Natural blues: structure meets function in plant natural products

Houghton, Alan (2023) Natural blues: structure meets function in plant natural products. Doctoral thesis, University of East Anglia.

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Abstract

Colour plays a crucial role in food manufacturing, providing product consistency, addressing off-colouring issues, and enhancing consumer appeal. However, the availability of blue food colorants is severely limited, with only a few options in the US (Brilliant blue FCF and indigo carmine) and an additional choice in Europe. Given the rising demand for naturally derived additives, confectionery companies have struggled to find a suitable naturally derived substitute. Anthocyanins, plant-based pigments that exhibit a range of colours from red to blue, have been explored as potential food colorants. However, their inherent instability at the pH required for generating blue colours has presented a significant challenge. The complex mixture of anthocyanins derived from butterfly pea consists of 15 delphinidin-3(6”-malonyl), 3',5'-O-triglucoside derivatives acylated with p-coumarate which are highly stable and produce a blue colour at mildly acid pH. In this study, a new flash chromatography method for the rapid fractionation of ternatins was developed, allowing for efficient and food safe separation based on the terminal sidechain residues. This method offers a high capacity and quick separation technique for food applications. Through this research, it was demonstrated empirically that acyl residues stabilised the anthocyanin against degradation by stacking over the delphinidin C-ring. Glycosylation weakens these sidechain interactions, thereby decreasing stability. In both cases, acylation and glycosylation resulted in a bathochromic shift. The mechanisms by which acylation and glycosylation cause bathochromic shifts were explored using a combination of molecular dynamics and quantum mechanical simulations. Quantum mechanics simulations of delphinidin-3-O-glucoside rotamers have demonstrated that UV-VIS absorbance λmax increases with an increasing dihedral angle. Molecular dynamics simulations of ternatins showed decreased interaction between the acyl residue and chromophore upon glycosylation, with an associated increase in dihedral angle. This thesis establishes ternatins as potential ‘natural’ replacements for synthetic blue food colourants.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Biological Sciences
Depositing User:	Nicola Veasy
Date Deposited:	10 Jul 2024 10:57
Last Modified:	10 Jul 2024 10:57
URI:	https://ueaeprints.uea.ac.uk/id/eprint/95855
DOI:

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