Absolute evaluation of barley for malting

Abstract

Many aspects of grain physiology relevant to malting have been extensively investigated. For example, a considerable body of research indicates that even feed varieties are capable of producing ample quantities of hydrolytic enzymes, if given correct stimulus. Other important parameters, such as endosperm structure, for instance the milling energy test, have been developed.

Four aspects of grain physiology which are essential for germination were identified. In each case little was known concerning the range of variation likely to be encountered within commercial varieties. In the course of this project each of these parameters have been evaluated for its likely contribution to malting quality.

The key findings in each area of investigation are summarised below:

1. Distribution of water. A technique has been developed whereby the extent of hydration of specific areas of the starchy endosperm can be measured from their reaction with iodine. The resulting purple colouration can then be assessed visually or measured very precisely by x-ray micro-analysis. The amount of water in the ventral endosperm close to the scutellum has been shown to relate to malting quality, with high grade barleys transporting more water into the endosperm from the scutellum than lower grade cultivars. This test requires only small amounts of seed, and could provide a useful technique for screening potential malting cultivars.

2. Key respiratory enzymes. Glucose-6-phosphate dehydrogenase was chosen for investigation since this enzyme occupies a key role in controlling flux through the pentose phosphate pathway. Development of this enzyme in barley embryos during malting was found to vary between cultivars, but the differences appeared unrelated to malting quality.

3. Production and migration of gibberellic acid. Antibodies which react with natural gibberellins have been prepared. These antibodies can be used to locate endogenous gibberellins in tissue slices and to trace their movement and distribution during germination. The antibodies can also be used to measure levels of gibberellins in extracts of barley and malt. There is no strong correlation between malting quality and the level of gibberellins in the raw barley; there was a tendency for good quality varieties to contain lower levels of gibberellins than did feed varieties.

4. The response of isolated aleurone layers to added gibberellic acid. This was measured in terms of the production of alpha-amylase. Although feed varieties produced more alpha-amylase than malting varieties at high levels of added gibberellic acid, they were more sensitive to hormone concentration than were the malting varieties. Thus at lower levels of gibberellic acid addition (closer to likely endogenous levels) malting varieties produced more amylase than feed varieties.

The findings summarised above strongly suggest that the single most important physiological factor for discriminating between varieties of different malting quality is the flux of water from embryo into endosperm. A technique, utilising X-ray micro-analysis, has been developed whereby this flux can be readily quantified, and utilised in the assessment of new barley varieties.