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Abstract
Starches from various botanical origins (rice, maize and potato starches) were cross-linked in the presence of epichlorohydrin (EPI), respectively. Then, the cross-linked starches were further oxidized with sodium hypochlorite (NaOCl, 2.5% w/w) to obtain oxidized cross-linked starches (OCS). The chemically modified methods on the physicochemical properties of different starches were investigated. It was found that cross-linking treatment increased peak, setback and final viscosities of rice and maize starches but decreased those of potato starch. The paste clarities of cross-linked rice and maize starches significantly reduced, whereas those of cross-linked potato starch increased. Oxidation treatment significantly decreased peak, final and setback viscosity values of all starches and significantly increased paste clarities. Dual-modified starches had higher peak, final viscosities and the ability to resistant to shear compared with oxidized starches, meantime it had lower tendency of retrogradation and higher paste clarities compared with cross-linked starches. Under those conditions of dual-modification, undesirable starch properties were counteracted. Key words: Rice, maize, potato, starch, cross-linking, oxidation, oxidized cross-linking.
Highlights
Potato and maize starches are widely used in food and non-food industry in the world
Carboxyl contents varied significantly according to starch types, oxidized potato starch had the highest carboxyl content (0.95%), and whereas oxidized rice starch had the lowest (0.48%)
The present results suggested that carboxyl contents varied significantly according to starch types, oxidized potato starch had the highest carboxyl content, and whereas oxidized rice starch had the lowest, which differed from those by Kuakpetoon and Wang (2001), but agreed with those by Hebeish et al (1999)
Summary
Potato and maize starches are widely used in food and non-food industry in the world. Starch origin and granule size have a significant influence on the physicochemical properties of native starch and modified starch (Morikawa and Nishinari, 2000). The numerous industrial and food applications of native starches are limited because of their tendency to retrograde. Chemical cross-linking imparts structural integrity of starch These chemically cross-linked starches are usually resistant to shear, low pH, and high temperature during food processing conditions. Singh et al (2007) observed 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. Jyothi et al (2006) showed that cross-linked starch has more pronounced synaeresis than native starch because of ordered structure in the starch paste, resulting in a higher degree of retrogradation
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