Physicochemical properties of corn flour and starch and their relation to gel texture of two dry-milled fractions

Ying-Pi Lin, Purdue University

Abstract

Ten corn cultivars with different kernel density and hardness scored were dry-milled to separate the grit and flour fractions. Causal relationships between physicochemical properties of corn flour and starch and their respective gel textural attributes were investigated. Texture profile analysis revealed that substantial differences were found in gel texture among ten corn Cultivars. Also, both flour and starch gels in the grit fraction had much higher values for hardness, guminess and chewiness than their flour counterparts. Starch gels were positively correlated with flour gel hardness in both dry-milled fractions implying that starch is a major determinant of gel texture. The influence of starch on the texture characteristics of starch and flour gels from the dry-milled grit and flour fractions appeared to be related to the fine structural differences of amylopectins. Starch from the grit fraction with higher amount of long chain amylopectin (DPn 70-75) was shown to significantly and positively correlate with stronger flour and starch gels from this fraction. Among the ten corn cultivars, amylose content determined from size exclusion chromatography was significantly correlated with textural parameters of starch gels from both two dry-milled fractions. We found that the thermal parameters of gelatinization and retrogradation revealed by differential scanning calorimetry (DSC) were also related to amylopectin structure. Both the onset temperature (To) and enthalpy ($\Delta$H) of gelatinization were positively correlated with the amount of the long chains (DPn 70-75) and negatively correlated with the extent of chain branching of the amylopectin. The enthalpy ($\Delta$H) of retrogradation was positively correlated with the proportion of the long chains and average chain length of the amylopectin among the ten corn cultivars. This study also showed that gelatinization and retrogradation properties of starch and flour correlated to some aspects of gel texture, particularly gel hardness. The findings suggest that fine structure of amylopectin, including chain length distribution, chain branching and average chain length, affects the crystalline structure of native starch and retrogradation of gelatinized starch. These genotypic and kernel spatial differences in starch structure have not been shown prior to this report and could have significant impact on those trying to tailor make corn flours and starches for precise applications in the food industry.

Degree

Ph.D.

Advisors

Hamaker, Purdue University.

Subject Area

Food science|Biochemistry

COinS