The use and production of natural antioxidants for food applications

Noon, John (2020). The use and production of natural antioxidants for food applications. University of Birmingham. Ph.D.

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Abstract

Antioxidant compounds are ubiquitous throughout the natural world where their properties are used to combat potentially damaging oxidative reactions which occur within living organisms. These antioxidant compounds can be extracted from their natural sources (including fruits, vegetables, spices, herbs, and grains) and incorporated into consumer goods to utilise their antioxidant properties for a specific purpose. A key focus of this thesis was to improve the efficacy of natural antioxidants in terms of, firstly, their ability to combat lipid oxidation (LO) in oil-in-water (O/W) food emulsions, and secondly, in their capacity to provide additional health benefits within food or pharmaceutical products. Therefore, this thesis investigated a specific use of antioxidants, which was in their ability to combat LO in a range of O/W emulsion formulations, in addition to the investigation of a novel antioxidant nanonisation technique which could be used to help improve the bioavailability of antioxidant compounds when incorporated into food or pharmaceutical products.

The use of natural antioxidants to combat LO in O/W emulsions served as the primary research focus of this thesis. The motivation for this work predominantly stemmed from high consumer demand for the sole use of natural, ‘clean label’ ingredients in food products coupled with the increased use of highly oxidisable unsaturated fats in O/W food emulsions which, due to their structure, are already highly susceptible to LO. Initial research into this area assessed the behaviour and efficacy of several natural antioxidant compounds (namely, quercetin, curcumin, rutin hydrate and ascorbic acid) in their ability to combat LO in a range of different O/W emulsion environments. This work developed into the assessment of one particular antioxidant, rutin hydrate (RH), in its ability to act as a Pickering emulsifier and offer dual-purpose functionality through providing O/W emulsions with both physical and oxidative stability. Research showed that emulsion environment was paramount in determining the efficacy of natural antioxidants at combatting LO. Furthermore, RH particles were found to be capable of physically stabilising O/W emulsions, however, the ability of these particles to provide oxidative stability in emulsions was found to be limited by their inability to form a continuous and effective barrier at the oil-water interface.

The secondary focus of this thesis was on the production of antioxidant nanoparticles through the development of a novel microwave-assisted antisolvent precipitation (MAP) technique to help overcome limited bioavailability issues which many natural antioxidants possess. Through use of the MAP technique, curcumin and silymarin antioxidant compounds were successfully nanonised and transformed from exhibiting crystalline structures to more amorphous structures; this is known to enhance dissolution velocity which is key in the bioavailability enhancement of many antioxidant compounds.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):