Agriculture Reference
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within breeding programmes, as they were carried out to facilitate selection for breadmaking
varieties. However, characters such as grain texture and protein content and composition, for
which genetic factors were located by Nelson et al [39], could also be relevant to selection for
distilling quality. Charmet et al. [10] also detected QTLs associated with the rate of N
accumulation in the grain and consequent effects on the composition of protein, particularly
the quantities of low molecular weight glutenins and gliadins. Selecting for differences in
gliadin storage would be particularly useful in distilling wheat [71] as low gliadin content in
the grain enhances alcohol yield.
Alcohol is produced through fermentation of the products of carbohydrate (essentially
starch) breakdown and Smith et al. [61] provided a formula to calculate the theoretical
alcohol yield from the starch content of the grain. Differences in starch content appear to be
mainly genotypic [70], so selection between breeding lines should be feasible. However,
several authors show that the association between starch content and alcohol yield, while
positive, is not particularly strong [49], [70]. These data were generally derived from different
varieties grown together in trials, where fertiliser applications would have been the same to
each plot, so higher yields would have diluted grain nitrogen contents. Starch and nitrogen
contents are inversely related, but the precise nature of this relationship varies with variety
[31]. While starch content is, therefore, likely to be a major component of alcohol yield,
achieving sufficiently similar grain N levels within trial plots to enable meaningful selection,
may be problematic. Direct selection for alcohol yield would be preferable, both within
breeding programmes and in detection and location of QTLs. Sylvester-Bradley and Kindred
[71] noted the development of an NIR calibration, to predict alcohol yield in wheat, as a
potentially valuable means of phenotype assessment.
Near Infra-Red (NIR) spectroscopy provides rapid, reproducible results, with little by
way of sample preparation, so is widely used, by maltsters and other grain processors, for
assessment of intake samples [7]. The original analysers, developed in the 1970s, measured
the amount of reflectance and required samples to be finely milled [79], but later machines
utilised the very-near infrared spectrum (800 - 1100 nm). These measured the amount of
transmission through samples of whole grain [79]. Routine analyses are predominantly for
nitrogen and moisture [30], but extending the use of NIR calibration, to predict processing
performance of raw materials for the malting and brewing industries has been investigated for
many years. Initial studies on hot water extract in barley, for example, began in the 1970s
[37]. The choice of calibration samples, to represent the complete range that will be covered
by samples for future assessment and estimates of precision of the reference method, against
which the NIR spectra will be calibrated, are key steps in the process [7]. With an NIR
calibration able to predict around 80% of the variation in alcohol yield [71], this appears to be
a very promising development, as a further advantage of NIR calibrations is ease of transfer
between machines [30]. This would make it possible to put the same type of equipment and
software into both a breeder's and a distiller's laboratory, thus enabling breeders to target
selection towards the industry's specifications.
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