ARS | Publication request: Effect of shrinkage on isothermal drying behavior of 2-phase olive mill waste

Submitted to: Journal of Food Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 9, 2010
Publication Date: April 1, 2011
Citation: Milczarek, R.R., Dai, A.A., Otoni, C.G., Mchugh, T.H. 2011. Effect of shrinkage on isothermal drying behavior of 2-phase olive mill waste. Journal of Food Engineering. 103(4): 434-441.

Interpretive Summary: When olives are pressed for olive oil, the leftover material, known as 2-phase olive mill waste (2POMW), contains fragments of pits, soft olive flesh tissue, some residual oil, and a large amount of water. Useful compounds could be extracted from the 2POMW, but scientists seek a way to decrease its moisture content before further processing. Previous work has been done to characterize how fast 2POMW can be dried by microwave energy and hot air, but the effect of sample shrinkage was not addressed in that work. In this experiment, both moisture loss and shrinkage were tracked over time. When shrinkage is taken into account, the measured propensity for water to leave the sample is much lower than when shrinkage is ignored. This work gives scientists a better idea of how 2POMW behaves during drying, which will lead to improved designs for industrial dryers and increased utilization of this byproduct of olive oil production.

Technical Abstract: The objective of this study was to determine the drying behavior of 2-phase olive mill waste (2POMW) under isothermal microwave-convection drying conditions. 2POMW samples were dried in a thin layer in a variable-power pilot microwave oven with impinging air, using a feedback controller to maintain sample temperature at one of four levels. Moisture loss and shrinkage of the samples were recorded during drying. The apparent diffusion coefficient of water was determined for the first falling rate period both with and without shrinkage. Apparent diffusivity was 28% lower when shrinkage was considered. Thus, shrinkage plays an important role in the drying behavior of this agricultural residue.