Influence of particle size and processing method on navy bean flour protein and starch digestibility

Abstract: Intact cell wall materials in pulses are known to limit starch digestibility by enzymes. Few studies have considered how the cell walls influence the extent of protein digestion in addition to raffinose family oligosaccharide (RFO) extraction. The objective of this study was to determine how changes in the particle size of navy bean flour influenced starch and protein digestibility. The in vitro starch and protein digestion and RFO extraction in 80% ethanol were examined for roasted, baked, and cooked navy bean flour fractions having large (297-500 mm), medium (74-297 mm), and small ( < 74 mm) particle sizes. The digestibility of both starch and protein was found to increase as the flour particle size decreased. In addition to the particle size, the different thermal treatments also influenced the starch and protein digestibility. The in vitro digestibility of both the starch and protein present in the fractions increased as flour’s moisture content increased in the order cooked > baked >roasted. Intact cotyledon cells did not affect the extractability of RFOs, and only roasting led to a small increase in their extractability. This study demonstrates different particle sizes of navy bean flours influences in vitro protein digestibility and its effect on nutrient availability should be considered when selecting pulse flours for food applications.