Analysis procedures and the formation of resistant starch during food processing

Sullivan, W 2018, Analysis procedures and the formation of resistant starch during food processing, Doctor of Philosophy (PhD), Science, RMIT University.


Document type: Thesis
Collection: Theses

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Title Analysis procedures and the formation of resistant starch during food processing
Author(s) Sullivan, W
Year 2018
Abstract Globally, wheat is a major grain crop and there has been extensive research into the protein components due to their functional significance particularly in breadmaking. There is now increasing recognition of the potential roles of starch both from nutritional and physicochemical perspectives. The benefits associated with the presence of resistant starch in foods have led to studies on a variety of starch sources, although relatively little of this has been on wheat starch. Therefore, the primary objective of this research has been to investigate resistant starch formation using starch sourced from wheat.

In the preliminary phases of this study, starches from a range of sources have been characterised using scanning electron microscopy and X-ray diffraction in order to compare external morphological characteristics and internal granular infrastructure. The starches including wheat, potato, corn, rice, tapioca and mung bean, all presented with expected granule sizes, shapes and X-ray patterns. The arrangements of amylopectin and chain length within the granule were explored in more detail and have been related to granule size and shape. The starch sourced from mung beans gave unexpected results, particularly for the X-ray patterns and further research into a range of pulse starches appears to be warranted.

In the following phase, bread was selected for evaluation as it is a staple food globally. The levels of resistant starch were measured in conjunction with the storage of loaves at various temperatures. For this, resistant starch was determined enzymatically and found to increase at a higher rate during storage under refrigeration conditions (4oC), followed by 22oC (room temperature) and finally -18oC (frozen). The samples were also concurrently subjected to X-ray diffraction. For this, an efficient, reliable and reproducible method of preparing bread samples for X-ray analysis was developed. When the data for the enzymatic analysis were related to the X-ray patterns, there was a statistically significant correlation between rates of resistant starch formation and X-ray patterns (R2 = 0.967). Therefore, X-ray diffraction could provide a useful, more rapid method for qualitatively evaluating the concentrations of resistant starch.

A variety of starches was also studied for their thermal properties using differential scanning calorimetry. The purpose was to establish gelatinisation properties of the commercial wheat starch in order to form the basis for subsequent experimentation.

For this, sample preparation and heating rates of 2oC, 5oC and 10oC per minute were optimised and compared statistically with one-way ANOVA and a post-hock Tukey’s test. Significant (P<0.001) differences were observed between the three approaches and the variables analysed including onset, offset, peak temperature and enthalpy. It was determined that a temperature rate of 10oC per minute gave the most repeatable endotherms and was then applied to various starches including rice, corn, potato, mung bean and tapioca. Large differences were found in comparison with literature values and this is attributed to starch manufacture, sample preparation and instrument conditions.

Previous research has indicated potential of hydrothermal treatments for increasing resistant starch concentrations for starch sources other than wheat. Therefore in the current study native wheat starch has been subjected to either heat-moisture treatments or annealing using various conditions selected so that gelatinisation does not occur. Scanning electron microscopy was used to confirm that gelatinisation had not taken place. It was observed that there were small changes to the surface of granules and this might relate to sites at which beneficial bacteria may be able to adhere and this might relate to these granules having prebiotic roles. The data from X-ray diffraction provided correlations with the increases in resistant starch concentration. These effects were more obvious following annealing treatments than for those involving heat and moisture. Therefore, wheat starch samples were subjected to extended incubation times with the annealing method and the resultant samples subsequently analysed with additional analyses including the determination of amylose content (enzymatically) and the degree of branching (nuclear magnetic resonance). The result was an overall increase in resistant starch content. From these results, a mechanism is proposed describing how amylose and amylopectin components rearrange within the internal granular structure during treatment.

In summary, starches have been characterised using a variety of methods including scanning electron microscopy, X-ray diffraction and differential scanning calorimetry with a particular emphasis on starch sourced from wheat. This information was then used to form the basis for investigating hydrothermal treatment of wheat starch and the effects on increasing resistant starch levels. Annealing gave larger increases in resistant starch than heat-moisture treatments. Further studies are now recommended and the results have been used to develop a model for the internal granular changes that contribute to the increases in resistant starch.
Degree Doctor of Philosophy (PhD)
Institution RMIT University
School, Department or Centre Science
Subjects Food Chemistry and Molecular Gastronomy (excl. Wine)
Analytical Chemistry not elsewhere classified
Keyword(s) Starch
Bread
Prebiotics
Health benefits
Resistant starch
X-ray diffraction
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Created: Wed, 28 Nov 2018, 10:14:43 EST by Anna Koh
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