Tribological properties of rice starch in liquid and semi-solid food model systems

This study investigated the tribological and rheological properties of liquid and semi-solid food model systems containing micro-granular rice starch. Native (uncooked) and gelatinized rice starch dispersions, o/w emulsions and emulsion-filled gelatin gels were studied as food model systems. Native rice starch particles behaved as active fillers and increased the gel modulus with increasing concentration. At low concentration, soft gelatinized rice starch particles decreased gel modulus. At high concentration, gelatinized rice starch increased the gel modulus due to dense packing of particles. Native and gelatinized rice starch increased friction coefficients with increasing concentration due to different mechanisms. Native rice starch particles increase friction probably due to their irregular shape and particle agglomerations (at high concentration) that indirectly increase surface roughness and asperity contacts. Gelatinized rice starch particles increase friction probably due to the stickiness of leached-out starch polymers. The presence of oil droplets in rice starch-o/w emulsions could reduce the friction caused by stickiness of gelatinized rice starch. The tribological behaviors of rice starch-emulsion-filled gels are more complex than liquids due to the bulk and breakdown properties of the gel matrix. We conclude that morphology and surface properties of the rice starch particles together with bulk and breakdown properties of matrices are the main factors determining the tribological properties of food model systems containing rice starch particles