Date of Award
Master of Science
Food Science and Human Nutrition
Pamela J. White
Ten parent corn lines, comprised of four mutants (dull sugary2, amylose-extender sugary2, amylose-extender dull, and an amylose-extender (ae) with introgressed Guatemalan (GUAT) germplasm) and six lines with introgressed exotic germplasm backgrounds were crossed with each other to create 20 progeny crosses. The parents and progeny crosses were characterized for % resistant starch (RS), gelatinization, and retrogradation characteristics. The RS was measured from the extracted starch targeting the measurement of RS 2, which is present in ungelatinized starch, by using the Megazyme Resistant Starch kit. The RS values from the 10 parent lines varied from 18.3 % to 52.2 %, and the values from the 20 progeny crosses ranged from 16.6 to 34.0 %. Greater RS in parents was correlated to greater RS in the progeny crosses (r = 0.63, P ≤ 0.05). The Differential Scanning Calorimeter (DSC) was used to measure the gelatinization and retrogradation characteristics of the starches. Peak gelatinization temperature and change in enthalpy were positively correlated to % RS (r = 0.65 and r = 0.67, P ≤ 0.05); however, the retrogradation parameters, a measure of RS 3, did not correlate with % RS (RS 2 type). All parents, with the exception of Guat ae, and progeny crosses had % RS greater than that of commercial cornstarch (8.9%), but lower than that of a high-amylose standard (50 % apparent amylose, 40.2 % RS). The % RS and onset temperature increased with the addition of the ae gene.
Tortillas are a simple food system made from whole corn that has been nixtamalized. A high-amylose, non-floury corn type with 55.2% RS, a floury corn type with 1% RS, and a 1:1 blend with 28.2% RS were used to make traditional tortillas. Whole corn was nixtamalized and ground to make masa. The masa was evaluated for pasting properties on a Rapid-Visco Analyser. The high-amylose masa slurry gelatinized only slightly, as noted by a small change in peak viscosity during the 95y C heat treatment. The floury masa had the greatest peak viscosity, whereas the blend was intermediate in value. Tortillas were evaluated by an 11-member sensory panel who evaluated the textural attributes of grittiness, moistness, chewiness, rollability, and tearability. The floury tortillas were chewier, more rollable, and grittier than the high-amylose tortillas. The blend tortillas were intermediate in most parameters. The cutting force of the high-amylose tortillas, as measured by a texture analyzer, was very low, whereas the blend and floury tortillas required more force. Chewiness was correlated to rollability (r = 0.99, P ≤ 0.05). The RS percentage was correlated to rollability (r = 0.99), and cutting force (r = 0.99). The floury and blend tortillas had a firm texture that would be expected when eating a tortilla with a filling. The high-amylose tortillas fell apart with very little force, and would not roll around a filling, making them unsuitable for this use. Although the high-amylose tortillas had increased dietary fiber in the form of RS, it had very poor textural attributes. The blend tortillas retained enough of the textural properties of the floury tortilla to make it a suitable product. Understanding the impact of RS on the gelatinization characteristics of starches and the texture of food products will help the food industry understand its impact on food processing, especially processing involving heating.
Kim Anne Rohlfing
Rohlfing, Kim Anne, "Thermal Characterization of Corn Starch Mutants and Textural Effects on Tortillas" (2009). Graduate Theses and Dissertations. 10763.