Versatile ingredients from rapeseeds for structuring plant-based soft materials

Eleni Ntone

Research output: Thesisinternal PhD, WU

Abstract

Oilseeds, containing high amounts of proteins and lipids -essential structuring and nutritional ingredients in foods- are one of the most promising ingredient sources for food applications. The current oilseed ingredient valorization process focuses on lipid extraction, while proteins are extracted from the residual defatted material. However, this process requires multiple energy consuming steps, and the heating and organic solvents applied to the defatted material have a negative impact on protein extractability and functionality. A solution to enhance the potential use of oilseed ingredients for foods might be offered from the development or improvement of the current process, by reducing the processing steps. This approach results in less purified plant-based ingredients instead of highly purified ingredients, with potentially different functionality in food systems. In this thesis we aim to enhance the potential use of less purified oilseed ingredients for food applications by providing a mechanistic understanding on the relation between extraction and functionality of less purified oilseed protein and lipid extracts.

In this research we show that an alternative extraction method, where defatting of the seeds is omitted, and proteins and lipids in their natural structures (oleosomes) are simultaneously extracted at low alkaline aqueous extraction conditions, results to less purified protein- and oleosome-rich fractions. Following this approach, proteins and oleosomes were extracted in high yields and the physicochemical properties of the proteins and oleosomes were preserved.

The functionality of the protein extracts was investigated in emulsions and emulsion-filled gels. The interfacial stabilization mechanism of less purified rapeseed protein extracts at oil/water interfaces was investigated at neutral (pH 7) and acidic (pH 3.8) pH conditions. The aim of this research was to identify the role of each protein species (i.e. napins and cruciferins) and of the coexisting non-protein molecules present on droplet formation and stabilization. At both pH conditions tested it was found that napins adsorb at the interface and cruciferins weakly interact with the adsorbed layer of napins, forming a secondary layer that provides stability to the emulsion droplets against coalescence during emulsification. The oleosomes and free phenols present did not hinder the ability of proteins to stabilize the interface at neutral pH. However, at acidic pH, phenols induced aggregation of cruciferins, hindering the formation of a sufficient secondary layer, and resulting in emulsions with larger droplets. Additionally, the different functionalities of each protein species present in the extracts were combined to create emulsion-filled gels, with napins stabilizing the oil droplet interface and cruciferins building the protein network. The effect of pH and oil concentration on the structural and rheological properties of the emulsion-filled gels were investigated. pH affected the rheological and structural gel properties, with lower pH resulting in less firm and heterogeneous gel structures compared to higher pH (pH 5 vs pH 7). Addition of emulsion droplets in the protein gel matrix increased the firmness of the gels with a more pronounced reinforcement at low pH. The type of gel network did not change by the addition of oil droplets.  

Finally, oleosomes were researched as potential functional ingredients. The relation between oleosome monolayer molecular density (number of molecules per area), lateral interactions and dilatability, with the ability of oleosomes to traffic lipids was investigated. Increasing the monolayer molecular density limited the adsorption of free lipid by oleosomes. Lipid absorption resulted in oleosome volume expansion and adjustment of the monolayer molecular density. Oleosomes released lipids from their core and deflated, indicating a release mechanism through a channel. Lipid absorption and release was initiated by hydrophobic forces. The ability of the oleosomes to reversibly expand in volume or shrink upon absorption or release of lipids respectively was assigned to the weak lateral interactions in the monolayer.

Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Wageningen University
Supervisors/Advisors
  • Bitter, Harry, Promotor
  • Nikiforidis, Costas, Co-promotor
  • Sagis, Leonard, Co-promotor
Award date15 Dec 2021
Place of PublicationWageningen
Publisher
Print ISBNs9789463957762
DOIs
Publication statusPublished - 2021

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