Wheat Tortilla Quality: Impact of Amylose Content Adjustments Using Waxy Wheat Flour

Cereal Cheill. XO(4):427·-436 Amy lose content is closely related to wheat flour pasting or thermal properties, and thus affects final food qualities. J:iourteen flour blends with amylose content ranges of < I to 29% were used to study tortilla production and quality parameters. Reduced amylose contents decreased dough stickiness and pliability; low amylose doughs were also very smooth in appearance. Very low flour amylose content was associated with earlier tortilla puffing and poor machinability during baking, darker color, low opacity, largcr diameters, and reduced flexibility after storage. Tortilla texture analysis indicated that lowering amylose content gave fresh tortillas higher extcnsibility; aftcr three or morc days storagc, however, low amylosc flours required more forcc to break thc tortillas Tortillas are unfermented flat breads or pancakes made from either corn or wheat. As the staple bakery food, tortilla products have been traditionally homemade and widely consumed in Mexico for centuries (Serna-Saldivar et al 1988; Wang and Flores 1999a). In the United States, tortillas, especially wheat tortillas, are more popular today than all other ethnic breads (Dally and Navarro 1999). According to the TOItilla Industry Association (TIA), tortilla sales for 2000 in the U.S. reached the $4.4 billion mark and are expected to hit $5.7 billion dollars in sales by the year 2002 (Anonymous 2001). Hot-press wheat tortillas, compared to die-cut or hand-stretched product'!, are smoother in surface texture, more elastic, slightly chewy, and resistant to tearing and cracking (SernaSaldivar et al 1988; Bello et al 1991; Friend et al 1993), making hot-press tortillas suitable to be used as the "wrap", "envelope" or "folder" for a countless array of fillings (Tortilla Industry Association, www.tortilla-info.com). Basic ingredients for wheat tortillas are wheat flour, water, salt, and shortening or oil; other ingredients such as leavening agents, preservatives, dough conditioners, emulsifiers, and flavorings may also be used. Bello et al (1991) developed a practical laboratory procedure for preparing and evaluating hot-press wheat tortillas. Friend et al (1993) investigated the effects of hydrocolloids on processing and qualities of wheat tortillas and found that the addition of natural or modified gums (0.3-0.5%) could improve the product's shelf life and freezethaw stability. They also indicated that tortillas containing higher levels (0.5-\.0%) of gums tended to have more undesirable translucent areas and less whiteness; proper gluten development appeared to be essential for good dough machinability, tortilla qualities, and tortilla shelf stability. Added wheat gluten significantly enhanced tortilla rollability, whereas other protein sources decreased storage stability (Suhendro et al 1993). I A joint contribution of the University of Nebraska Agriculture Research Division and the United States Ocpartment of Agriculture, Agriculture Research Stlrvice as Journal Series Paper No. 13783. Mention of firm namcs or trade products docs not imply that they are cndorsed or recommended by the Univcrsity of Nebraska or USDA over other firms or products not mentioned. 2 Postdoctoral research associate and professor, respectively, Department of Food Science and Technology, University of Nebraska, Lincoln, NE 6gSK3-0919. 3 Corresponding author. E-mail: [email protected]. Fllx: 402-472-1693. 4 USDA-ARS, 362C Plant Sciencc Hall, University of Nebraska, Lincoln, NE 68583-0915. 5 Professor, Department of Biometry, University of Nebraska, Lincoln, NE 68SK30712. Publication no, C-2003-0615-04R. This article Is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. American Association of Cereal Chemists, Inc., 2003. and the rupture distances became shortcr. These results, as reflected in covariate analysis, were not signiticantly alTccted by the Ilour blend's protein content, swelling volume/power, SDS-sedimcntatioll volulllc, mixograph dough development time, or mixograph tolerance score. Based on our observation of an initial in(;rcase in extensibility with reduced-amylose tortillas, adding 10-20% waxy flour into wild-type flours should be ideal for restaurant (on-site) tortilla production or circumstances where tortillas are consumed shortly (within a day) after produ(;tion. The optimal flour amylose content for hot-press wheat tortilla products is 24-26%. Wheat flour is the primary tOltilla ingredient and accounts for 80-95% of the dry matter in tOltillas (Waniska 1999). Thus, flour characteristics primarily determine wheat tOltilla qualities. Typical commercial tortilla nours are milled tium hard red wintcr wheats with moderate to strong dough strength; the protein content ranges from 9.5 to 11.5% for hot-press tortillas or from 10,0 to 14.0% for other products (Serna-Saldivar et al 1988; Waniska 1999). McDonough et al (1996) found that the texture of tortillas depended on the retention of steam and leavening gases by the gluten matrix. Wang and Flores (1999a) studied the impact of wheat classes and flour milling streams on tortilla texture properties. Their results indicated that both tlour protein content and farinograph water absorption were positively correlated to tortilla foldability, and sort wheat tlours were not suitable for tortilla products. In another study, they found that both wheat starch and gluten had significant effects on tortilla rupture distance; starches from different wheat classes affected foldability of tortillas (Wang and Flores 199%). Because the fractionation and reconstitution method was used for their study, certain water-soluble components were not included in the tortilla fornlllla, and the natural bonds between prntein and stm'Ch granules were thus different in those systems. The reconstitution method was not suitable for the study of a high-fat (shortening) tortilla system (Wang and Flores 1999b). Wang and Flores (2000) also observed that flour protein content, particle size, and protein quality (high molecular weight proteins and low molecular weight proteins) affected tortilla texture; the particle size was the primary contributor to tortilla extensibility and rollability. Mao and Flores (200 I) found that damaged starch affected tortilla's stretchability, firmness, and rollability. Wheat starch, as the most abundant component in wheat flour, is composed of amylose and amylopectin. Lower amylose (partial waxy) or amylose-free (waxy) wheat flours have unique l1ourstarch pasting properties (Graybosch et al 20(0), and the amylose contcnt has a significant impact on Asian salted noodle products (Seib 2000). Lee et al (200 I) found that low flour amylose content was associated with high gas formation during fermentation, while the gas retention coefficient decreased. Bread products prepared using lower amylose flours had larger volumes, more porous crumb structure, and higher moisture contents aftcr seven days of storage at 4 DC (Lee et al 200 I). With the availability of waxy wheat, it is possible to manipulate tlour amylose content without dilution of wheat gluten (Graybosch 1998; Grayboseh et al 1998). Up to now, therc has been only one report of the impact of amylose content on wheat tortilla processing and product quality (Waniska et al 2(X)2), and pm1ial waxy wheats with slightly (\.0-3.3%) lower amylose content were used Vol. 80, No.4, 2003 427 ~A.Bl.E-1 Hot~Press-WheatFiourThnifiaFonnulatWn