(332g) Equilibrium Swelling of Starch Suspensions in Presence of Xanthan Gum upon Heating

Starch swells significantly after a certain temperature in a process called gelatinization, which is a crucial factor that dictates the viscoelasticity, rheology, and hence, function of starch-based products. Xanthan gum is a polysaccharide used widely in many applications to control pasting behavior and rheology of the starch paste. This work aims to study equilibrium swelling of starches with xanthan as an additive during the pasting process. Experimental data are presented for equilibrium swelling of two starches: normal maize starch and waxy maize starch for two starch concentrations, dilute (0.1%w/w solvent) and concentrated (5%w/w solvent), where xanthan concentration is varied from 0 to 0.5%w/w. The starch gelatinization temperature is inferred from viscosity-temperature profiles, which shows an increasing trend with starch to xanthan ratio. As a result, the swelling for dilute starch suspensions, where starch to xanthan ratio is low, increases with addition of gum. For concentrated waxy maize starch suspensions, the swelling increases abruptly after a certain xanthan concentration. This may be explained because for highly swollen granules at high starch content, xanthan gets excluded from the thin films between granules, which gives rise to attractive depletion forces between the granules. However, for normal maize concentrated suspension, swelling negligibly decreases with xanthan, possibly due to osmotic pressure effects. Differential scanning calorimetry experiments are performed to determine effect of xanthan on the enthalpy of gelatinization. For both starches, the gelatinization enthalpy is shown to decrease with xanthan addition. A previously developed mathematical model, based on Flory’s polymer swelling theory, is extended to predict the equilibrium swelling taking into account osmotic pressure and depletion forces due to presence of xanthan in the dispersion medium.