Drying ability of whole black olive (Olea europaea L.) fruits in Kabylian region (North-East Algeria)

The present work aimed to investigate the drying ability of whole fresh black olive (Olea europaea L., var. chemlal) fruit (BO). Static oven-drying was applied to emulate the traditional open-air drying procedure applied in some localities of Kabylian region, in North-eastern Algeria. The drying ability, with and without applying freezing-thawing as pretreatment of fresh BO, was evaluated in terms of: i) equilibrium drying time which is needed to reach equilibrium water content, and ii) corresponding concentration of oleuropein, a well known bitter bioactive molecule of olive fruits. Dried and undried fruit were also analyzed for weight, length, width, K, Ca, Mg, Cu and fat. Dried olives were analyzed for water and oil uptake capability. Results showed that the equilibrium drying time decreased exponentially with drying temperature, regardless of whether the olive fruits were pretreated by freezing-thawing or not. However, the application of freezing-thawing as pretreatment enhanced the drying process by reducing the equilibrium time. The drying process implicated also a substantial debitterring of BO since 47 to 70 % of the initial oleuropein content was eliminated, under the drying conditions. Dried BO showed an interesting water uptake (similar to 40 %), compared to oil uptake (similar to 9 %), which could be useful to better design of their preservation process by pickling.