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Author ORCID Identifier


Open Access Dissertation

Document Type


Degree Name

Doctor of Philosophy (PhD)

Degree Program

Food Science

Year Degree Awarded


Month Degree Awarded


First Advisor

David Julian McClemennts

Subject Categories

Food Biotechnology | Food Chemistry


Food, nutrition, and pharmaceutical scientists are trying to elucidate the major factors impacting the bioavailability of macronutrients (e.g., lipids), micronutrients (e.g., vitamins), and nutraceuticals (e.g., carotenoids) so as to improve their efficacy. Currently, however, there is a limited understanding of how food matrix effects impact nutrient digestion and bioavailability. In this thesis, the impact of food matrix effects was elucidated by systematically examining the influence of several important factors (including oil type, oil concentration, droplet size, emulsifier type, and nutrient type) on lipid digestion and the bioaccessibility of hydrophobic bioactive agents. Oil-in-water emulsions were used as model foods because their compositions and structures can easily be varied. An in vitro gastrointestinal model was used to measure the physicochemical and structural properties of the emulsions within the gastrointestinal tract, as well as lipid digestion and bioaccessibility. Studies of the impact of oil droplet concentration (2.5 to 20%) showed that complete lipid digestion was achieved under fed-state gastrointestinal conditions, but could only be observed after a back-titration was performed. This effect was observed all experiments where long chain triacylglycerol oils were used. The maximum β-carotene bioaccessibility (93.2%) was measured at an intermediate oil level (10%). This effect was attributed to the fact that low oil droplet concentrations reduce the solubilization capacity of the mixed micelles, whereas high oil droplet concentrations lead to precipitation and sedimentation of some of the β-carotene. Studies of the impact of oil droplet diameter (0.16, 1.1 and 8.2 μm) on lipid digestion and bioaccessibility showed that the extent of lipid digestion fell from around 117% to 78% as the droplet size was increased (p < 0.001), which was attributed to the decrease in specific surface area of the oil droplets. In addition, there was a reduction in β-carotene bioaccessibility from 83 to 15% (p < 0.001) with increasing droplet diameter, which was mainly linked to a reduction in the amount of hydrophobic carotenoids released from the non-digested oil droplets. The impact of emulsifier type was also investigated by creating emulsions stabilized by synthetic surfactants (Tween 20), natural surfactants (quillaja saponin), proteins (caseinate), polysaccharides (gum arabic), or phospholipids (soy lysolecithin). The lipid digestion degree was considerably lower for the emulsions stabilized by soy lysolecithin (93%) or caseinate (93%), which was attributed to the relatively large droplet size of the initial emulsions for lysolecithin (low emulsification ability) and to droplet aggregation in the stomach for caseinate (poor gastric stability). The overall bioaccessibility of the b-carotene increased in the following order: lysolecithin (25%) < gum arabic (51%) < caseinate (55%) < quillaja saponin (56%) < Tween 20 (62%). These effects were mainly attributed to reduced digestion (i.e. lysolecithin, and caseinate), the antioxidant activity of the emulsifiers (i.e., lysolecithin, and caseinate), or sedimentation promoted by the emulsifiers (i.e., lysolecithin). This series of experiments underlined the critical importance of considering the droplet size in foods before, during, and after gastrointestinal digestion when developing emulsified foods loaded with carotenoids. The impact of oil digestibility was also investigated by comparing the bioaccessibility of oil-soluble vitamins encapsulated in nanoemulsions made from digestible or indigestible oils. The bioaccessibility of vitamin D was considerably lower when dissolved in an indigestible oil than in a digestible oil. For the nanoemulsions prepared with digestible oils, the vitamin bioaccessibility increased to a maximum value after around 30 minutes, but then decreased during the following 24 h. This effect was attributed to an initial solubilization of the vitamin within the mixed micelles, followed by their precipitation during prolonged incubation. The effects of calcium levels (0.525-10 mM) on lipid digestion and bioaccessibility was then investigated because foods often contain different amounts of this micronutrient. Even though the lipid phase was completely digested in all samples, the bioaccessibility of β-carotene decreased with increasing calcium levels: from 65.5% at 0.525 mM Ca2+ to 23.7% at 10 mM Ca2+. This effect was attributed to the ability of the calcium ions to precipitate the β-carotene-loaded mixed micelles by forming insoluble calcium soaps. The addition of chitosan (0.1-0.5%) did not influence the lipid digestion, despite causing severe droplet flocculation in the small intestine phase. However, its presence did decrease the bioaccessibility of vitamin D by about 37%, irrespective of the chitosan concentration used (0.1-0.5%). It was proposed that the cationic chitosan may have bound and precipitated some of the anionic vitamin-loaded mixed micelles. The impact of oil droplet size was further investigated for different oil-soluble vitamins (A, D, E). In general, similar trends were observed for all vitamins but there were some differences. The vitamins with higher hydrophobicity (vitamin A palmitate and vitamin E acetate) were mainly located in the inner core of the oil droplets, which retarded their release. The vitamins with larger molecular dimensions, such as vitamin E acetate, could not be fully accommodated in small hydrophobic domains within the mixed micelles, which reduced their bioaccessibility. Moreover, there was extensive hydrolysis of vitamin A palmitate under GIT conditions, whereas vitamin E acetate only exhibited slight hydrolysis. In summary, food matrix effects were shown to have a major impact on the bioaccessibility of fat-soluble bioactive agents. These effects should therefore be considered when designing functional food products and when making nutritional recommendations. More research is clearly needed, using both in vitro and in vivo methods, to establish the influence of specific food components on the bioaccessibility of lipids, vitamins, and nutraceuticals in real food products.