Measurement and control of blackpoint

Abstract

Introduction

Blackpoint describes the brown to black discoloration of the bran over the germ region of cereal grains, which is a severe problem in wheat approximately one year in ten. Grain quality is affected by the inclusion of dark bran specks in flour upon milling; therefore, grain lots with high proportions of discoloured grains are likely to be rejected by mills.

The wheat is otherwise healthy. Lowering the percentage flour yield or removing bran layers from the grain prior to milling reduces the amount of bran included in the final blended flour. Alternatively a pre-milling procedure can be used to remove discoloured grains from the bulk.

Aims

Develop and validate an objective measure of blackpointed (or otherwise discoloured) kernel content within bulk grain samples arriving at mill intake.

Test current winter wheat varieties for relative levels of blackpoint resistance in order to provide more information to breeders, growers and millers.

Examine the effectiveness of established and novel methods for grain separation and cleaning to provide information on possible ways to salvage unacceptable grain samples prior to milling.

Determine whether there is a level of blackpoint severity in wheat, above which the white flour extraction rate must be lowered in order to retain a clean flour product.

Test for the presence of microbes and mycotoxins in grain samples, relating results to blackpoint severity.

Compare different varieties of wheat, in terms of compounds thought to be causing or associated with blackpoint and formed at different stages of grain development.

Conclusions & implications

Visual assessment is a reliable method for measuring blackpoint severity of wheat samples once the assessor has been trained. A set of standard /images assists in making the test more reproducible.

Differences in blackpoint severity between wheat varieties are very clear, but are affected by the site at which they are grown. This information should be useful to plant breeders, growers and millers as a base on which to make informed decisions.

Image analysis is able to distinguish between clean and discoloured grains, but the development of a purpose-built machine would be time-consuming and expensive. The high cost of such equipment could be offset by other applications.

The GrainCheck 312 was able to distinguish and count discoloured grains after appropriate configuration. It showed greater accuracy in identifying discoloured grains from more severely affected samples. As with image analysis, the high cost of the instrument requires it to be suitable for other uses.

Reducing flour extraction rate improved the flour colour grade. However, within the samples examined, flour colour was still acceptable at extraction rates over 80%.

The Sortex 90000 Series High Performance Colour Sorter is capable of separating out discoloured grains from bulk samples to give a cleaner product when milled. As a large proportion of the pre-milled sample is lost during this process, it is useful to growers rather than millers. A crop containing a high percentage of blackpoint can be sorted to salvage part of it for milling, thus gaining a premium.

Scouring reduced the effect of blackpoint on colour of milled flour. However, further large-scale trials using commercial equipment would be required to assess the full impact of this in terms of loss of wheatfeed and final product quality.

Gravity separation could be used to remove the largest grains from samples that also show the most severe blackpoint symptoms. Further studies could be carried out to produce larger amounts of grain fractions for milling into white flour to investigate potential milling losses incurred.

Biochemical components of grain change over time, but the differences seen could not be related to varietal blackpoint resistance or susceptibility. Further more detailed studies are necessary to clarify the biochemical mechanisms behind the production of the discoloration seen in the mature grains.

No traces of mycotoxins were found in any of the samples tested, despite the isolation of some fungal colonies from the same samples.