Abstract
: Rice starch was cross-linked with epichlorohydrin (0.3%, w/w, on a dry starch basis) and oxidized with sodium hypochlorite (2.5% w/w), respectively. Two dual-modified rice starch samples (oxidized cross-linked rice starch and cross-linked oxidized rice starch) were obtained by the oxidation of cross-linked rice starch and the cross-linking of oxidized rice starch at the same level of reagents. The physicochemical properties of native rice starch, cross-linked rice starch and oxidized rice starch were also studied parallel with those of the two dual-modified rice starch samples using rapid visco analysis (RVA), differential scanning calorimetry (DSC), dynamic rheometry and scanning electron microscopy (SEM). It was found that the levels of cross-linking and oxidation used in this study did not cause any significant changes in the morphology of rice starch granules. Cross-linked oxidized starch showed lower swelling power (SP) and solubility, and higher paste clarity in comparison with native starch. Cross-linked oxidized rice starch also had the lowest tendency of retrogradation and highest ability to resistant to shear compared with native, cross-linked, oxidized and oxidized cross-linked rice starches. These results suggest that the undesirable properties in native, cross-linked and oxidized rice starch samples could be overcome through dual-modification.
Highlights
Starch is a common ingredient used widely in many food and non-food applications
The bonding forces within the granules of starch were strengthened by the cross-linked reactions, which result in an increase in Swelling Power (SP)
A previous work reported that higher level of cross-linking caused a reduced swelling power
Summary
The application of native starches is often limited because of shortcomings in their physiochemical properties such as low shear resistance and thermal stability, thermal decomposition and high retrogradation tendency [1,2,3]. Most commercial starches employed in either food or industrial applications have been chemically modified to improve their functionality. Native rice starches have poor freeze-thaw stability, resistance to shear, and fair stability to retrogradation with moderate clarity and soft texture [4]. The performance and properties of starch solutions can be altered through chemical modifications, by oxidation or addition of charged substituents to the polysaccharide backbone such as cross-linking. Cross-linking will reinforce the granules of starch to be more resistant towards acidic media, heat and shearing [4]. A study revealed a decrease in retrogradation rate and increase in gelatinization temperature with cross-linked starch, and these phenomena are related to the reduced mobility of amorphous chains in the starch granule as a result of intermolecular bridges [1]
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