Microstructure engineering with quinoa protein for the design of plant-based soft materials

Campos Assumpção de Amarante, Marina ORCID: 0000-0001-8458-2674 (2024). Microstructure engineering with quinoa protein for the design of plant-based soft materials. University of Birmingham. Ph.D.

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Abstract

The movement towards the reduction in production and consumption of animal proteins combined with the increase in world population has prompted the food industry to consider more sustainable protein sources. Quinoa is a pseudocereal that has recently gained popularity worldwide as an alternative to rice due to its higher protein content and to its complete essential amino acid profile. Quinoa protein isolate (QPI) is a protein mixture commonly extracted from quinoa flour by wet fractionation, consisting of alkalinisation of the flour suspension at pH 8 – 11 followed by acid precipitation by HCl addition to pH 4 – 5. Its physico-chemical and functional properties have been increasingly investigated in the last few years, however, there are a few gaps in literature regarding its potential to create microstructures in food systems. Thus, this study aimed to explore different approaches to enable the use of QPI in the microstructure engineering of plant-based foods.
Firstly, the phase behaviour of mixtures of QPI and maltodextrin (MD) was investigated as a function of MD dextrose equivalent, protein heat pre-treatment and salt conditions. It was found that the mixtures phase separated by depletion flocculation, where fractions of MD were entrapped within the aggregated QPI network. This behaviour does not allow for structure formation by droplet deformation under shear and limits the application of these mixtures in microstructure design. Thus, in the following steps of this research, the focus was shifted to the adjustment of the physico-chemical and technofunctional properties of QPI through the modification of its extraction conditions.
Improved soluble protein content, thermal properties and gelation properties were achieved by substituting HCl for the more kosmotropic acids acetic acid and citric acid during the acid precipitation step of QPI extraction. It was also found that the functional properties of QPI could be further modulated by the dispersion conditions. A longer dispersion time improved the functional properties of QPI precipitated with HCl, while dispersion in 0.1 M NaCl and dialysis before dispersion resulted in extensive protein aggregation and hindered gel formation in the QPI extracts.
Results further showed that QPI can be extracted with a significant content of lipids, which are originally found in quinoa seeds in the form of oil bodies. These natural oil droplets have interesting applicability in the formulation of plant-based foods to confer desired textures and improve organoleptic properties, especially due to their naturally emulsified structure, but there is a gap in literature pertaining those sourced from quinoa. Thus, a strategy was developed to recover quinoa oil bodies (OB) before QPI extraction from cryo-milled quinoa seeds. OB of good stability against acid treatment were obtained, while a further improvement in the gelation properties of QPI precipitated with citric acid was observed. Overall, this thesis provided insights on the phase behaviour of QPI, as well as processing routes for the modulation of its properties for the design of a range of plant-based products of different textures. It also presented a combined strategy to recover two highly functional ingredients for plant-based food formulations.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):

Supervisor(s)	Email	ORCID
Wolf, Bettina	UNSPECIFIED	orcid.org/0000-0003-4007-9609
Spyropoulos, Fotis	UNSPECIFIED	orcid.org/0000-0002-0872-9328
Gras, Sally	UNSPECIFIED	orcid.org/0000-0002-4660-1245
Ong, Lydia	UNSPECIFIED	orcid.org/0000-0003-3859-6180