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Application of a Micro Z-Arm Mixer to Characterize Mixing Properties and Water Absorption of Wheat Flour

¹CSIRO Plant Industry, North Ryde, NSW, and Canberra, ACT, Australia. ²Corresponding author. Phone: 02-6246-4975. E-mail: reka.haraszi@csiro.au ³Dept. Biochemistry and Food Technology, BUTE, Budapest, Hungary.

This study applied the use of a new small-scale apparatus, the micro Z-arm mixer, which has analogous mixing action to that of the traditional valorigraf and farinograph. A novel methodology has been developed for prediction of water absorption replacing the traditional titration method. The basis of this technique is a common characteristic of wheat flour samples: a reasonably constant slope (20–25.7 BU%) of the relationship between dough resistance and the amount of water present during mixing. Using an average slope value, prediction of water absorption was possible from a single measurement using a simple equation and with a standard error of 1.65%. Applications of the new mixer to cereal research are highlighted, including investigation of the effects of flour protein content and protein composition on mixing properties and water absorption. When protein content and protein composition have been systematically altered by the addition of isolated proteins into the flour, both dough development time (DDT) and water absorption increased when protein content was increased by glutenin addition and decreased when protein content was decreased by starch addition. Gliadin addition decreased DDT; gluten addition slightly increased DDT; glutenin addition significantly increased DDT. Water absorption was not affected by altering the glutenin-to-gliadin ratio, but it changed in proportion to the amount of protein added. The effect of HMW-GS composition on the mixing requirement obtained with the micro Z-arm mixer and with the 2-g mixograph was also investigated using a set of single-, double-, and triple-null lines for HMW-GS coding genes. While subunits coded on the GluD1 locus were most important for determining the mixing requirement in both cases, the sample ranking was different in the two mixing actions. A better differentiation ability of the micro Z-arm mixer was established for triple- and double-null lines.