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Composition and Distribution of Pentosans in Millstreams of Different Hard Spring Wheats

¹Canadian International Grains Institute, Winnipeg, MB Canada R3C 3G7. ²Department of Food Science, University of Manitoba, Winnipeg, MB Canada R3T 2N2. ³Corresponding author. Phone: 1-204-474-6481. Fax: 1-204-474-7630. E-mail: harry_sapirstein@umanitoba.ca ⁴Grain Research Laboratory, Canadian Grain Commission, Winnipeg, MB R3C 3G8, Canada.

Six commercially grown samples of hard spring wheat were milled using a tandem Buhler laboratory mill. Individual flour streams and branny by-products, as well as whole-grain wheat and straight-grade flour, were characterized in terms of total (TP), water-extractable (WEP), and water-unextractable (WUP) pentosans. One representative cultivar sample was analyzed for its ratio of arabinose to xylose (A/X). TP and WEP of whole grain wheat of the six samples had ranges of 5.45–7.32% and 0.62–0.90% (dm), respectively. Neither TP nor WEP of whole grain was related to ash content variation. There was significant variation in the distribution and composition of pentosans in 16 millstreams of all the wheat samples, including bran and shorts fractions; TP and WEP contents had ranges of 1.69–32.4% and 0.42–1.76% (dm), respectively. When ash contents exceeded ≈0.6% (dm), strong positive correlations were obtained between ash and TP contents, and between ash and WUP contents for all the millstreams. Among bran and shorts fractions, TP and WUP content increased in the order of coarse bran > fine bran > shorts; while WEP, WEP/WUP and A/X showed the opposite pattern of variation of shorts > fine bran > coarse bran. Bran and shorts fractions had pentosan contents several times higher than would be predicted from the relationship between pentosan and ash contents of the flour streams. Pentosans therefore represented a much more sensitive marker of flour refinement compared with ash content. Pentosans of endosperm were substantially different in their extractability and composition from those of bran. On this basis, different functionalities of pentosans of bran and endosperm would be expected. Results demonstrated the importance of milling extraction and millstream blending in the functionality and quality of wheat flour for breadmaking.