Influence of thermal treatments on the antioxidant activity of hemp cake polar extracts

The effect of preheating temperature (X 1 ), preheating time (X 2 ) and the nature of the extracting solvents (X 3 ) on the antioxidant activity of ultrasonic extracts of hemp cake was evaluated using a factorial design with a general linear multiple regression method using the three variables (X 1 , X 2, and X 3 ) and three levels including low (-1), intermediate (0) and high (+ 1). The results indicated that the extracting solvent and the preheating temperature levels were the principal effects influencing the total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity (DPPH and FRAP). The highest level of preheating temperature (+ 1 = 180 °C) and extracting solvent (+ 1 = Ac80) were the optimal conditions for enhancing the extraction of the total phenolics and providing the highest antioxidant activity in hemp cake extracts. The interaction between temperature (X 1 ), and the type of solvent (X 3 ) significantly ( p < 0.05) affected all the dependent variables examined.