Investigating the relationship between lentil carbohydrate fractions and in vivo postprandial blood glucose response by use of the natural variation in starch fractions among 20 lentil varieties.

Consumption of pulses is associated with many health benefits by mechanisms that are not fully understood. This study sought to identify the starch component(s) in cooked lentils responsible for lowering postprandial glycemic response (PPGR). Rapidly digestible (RDS), slowly digestible (SDS) and resistant starch (RS) content of 20 varieties of cooked lentil were determined by in vitro methods and 8 varieties, representing a linear range of SDS, were chosen for a human trial with 10 participants to determine PPGR and glycemic index (GI). Among the 20 lentil varieties, RS accounted for 35% of the variation of in vitro area under the starch hydrolysis curve (SHAUC) (r = -0.587; p < 0.01), but RDS (r = 0.401; p = 0.080) and SDS (r = -0.022; p = 0.927) were not significantly related to SHAUC. Multiple linear regression of in vitro data resulted in an equation [SHAUCest = 30.9RDS - 63.6RS + 9680] that accounted for 70% of the variance in SHAUC, with SDS excluded due to collinearity. In the human trial all 8 lentils had low GI values (10 to 23). Neither GI nor area under the glucose response curve (AUC) was significantly related to RDS, SDS or RS (minimum p = 0.24). However, SHAUC and SHAUCest, respectively, were related to both GI (r = 0.704, p = 0.051; r = 0.773, p = 0.024) and AUC (r = 0.765, p = 0.027; r = 0.822, p = 0.012). These results confirm that lentils have low GI values, which is not reliably predicted by their RDS, SDS and RS contents when considered individually. However, in vitro SHAUC and a combination of RDS and RS may be predictive of the PPGR of lentils.

Evolution of amylopectin structure in developing wheat endosperm starch.

In this study, starches extracted from wheat grains harvested at 7, 14, 28, and 35 days after anthesis (DAA) were used as a means of examining the molecular structure of amylopectin (AP) from developing wheat grain. Scanning electron microscopy of wheat grain cross-sections revealed the presence of endosperm at 7 DAA and contained lenticular-shaped developing large (A-type) granules. From 14 DAA onward, spherical-shaped small (B-type) granules coexisted with large granules in the endosperm. During granule development, the fine structure of AP varied with maturity in both large and small granules. Towards the end of the pre-physiological maturity stage (28 DAA), AP in small and large granules had shortest external chain length (ECL), longest internal chain length (ICL) and lowest amount of A-chains. At physiological maturity (35 DAA), these changes in ECL, ICL and amount of A-chains were reversed when compared to 28 DAA. In both large and small granules, the external AP structure was apparently more organized at physiological maturity than at pre-physiological maturity.

Structure of clusters and building blocks in amylopectin from developing wheat endosperm.

Changes in internal structure of amylopectin (AP) during wheat endosperm development were studied by isolating clusters and building blocks of AP from both large A-type and small B-type starch granules at different maturity stages up to harvest time at 49 days after anthesis (DAA). Clusters isolated from B-type granules had a degree of branching (DB) of 16.5-16.8% and were more tightly branched than those isolated from A-type granules (DB 15.7-16.2%). The degree of polymerization (DP) of the clusters increased in both types of granules during the pre-physiological maturity stage up to 28 DAA. Clusters at maturity were smaller with less branches and building blocks than at the end of the pre-maturity stage. It is suggested that this was due to a continuous trimming of the cluster structure after the active period of starch synthesis. Differences were evident between A- and B-type granules with regards to glucan trimming and the type of new chains produced.