Location: Corn Insects and Crop Genetics ResearchTitle: Exotic Corn Lines with Increased Starch and Impact on Starch Thermal Characteristics Author
Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/17/2010
Publication Date: 5/3/2010
Citation: Rohlfing, K.A., Pollak, L.M., White, P.J. 2010. Exotic Corn Lines with Increased Starch and Impact on Starch Thermal Characteristics. Cereal Chemistry. 87:190-193. Interpretive Summary: Both cancer and diabetes are causally linked to obesity, now considered an epidemic in this country. Resistant starch (RS), the fraction of dietary starch escaping digestion in the small intestine, contributes to a healthy diet because it is fermented in the large intestine which results in a reduced glycemic index to control type II diabetes, produces health-promoting bifida bacteria in the intestines to reduce colon cancer incidence, and enhances satiety to help with weight maintenance and control of obesity and its associated health risks. We developed corn lines with wide amounts of RS to use to breed healthier food corn and to study the relationships between the ways RS is measured to the types of RS whether present in raw starch or created by heating. The objectives were to identify the best breeding lines from the set of germplasm, and to compare RS values from two techniques that measure amounts in raw starch versus amounts in cooked starch. The breeding lines had higher RS than normal cornstarch when measured by the method for raw starch, but starch is not usually eaten unless cooked. Upon cooking, much of the RS is lost because little RS was found when evaluated with the method for cooked starch. Using traditional plant breeding to develop corn for increased RS is promising but more attention needs to be paid to the amount measured by the method for cooked starch, rather than the method for raw starch. The results give breeders information about variation of RS in germplasm and the best way to monitor results when selecting for RS. They also give food scientists information on the relationship of RS on starch cooking properties, which will be important as the foods undergo processing involving heating.
Technical Abstract: Ten parent corn lines, comprised of four mutants (dull sugary2, amylose-extender sugary2, amylose-extender dull, and an amylose-extender with introgressed Guatemalen germplasm (GUAT ae)) and six lines with introgressed exotic germplasm backgrounds, were crossed with each other to create 20 progeny crosses. The parents and progeny crosses varied in resistant starch (RS) percentage. The lines and crosses with increased RS might be used in breeding corn to use as a means to increase dietary fiber in cornstarch-based foods. 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 %. The % RS of parents was not additive in the offspring, but greater RS in parents was correlated to greater RS in the progeny crosses (r = 0.63). 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 and progeny crosses, with the exception of the Guat ae parent (52.5 %), had % RS greater than that of commercial corn starch (8.9%), but lower than that of a high-amylose (ae) standard (50 % apparent amylose, 40.2 % RS). The % RS and onset temperature increased with the addition of the ae gene. Understanding the impact of RS on the gelatinization characteristics of starches will help the food industry understand its impact on food processing, especially processing involving heating.