Preparation of Ca-alginate beads containing high oil content: Influence of process variables on encapsulation efficiency and bead properties

The encapsulation of model oil in Ca-alginate beads using high oil loading was studied. It was found that the alginate concentration, oil volume fraction and alginate type each have a significant influence on the encapsulation efficiency and on bead properties. The alginate-oil emulsion, comprising an oil loading up to 30 vol% and 25 g/L of high G alginate solution (equivalent to an oil-to-wall weight ratio of up to 15 g/g), was found to be stable and resulted in an encapsulation efficiency of 90% before drying. The oil-loaded, wet beads were spherical. The encapsulation efficiency was dependent on the degree of cross-linking at the surface of the extruded emulsion droplet as well as on the emulsion stability. The oil extraction profile of dried beads may be related to the structural properties of the beads, which are dependent on both the drying method and the oil loading. The overall encapsulation efficiency after freeze-drying and oven-drying were 90% and 79%, respectively, with an oil content of over 85 wt% for both types of dried beads. The freeze-dried beads were non-oily and free flowing, whereas the oven-dried beads were oily and sticky. The results of this work are compared to those in the literature, and the merits and the drawbacks associated with different methods are discussed. (C) 2011 Elsevier Ltd. All rights reserved.