Neutral ose composition of wheat grain tissues and its use to assess tissue composition in mill streams
Résumé
Conventional wheat grain milling processes aim at dissociating and isolating the starchy
endosperm, recovered in flour or semolina, from the outer layers as bran fractions.
Proportions of each tissue in mill streams impact their nutritional quality or their end-use
properties. Among various methodologies, measurement of biochemical markers specifically
located in the different wheat grain tissues was successfully applied to evaluate these tissue
proportions within fractions. However this method implies at least four different
measurements and, due to variability in marker amounts, could lead to some loss of accuracy.
Considering the diversity in neutral ose composition between each grain tissue, this data,
coming only from one biochemical analysis, could be useful to quantify the tissue proportion.
The objective of this study was first to evaluate the specificity and variability of neutral ose
composition in durum and common wheat grain tissues and then to evaluate its ability to
predict tissue composition in various mill streams based on this characterization. Pure starchy
endosperm, aleurone layer, outer pericarp were dissected as well as a composite layer made of
nucellar epidermis+testa+inner pericarp. Starchy endosperm, with high amount of glucose
(related to the presence of starch) was easily differentiated from peripheral tissues (richer in
arabinose and xylose present in wheat cell wall polysaccharides). Based on measured tissue
proportion obtained by another method, the ose composition in mill streams was predicted
from pure tissue composition: the best results were obtained for arabinose and xylose content
but with a global error of 13 %. On the other hand, multiple regression methods (PLS, MCR)
were used to predict tissue proportion in mill streams based on ose composition. If outer
pericarp and starchy endosperm could be predicted with a satisfactory error of 5%, prediction
of the aleurone layer and intermediate layer containing testa was not straightforward with
error higher than 10%. The high similarity between these tissues could be part of the
explanation. Therefore even if variability in ose composition due to different cultivars was not
found significant, the specificity for each tissue appeared insufficient to envision such
analyses to determine the tissue composition in mill streams.