Manipulating starch digestibility by influencing molecular and microscale starch structure in 3rd generation extruded snack foods

McClure, Jennifer (2022) Manipulating starch digestibility by influencing molecular and microscale starch structure in 3rd generation extruded snack foods. Doctoral thesis, University of East Anglia.

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Abstract

Pulses are high in several nutritional properties. Prior to consumption, pulses must undergo time consuming pulse preparation methods. These are necessary to minimise anti-nutritional factors intrinsic in legumes and improve functionality. In comparison to cereal and tuber starches, most pulse starches have greater thermal stability and can withstand more mechanical shear. This results in increased resistance to digestion.

This study explores the effects of extrusion processing and formulation moisture on the starch digestibility and structure of chickpea and red lentil flours. It is hypothesised that extrusion of pulses will result in increased starch digestibility.

Red lentil and chickpea flour were extruded (80°C; 30 rpm) at 10%, 40% and 80% potato starch substitution using 25% and 35% formulation moisture. The degree of starch gelatinisation was quantified using DSC (Differential Scanning Calorimetry) and XRD (X-ray Diffraction). Starch digestibility of raw flours, extrudates and expanded final products was quantified using static in vitro digestion methods using PAHBAH (4-hydroxybenzoic acid hydrazide) assay as an endpoint to obtain starch digestibility kinetics.

A complex non-linear relationship was observed between formulation moisture content and pulse incorporation. Increasing pulse content resulted in decreased starch gelatinisation (4.2 J/g in 80% chickpea flour incorporated vs 1.4 J/g in 10% chickpea flour incorporated extrudates) during extrusion, conversely increasing starch crystallinity (22.9% starch crystallinity in 80% chickpea flour incorporated, vs 20.0% starch crystallinity in 10% chickpea flour incorporated extrudates). Formulation moisture did not significantly affect gelatinisation, but high formulation moisture was found to increase retrogradation 0.4 J/g in 10% chickpea flour incorporated extrudates with low moisture formulation vs 2.4 J/g in 10% chickpea flour incorporated extrudates with high moisture formulation.

The degree of gelatinisation correlated strongly with the extent of starch digestibility in expanded snacks (P-value (Pearson correlation) < 0.00001), but not with overall crystallinity (P-value (Pearson correlation) = 0.51, indicating that the presence of ungelatinised starch was the main factor limiting starch digestion in these systems. These insights provide knowledge on the design of nutritious third generation snacks with the aim of lowering starch digestibility.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Pharmacy
Depositing User:	Chris White
Date Deposited:	02 Aug 2023 09:55
Last Modified:	02 Aug 2023 09:55
URI:	https://ueaeprints.uea.ac.uk/id/eprint/92760
DOI:

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