Integrated microwave-steam sterilisation of loose oil palm fruits: enhanced heating uniformity, crude palm oil quality and energy savings

Loose oil palm fruits are often left uncollected in large quantities while harvesting fresh fruit bunches, which incurs considerable losses in crude palm oil yield. Although the free fatty acid content in loose fruits is undesirably high, microwave sterilisation is known to reduce it significantly. The present study enhanced microwave sterilisation using a new integrated microwave-steam method in which steam exiting the fruits during vaporisation is entrapped and used to complement the heat treatment process. The effect of this new method on the heating uniformity, drying rate, oil extraction rate, crude palm oil quality and energy consumption/cost was investigated. Results showed that up to 25.7% and 13.6% reduction in temperature non-uniformity and energy consumption/cost was achieved with MW-steam heating. Moreover, sterilisation duration was reduced by up to 11.6%. The stacked arrangement of fruits improved microwave absorption efficiency, reducing temperature non-uniformity by up to 45.0% and energy consumption by up to 19.2%. MW-steam sterilisation achieved up to a 10.5% increase in oil extraction rate. Crude palm oil with excellent hydrolytic and oxidative stability was acquired, thus, boosting oil value that can facilitate post-processing in palm oil mills.