Altering the fatty acid composition of Corn Belt corn through Tripsacum introgression

Breeders need sources of genes for altering the fatty acid content of oil in maize (Zea maize L.) that are not available in Corn Belt germplasm. Previously we determined lines developed from maize introgressed with genes from Tripsacum dactyloides had useful variation for fatty acid composition. We conducted this study to validate the variation, thereby showing that the trait could be transferred to Corn Belt inbreds using traditional plant breeding methods to create maize lines with altered fatty acid composition useful for an oil quality breeding program. Based on their fatty acid profiles, maize lines were selected from an open pollinated population that was introgressed with genes from Tripsacum dactyloides. These introgressed lines were both self-pollinated and backcrossed to Corn Belt lines while undergoing selection for various fatty acid compositions. The parental lines and S1 and S3 progeny from the backcrosses were compared to commercial Corn Belt hybrids and inbreds in an experiment using a randomized complete block design with two replications at two locations near Ames, Iowa. The plants were hand pollinated and hand harvested. The fatty acid compositions were analyzed by using Gas Chromatography to characterize the fatty acid methyl esters made from the oil of five individual kernels from each ear. The relative amounts of the two types of fatty acids of interest, a monounsaturated fatty acid, (oleic acid) and saturated fatty acids (palmitic and stearic acids), were greatly increased by selection breeding within the Tripsacum introgressed germplasm. New oil products with more healthful fatty acid compositions and products with reduced trans fats can be developed from these new lines

Thermal Properties of Starch from 62 Exotic Maize (Zea mays L.) Lines Grown in Two Locations

The variability in thermal properties among 62 S3 lines derived from a high-yielding exotic corn (Zea mays) population, Antigua 1 (PI 484990), was evaluated by differential scanning calorimetry (DSC). The S3 lines were grown in Puerto Rico (1990–1991) and Georgia (1994). Separate single-kernel starch extractions for five kernels (five replicates) from each line grown in each location were performed, and the starch was analyzed. The DSC values reported included gelatinization onset (ToG), range (RG), enthalpy (ΔHG), and peak height index (PHI) and retrogradation onset (ToR), range (RR), enthalpy (ΔHR), and percent retrogradation (%R) (an indication of the stability of gelatinized starch after storing at 4°C for 7 days). Significant differences (P\u3c 0.05) were found among the 62 lines of Antigua 1 for ToG, RG, and PHI and highly significant differences (P \u3c 0.01) were found for ΔHG. The starches from plants grown in Georgia (1994) had significantly (P \u3c 0.05) greater ToG, ΔHG, and PHI but a significantly lower RG than those from Puerto Rico (1990–1991). These data suggest that the starch from plants grown in Georgia (1994) might have a greater degree of crystallinity than that from Puerto Rico (1990–1991). None of the retrogradation values were significantly different among starches of the 62 lines of Antigua 1 and the starches from plants grown in the two locations

Relationship of electronic nose analyses and sensory evaluation of vegetable oils during storage

Off-flavors associated with oxidized oils make it difficult to recruit sensory panelists to evaluate the oils. Using an instrument called the “electronic nose” to monitor the formation of volatile compounds associated with off-flavors could help to interpret oil oxidation studies in part to supplement human sensory panels. No published studies evaluate the correlation of oil oxidation sensory data and “electronic nose” analyses. Therefore, this project was designed to determine the correlation between sensory evaluation and “electronic nose” analyses. Canola, corn, and soybean oils were stored at 60°C in the dark until sufficiently oxidized. On days 0, 3, 6, 9, and 12, oils were evaluated for peroxide value, for volatile compounds by “electronic nose,” and for off-flavor by sensory evaluation. The results suggest that the “electronic nose” is capable of measuring changes in volatile compounds associated with oil oxidation and could be used to supplement data obtained from sensory evaluations

Characterization of Corn Grains for Dry-Grind Ethanol Production

The objectives of this study were to understand how the composition of corn kernels and starch structure affected the enzyme hydrolysis of starch in dry-grind corn and the ethanol yield from yeast fermentation. Four selected corn inbred lines were used in this study. Starch in uncooked dry-grind corn samples showed greater enzyme digestibility than did the uncooked starch isolated from the same source by wet-milling process. The greater digestibility of starch in uncooked dry-grind corn correlated with a physical damage of starch granules. In contrast, starch in cooked dry-grind corn samples displayed less enzyme digestibility than did the cooked isolated starch. The difference could be attributed to interference caused by non-starch components in the dry-grind corn. The entrapment of starch in protein matrix and the formation of amylose-lipid helical complexes and/or retrograded starch may decrease the enzyme digestibility of starch in cooked dry-grind corn. Lab-scale ethanol production showed that ethanol yield after 72 h fermentation of the four corn inbred lines ranged between 34.3 and 38.0 g ethanol/100 g dry-grind corn. The conversion efficiency at 72 h of fermentation ranged between 86.8 % and 90.3 % of the theoretical ethanol yield. The highest ethanol yield was found in the corn line containing the largest starch content and the smallest amounts of lipid and protein

Thermal and structural properties of unusual starches from developmental corn lines

Starches from exotic corn lines were screened by using differential scanning calorimetry (DSC) to find thermal properties that were significantly different from those exhibited by starches from normal Corn Belt lines. Two independent gelatinization transitions, one corresponding to the melting of a peak at ∼66 °C and the other to a peak melting at ∼69 °C, were found in some starches. The melting characteristics were traced to two separate types of granules within the endosperm. Strong correlations were found between DSC properties and proportion of large granules with equivalent diameter ≥17 μm. Starches with a lower peak onset gelatinization temperature (ToG), had a lower normalized concentration of chains with a degree of polymerization (dp) of 15–24 and/or a greater normalized concentration of chains with a dp of 6–12. These studies will aid in understanding structure–thermal property relationships of starches, and in identifying corn lines of interest for commercial breeding

Resistant Starch and Starch Thermal Characteristics in Exotic Corn Lines Grown in Temperate and Tropical Environments

Corn as a food that is heated and cooled to allow starch retrogradation has higher levels of resistant starch (RS). Increasing the amount of RS can make corn an even healthier food and may be accomplished by breeding and selection, especially by using exotic germplasm. Sixty breeding lines of introgressed exotic germplasm backgrounds, selected for high yield, were grown in three tropical and temperate locations and analyzed for starch thermal characteristics and RS levels. Although actual values for all starch characteristics were within normal levels, most characteristics had significant genotypic effects, and all had significant location effects. Thermal properties of retrograded starch were more influenced by the environment than the thermal properties of raw starch, making retrograded starch traits more heritable than raw starch traits. This suggests that a breeding strategy based on retrograded starch traits will have a better chance of success than a breeding strategy based on raw starch traits. A significant genotype effect for RS levels indicates that genotypic selection to raise the level of RS and increase the healthful aspects of corn food should be successful. Significant location effects indicate that breeders using winter nurseries to accelerate their breeding progress need to be careful when making selections using RS data collected on seed grown in the tropics. A small but highly significant correlation between RS and some thermal characteristics, especially percentage of retrogradation, indicates that we may be able to select promising genotypes for RS selection based on our extensive database of thermal characteristics collected on a wide number of diverse corn lines