Godrich, Joseph
(2024)
Nutritional and functional properties of popped chickpea and red kidney bean.
PhD thesis, University of Nottingham.
Abstract
The aim of this PhD thesis was to maximise the nutritional and sensory potential of pulses using an underexplored form of high temperature, short time processing called compression popping. Chickpea and red kidney bean, which are known to contain ample quantities of nutrients but also antinutritional factors, were compression popped prior to nutritional analysis. Research was conducted to see if high temperature and pressure treatment could sufficiently reduce antinutritional factors and enhance nutrient digestibility and bioavailability, increasing the nutritional value of pulses as a form of food or food ingredient.
Popping demonstrated an ability to degrade and reduce phytic acid to a higher degree than traditional soaking, boiling and roasting techniques. Water treatment (soaking and boiling) was more effective at removing soluble condensed tannins and phenolics, whereas thermal treatment (roasting and popping) appeared to depolymerise condensed tannins and liberate bound phenolics, potentially increasing the bioaccessibility of protein and minerals to which they were bound.
Soaking and boiling pre-treatment offered the opportunity to combine water treatment with dry thermal treatment (popping) to remove both phytic acid and condensed tannins. Soak-popping and boil-popping were effective at reducing phytic acid levels, but to a lower degree than raw-popping, which was attributed to greater extractability. Likewise, soak-popping appeared to enhance the release of condensed tannin compounds in both pulses.
Soaking and boiling resulted in significant losses to key minerals such as iron and calcium, whereas popping had no effect. As a result, popping was effective at reducing phytate:mineral molar ratios in both pulses, although only one sample was below the critical level for phytate to not have an inhibitory effect on mineral bioavailability. Popping also increased the in vitro digestibility and proxy DIAAR of pulse protein. However, significant losses in lysine were observed for popped samples, particular after longer popping durations.
Consideration was also given to the effect of pre-treatment on the functionality and product quality (expansion) of popped pulses. Soaking and boiling appeared to influence starch granular integrity and arrangement of protein molecules. Boiled pulses contained gelatinised starch, validated by low birefringence and crystalline order, as well as denatured protein; confirmed with differential scanning calorimetry, polarised light microscopy, and soluble protein. Popped flours had low gelatinisation enthalpies as well as higher water absorption and non-protein solubility, characteristic of starch conversion and a transformation of starch from a semi-crystalline to a more amorphous state.
Soaking pre-treatment resulted in significantly lower popping densities than raw-popping alone, producing comparable densities to commercial snacks. The effect of boiling pre-treatment varied between pulses, possibly due to differences in water uptake influencing the degree of starch gelatinisation and granular rupture.
Fundamentally, popping shows high potential as a method of improving the restricted protein quality and mineral bioavailability seen in raw pulses. Overall, this work has validated that high temperature, short time processing can be successfully employed to reduce the antinutritional risk in pulses and deliver protein in a more digestible state. Popping should be explored further as a method of supplying quality nutrients to humans and animals.
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