to apply a previously developed kinetic modeling which considered the external mass transfer resistance. Oil solubility dramatically decreased with the water present in ethanol (from 92% to 99.9%). The influence of temperature was high for absolute ethanol (99.9%), the values varying between 40 g/L at 20 °C and 140 g/L at 60 °C, whereas decreased with ethanol percentage, being 15 g/L at 20 °C and 45 g/L at 60 °C for 96% .The effective diffusivity Deff and kR/Deff modulus, being “k” the external mass transfer coefficient and R the radius, were calculated. The diffusivity values were between 1.2 × 10−11 and 2.2 × 10−10 m2/s, being the highest value for 96% ethanol. This parameter increased with particle size, whereas the kR/Deff values were between 0.1 and 0.3, the higher values for the higher liquid:solid ratio were. An acceptable prediction of extraction yield for wide time ranges and liquid–solid ratios between 15 and 50 mL/g solid, especially with 92% ethanol was achieved.