Microstructure design strategies to enhance aroma and tastant availability in foods

Su, Katy (2021) Microstructure design strategies to enhance aroma and tastant availability in foods. PhD thesis, University of Nottingham.

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Nutritionally improving foods through reduction of sugar, salt and fat in foods is important to decrease the prevalence of diet related diseases. Common strategies used in the food industry often result in changes in perception of texture and flavour. The role of sugar in confectionery gels extends beyond just taste and sweetness purposes, as it also affects a variety of properties such as structure, texture and shelf life. Therefore, nutritionally improving confectionery gels using conventional strategies is difficult and it is important to develop novel routes to reformulate and modify energy density without compromising sensory quality.

Two microstructure design strategies were investigated based on the properties of the hydrocolloids chosen, gelatine and starch, and the thermodynamic incompatibility of these hydrocolloids under certain conditions. Microstructure design strategies in literature have focused on sensory perception of modified products. However only few of these studies have investigated flavour release. Also there is limited understanding of how these strategies affect a matrix with mixed hydrocolloids and high solute concentration. This research addresses these gaps of knowledge.

Firstly, gelatine and acid thinned starch gels were developed with the hydrocolloids existing as a miscible single phase, containing different gas inclusions as a dispersed phase. Different methods, chemical and mechanical, were trialled to produce gas filled gels (air, carbon dioxide, helium and nitrogen). An easy and quick way to produce gas filled gels by generating CO2 in situ was developed using sodium bicarbonate to react with acid in the gel. Maximum intensity of aroma release and sucrose release was significantly greater from gas filled gels compared to control gels of the same mass without CO2 inclusions (P<0.05, panellists n=1 for analytical method development). Aerated confectionery gels were developed using a thermally controlled mixing method. By correlating aroma and sucrose release with sensory time intensity analysis, for the first time, changes in flavour perception over time as a result of air inclusions was investigated. Overall flavour perception over time of aerated gels with 23% and 38% reduced density, and therefore a lower total mass of aroma and sugar and reduced calories, did not differ from the control non-aerated gel, as assessed by trained sensory panellists (n=10). X-ray CT scans of the gels provided a 3D view of bubble distribution inside the gel, and a quantitative comparison of bubble size between the gels. Bubble properties were investigated through addition of different gases, and significant differences in texture parameters of the gels produced with different gases such as hardness and springiness was observed (P<0.05). Initial aroma release rates in vitro were significantly slower for gels formed by incorporating helium (P<0.05), showing an extended release compared to the other gas types. Thus, offering a different release profile depending on desired flavour release profiles of a product.

The second microstructure consisted of a phase separated gelatine-starch network, with a continuous phase rich in gelatine and a dispersed phase consisting of starch, and vice versa. A phase diagram was produced to investigate gels of different microstructures with the same effective concentration of gelatine and starch in each phase. Aroma release significantly differed in vitro but not when gels were consumed in vivo by panellists (n=5). The effects of sucrose concentration (0-60%) on the phase separated network was investigated. The microstructure changed with increased sucrose concentration as the dispersed starch phase became less aggregated at sucrose concentrations >40%. This resulted in increased interactions with more hydrophobic, less volatile compounds as a significant increase in affinity for the starch phase was observed for a majority of these compounds. Physicochemical properties of the aroma compound influence the interactions with gelatine or starch phase, and when the microstructure is changed the affinity for each phase may also change. Therefore, changes in matrix properties and resulting changes in aroma balance need to be carefully taken into consideration when changing the concentration of sucrose in hydrocolloid based foods.

The aims of this research were to develop methods to produce different model systems and investigate the mechanisms of flavour release from gels with gas or a second hydrocolloid as a dispersed phase. Also, to investigate how changes in sucrose concentration affects components of the gel network for optimised delivery of aroma and tastants. Many studies have investigated sensory perception of gels with modified microstructures, however little is known about actual flavour release. Research into these microstructure design strategies has applications in foods that may be aerated such as protein bars, and foods with phase separated microstructures such as dairy desserts. Organoleptic quality of food is largely influenced by flavour, therefore understanding flavour release mechanisms is vital to be able to successfully reformulate foods to meet nutritional guidelines without affecting sensory perception and reducing product quality.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Fisk, I
Foster, T
Ayed, C
Yang, N
Yang, Q
Keywords: Food science, Food chemistry, Flavour, Aroma, Gel, Microstructure
Subjects: T Technology > TP Chemical technology > TP 368 Food processing and manufacture
Faculties/Schools: UK Campuses > Faculty of Science > School of Biosciences
Item ID: 64462
Depositing User: Su, Katy Xinyu
Date Deposited: 31 Jul 2021 04:40
Last Modified: 31 Jul 2021 04:40
URI: https://eprints.nottingham.ac.uk/id/eprint/64462

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