Abstract
Treatment of barley (Hordeum vulgare L) grains with gibberellic acid (GA3) during malting has desirable effects such as increased malt extract yield and increased malt modification. GA3 also causes some undesirable effects such as increased proteolysis and rootlet growth. This study assessed the potential of treatment with ethylene, a plant hormone with germination promotion and rootlet growth reduction effects in many plant species, as an alternative to GA3 treatment. This was achieved by comparing the germinability, rootlet growth characteristics, respiration rate, starch hydrolysis and protein metabolism of ‘Puma’ barley seeds treated with ethylene, GA3, 1-MCP (inhibitor of ethylene binding), daminozide (inhibitor of GA synthesis) and combinations of these in a germination test. The quality of malt produced from ‘Puma’ barley seeds treated with ethylene, GA3 and 1-MCP during experimental malting was also assessed. Ethylene treatment delayed germination, suppressed rootlet growth, had no effect on respiration and protein metabolism, but promoted starch hydrolysis. Inhibition of ethylene perception with 1-MCP increased the rate of germination, promoted rootlet growth and had no effect on respiration, starch hydrolysis and protein metabolism. GA3 treatment had no effect on percent germination, respiration rate and rootlet growth, but promoted starch and protein hydrolysis. Inhibition of GA synthesis with daminozide suppressed germination, rootlet growth, respiration rate, starch hydrolysis and protein synthesis. Ethylene treatment failed to restore germination in daminozide treated seeds, indicating that the mechanism of ethylene action during germination is different from that of GA. Differences in the effects of ethylene and GA3 were also observed on malt quality. GA3 had positive effects on malt friability and β-glucan content whereas ethylene had negative effects compared to the control. GA3 had positive effects on malt extract, percent partially unmodified grain (% PUG), percent wholly unmodified grains (% WUG), malt homogeneity and wort viscosity while ethylene treatment did not affect these malt characteristics. GA3 also increased wort colour, total soluble nitrogen and Kolbach Index which ethylene treatment did not affect. These results suggest that, under similar malting conditions, GA3 treatment produces better malt compared to ethylene treatment. It was therefore concluded that ethylene treatment may not be a good replacement for GA3 treatment during malting of ‘Puma’ barley.
Ph.D. (Botany)