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Effects of sorghum polyphenols on wheat protein profile during tortilla processing
K. L. Dunn (1), A. L. GIRARD (1), S. R. Bean (2), J. M. Awika (1). (1) Texas A&M University, College Station, TX, U.S.A.; (2) USDA-ARS-GMPRC, Manhattan, KS, U.S.A.

Polyphenols, specifically proanthocyanidins (PA), from sorghum have been shown to bind with starch in pure starch systems to form resistant starch (RS). However, less is known about the behavior of PA in processed food matrices where protein is also present. Protein and starch profiles of flour tortillas made with no bran (NB) and 23% bran from wheat (WH) and white (WS), black (BS), and tannin (TN) sorghum were investigated. Insoluble (IP), extractable (EP), and soluble polymeric proteins (SPP) and <i>in vitro</i> starch digestibility were determined. Phenolic profile was determined by UV-Vis spectroscopy and HPLC. Dough prepared with TN treatment contained more IP (46%) than the NB and WH doughs (38%) and the WS and BS doughs (33%). The TN treatment had the largest decrease in total polyphenols (49%) after dough formation versus BS (4%), the only other sample with a significant decrease (p<0.05). Extractable PA in TN also decreased 55% in the dough suggesting that PA complexed with proteins during gluten network formation. TN dough contained less EP (54%) than the NB and WH doughs (62%) and the WS and BS doughs (67%). Among sorghum brans, SPP decreased the most (60%) in TN samples from dough to Day 0 as compared to the WS and BS samples (44%). TN samples had significantly higher slowly digestible starch (19%) than the control and other treatments (13%). However, formation of RS in TN treatments was not different from the control.  This suggests that PA from TN may preferentially bind protein, specifically SPP, over starch in a flour tortilla matrix in a way that increases slowly digestible starch.

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