The effect of alginate inclusion on the extrusion behaviour of soya

Abstract

The effect of the addition of a range of polysaccharides on the extrusion behaviour of soya grits has been investigated. Guar gum, locust bean gum, sodium carboxymethyl cellulose, pectin and carrageenan had little effect when incorporated in the feed at the 1% level. The addition of alginates and low viscosity hydroxypropyl and hydroxyethyl celluloses resulted in a significant reduction in extruder torque and product temperature. The alginate effect was investigated in detail and was observed both for moderate temperature (∼120°C) and high temperature (∼180°C) extrusion. In the latter case an expanded textured product was produced and alginate addition resulted in a reduction in expansion ratio. High mannuronate alginates had the greatest influence on extrusion behaviour and there was evidence to suggest that very low molecular weight samples of the polysaccharide did not function in the same way as materials of moderate or high molecular weights. Pressure measurements at the die confirmed that the effect of alginate on extruder torque and product temperature was due to a lowering of the viscosity of the soya melt. The molecular origin of this effect still needs to be understood.