Results and Discussion
The weight percentages from each sieve for the SBM samples are presented in Table 2. The particle sizes obtained (948-, 600-, 328-, and 184-microns) were close to the targeted values of 900, 600, 300, and 150-microns. Particle size distribution is shown graphically for the 900- and 600-micron treatments in Figure 1.
The digestibility of amino acids was affected by particle size and is presented in Table 3. Isoleucine, methionine, phenylalanine, and valine digestibilities each increased linearly (P < 0.05) as particle size decreased, with the greatest increase occurring between the 900- and 600-micron treatments. Leucine and aspartate digestibility showed a linear trend of increasing as particle size decreased, but was not statistically significant (P < 0.10). All amino acid digestibilities, with the exception of glutamate, increased numerically from the 900- to 600-micron treatment. This response is illustrated by the four most commonly limiting amino acids (lysine, methionine, threonine and tryptophan) presented in Figures 2, 3, 4, and 5, respectively.
These results suggest that grinding SBM to smaller particle sizes increases the digestibility of its amino acids. This increase is likely due to the greater surface area increasing the effectiveness of the digestive enzymes. The greatest increase in digestibility is evident between the 900- and 600-micron treatments. The results also indicate that the reduction in particle size was largely a reduction of the larger particles in the 900-sample thus accounting for the higher digestibility of amino acids.