4.1.2. Ionic gelation
4.1.2.1. Beads. About 50 years ago, Thiele and Andersen (1955), Thiele and Cordes (1967) observed the formation of a highly or- dered hydrogel when a solution of divalent cations is brought into contact with a solution of some polyuronic acids such as alginates. For the formation of beads a solution of sodium alginate, sodium pectinate or guar gum derivates containing the living microbial biological control agents is dropped into a crosslinking solution containing divalent cations, e.g., Ca2+. Solidification of droplets starts within milliseconds on the droplet surface by ionotropic gelation where Ca2+ ions react with the negatively charged