Prediction of Swelling and Pasting Behavior of Starch Suspensions
thesisposted on 12.10.2021, 15:13 authored by Gnana Prasuna Reddy DesamGnana Prasuna Reddy Desam
Starch pasting behavior greatly influences the texture of a variety of food products such as canned soup, sauces, baby foods, batter mixes etc. The annual consumption of starch in the U.S. is 3 million metric tons. It is important to characterize the relationship between the structure, composition and architecture of the starch granules with its pasting behavior in order to arrive at a rational methodology to design modified starch of desirable digestion rate and texture.
In this research, polymer solution theory was applied to predict the evolution of average granule size of starch at different heating temperatures in terms of its molecular weight, second virial coefficient extent of cross-link and electrostatic interaction within a granule. Evolution of granule size distribution of normal maize starch (NMS) and NMS crosslinked to different extents with sodium trimetaphosphate, waxy rice starch, normal rice starch and normal potato starch when subjected to heating at a rate of 15 C/min to 65, 70, 75, 80, 85 and 90 C was characterized using static laser light scattering. As expected, granule swelling was more pronounced at higher temperatures and resulted in a shift of granule size distribution to larger sizes. Most of the swelling occurred within the first 10 min of heating except for potato starch. Novation 1600 (Modified Potato Starch) is also found to shift to larger sizes at longer holding times and higher temperatures, but this shift is found to be gradual and for penpure 80, even at 60 C, the size distribution shifts to smaller sizes at longer holding times indicating breakup of the granule.
The structure of normal maize starch was characterized by cryo scanning electron microscopy. The number of crosslinks in the starch network was inferred from equilibrium swelling. This is related to peak viscosity and zeta potential of granule for NMS and its crosslinked starches. Chemical potential profile as well as the temperature profile within the granule at different times were predicted which were then employed to evaluate the granule size at different times. The proposed model is able to describe the swelling behavior of different varieties of starch and also the effect of crosslinking.
The viscoelasticity for different starch types, heating rates, and heating temperatures were characterized. A methodology to predict the storage modulus of starch paste due to granule swelling, given the physical properties of the starch granule is presented. In high-volume fraction regime, classical model for foam rheology enabled calculation of limiting storage modulus for different starches. By scaling the storage modulus with limiting storage modulus, the storage modulus of a wide range of starches forms a master curve. This master curve when employed along with the swelling model resulted in the successful prediction of development of texture for different types of starches.
In low-volume fraction regime (below 65%), Stokesian dynamics simulations are used to predict the viscoelasticity of polystyrene micro particles and fractionated starch suspension and compared with experiments. Predicted values of storage modulus from stokesian dynamics simulation at 4 HZ for different volume fractions of monodispersed polystyrene spheres of two different sizes namely 25 and 116 micrometer compared well with experimental values. Stokesian dynamics also describes the storage modulus of fractionated starch granules for volume fractions between 0.4 - 0.5
The average granule size of starch in presence of sucrose was initially increasing and then decreasing with maximum swelling at 5% and 10% sucrose concentration for NMS and WRS. The average granules size continuously increases for WMS and decreases for NRS with increase in sucrose concentration. The Gelatinization Temperature increases with increase in sucrose concentration for all starches. Enthalpy of Gelatinization increases with increase in sucrose concentration for Normal starches where as there is no effect of sucrose concentration for waxy starches. Flory Huggins starch-sucrose interaction parameter was characterized which is used to predict the equilibrium swelling power using a mathematical model proposed to quantitatively describe the equilibrium swelling in the presence of solute (sucrose) based on Flory Huggins polymer solution theory to develop rational guidelines for identification of sugar substitute with desirable functional properties. The model predictions of equilibrium swelling power agrees with experimental results.