Encapsulation of sunflower oil in starch matrices via extrusion: effect of the interfacial properties and processing conditions on the formation of dispersed phase morphologies

In this study, the encapsulation of sunflower oil in a starch matrix via extrusion was investigated. The aim of this study was to get insight into the relations between the processing parameters, the hydrophile¯lipophile balance (or the hydrophobic¯hydrophilic balance; HLB) value of the emulsifier and the morphology of the dispersed phase. The obtained samples were analysed for their dispersed phase morphology using scanning electron microscopy. It was seen that the HLB value of the emulsifier affected the dispersed phase morphology. The average size of the dispersed oil droplets decreased with increasing HLB value, and was explained by the observed decrease in the interfacial surface tension between the starch melt and the oil phase. Average sizes of oil droplets also decreased with increasing screw speed, increasing melt temperature and decreasing throughput. The screw configurations also affected the average sizes of dispersed oil droplets. Especially dispersive mixing elements and kneading blocks favour the formation of smaller dispersed oil droplets.