Effect of Abscisic Acid Optical Isomers, Alone or in Combination with Gibberellic Acid, on Barley Malt Quality. Yueshu Li and Mustafa Rehmanji, Prairie Malt Ltd., Biggar, Saskatchewan, S0K 0M0, Canada; Suzanne R. Abrams, Plant Biotechnology Institute, National Research Council of Canada, Saskatoon, Saskatchewan, S7N 0W9, Canada; and Lawrence V. Gusta, Crop Development Centre, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 0W0, Canada. J. Am. Soc. Brew. Chem. 52:0048, 1994.

The effect of racemic abscisic acid (ABA) and the individual optical isomers, (+)ABA and (-)ABA, alone or in combination with gibberellic acid (GA₃), on the malting quality of Bonanza barley was determined. When GA₃ was the sole treatment, it was applied after 0, 6, 12, 18, and 24 hr of germination. In combination experiments, GA₃ was added at 0 hr and the abscisins were added after 0, 6, 12, 18, and 24 hr of germination. All chemicals were added at a concentration of 10^-5 M. GA₃ increased extract yield and enhanced α-amylase activity and diastatic power but resulted in an undesirably high soluble protein content and increased malting losses. The optimal time for GA₃ addition varied with the parameters measured. Natural ABA, the (+) isomer, had little or no effect on any of the parameters and did not inhibit the effect of GA₃ on malting. In contrast, (-)ABA and racemic ABA reduced the fine grind extract, soluble protein, diastatic power, α-amylase, friability, and malting losses. In combination with GA₃, these two treatments reduced the effect of GA₃ on soluble protein and malting losses but still produced a malt with higher fine grind extract, diastatic power, and α-amylase activity than did the controls. These results indicate that (-)ABA and racemic ABA, in combination with GA₃, can produce a desirable malt in a shorter time than can non-GA₃ treated barley.

Keywords: Abscisic acid optical isomers, Barley malt quality, Gibberellic acid