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Title: Effect of Heating Temperature on Particle Size Distribution in Hard and Soft Wheat Flour

item Gaines, Charles

Submitted to: Journal of Cereal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/26/2004
Publication Date: 7/15/2004
Citation: Kim, W., Choi, S.G., Johnson, J.W., Gaines, C.S. 2004. Effect of Heating Temperature on Particle Size Distribution in Hard and Soft Wheat Flour. Journal of Cereal Science. 40(1):9-16.

Interpretive Summary: The particle size of wheat flours varies with wheat class.  However, how particle size changes upon heating relative to wheat class has not been studied.  Flours, isolated starch, and gluten protein from both hard and soft wheat classes were heated from 30°C to 80°C, for 20 to 60 min in water.  Particle size distributions of each class were compared at each temperature.  Three peaks of particles were observed.  Soft wheat produced more small free starch granules and hard wheat produced more particles with associated starch and gluten.  Heating changed the particle distributions dramatically.  The main difference in particle size between soft and hard wheat resulted from the strength of starch-protein interactions, which may also influence end-use qualities of classes of wheat flour.  Wheat breeders can utilize this information to attempt to either reduce or increase those interactions to influence potential end-use characteristics.

Technical Abstract: The particle sizes of soft and hard wheat (Triticum aestivum L.) flours at isothermal temperatures were determined by laser diffraction analyzer.  Flour sample were suspended in water at temperatures ranging from 30°C to 80°C, for 20 to 60 min.  All flour particles exhibited trimodal size distributions: first mode ranged < 10 mm, the second mode ranged from 10 ~ 40 mm, and the third mode ranged from 41 ~ 300 mm.  Control experiments with isolated starch and gluten indicated that the first and second modes were mainly associated with starch granules, while the third mode was related to gluten and particle cluster.  Soft wheat flours had higher volume fractions of the first and second mode of the particle, indicating higher dissociated starch granules from particle cluster during milling compared to hard wheat flours.  Particle size distributions of the wheat flours were dependant temperature.  At 60°C, significant changes in mean particle size and distribution of flours were observed.  This result was attributed to swelling of starch granules in response to elevated temperature.  In addition, gelatinization of starch may facilitate dissociation of starch granules from particle clusters.  As temperature increased, the mean particle size increased.  Hard wheat flours had a higher volume fraction of particles, ranging above 120 mm at elevated temperature.  Our results suggest that the difference in particle size between soft and hard wheat due to the strength of starch-protein interaction may influence end-use quality of flour.