In vitro protein and starch digestibilities of multigrain sorghum-barley mixtures

In vitro protein and starch digestions in five sorghum-barley mixtures were investigated, revealing monophasic, and rapid-slow and slow-rapid multiphasic digestograms. The digestograms were adequately (r² > 0.93, p ≤ 0.001) modelled by the Sopade Objective Procedure (best for the starch digestograms), and multiterm exponential (best for the protein digestograms) and non-exponential equations. The mixtures varied in physicochemical and digestion properties, showing low sorghum digestibilities. The sorghum delayed pasting and increased anthocyanins to possibly inhibit the digestions. Towards better predicting in vitro protein digestibility, a hydrolysis index relative to casein (HI_PROTEIN) is presented and correlated (r² > 0.98, p ≤ 0.001) with the hydrolysis index for starch digestion (HI_STARCH) relative to white wheat bread. Using five published in vitro-in vivo protein digestibility data, a general equation (INVIVO_PROTEIN = 0.29 HI_PROTEIN + 61.89; r² = 0.960, p = 0.003) was obtained to, with the existing glycaemic-index-HI_STARCH equation, better understand food digestions.