Abstract
Evidence from epidemiological studies indicates that the consumption of berry anthocyanins is associated with health benefits. To exert their bioactivity, anthocyanins must first be released from plant cells through mechanical forces or processing and transported to the target sites for potential uptake. When the whole fruit is ingested, plant cell walls are a critical factor in limiting the bioaccessibility of anthocyanins by not only providing a physical barrier, but also acting as a substrate for binding interactions. Studies of anthocyanin bioaccessibility are limited in particular from fresh blueberries.The aims of this PhD project are 1) to investigate the bioaccessibility of blueberry anthocyanins throughout the whole digestion tract, including oral mastication, gastric, small and large intestinal digestion, and 2) to explore the effects of matrix structure on anthocyanin bioaccessibility.
A number of in vivo, in vitro and ex vivo studies were conducted. Anthocyanins were analysed in foods and digested samples using ultra-high-performance liquid chromatography coupled with electrospray ionisation and triple quadrupole mass spectrometry (UHPLC-ESI-QqQ-MS/MS), as well as the optical and laser confocal fluorescence microscopy. An in vivo mastication study was conducted to investigate the oral bioaccessibility of anthocyanins in blueberries, raspberries, and strawberries, as well as the effects of masticatory parameters, berry matrix structures, and food processing strategies. An in vitro simulated gastrointestinal digestion was conducted according to the INFOGEST 2.0 protocol, and anthocyanin bioaccessibility of fresh, frozen-thawed, and blended blueberries was investigated. Finally, an ex vivo batch-cultured colonic fermentation model was used to investigate the bioaccessibility of blueberry anthocyanins in the large intestine, as well as the impact on the gut microbiota and the generation of short-chain fatty acids.
From our results, most blueberry anthocyanins were concentrated in the epidermal cells of skin tissues, with malvidin being the predominant anthocyanidin. Anthocyanin bioaccessibility of fresh blueberries in the oral cavity and gastrointestinal tract was 4.9% (oral phase), 33.2% (gastric phase), and 15% (duodenal phase), respectively, which was negatively correlated with the particle size of masticated bolus and influenced by the matrix structure of blueberries. Both food processing strategies such as freeze-thawing and in vitro oral processing method increased the bioaccessibility of blueberry anthocyanins in oral and gastric phase, while decreased the release in the duodenal phase. These differences are likely to be explained by the reducing particle size of blueberries as well as the changes in the matrix structure. Incompletely digested fresh blueberry pellets are further digested and fermented by the gut microbiota in the colon of large intestine. Encapsulated anthocyanins were released from the pellets, with an initial level of 5.8% reaching a peak of 14% after 4 hours of fermentation, and decreasing to 3.47% at the end of 48-h fermentation. Colonic fermentation of blueberry pellets was able to modulate the SCFA production as well as the diversity, community structure and relative abundance of the gut microbiota to some extent.
In conclusion, the work described in this thesis provides further evidence on the effects of blueberry matrix structure affected the evaluation of anthocyanin bioaccessibility during the digestive tract. It has illustrated the importance of combining in vitro, in vivo and ex vivo studies, which can achieve a more complete perspective of human digestion and thereby contributed to the process of defining the mechanisms of fruits and vegetables on health-promoting bioactivities as suggested by many epidemiological studies.
Date of Award | 1 Aug 2024 |
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Original language | English |
Awarding Institution |
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Supervisor | Ana Maria Rodriguez Mateos (Supervisor), Peter Ellis (Supervisor) & Balazs Bajka (Supervisor) |