Comparative study on morphological, rheological and functional characteristics of extruded rice starch citrates and...

Two levels of chemically modified starches (starch citrates and lactates) prepared at 20% and 40% w/v concentration was subjected to extrusion to produce pregelatinized starches (PG). Starch citrates and lactates modified at 20% and 40% level were referred as (SC20 and SC40) and (SL20 and SL40), respectively. These PG starches underwent significant structural changes during extrusion as depicted by scanning electron micrographs. Native starches showed lower swelling power and water binding capacity but formed harder gels compared to chemically modified pregels. The dynamic rheology of these polymers (extruded modified starches) suggested visco-elastic property i.e. (G' > G''). Citrates demonstrated higher G' than lactates in both frequency and temperature sweep tests. Stability of storage moduli over entire temperature range confirmed that addition of citrates and lactates led to strengthening of gel structure through cross linking and esterification. Non-newtonian behavior was shown by all samples as determined through steady shear flow test with flow behavior index <1. Starch citrate (SC20-PG) demonstrated higher shear stress values. While, SC40-PG depicted anti-thixotropic behavior as measured through in-shear structural recovery measurements. On the basis of results obtained, the dual modification (chemical followed by extrusion) may impart fruitful applications in various food products.