Effects of various processes of fractionation, grinding and storage of peas on the digestibility of pea starch in chickens

Abstract

Digestibility of pea starch was measured in 3 week-old chickens. In the first experiment, pure starch fractions introduced at a 200 g/kg dietary level were studied. Digestibility of high amylose pea starch was 75.2%, while that of normal peas and maize was 94.4 and 98.8%, respectively. The digestibility of starch of 3 mm ground unfractionated seeds from normal pea genotype, tested in the same experiment, was 76.1%. In the second experiment, pea cotyledon fractions separated into fine (<100 μm) and coarse (>100 μm) particles were studied at 480 g/kg dietary inclusion. Mean starch digestibilities were 95.7 and 84.4% for fine and coarse particle fractions, respectively. In the third experiment, whole seeds were either dehydrated (6.6% final water content) or slightly moistened (17.5% final water content) before grinding, which resulted in a three-fold increase in the mechanical energy supplied by grinding in the case of moistened seeds. After grinding, peas were introduced at a 480 g/kg level in diets. Dehydration resulted in either no change or 10% increase in the pea starch digestibility, while moistening resulted in 6.9–19.8% increases. In the fourth experiment, storage conditions of pea seeds for 5 weeks were tested. Temperature, water content of seeds and their physical state (ground vs. unground) during storage had no effect on their starch digestibility. In all experiments metabolisable energy values were also measured and showed good agreement with starch digestibilities. It was concluded that the variations in starch digestibility of ground peas result from interactions between the resistance of pea starch granules and the accessibility defect in coarse particles, and that these interactions depend on the amount of mechanical energy supplied by grinding.