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• W184092321 abstract "This thesis is the first comprehensive study into the relationship between starch structure and the functional properties of its derivatives made by modification with octenylsuccinic anhydride (OSA). Several new methods have been developed in the process of this work, using a range of purposefully created octenylsuccinylated (OS) starches with controlled structures. Chapter 1 is a general introduction to the science involved and the state of the art. Chapters 2 to 4 explore methods in the development of structurally targeted OS starches. Chapters 3, 5 and 6 report the results from some analyses. As outlined in Chapter 1, OS starches represent an economically important product that has existed for many decades, but has recently shown significant growth in interest as seen in scientific literature. The reasons for this impressive surge in interest reflects the wide range of applications and versatility OS starches, determined primarily from the structural properties of the starch substrate. With that in mind, it is surprising that, to date, most interest has been focussed on conditions of the OSA modification process, rather than the structure-function relationships. After a comprehensive state-of-the-art review, this thesis has identified the important areas where structure-function research of OS starches should focus in-depth to provide the most thorough innovation in the field. Throughout, size exclusion chromatography (SEC) and nuclear magnetic resonance (NMR) have been used for structural analysis, while gel properties and emulsion function have been determined using a wide range of methods. Chapter 2 outlines NMR methods that were developed specifically for this project. It has been determined that the ideal system for analysing OS starches by NMR utilises 64 to 128 scans in deuterated dimethylsulfoxide (DMSO-d6) of at least 50 °C containing at least 22 mg mL-1 deuterated trifluoroacetic acid (TFA-d1), as has been published and improved upon during the course of this thesis. The method utilises the signal from the proton attached to the 5th Carbon residue of the octenyl tail to determine the number of OS groups, and compares that to the total number of monomers by the addition of α-(1→4), α-(1→6) and reducing end signals. The signal of the 5th proton is unique, because it neighbours the double bond. Due to the susceptibility of the double bond to the effects of TFA-d1, the analysis must be performed very quickly for best results. By this method it is possible to determine the degree of branching (DB) and the degree of OS substitution (DS) using the one simple analysis. Because it also accurately measures DB, the same method has proven useful for non-OSA-modified starches. Chapter 3 is an overview of the development and initial application of a method to determine the critical aggregation concentration (CAC, sometimes called “critical micelle concentration”, though the aggregates formed by OS starches are not by definition micelles). The method uses pyrene fluorescence and can be adapted for other polymeric surfactants, and has been used in this first instance to investigate a range of acid-hydrolysed starches. These starches were prepared by reaction with HCl in various alcoholic solvents. Acid hydrolysis has been found to be ideal for creating starch substrates of tailored hydrodynamic volume (Vh), with fairly low dispersity. The values determined by CAC analysis reflect the capacity of the surfactant to interact with itself and with interfaces, and are a useful and simple method of comparing surfactants; however, the results do not always translate directly into emulsion stability or overall quality. As outlined, OS starches from highly branched substrates show similar CAC characteristics to those seen with more linear synthetic polymer surfactants. Chapter 4 deals with the β-amylolysis of OS starch, particularly the effect of OS groups on the β-amylase activity. To achieve this, starches from waxy sorghum and waxy maize were modified with OSA to a range of DS, including very high levels beyond those used in industry. Hydrolysis by β-amylase was performed on both granular and gelatinised starches. Because the OSA modification process is on starch in granular form the reaction is heterogeneous with those areas accessible to the solvents more readily accessible; similarly, β-amylolysis in granular form restricted access of the enzyme to many of the same areas of the granule in which the esterification had predominantly occurred, whereas in gelatinised form the β-amylase activity was much more unhindered. The activity of the enzyme was somewhat diminished by the presence of OS groups, though the results were not so conclusive as to indicate complete blocking of the enzyme activity along individual branches. Chapter 5 introduces the critical test of emulsion capacity and stability, as well as an important method for determining the breakdown of β-carotene in the oil phase of emulsions. The method is an accelerated test at high storage temperature that can determine the oxidative effects on any labile components in the oil phase. The methods of acid hydrolysis used in Chapter 5 are similar to those in Chapter 3; however, the spectrum of samples is more broad and encompasses a range of structural variables. Amylose/amylopectin ratio is used as a simple method of controlling the DB, and the molecules are reduced to controlled sizes through the use of acid hydrolysis in alcohols. Methods for determining the quality of starch surfactants in the formulation and stabilisation of emulsions use high-pressure homogenisation (HPH) and track the development of pigment and droplet size during incubation at 55 °C over 20 days. The results of these tests indicate that samples containing many short branches from amylopectin are more stable than those containing longer amylose chains, regardless of the overall degree of branching (DB) of the surfactant. The effects of shear scission during HPH are also elucidated in this chapter to a greater extent than has previously been demonstrated with OS starches. Chapter 6 brings together the methods from all previous chapters to determine the CAC, emulsion capacity and stability and oxidative stability of β-carotene dissolved in the oil phase of several waxy maize and sorghum starches, after they were modified with OSA, structurally modified with β-amylase or pullulanase, and characterised using SEC and NMR. The size of oil droplets in emulsion can be higher in samples of larger Vh without any sacrifice to emulsion stability, probably due to the layer thickness at the interface. Larger molecules of amylopectin also result in better chemical stability of β-carotene and lower CAC; however, attempts to artificially increase DB by treatment with β-amylase have a detrimental effect to emulsion stability, while lowering the degree of branching with pullulanase does not show the inverse effect. As a result of this thesis, several advances have been made in the field of OS starch science. The common empirically based tendency of industrially prepared OS starches to be based on waxy starches and prepared by HPH has been validated by the findings that hydrodynamic size and short branch length contribute to the quality of emulsion formulations. Treatment of industrial starches with β-amylase does not lead to useful surfactant properties, and from the results of this study such methods can be excluded from future consideration. This thesis is the first document in the field to indicate that higher DB does not directly lead to better emulsions, rather than the presence of short linear branches in a mix also containing larger, branched molecules. Waxy sorghum has been established as a viable source of OS starch substrate, opening up opportunities for future research and industrial production in the Australian market." @default.
• W184092321 created "2016-06-24" @default.
• W184092321 creator A5056009755 @default.
• W184092321 date "2014-12-02" @default.
• W184092321 modified "2023-09-25" @default.
• W184092321 title "Octenylsuccinylated starches: Structure and function" @default.
• W184092321 doi "https://doi.org/10.14264/uql.2014.488" @default.
• W184092321 hasPublicationYear "2014" @default.
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