Structural and functional properties of OSA-starches made with wide-ranging hydrolysis approaches

Octenyl succinic anhydride modified starches (OSA-starches) are widely used as emulsifiers and stabilizers in the food industry. This study investigates the relationships between molecular structure and emulsifying and antioxidant properties of OSA-starches with a wide range of structures, formed by hydrolysis by α-amylase, β-amylase and HCl for various hydrolysis times. Structural parameters, namely molecular size distribution, chain-length distribution, degree of branching (DB) and degree of OSA substitution (DS) were characterized using size-exclusion chromatography and H nuclear magnetic resonance. These parameters were then correlated with viscosity, emulsification performance and antioxidant properties for OSA-stabilized oil emulsions, to gain improved understanding of structure-property relationships. The average chain length (DP) and DB respectively showed positive and negative correlations with the viscosity, total antioxidant activity (TAC), creaming extent and the emulsion z-average droplet size for all the hydrolyzed samples. The OSA-starches treated by α-amylase generally had the smallest average DP and largest DB, resulting in the lowest viscosity and the best droplet stability with the smallest creaming extent. The acid-hydrolyzed OSA-starch samples presented larger average DP than the enzyme-hydrolyzed samples, in agreement with their better TAC, while larger creaming extent. The β-amylase-hydrolyzed samples produced moderate structural degradation and emulsifying properties compared to the OSA-starches treated by α-amylase and HCl. The structure-property correlations indicate that the average chain length and DB are the two most important structural parameters in determination of the functional properties for the OSA-modified starches. These findings will help develop improved food additives with desired functions

Molecular-size dependence of glycogen enzymatic degradation and its importance for diabetes

Glycogen, a hyperbranched glucose polymer, is the blood-sugar reservoir in animals. Liver glycogen comprises small β particles, which can join together as large composite α particles. It had been shown that the binding between β in α particles in the liver of diabetic mice is more fragile than in healthy mice. This could be linked to the loss of blood-sugar control characteristic of diabetes if the rate per monomer unit of the enzymatic degradation to glucose of α particles were significantly slower than that of β particles. This is tested here by examining the in vitro time evolution of the molecular size distribution of glycogen from the livers of healthy and diabetic mice and rats, containing distinct components of both α and β particles; this treatment is analogous to the “competitive growth” method used to explore mechanisms in emulsion polymerization. Simulations for the time evolution of the molecular size distribution were also performed. It is found that the degradation rate per monomer unit is indeed faster for the smaller particles, supporting the hypothesis of a causal link between chemical fragility of glycogen from diabetic liver with poor control of blood-sugar release. Comparison between simulations and experiment indicate that α and β particles have significant structural differences

Effects of pectin on molecular structural changes in starch during digestion

Starch digestion rate is strongly related to metabolic diseases such as obesity and diabetes. Starchy foods always contain non-starch components, which can affect starch digestibility. Mixtures of ungelatinized corn starch with a common non-starch component, pectin, were used to investigate pectin's effect on starch digestibility rate and evolution of starch molecular structure during digestion using amyloglucosidase and pancreatin. The whole-molecule size distribution and the chain-length distribution of chains were measured by size-exclusion chromatography and fluorophore-assisted carbohydrate electrophoresis. Digestion profiles and changes in molecular size distributions of whole and debranched digesta during digestion show that addition of pectin significantly decreased starch digestion rates. While pectin did not change the amylose/amylopectin ratio during most of the digestion, it decreased the digestion rate of short amylopectin chains compared to long ones. UV–visible spectral data suggested that a major contributor to this digestion rate change is from substantial pectin/amyloglucosidase interaction. This suggests an approach to designing nutritionally more beneficial starch-based foods by taking account of interactions between pectin and digestive enzymes

Relationships between amylopectin molecular structures andfunctional properties of different-sized fractions of normal andhigh-amylose maize starches

The amylopectin molecular structures and functional properties of different-sized fractions of normal and high-amylose maize starches were investigated and compared in this study. The different-sized fractions of normal starch showed similar amylopectin molecular structures and functional properties. The small-sized fraction of high-amylose starch had significantly higher amylopectin long branch-chain and average branch-chain length than its counterpart medium- and large-sized fractions. The swelling power, gelatinization enthalpy, and hydrolysis and digestion degrees of high-amylose starch significantly decreased with decrease of granule size, and were significantly positively correlated with amylopectin short branch-chain and negatively correlated with amylopectin long branch-chain and average branch-chain length. The gelatinization peak temperature and resistant starch content increased with decrease of granule size, and were significantly positively correlated with amylopectin long branch-chain and average branch-chain length and negatively correlated with amylopectin short branch-chain. The hierarchical cluster analysis indicated that the large-sized fraction of high-amylose starch was significantly different from the medium- and small-sized fractions of high-amylose starch but more relative with normal starch. The above results could provide important information for the applications of different-sized fractions of high-amylose maize starch

Implications for biological function of lobe dependence of the molecular structure of liver glycogen

Liver glycogen, a complex branched polymer of glucose, plays a major role in controlling blood-sugar levels. Understanding its molecular structure is important for diabetes, especially since it has been found that this structure is more fragile in diabetic than in healthy mouse liver. However, there are differences in metabolic processes between liver lobes, which would be expected to be reflected in differing glycogen molecular structures. This structure was examined for separated lobe regions in rat livers, using size-exclusion chromatography (SEC) and fluorophore-assisted carbohydrate electrophoresis. The results show that the SEC weight distribution of glycogen, and the molecular weight distribution of individual branches (chains), from different lobes are similar. This shows that (a) molecular structural characterization of glycogen from whole-liver biopsy is representative (which is convenient because the commonest animal model for diabetes is the mouse, whose livers are very small), and (b) the fact that molecular structure is conserved (regulated) in different lobes suggests that this structure plays an important role in blood-sugar regulation

Milling of rice grains: effects of starch/flour structures on gelatinization and pasting properties

Starch gelatinization and flour pasting properties were determined and correlated with four different levels of starch structures in rice flour, i.e. flour particle size, degree of damaged starch granules, whole molecular size, and molecular branching structure. Onset starch-gelatinization temperatures were not significantly different among all flour samples, but peak and conclusion starch-gelatinization temperatures were significantly different and were strongly correlated with the flour particle size, indicating that rice flour with larger particle size has a greater barrier for heat transfer. There were slight differences in the enthalpy of starch gelatinization, which are likely associated with the disruption of crystalline structure in starch granules by the milling processes. Flours with volume-median diameter ≥56 μm did not show a defined peak viscosity in the RVA viscogram, possibly due to the presence of native protein and/or cell-wall structure stabilizing the swollen starch granules against the rupture caused by shear during heating. Furthermore, RVA final viscosity of flour was strongly correlated with the degree of damage to starch granules, suggesting the contribution of granular structure, possibly in swollen form. The results from this study allow the improvement in the manufacture and the selection criteria of rice flour with desirable gelatinization and pasting properties