CHANGES IN THE FREE SUGAR CONTENT OF BARLEY KERNELS DURING MATURATION

Abstract

The free sugars extracted from kernels of a two-row barley variety, Betzes, were separated and determined quantitatively as negatively-charged borate derivatives by anion-exchange chromatography on substituted polystyrene resin. Sugars were determined at 2 or 3 day intervals immediately following anthesis, until kernels achieved harvest ripeness. Initially, the free sugars accounted for 6.5% of kernel dry matter; reducing sugars comprised 80% of the total free sugars, primarily as fructose (3% of the kernel dry matter) and glucose (2% of kernel dry weight), with lesser amounts of galactose, mannose, and maltose. Sucrose was the principal non-reducing sugar (1.8% of the kernel dry weight), but traces of raffinose were also detected. As kernel dry matter increased, the relative amount of free sugars decreased rapidly and comprised 2% of the kernel dry matter in mature kernels. At harvest ripeness, non-reducing sugars comprised 90% of the total free sugars. Sucrose decreased slightly from 1.8 to 1.2% of total kernel dry matter, but actually increased from 90 μg in immature kernels to 500 μg in mature kernels; raffinose increased relative to kernel dry matter from trace amounts 20 days after anthesis to 0.7% of kernel dry matter (i.e., 250 μg/kernel) 36 days after anthesis, and declined to 0.4% in mature kernels. Non-reducing, soluble fructosans were present at all stages of kernel maturation, but were not determined quantitatively.