The development of routine assays for water uptake in barley

Abstract

Seven techniques were assessed to determine their potential for rapid measurement of water distribution through barley grains. Four were based on iodine vapour staining and two on the use of manganese as a tracer ion for water, both methods being originally developed under a previous HGCA-funded project (0031/1/87 - now reported as Project Report No 23 at BRF International with the aim here being to adapt them into a simple and rapid form.

Insufficient iodine can be extracted from iodine vapour-stained grains for detection by titration, spectrophotometry or an iodide-specific electrode.

The rise in temperature of samples heated in a microwave oven has been ruled out as a method for determining moisture in the small sections of endosperm required for this work. This is due to poor repeatability.

A comparison of X-ray microanalysis (XRMA) data (The BRFI Malting Index) with a SEESCAN image analysis system or fibre optic probes from KIRSTOL in reflectance or transflectance modes, has shown potential for assessing water distribution in iodine vapour- stained samples. The image analysis does, however, require substantial manual input.

Manganese distribution, following steeping in manganese chloride, can be measured using the fluorescent marker hydroxynaphthaldehydethio-semicarbazone (HNTS). The fluorescent tag is sensitive to very low levels of manganese. The amount of manganese in aqueous extracts of steeped grains can be measured quantitatively. Further development may allow manganese distribution to be mapped and/or quantified in grain sections by epifluorescence on a light microscope.