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Native starches from twenty-six botanical sources were determined for their structural features and stability against freeze–thaw treatments. Starch gels (5%, w/w) were prepared and repeatedly freeze–thawed up to five cycles by storing at −18 °C for 21 h and then at 30 °C for 3 h. Water release (syneresis) from the thawed gel after the 1st, 3rd and 5th cycle was measured gravimetrically, and evaluated in relation to apparent amylose content (AAC) and distribution of amylopectin branch chains with degree of polymerization 6–12 (APC ratio). Syneresis was not observed for starch gels of cassava, normal and waxy japonica rice up to the 1st, 3rd and 5th cycle, respectively. On the other hand, syneresis rapidly occurred for starch gels of elephant yam, new cocoyam, potato, edible canna, and water yam. Optimal multiple linear regression models were generated to predict individual effect of AAC and APC ratio on syneresis of starch gels. The prediction models illustrated the positive unit-contribution of AAC and negative unit-contribution of APC ratio to syneresis (P

Structural changes from the octenylsuccinylation of high-amylose maize starch were investigated by FT-IR and differential scanning calorimetry (DSC), with observations made on the distribution of octenyl succinate (OS) groups using confocal laser scanning microscopy (CLSM). Results of the octenylsuccinylation on in vitro digestion property (uncooked and cooked) were also determined. DSC data revealed a broad gelatinization endothermic peak ranged from 72.5 °C to 96.4 °C for the native starch, and a downward trend for products of increasing degree of substitution (DS). The OS groups appeared to be distributed throughout the OS-starch granules, especially on the surface. Octenylsuccinylation decreased the slowly digestible starch content of low DS OS-starch after cooking, while increased the resistant starch (RS) level in uncooked OS-starch. Even though uncooked OS-starch (DS ≈ 0.04) has 86.3% RS content, its RS content was reduced to 7.5% after cooking.

The objective of this study was to understand the crystalline structures of maize ae-mutant starches by analyzing the structures and properties of their Naegeli dextrins. After an exhaustive acid hydrolysis of the starch granules with sulfuric acid (15.3%, v/v) at 38 °C for up to 102 days, the maize ae-mutant starches produced 18.3–39.5% Naegeli dextrins. The Naegeli dextrins showed the B-type polymorph and displayed similar onset (45.1–51.4 °C), peak (113.9–122.2 °C), and conclusion (148.0–160.0 °C) gelatinization-temperatures and large enthalpy changes (21.8–31.3 J/g) and percentage crystallinity (77.0–79.2%). The Naegeli dextrins showed unimodal molecular-size distributions with the peak molecular-size at degree of polymerization (DP) 16. The molecular-size distributions of the Naegeli dextrins did not significantly change after debranching with isoamylase, indicating predominantly linear molecules. The isoamylase-treated Naegeli dextrins had average chain lengths of DP 23.8–27.5 and large proportions of long chains (DP ≥ 25, 36.7–52.7%), resulting from hydrolysis of amylose double helices.

GEMS-0067 maize starch contains up to 32% elongated starch granules, much higher than amyloseextender (ae) single-mutant maize starch (7%) and normal (non-mutant) maize starch (0%). These elongated granules are highly resistant to enzymatic hydrolysis at 95–100 C, which function as resistant starch. The structure and formation of these elongated starch granules, however, were not known. In this study, light, confocal laser-scanning, scanning electron, and transmission electron microscopy were used to reveal the structure and formation of these elongated starch granules. The transmission electron micrographs showed fusion through amylose interaction between adjacent small granules in the amyloplast at the early stage of granule development. A mechanistic model for the formation of elongated starch granules is proposed.

GEMS-0067 maize ae -line starches developed by the Germplasm Enhancement of Maize (GEM) project consist of 39.4–43.2% resistant starch (RS), which is larger than the existing ae -line starches of H99 ae , OH43 ae , B89 ae , and B84 ae (11.5–19.1%) as reported in part I of the study. The objective of this study was to understand the mechanism of the RS formation in the GEMS-0067 ae -line starch. In the current study, we analyzed the structures and properties of the RS residues that remained after enzymatic hydrolysis of the ae -line starches at 95–100 °C. The RS residues consisted of two major components: large starch molecules of average degrees of polymerization (DP) 840–951 with a few branches and small starch molecules (average DP 59–74) with mostly linear chains. All the RS residues had a semi-crystalline structure with the B-type polymorph and displayed high onset (100.7–107.7 °C), peak (118.6–121.4 °C), and conclusion (139.7–158.8 °C) gelatinization temperatures. After the maize ae -mutant starches were defatted with methanol, the RS contents decreased to 27.8–28.9% for the GEMS-0067 ae -line starches and 9.0–11.0% for the existing ae -line starches. The RS residues were attributed to the presence of long-chain double-helical crystallites derived from amylose and the intermediate component (IC). These crystallites present in native ae -line starches had gelatinization temperatures above 100 °C and maintained the semi-crystalline structures after enzymatic hydrolysis at 95–100 °C.

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.

Breeding projects aimed at increasing starch amylose would benefit by having a rapid starch extraction method requiring only non-hazardous reagents and leaving the native granule intact for functional analyses. A study was, therefore, designed to investigate the use of a neutral protease for the removal of protein during the starch extraction process from the grain of high-amylose corn. Sets of F2 ears presumed to be homozygous for the recessive amylose-extender (ae) allele and segregating high amylose modifier gene(s) were used in the study and ranged in amylose content from 55% to around 70%, although several non-mutant genotypes (∼25%) occurred because of visual misclassification of the ae kernels. Starches from samples were all initially extracted by grinding and filtering, then further treated in three ways including either 1) no protein removal, 2) toluene and saline washes or 3) use of neutral proteases. In general, amylose values corresponded among samples extracted using the three methods. Samples purified using proteases had higher mean amylose values (62.5%) attributed to the lower presence of contaminating protein compared to samples prepared with toluene (61%) and grinding/filtration only (57.5%). Little change occurred among the starches as a result of the protease treatments according to thermal properties obtained using differential scanning calorimetry. In addition, gel permeation chromatography profiles (GPC) were unaffected by this treatment. A low level of amylase activity from the protease was found which degraded less than 1 % of the starch sample. The results demonstrated that this protease method gave an increased yield of starch with a quality similar to that of starch prepared with toluene.

Physicochemical properties and digestibility of pinto bean, red kidney bean, black bean and navy bean starches were analyzed. All the common bean starches had oval and spherical granules with average diameter of 25.3-27.4 μm. Amylose contents were 32.0-45.4%. Black bean starch showed the highest peak viscosity, breakdown, final viscosity and setback, whereas red kidney bean starch showed the lowest pasting temperature, peak viscosity, breakdown, and setback. Pinto bean starch showed the highest onset and peak gelatinization temperatures, and the lowest gelatinization temperature range; whereas navy bean starch exhibited the lowest values. Amylopectin of red kidney bean had the highest molecular weight (Mw) and z-average gyration radius (Rz), whereas black bean amylopectin had the lowest values of Mw and Rz. The proportions of DP 6-12, DP 13-24, DP 25-36, and DP ≥ 37 and average branch-chain lengths were 23.30-35.21%, 47.79-53.53%, 8.99-12.65%, 6.39-13.49%, and 17.91-21.56, respectively. All the native bean starches were highly resistant to enzyme digestion.