Structural And Functional Properties Of Normal Rice Starches

Starch is the main storage component in rice grain. The composition and properties of starch determine the quality of rice. Amylose content has an important effect on the properties and applications of rice starch. In this study, starches were isolated from normal rice varieties with different amylose contents. Their morphological structures, molecular structure, crystalline properties, gelatinization properties, hydrolysis properties, and digestion properties were investigated, and the relationships between structural and functional properties were analyzed. This study not only could add some information for the relationships between starch structural and functional properties, but also was useful for the exploitations and applications of rice starch. The main results were shown as followings:Structural properties of normal rice starch The morphological structure and granule size of rice starch were investigated using light microscope, scanning electron microscope, and image analysis system. The molecular structure of rice starch was analyzed using gel permeation chromatography and the crystalline structure was analyzed using a range of spectroscopy techniques. The results showed that normal rice starches with different amylose contents had similar granule morphology and size. The starch granules all showed polygonal shape with sharp angles and edges. The surfaces were smooth and flat. The granules with central hilum had size of 3-5 μm. The contents of amylopectin short branch-chain, amylopectin long branch-chain, and amylose varied from 51.6% to 63.8%,19.1% to 23.1%, and 13.1% to 26.9%, respectively. The amylopectin branching degree varied from 2.3 to 3.1. Normal rice starches with different amylose contents all showed A-type crystallinity. However, the relative crystallinity, short-range order degree, and lamellar peak intensity varied from 25.0% to 32.9%, 0.548 to 0.592, and 134.2 to 247.2, respectively.Functional properties of normal rice starch The functional properties of normal rice starches with different amylose contents were investigated. The results showed that the gelatinization, hydrolysis, and digestion properties were significantly different among rice starches with different amylose contents. The gelatinization onset temperature, peak temperature, conclusion temperature, and enthalpy varied from 55.6 to 64.4℃,63.0 to 74.0℃, 71.3 to 79.6℃, and 9.0 to 13.0 J/g, respectively. The swelling power and water solubility at 95 ℃ varied from 19.4 to 29.8g/g and 3.2% to 11.3%, respectively. The hydrolysis degree of HCl for 4 d varied from 58.1% to 79.4%, and that of a-amyase and amyloglucosidase for 12 h varied from 70.0% to 83.0% and 58.3% to 80.9%, respectively. The rapidly digestible starch, slowly digestible starch, and resistant starch in native starch varied from 12.4% to 22.9%,19.5% to 33.7%, and 43.8% to 68.1%, respectively; those in gelatinized starch varied from 69.4% to 81.2%,9.1% tp 12.6%, and 8.1% to 20.5%, respectively; those in retrograded starch varied from 65.0% to 78.6%,9.5% to 13.1%, and 11.0% to 21.9%, respectively.The relationships between structural and functional properties of normal rice starch The correlation coefficients showed that amylopectin short branch-chain was significantly negatively correlated with amylose content and positively correlatied with amylopectin branching degree. The relative crystallinity, short-range order degree, and lamellar peak intensity were significantly negatively correlated with amylose content. The gelatinization temperature was significantly positively correlated with amylose content and negatively correlated with amylopectin short branch-chain and lamellar peak intensity. The gelatinization enthalpy was significantly positively correlated with amylose content. The swelling power was significantly positively correlated with amylopectin short branch-chain, amylopectin branching degree, relative crystallinity, short-range order degree, and lamellar peak intensity and negatively correlated with amylose content. The water solubility was significantly positively correlated with amylose content and negatively correlated with amylopectin short branch-chain. The hydrolysis degree was significantly positively correlated with amylopectin short branch-chain, short-range order degree, and lamellar peak intensity and negatively correlated with amylose content. The digestion rate was significantly positively correlated with amylopectin short branch-chain, amylopectin branching degree, relative crystallinity, short-range order degree, and lamellar peak intensity and negatively correlated with amylose content.