Characterisation of polyphenolic compounds in herbal tea and berries: in vivo and in vitro studies on the bioavailability of anthocyanins

AlGamdi, Noura Ahmad (2013) Characterisation of polyphenolic compounds in herbal tea and berries: in vivo and in vitro studies on the bioavailability of anthocyanins. PhD thesis, University of Glasgow.

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Flavonoids and polyphenolic compounds are widely distributed in commonly consumed foods, beverages and herbs. Their consumption has been associated with improving the health and reducing the risk of several chronic diseases. In Saudi Arabia, recent interest in the health-promoting properties of traditional herbs has been increased. To-date researchers have focused on testing these therapeutic properties. However, information about their chemical profile is largely unexplored. Thus, the beginning of this project aimed to use HPLC–PDA–MS2 to identify polyphenolic compounds in a medicinal herbal tea made from seeds of Anastatica hirerochuntica. Twenty compounds comprising a series of flavone C- and O-linked glycosides, phenolic acids, chlorogenic acids and flavonols were identified or partially identified on the basis of co chromatography with reference compounds and MS2 and MS3 fragmentation patterns. The flavones were the principal components, occurring as luteolin, apigenin and diosmetin conjugates. The antioxidant potential of individual compounds in Anastatica was assessed using HPLC with an on-line ABTS•+ detection system. Under the experimental conditions, 14 compounds exhibited antioxidant activity. The highest contribution to the antioxidant capacity of the tea, 56%, came from 3,4-dihydroxybenzoic acid and caffeoyl- and dicaffeoylquinic acids while 6-C-glucosides of luteolin and apigenin contributed 41%. These findings together with tests in the FRAP antioxidant assay and the Folin–Ciocalteu total phenolics assay revealed that aqueous infusion of A. hirerochuntica seed is rich in polyphenolic compounds.

Another perspective of investigating these polyphenolic compounds is not just knowing their chemical constituents but also studying their bioavailability upon ingestion. Therefore, blackberries and strawberries were chosen for intervention studies with human subjects to examine the bioavailability of anthocyanins, a group of flavonoids, due to their importance as natural antioxidants that have been linked with beneficial effects on health to humans. In the first in vivo study, plasma and urine were collected from eight healthy subjects after ingestion of 180 g of blackberries and analysed by HPLC-PDA-MS2. Cyanidin-3-O-glucoside was metabolised principally to peonidin-O-glucuronide. Cyanidin-3-O-glucoside and its metabolites appeared rapidly in the plasma in low concentrations ranging from 5 to 20 nmol/L with low urinary excretion of ~0.08% of the total intake. In the second in vivo study, both blackberry and strawberry were used to examine the small intestinal absorption and metabolism of both cyanidin-3-O-glucoside and pelargonidin-3-O-glucoside by feeding five ileostomy volunteers with 180 g of berries. Samples of urine and ileal fluid were collected over a 0-24 h period after ingestion and analysed by HPLC-PDA-MS2 Unmetabolized anthocyanins of blackberries and strawberries were recovered in ileal fluids at a level of 5.1% and 13.6%. This indicates either low level of absorption or lack of stability at the non-acid pH in the small intestine. The overall urinary excretion of anthocyanins was 0.06% and 0.87% of intake of blackberries and strawberries respectively. The urine data shows that both cyanidin and pelargonidin glucosides were metabolised primarily to peonidin-O-glucuronide and pelargonidin-O-glucuronide respectively. Although low recoveries of the two compounds are reported in this investigation in both ileal fluid and urine, pelargonidin-3-O-glucoside showed a slightly higher recovery compared to cyanidin-3-O-glucoside. The data from both in vivo studies reflect the influence of the aglycone structure on the bioavailability of these anthocyanins.

The stability of anthocyanins in the gastrointestinal tract was also assessed using in vitro models (Chapter 5). The results indicated that at neutral pH the salivary enzymes and oral microbiota had no impact on cyanidin-3-O-glucoside but degraded pelargonidin-3-O-glucoside by ~20%. With simulated and human gastric juice, both anthocyanins were unstable and the breakdown continued dramatically under pancreatic digestion where a 5.1% recovery was obtained. Their low recovery levels were comparable to those obtained in vivo with ileal fluid. These findings imply that the chemical structure of both anthocyanins influence their stability similarly. However, the data provide no explanation about the higher bioavailability of pelargonidin-3-O-glucoside compared to cyanidin-3-O-glucoside in vivo. This presumably is a consequence of the more ready access of pelargonidin-3-O-glucoside to the enterocytes of the small intestine.

In conclusion, the work here has shown the diversity of compounds with potential health benefits that are present in a natural product from Saudi Arabia. Experiments were carried out, using local products from the UK, to investigate factors that would affect their potential to provide health benefits. The in vivo and in vitro experiments show the complexity of investigations of potential bioactive compounds in human nutritional research. Polyphenols which differ by only a single hydroxyl group show very different absorption, metabolism and stability properties.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Flavonoids,Herbal tea, Flavone C- and O-glycosides, Chlorogenic acids, Antioxidants, Anthocyanins,Blackberry,Strawberry,Bioavailability, Absorption,Metabolism,in vitro digestion.
Subjects: Q Science > QH Natural history > QH345 Biochemistry
Q Science > QK Botany
Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Medicine, Dentistry & Nursing
Supervisor's Name: Crozier, Prof. Alan and William, Dr. Mullen
Date of Award: 2013
Depositing User: Noura AlGamdi
Unique ID: glathesis:2013-4768
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 15 Jan 2014 10:29
Last Modified: 20 Dec 2016 16:30

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