Dunn, Kristen Lea (2014-04). Effects of Sorghum Polyphenols on In Vitro Starch Digestibility and Protein Profile of Wheat Flour Tortillas. Master's Thesis.
Thesis
As incidences of diseases associated with dietary patterns increase in the United States, focus has been placed on improving nutritional quality of processed foods. Carbohydrates contribute the most calories in the American diet (55%), making starch-based foods a target for improvement. Tortillas are increasingly popular among American consumers, serving as a good target to address this problem. This study investigated the use of sorghum bran to increase polyphenols and dietary fiber in wheat flour tortillas and the effect on starch digestibility and protein profiles. Refined wheat flour tortillas were substituted at 10%, 15%, and 25% (Baker's) with brans from wheat and white, brown, and black sorghum. Dough rheology, phenolic profile, starch digestibility, and protein profiles were evaluated after dough formation, hot pressing, baking, and over 14 days of storage. Bran substitution affected dough rheology, producing rougher, stiffer, less extensible dough compared to the refined control. Processing, storage, and bran source significantly affected the phenolic profile of the tortillas. Total phenols, 3- deoxyanthocyanins, and proanthocyanidins (PA) decreased with processing and storage. Dough formation drastically decreased phenol content in brown sorghum bran dough compared to other treatments. Extractable high molecular weight PA also decreased dramatically after processing by 58 - 76% in brown sorghum bran tortillas. These tortillas had less rapidly digestible starch and more slowly digestible starch than other treatments at 25% substitution. Compared to the expected total dietary fiber (TDF), sorghum brans doubled the formation of TDF (20 - 26%) as compared to wheat bran (11%). The largest increase was observed in brown sorghum bran tortillas. In tortillas substituted at 25%, insoluble protein (IP) increased with baking and storage as extractable protein (EP) decreased. Within the EP fraction, soluble polymeric protein (SPP) decreased by 40 - 61% after baking. Brown sorghum bran dough contained significantly higher IP and lower SPP than other treatments; however, this effect was reduced after baking. Sorghum brans provided polyphenols that interacted with protein and starch in wheat flour tortillas. PA and SPP largely contributed to these interactions, forming insoluble complexes that decreased tortilla digestibility and may positively benefit weight management.
