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

Background and objectives Intact cotyledon cells in pulses are known to limit the access of digestive enzymes and to decrease starch digestibility. The objective of this study was to study the effect of the cells on starch and protein digestibility and raffinose family oligosaccharide (RFO) extraction. The in vitro starch and protein digestion and RFO extraction in 80% ethanol were studied for roasted, baked, and cooked navy bean flour fractions having large (297-500 mu m), medium (74-297 mu m), and small (<74 mu m) particle sizes. Findings The starch digestibility and protein digestibility were highest for the smallest particle size flour. The digestibility was lowest for roasted flours and highest for cooked flours. Intact cotyledon cells did not affect RFO extraction. Conclusions The in vitro protein digestibility increased as the particle size of the navy bean flour decreased for the three fractions that had been roasted, baked, or cooked. Significance and novelty This is the first study showing that navy bean flours with different particle sizes have different in vitro protein digestibility. The effect on nutrient availability should be considered when selecting pulse flours for food applications.