Characterization of maize amylose-extender ( ae) mutant starches. Part I: Relationship between resistant starch contents and molecular structures

Abstract

Endosperm starches were isolated from kernels of seven maize amylose-extender ( ae) lines: three new ae-lines, derived from a Guatemalan breeding cross with pedigrees of GUAT209:S13 × (OH43 ae × H99 ae) B-B-4-1-2-1-1, GUAT209:S13 × (OH43 ae × H99 ae) B-B-4-4-2-1-1, and GUAT209:S13 × (OH43 ae × H99 ae) B-B-4-4-2-1-2, designated as GSOH1, GSOH2, and GSOH3, respectively, were developed by the USDA-ARS Germplasm Enhancement of Maize (GEM) Project, and four existing inbred lines, H99 ae, OH43 ae, B89 ae, and B84 ae. The resistant starch (RS) contents, measured using AOAC method 991.43 for total dietary fiber, showed that the three new-line starches had larger RS contents (39.4–43.2%) than the four inbred lines (11.5–19.1%). This study was conducted to understand relationship between the RS content and molecular structure of the maize ae-mutant starch. Analytical results showed that the three new-line starches had larger apparent (83.1–85.6%) and absolute amylose-contents (57.4–62.6%) than the starches of the inbred ae-lines (61.7–67.7% and 35.5–44.7%, respectively). The RS content of the ae-mutant starch was positively correlated with both the apparent and absolute amylose-contents of the starch with correlation coefficients of 0.99 and 0.96, respectively. Gel permeation chromatograms revealed that all seven ae starches contained large proportions of intermediate components (IC), 22.4%–52.0%. All seven ae starches displayed similar onset gelatinization temperatures (64.5–65.8 °C), but the three new-line starches displayed higher conclusion temperatures (122.0–130.0 °C) than the four inbred-line starches (100.5–105.3 °C). These results indicated that the crystalline structure of the three new ae-line starches was retained after boiling at ∼100 °C. The crystalline structure was resistant to enzyme hydrolysis and resulted in greater RS contents.