Effect of Time and Temperature of Baking on Oil Recovery
The effect of time of baking on OR is shown in Fig. 2. The OR was only 77% without baking. It gradually increased as the baking time was increased from 0.0 to 8 minutes. However, it dramatically decreased when the baking time was further increased to 10 minutes. Among the baking time studied, baking for 8 minutes was the most suitable for recovering oil from the pecan kernel slurry. Therefore, proper baking time will increase the OR though baking for too long adversely affected the OR.
The effect of temperature of baking on OR is also shown in Fig. 2. The OR was only 77% without baking. It gradually increased as the baking temperature was increased from 24 to 95 ℃. However, it decreased when the baking temperature was further increased to 120 ℃. Among all the baking temperature investigated, baking at 95 ℃ resulted in the highest OR.
Baking the pecan kernels ahead of grinding is necessary for deactivating lipase and removing water. Lipase deactivation is able to prevent neutral oils from hydrolysis during grinding and extraction by water. Undesirable losses of neutral oil can be reduced if its hydrolysis is prevented so that di- or mono-glycerides, glycerols and free fatty acids formation can be decreased. This step may also be important for avoiding emulsion during aqueous extraction or grinding. This should also be a critical factor of obtaining the best OR. Furthermore, proper baking may facilitate the disruption of cell wall by grinding. However, increases in baking time or temperature might elevate the extent of protein denaturation, which might decrease OR because of an increase in oil absorption.