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Engineering high alpha-amylase levels in wheat grain lowers Falling Number but improves baking properties.
J. P. F. RAL (1), A. Whan (1), O. Larroque (1), J. Pritchard (2), E. Leyne (1), C. Howitt (1), M. Newberry (1). (1) CSIRO Agriculture Flagship, Canberra, Australia; (2) CSiro Agriculture Flagship, Canberra, Australia

Some wheat genotypes are prone to Late Maturity alpha-Amylase (LMA) and Pre Harvest Sprouting (PHS).  When finishing environments have triggered these conditions, the grain is characterised by elevated levels of  alpha-amylase isoforms. The enhanced expression of alpha-amylases results in a reduction in Falling Number, a test of gel viscosity, and a reduction in price for growers. The Falling Number test is unable to distinguish between LMA and PHS, thus both defects are treated similarily when grain is traded. Consequently any grain sample that has a low Falling Number is automatically considered poor for baking quality. While there is clear evidence linking PHS with poor baking quality, no such relationship has been demonstrated with LMA. Our work has demonstrated that wheat in which one isoform of  alpha-amylase (TaAmy3), was overexpressed in the endosperm of developing grain to levels of up to 100 fold higher than the wild-type, resulted in low Falling Number similar to those seen in LMA or PHS affected grains. This increase had no detrimental effect on starch structure, flour composition and enhanced baking quality, in small scale 10g baking tests. In these tests loaf volume was increased and Maillard related browning was enhanced even without added baking improver, to levels higher than those seen in control flours when baking improver was added. These findings highlight the need for a better understanding of the impact of alpha-amylase expression alone on end product quality. 

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