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Physicochemical and Structural Characteristics of Flours and Starches from Waxy and Nonwaxy Wheats1
ABSTRACT
A waxy spring wheat (Triticum aestivum L.) genotype was fractionated into flour and starch by roller and wet-milling, respectively. The resultant flour and starch were evaluated for end-use properties and compared with their counterparts from hard and soft wheats and with commercial waxy and nonwaxy corn (Zea mays L.) starches. The waxy wheat flour had exceptionally high levels of water absorption and peak viscosity compared with hard or soft wheat flour. The flour formed an intermediate-strength dough that developed rapidly and was relatively susceptible to mixing. Analysis by differential scanning calorimetry and X-ray diffractometry
showed waxy wheat starch had higher gelatinization temperatures, a greater degree of crystallization, and an absence of an amylose-lipid complex compared with nonwaxy wheat. Waxy wheat and corn starches showed greater refrigeration and freeze-thaw stabilities than did nonwaxy starches as demonstrated by syneresis tests. They were also similar in pasting properties, but waxy wheat starch required lower temperature and enthalpy to gelatinize. The results show analogies between waxy wheat and waxy corn starches, but waxy wheat flour was distinct from hard or soft wheat flour in pasting and mixing properties.
Starch, the major component in the wheat (Triticum aestivum L.) kernel, affects quality and staling properties of wheat-based products. Starch granules are composed of two types of glucose polymers, the essentially linear amylose and the highly branched amylopectin, and other minor components such as proteins and lipids. The structure of amylose and amylopectin and their contents in starch granules determine pasting, gelation, and retrogradation properties of starch, and hence product quality and stability. Eating quality of Japanese and Australian noodles, for example, was negatively correlated with amylose content of wheat flour (Oda et al 1980; Miura and Tanii 1994; Wang and Seib 1996). The low content of amylose is associated with high noodle quality and can be predicted from alleles at genetic loci encoding the granule-bound starch synthase (waxy protein), the key enzyme in amylose biosynthesis (Miura and Tanii 1994). A reduced level of amylose also is associated with high values of swelling power in wheat flours or starches (Wang and Seib 1996; Sasaki and Matsuki 1998). Swelling power is a simple...