The role of non-starch components and granule size on starch digestibility

Abstract

Starch with different granule size contains small quantities of non-starch components (NSC) that may affect its characteristics. The aims of this study were to elucidate the impact of granule size and NSC on digestible starch and its digestion rate constant. The effect of NSC and granule size of four different banana cultivars (Kepok, Ambon, Nangka and Kapas) on digestion rate constants and digestible starch was examined using Logarithm of Slope (LOS) method along with Pearson correlation and Principal Component Analysis (PCA). Mean starch granule size ranged from 24.5 to 31.77 µm. Amongst NSC, pectin was present in the highest quantity while phenolic compounds were the lowest ranging from 26.81 to 71.94 ppm. All cultivars exhibited 2 fractions of starch, one digested rapidly (C_1∞) ranging from 0.44-0.63% and the second slowly (C_2∞) from 0.51-0.62% with the rate constants of k₁ and k₂ being respectively 8.7-11.20 x 10^-2 min^-1 and 1.83-2.34 x 10^-2 min^-1. Lipid, pectin, and granule size were negatively correlated with k₁ and total digestible starch (tot C_∞), while C_1∞ was negatively correlated with lipid and granule size. LOS-plot combined with PCA and Pearson correlation allows to reveal the correlation of granule size, lipid and pectin with both the amount of digestible starch and digestion rate constant. Granule size and NSC did not affect digestible starch and rate constants at slow phase. Lipid, pectin, and granule size however affected digestion parameters at rapid phase. PCA characterization indicated that all banana cultivars exhibited different characteristics in chemical composition, mean particle size and digestibility.