Qingsu, Liu
(2024)
Healthy rice products - understanding the effect of protein-starch matrices during digestion.
PhD thesis, University of Nottingham.
Abstract
White rice is one of the most cultivated and consumed rice types worldwide and is growing in popularity as an ingredient in gluten-free products. However, white rice consumption can significantly affect glycaemic homeostasis due to its high and rapidly digestible starch content, which may pose health risks if not managed properly. There is an increasing need to understand better how rice microstructure may influence rice starch’s conversion to glucose during digestion and the relationship between rice microstructure and its health-benefiting properties. Therefore, this thesis presents a comprehensive investigation of the relationship between the cooked white rice microstructure and the in vitro digestibility. An emphasis is placed on the influence of the rice protein network, which entraps starch granules in “protein-starch matrices,” on controlling starch digestibility. Moreover, the addition of low acyl gellan gum (LAGG) was evaluated as an innovative approach to further reduce starch digestibility upon rice cooking by simulating the starch entrapment mechanism used by the proteins in the protein-starch matrices. The primary objectives of this study were i) to investigate the complex interaction between the microstructure of white rice and in vitro starch digestion and ii) to identify the feasibility of developing innovative rice-based formulations with a low-glycaemic index potential.
This study begins with investigating how microstructure influences the textural characteristics and in vitro oral starch digestion of two types of white rice, non-parboiled white jasmine rice (JR) and parboiled white rice (PR), from high- and low-glycaemic index (GI) categories, respectively. Despite the similar total starch content, PR had higher amylose and protein content than JR; moreover, PR had more compact protein-starch matrices than JR, which has limited starch gelatinisation capacity during the cooking process. Additionally, LAGG addition was investigated for its effects on the physicochemical and microstructural attributes of cooked rice. LAGG induces a distinct viscosity increase of JR and a change in its thermal properties by hindering starch gelatinisation. Microstructural alterations, such as the formation of β-sheet structures and V-type starch-LAGG complexes, were also observed, with microscopic analysis confirming a coating on the rice grain surface. All these changes were less evident in PR, perhaps due to the already partially denatured protein network and pre-gelatinised starch, forming more compact protein-starch matrices. This increased compactness of the matrices in PR can act as a physical barrier between digestive enzymes and starch, thus decreasing starch digestibility, and modifying the starch digestion kinetics. In parallel, the addition of LAGG on cooked JR or PR resulted in promising for reducing starch digestibility by mirroring the encapsulating effect of a protein network.
The study extends to the digestion kinetics, which were quantitatively evaluated by a static in vitro digestion model combined with a multi-enzyme system which progressively removed rice protein networks, revealing two-phase starch digestion patterns. Starch digestibility became higher when the protein network was previously physically disintegrated by homogenisation. As the homogenisation process was prolonged, the degree of granular-scale disintegration was increased, as well as enzymatic accessibility and protein and starch digestibility.
It is important to note that starch digestibility is affected by the in vitro digestion conditions adopted. In this thesis, a semi-dynamic in vitro digestion model, characterised by controlled pH changes in the gastric phase and simulated peristalsis, was also used. Compared to the static digestion model, the effect of homogenisation (oral processing simulation) on starch digestibility became less evident in the semi-dynamic model due to the constant structure disintegration provided by the simulated peristalsis. However, LAGG-cooked rice displayed lower starch digestibility under both digestion models than non-LAGG controls, indicating LAGG multi-functionality (viscosity increase- and physical barrier properties) in mitigating starch digestibility.
Based on the above findings, a gluten-free orzo-shaped pasta with low predicted glycaemic index (pGI) potential was developed from rice flour, incorporating rice protein and/or LAGG. Formulations including LAGG and/or protein exhibited altered pasting properties due to limited starch gelatinisation and formation of starch/LAGG complexes, resulting in reduced starch digestibility and improved cooking quality and texture.
Overall, this collective research provided insight into the role of rice microstructure (specifically the protein-starch matrices) and the addition of LAGG in controlling starch digestibility. This approach would offer a pathway to innovate and develop healthier rice-based products.
| Item Type: |
Thesis (University of Nottingham only)
(PhD)
|
| Supervisors: |
Watson, Nicholas James/NJW
Bari, Vincenzo Di/VDB
Binner, Eleanor |
| Keywords: |
rice-based product, low acyl gellan gum, protein-starch matrices; in vitro digestibility |
| Subjects: |
T Technology > TX Home economics |
| Faculties/Schools: |
UK Campuses > Faculty of Engineering > Department of Chemical and Environmental Engineering |
| Item ID: |
78554 |
| Depositing User: |
Liu, Qingsu
|
| Date Deposited: |
12 Nov 2025 13:10 |
| Last Modified: |
12 Nov 2025 13:10 |
| URI: |
https://eprints.nottingham.ac.uk/id/eprint/78554 |
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