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A new wheat protein fractionation method using the modified Dumas nitrogen assay. J. SUCHY (1), O.
M. Lukow (1), and B. X. Fu (2). (1) Cereal Research Centre, Agriculture and Agri-Food Canada,
Winnipeg, MB; (2) Canadian International Grains Institute, Winnipeg, MB.
The quantitative variations of monomeric and polymeric proteins
contribute significantly to the differences in rheological properties between cultivars. Most wheat protein
fractionation and quantification methods cannot be used as early generation screening tests due to their poor
resolution between protein solubility groups and the time and labour required. The purpose of this study
was to develop a routine protein fractionation method that will allow quantification of relatively pure wheat
protein groups using small scale automated nitrogen analysis. The procedure was based on differential
solubility of various wheat protein groups in aqueous 1-propanol solutions with or without sodium iodide,
and quantification of total nitrogen content of the protein fractions directly from the dried residue by a
modified Dumas method. For all the protein fractions, there were no significant differences between the
protein contents obtained by the modified Dumas method and by the micro-Kjeldahl method. The
usefulness of the developed procedure was evaluated through protein fractionation and quantification of a
set of Canadian wheat cultivars with identical high molecular weight composition (2*, 7+8, 5+10). The
wide variation of their dough rheological properties can be explained by the relative amounts of different
protein solubility groups.
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