Tea polyphenols enhance binding of porcine pancreatic α-amylase with starch granules but reduce catalytic activity.

The effects of tea polyphenols on binding of porcine pancreatic α-amylase (PPA) with normal maize starch granules were studied through solution depletion assays, fluorescence spectroscopy and initial rate kinetics. Only polyphenols which have inhibitory activity against PPA increased the binding of PPA with starch. The results are consistent with a binding equilibrium between polyphenols, starch and PPA. The dissociation constant (Kd) for PPA binding was decreased by tea polyphenols, with the effects greater for theaflavins than catechins and for galloylated than non-galloylated polyphenols. Tea polyphenols were also shown to increase the binding rate of PPA to starch. In addition, there were positive linear correlations between 1/Kd and reciprocal of competitive inhibition constant (1/Kic) and between 1/Kd and fluorescence quenching constant (KFQ). Despite the greater amount of PPA on the granules, starch hydrolysis is reduced because the polyphenol inhibition of PPA persists after binding to starch.

Investigating the mechanisms of amylolysis of starch granules by solution-state NMR.

Starch is a prominent component of the human diet and is hydrolyzed by α-amylase post-ingestion. Probing the mechanism of this process has proven challenging, due to the intrinsic heterogeneity of individual starch granules. By means of solution-state NMR, we demonstrate that flexible polysaccharide chains protruding from the solvent-exposed surfaces of waxy rice starch granules are highly mobile and that during hydrothermal treatment, when the granules swell, the number of flexible residues on the exposed surfaces increases by a factor of 15. Moreover, we show that these flexible chains are the primary substrates for α-amylase, being cleaved in the initial stages of hydrolysis. These findings allow us to conclude that the quantity of flexible α-glucan chains protruding from the granule surface will greatly influence the rate of energy acquisition from digestion of starch.

Perception of HIV risk and the quantity and quality of children: The case of rural Malawi.

The empirical literature on the impact of HIV on the quality (Q) and quantity (N) of children provides limited and somewhat mixed evidence. This study introduces individual HIV risk perceptions, as a predictor of mortality, into a Q-N investment model. In this model, higher maternal mortality predicts lower N while higher child mortality predicts lower Q. Thus the two effects together make likely negative associations between HIV and both Q and N. Based on longitudinal micro data on mothers and their children in rural Malawi, our results suggest that higher mothers' reported HIV risk reduces both child quality, as reflected in children's schooling and health, and child quantity, when the perceived risk is already moderate or high. The effects are sizable, and, in the case of Q (schooling and health) are found for children and teenagers, both boys and girls, while in the case of N they are found for young and mature women.