Refraction as a measure of soluble carbohydrates in storage roots of asparagus

The objective of our study was to determine how accurately refractometry can quantify soluble carbohydrates in the storage roots of asparagus (Asparagus officinalis L.). Fructose, glucose, sucrose, and fructans as well as refraction were measured in 51 root samples that were taken from commercial fields. There was substantial variation in refraction both within roots of the same plant (cv, 6%) and within plants in the same field (cv, 20%). Samples of asparagus root sap contained fructose, glucose, sucrose, and fructans in varying fractions and, in addition, significant amounts of other solubles, which contributed considerably to refraction. Therefore, refraction readings are no direct measure of fructose, glucose, sucrose, and fructans in asparagus root sap. However, the concentration of these carbohydrates can be well estimated by a regression function, which uses refraction readings as input (r = 0.89).