Physicochemical properties and end-use quality of wheat starch as a function of waxy protein alleles

Soft wheat (Triticum aestivum L.) quality tests (milling and baking quality) and starch characteristics (amylose concentration, X-ray diffractograms, thermal properties and pasting properties) were determined for eight granule-bound starch synthase (GBSS: waxy protein) genotypes in a soft wheat background. Lines carrying two null alleles showed reduced amylose concentrations relative to those of single null and wild-type lines. Milling and baking quality traits were clearly different between waxy (triple null) and the other genotypes. Waxy lines showed the highest alkaline water retention (AWRC) capacity; even though, the protein concentration was not significantly different from some double null and single null lines. The typical A-type patterns of X-ray diffractograms were observed for all starches. Waxy starch showed higher crystallinity than non-waxy starches. Analysis by Rapid Viscoanalyser (RVA) showed distinctive differences among the eight genotypes. Waxy starches showed higher peak viscosity, lower peak temperature and shorter peak time than those of all other genotypes. The results suggest that baking quality of waxy wheat can not be predicted by either AWRC or protein concentration. The interactions based on biochemical analysis between protein and other fractions (amylose and amylopectin, damaged starch) of partially and fully waxy wheat flours must be assessed before baking quality can be predicted. Furthermore, waxy wheat may not be suitable for current application of soft wheat products; however, distinct properties of waxy starch may open the possibility of commercial use in novel applications. Also, double null and single null genotypes may be a good source of variation for specific end-use products. (C) 2003 Elsevier Science Ltd. All rights reserved.