Modelling and simulation of heat penetration in palm fruitlets during thermal treatment process

Abstract

Crude palm oil (CPO) is derived from the fleshy mesocarp of the oil palm fruits, Elaeis guineensis. The mesocarp of the fruit contained an endogenous enzyme (lipase), which is activated upon detachment or bruising of the fruit. The lipolytic activity of the enzyme leads to the accumulation of free fatty acid (FFA) which is a major quality index of CPO. Heat treatment is used to substantially inactivate the lipase in the mesocarp fibre of palm fruitlets. However, the current practice of using steam has been faced with the challenges of improper steam distribution within the vessel which in conjunction with the complex matrix of the bunch and whole loading of the fruit bunch into the sterilizer brings about the differential cooking of the fruit, thereby causing partial inactivation of the enzyme. A COMSOL Multiphysics 5.3 was used to simulate heat treatment of the fruit using hot water. The simulation results reveal that the surface temperature of the kernel will attain at 70°C within 50 mins when submerged in hot water at 70°C. A series of experiments were also conducted to verify whether a temperature of 70°C will completely inactivate the enzyme. The result shows that the residual activity of the lipase was inactivated completely after 50 mins of heat treatment at 70°C. Since simulation result shows that the surface temperature of the kernel will be 70°C when the fruit is heat treated at that temperature, therefore, it implies that heat treatment of the fruit with hot water at 70°C will be an effective heat treatment to inactivate the endogenous lipase of palm fruits.