Master of Science / Department of Grain Science and Industry / Rebecca Miller / Wheat flour tortillas are the second most consumed bread product after white pan bread. Commercial tortillas are formulated with highly viscoelastic hard wheat flours selected and grown for breadmaking. However, the inherent properties of bread flours require costly formula adjustments to enhance dough extensibility necessary for tortilla production. The objective of this study was to identify the biochemical and physical factors in wheat affecting wheat tortilla quality. Six popular hard winter wheat cultivars (1863, Armour, Clara CL, Denali, Everest, Tiger) were grown in five locations in Kansas. Wheat and flour properties were characterized using approved AACCI methods. Protein composition was determined using size-exclusion high performance liquid chromatography. Flour particle size and starch granule size were measured with laser diffraction. Tortillas were made with a laboratory hot press method. Tortilla shelf-stability over 14 days, opacity, appearance, dough machinability and specific volume were measured. Data collected from flour and tortilla tests were analyzed using ANOVA and means were compared with Tukey-Kramer HSD. In general, the flours did not differ significantly in flour or tortilla properties. Regression analysis (Pearson) showed flour protein content was highly and significantly correlated with tortilla opacity (r=-0.81), L color value (r=-0.79), a color value (r=0.80), and day 14 shelf-stability (r=0.76). Flour water absorption showed highly significant correlations with tortilla opacity (r=-0.81), L color value (r=-0.79), a color value (r=0.77) and day 14 shelf-stability (r=0.73). Tortilla opacity was highly correlated with B-type starch granules (r=-0.83). This study showed that starch granule size, flour protein content and flour water absorption appeared to influence tortilla appearance. However, repeating the study with a larger and more diverse sample set is recommended.

Master of Science / Food Science Institute, Agriculture / Katherine A. Tilley / Michael Tilley / The wheat tortilla is a chemically leavened circular light colored flat bread. Desirable characteristics for good quality tortilla include large diameter, softness, flexibility and long shelf stability. Important components influencing quality are wheat flour properties, which have not been optimized for tortilla industrial production thus far. The studies presented here investigated the effects of high molecular weight glutenin subunits (HMW-GS) on tortilla quality. Two approaches were employed: biotypes derived from Centurk and OK102 cultivars expressing defined HMW-GS compositions and transgenic wheat lines over-expressing HMW-GS 10. Analysis of protein expression and protein extractability were conducted to characterize wheat flours and suitable assays carried out to determine the respective dough properties. Tortillas were prepared by the hot-press method and quality parameters were measured at days 0, 2, 4, 7 and 14. Tortillas derived from Centurk biotypes possessing HMW-GS 2*, 7+9, 2+12, 2*, 7+8, 5+10 and 2*, 7+9, 5+10 exhibited superior texture profiles over time, but smaller diameters than the biotype 2*, 7+8, 2+12. Tortillas containing HMW-GS 7+9 and 2+12 revealed a texture profile similar to tortillas containing 5+10. Tortillas from the OK biotype 2*, 7+9, 3+12 exhibited larger diameter and texture profiles equivalent to tortillas containing 5+10. Therefore, this biotype showed the best quality within this cultivar. Tortillas derived from transgenic flours over-expressing HMW-GS 10 exhibited an undesirable rough appearance with decreased diameter, greater thickness, lower rollability scores, lower stretchability and greater rupture force over time. Over-expression of HMW-GS 10 in a wheat line containing 1RS-translocation did not promote the same deleterious effects in tortilla quality as it did in transgenic lines without 1RS translocation.

Tortilla sales are projected to exceed 9.5 billion by 2014. However, currently no wheat cultivars have been identified that possess the intrinsic quality attributes needed for the production of optimum quality tortillas. Tortillas made with refined wheat flour low in dietary fiber (DF) are popular in the United States due to their sensory properties. This study explored the use of wheat lines (WL) possessing variations in high molecular weight glutenin allele sub-units (HMW-GS) for production of tortillas and also investigated the use of corn based resistant starches (RS), type II (RS2) and wheat based RS type IV (RS4) to increase DF in tortillas. Tortillas were made with 0-15 percent RS and 100 percent whole white wheat (WW). Flour protein profiles, dough, and tortilla properties were evaluated to determine the effects of the allelic variations and RS substitution on tortilla quality. Sensory properties of tortillas with RS were determined. Variations in HMW-GS composition significantly affected the protein quality and tortilla properties. Flour from WL possessing allelic combinations (2*, 17+18, 7, 2+12), (1, 17+18, 5+10), (2*, 17, 2+12) and (1, 2*, 17+18, 2+12) had 12.8-13.3 percent protein. These WL had extensible doughs and produced large diameter tortillas with superior (greater than or equal to 3.0) flexibility after 16 days compared to control. However, WL with (17+18 and 5+10) and (2*, 17+7, 5) produced extensible doughs, large, but less flexible, tortillas compared to control. WL with (2*,17+18,5+10) and (1,2*,7+9,5+10) produced smaller diameter tortillas, but with superior flexibility compared to control. RS2, WW, and cross-linked-pre-gelatinized RS4 (FiberRite) produced hard, less-extensible doughs and thinner tortillas compared to control, due to high water absorption. Cross-linked RS4 (Fibersym) dough and tortillas were comparable to control. 15 percent of RS2 and RS4 increase DF in control to 6 and 14 percent respectively, compare to control (2.8 percent DF). WW tortillas were less acceptable than control in appearance, flavor and texture, while tortillas with 15 percent Fibersym had higher overall acceptability than control. RS2 negatively affected dough machinability and tortilla shelf stability. However, 15 percent RS4 improved the DF in refined flour tortillas to meet FDA's "good source of fiber claim," without negatively affecting dough/tortilla quality.