Studies on the Free Sugars of the Barley Grain

The concentrations of the principal free sugars and oligosaccharides of a sample of Ymer barley were estimated at approximately 24-hr. intervals from the commencement of steeping till the completion of kilning. Whilst sucrose, raffinose, glucodifructose and the lower fructosans generally diminished in steeping and on the first day on the floor, glucose and maltose contents during these periods showed little variation. Concurrently with the disappearance of raffinose from the germinating grain, there was a gradual accumulation of an oligosaccharide resembling maltotriose. The first appearance of free pentoses coincided with a marked increase in maltose content; glucose, maltose and the apparent maltotriose increased regularly during active growth on the floor. After the initial fall in sucrose, there was a rise in concentration till the final sucrose content was some five times that of the ungerminated grain. From a study of these malting changes it is suggested that oligosaccharides containing a glucopyranose-fructofuranose unit (sucrose, raffinose, glucodifructose and some fructosans) are intimately associated with respiration, while glucose, maltose and “maltotriose” primarily represent products of amylolysis. The relationship of the sugars produced by starch degradation to the predominant free sugar of the germinating grain—sucrose—has not yet been established.