Effects Of Starch Structure On Rice Starch Biosynthesis And Waxy Corn OSA-starch Functional Properties

Amylose and amylopectin are the two main components of starch,which is a complex branched glucose polymer.Amylose has moderate molecular weight with a small number of long-chain branches,and amylopectin has large molecular weight with a vast number of short-chain branches.The chain-length distribution of amylopectin and amylose plays an important role in the study of starch biosynthesis.Starch is the bulk energy storage molecule in plants,and is widely available as a resource for industry.Starched-based products are usually safe for human consumption.In roles as food additives,modified starches present several benefits over alternative products.Native starches generally have limited solubility in water and are limited in their industrial applications.Nineteen rice varieties with amylose contents up to 28%were used.The molecular structure,in the form of the chain-length distribution(CLD,the distribution of the number of monomer units in each branch)was measured after enzymatic debranching,using fluorophore-assisted carbohydrate electrophoresis for amylopectin and size-exclusion chromatography for amylose.The resulting distributions were fitted to two mathematical models based on the underlying biosynthetic processes,which express the CLDs in terms of parameters reflecting relevant enzyme activities.Finding statistically valid correlations between the values of these parameters showed that GBSSI and SBEI compete for substrates during rice starch biosynthesis,and synthesis of amylose short chains involves several enzymes including GBSSI,SBE and SSS(soluble starch synthase).Since the amylose CLD is important for a number of functional properties such as digestion rate,this knowledge is potentially useful for developing varieties with improved functional propertiesSpecific Octenyl succinic anhydride modified starches(OSA-starches)are widely used as emulsifiers and stabilizers in the food industry.OSA starches with a wide range of structures,formed by hydrolysis by ?-amylase,?-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 1H 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(X)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 ?-amylase generally had the smallest X 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 chain length than the enzyme-hydrolyzed samples,in agreement with their better TAC,while larger creaming extent.The ?-amylase-hydrolyzed samples produced moderate structural degradation and emulsifying properties compared to the OSA-starches treated by ?-amylase and HCl.The structure-property correlations indicate that the average chain length(X)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.