A novel stepwise microwave hydrodistillation and extraction process for separating seed oil and essential oil simultaneously from perilla seeds

Stepwise microwave hydrodistillation and extraction (SMHDE) was utilized to separate perilla essential oil as a byproduct while boosting perilla seed oil yield and quality. The optimal process for producing perilla seed oil was determined by Plackett–Burman and Box–Behnken design experiments based on a factor screening experiment. Under ideal working conditions, the yield of seed oil was 36.49% ± 0.07%. The content of α-linolenic acid in perilla seed oil obtained by SMHDE was 69.90%, which was significantly greater than that obtained by Microwave-assisted method (MAE) (66.59%) and that obtained by Soxhlet extraction (SE) (66.51%). The yield of perilla seed essential oil obtained by SMHDE was 0.55 ± 0.14 mL/kg, and the main component was perillaldehyde, which was present at a concentration of 20.50%. GC‒MS analysis revealed that the content of volatile compounds in seed oil obtained by SMHDE (9.20%) was significantly lower than that obtained by MAE (10.94%) and SE (15.23%). Compared with traditional methods, SMHDE can effectively increase seed oil yield and quality without negatively influencing its fatty acid composition or physicochemical properties. These findings support the use of SMHDE to increase the production and quality of seed oil and prevent the waste of perilla essential oil resources.