Evaluation of double-roll crusher on oil palm fruit bunches and effect of bruising level on free fatty acids content

Sterilisation of oil palm fruit bunches at atmospheric pressure employed in palm oil mills hinders the penetration of steam into the inner layers of the bunch. Therefore, a double-roll bunch crusher was developed to increase the surface area of the bunch. However, this process will also contribute to bruised fruitlets, as well as exposing the oil to oxidation and increasing free fatty acids content. This study was carried out to evaluate the bruising level of the oil palm fruitlets after crushing, and the effect of preheating of the crushed fruit bunches on the increase of free fatty acids. The comparison was made to the bruising level of oil palm fruitlets at various points in the milling process and after crushing with the control sample of bunch collected from the plantation. It was found that the percentage of moderately-bruised fruitlets and heavily-bruised fruitlets after crushing increased from 5.96% to 13.06%, and 2.15% to 14.14%, respectively. Harsh handling during transportation of oil palm fruit bunches was found to increase the bruising level by 23%. The increment of free fatty acids was successfully halted through the preheating of the crushed bunches. Results also showed that the use of bunch crusher was effective in allowing penetration of steam into the inner parts of the oil palm fruit bunches. The crushing also shortened the sterilisation process of the oil palm fruit bunches at atmospheric pressure compared to that of the pressurised batch sterilisation process