Assessment of variance in measurement of hectolitre mass of wheat and maize, using equipment from different grain producing and exporting countries

Engelbrecht, Mandy L. (2008-03)

Thesis (Msc Food Sc (Food Science))--University of Stellenbosch, 2008.


South Africa as well as other grain producing and exporting countries’ grading systems strongly relies on hectolitre mass (HLM) as a guide to grain quality. It is known that these countries use either one of two types of HLM equipment. These devices consist of either a funnel or a cylindrical device (chondrometer) with a measuring cylinder of known volume underneath which is then filled with grain in a controlled manner. Subsequently the HLM devices from Australia, Canada, France, Germany, South Africa, the United Kingdom (UK) and the United States of America (USA) were compared using impurity free mixed wheat, single South African cultivars as well as maize samples. Very little variation in HLM measurements within the HLM devices was observed with intra-class correlation (ICC) agreement values close to one. Comparing the actual HLM values obtained with the respective devices showed that the results obtained with the Australian device was significantly (P < 0.05) higher, and those obtained with the South African devices significantly (P < 0.05) lower compared to the other devices. As would be expected the devices showed better overall ICC agreement when the HLM tests were performed with the single cultivar samples (ICC agreement = 0.762) as opposed to the mixed wheat samples (ICC agreement = 0.523). However, the HLM values obtained with all the devices correlated well with each other (ICC consistency >0.90) indicating that correction factors can therefore be developed to convert the HLM results between devices. When ten South African devices were compared statistical differences were observed, but the overall ICC agreement (0.975) and consistency (0.993) values indicated that the differences would not be significant in practice. Hectolitre mass determinations performed on samples prior to and after impurities have been removed revealed that the removal of impurities resulted in a significant (P < 0.05) increase in HLM. The effect of operator was shown to be significant (P < 0.05) when operators with three levels of competency, i.e. skilled, semi-skilled and unskilled, were investigated. The effect of wet and dry cycles on the HLM measurements was investigated and the results showed that wetting and drying could change the integrity of the wheat. Moisture correction factors cannot be applied to convert the HLM values of grain that underwent moisture changes as different samples responded differently to the moisture treatments. Comparing the respective devices with mixed maize samples (impurities not removed) very little variation in HLM measurements within each device was observed. The comparison of the devices revealed that the HLM measurements obtained with the Australian and French devices were significantly (P < 0.05) higher and that obtained from the Canadian device significantly (P < 0.05) lower compared to those obtained with the other devices. Again it was shown that the devices correlate well (ICC consistency > 0.97) and that correction factors can be applied to convert HLM results between devices. An alternative to the use of correction factors could be the replacement of the South African device with the German device for both wheat and maize. The removal of impurities from the maize samples significantly (P < 0.05) increased the HLM values. Therefore, it is likely that correction factors can be used to convert HLM values of maize samples before and after removal of impurities.

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