The objectives of this study were to determine the range of variation in the rate and extent of in situ ruminal starch degradation of 14 corns differing in vitreousness and to predict ruminal starch degradability by physical characteristics of corn grains. This study was conducted with eight dent and six flint corns. Ruminal starch degradability was determined by an in situ technique on 3-mm ground grains. Physical characteristics of corn grain were measured: hardness by grinding energy and particle size distribution, apparent and true densities, and specific surface area. Ruminal DM and starch degradabilities averaged 50 and 55.1% and varied from 39.7 to 71.5% and from 40.6 to 77.6%, respectively. Ruminal starch degradability averaged 61.9 and 46.2% in dent and flint types, respectively. The proportion of coarse particles (61.9 vs. 69.6% for dent and flint, respectively), the apparent density (1.29 vs. 1.36 g/cm3 for dent and flint, respectively), and the specific surface area (.13 vs. .07 m2/g for dent and flint, respectively) varied with the vitreousness. Ruminal starch degradability could be predicted accurately by vitreousness (r2 = .89) or by the combination of apparent density and 1,000-grain weight (R2 = .91), a measurement faster than the vitreousness determination.

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The particle size distributions of wheat flours collected along a milling diagram were assessed. Nine wheat varieties from the genetic trait Triticum aesticum vulgare and differing in hardness were studied for two consecutive years. Break, sizing and middling flours were collected for each wheat at different stages in an experimental mill, with all the milling conditions being kept constant. The particle size distributions were measured from 1·5 to 600 μm by using a laser light diffraction apparatus. The distributions were compared by principal component analysis. The method provided a global and synthetic comparison of all the flour fractions. In the case of the soft varieties, the distributions exhibited a first mode around 25 μm, corresponding mainly to isolated starch granules. The distribution of this mode was very low or non‐existent for the hard varieties. As the milling conditions were the same for all the wheats, the different proportions measured for this mode were interpreted as being directly representative of the wheat hardness. The proportion of the 25 μm mode was considered as a measure of the ability of the wheat to release starch granules and could be used to follow a grinding or milling process. © 1998 Society of Chemical Industry

The particle size distributions of wheat Ñours collected along a milling diagram were assessed. Nine wheat varieties from the genetic trait T riticum aesticum vulgare and di †ering in hardness were studied for two consecutive years. Break, sizing and middling Ñours were collected for each wheat at di †erent stages in an experimental mill, with all the milling conditions being kept constant. The particle size distributions were measured from 1É5 to 600 lm by using a laser light di †raction apparatus. The distributions were compared by principal component analysis. The method provided a global and synthetic comparison of all the Ñour fractions. In the case of the soft varieties, the distributions exhibited a Ðrst mode around 25 lm, corresponding mainly to isolated starch granules. The distribution of this mode was very low or non-existent for the hard varieties. As the milling conditions were the same for all the wheats, the di †erent proportions measured for this mode were interpreted as being directly representative of the wheat hardness. The proportion of the 25 lm mode was considered as a measure of the ability of the wheat to release starch granules and could be used to follow a grinding or milling process.1998 Society of Chemical Industry ( J Sci Food Agric 78, 237È244 (1998)