Irregular textural features of dried alginate–filler beads

Abstract

Freeze-dried hydrocolloid beads can be used as carriers for many food, non-food and biotechnological operations. Information on their shape and surface properties, how different features are produced on their outer surface as a result of technological procedures, and the influence of fillers and other ingredients on external and internal shape and texture have never been investigated in detail. These parameters are very important since the surface of the bead is the first part to come into contact with its fluid, solid or gaseous environment and together with its internal structure, will influence, if not determine, its suitability to a predetermined task. In our study, projections formed on the surface of the bead during freezing. Smaller-sized fillers (such as kaolin) gave a smoother surface; a rougher surface was achieved with a bigger-diameter filler, such as bentonite. The presence of filler and/or glycerol in the bead increased the number of mid-area ‘craters’ and reduced the number of the smaller ‘craters’ formed on the bead's dried surface. Moreover, the inclusion of glycerol had a large influence on the distribution of pores within the beads. Filler inclusion in the dried product reduced its collapse and roundness distortion during the drying process. In conclusion, the components and the method by which the dried bead was formed completely determined its weight, volume, shape and surface features. Taking these parameters into consideration provides the researcher with a useful tool for creating tailor-made dried beads for a predetermined operation, thereby increasing the probability of success. This was proven by the improved antifungal activity of entrapped Pantoae agglomerans (biocontrol agent) within alginate–glycerol–chitin beads.