Isic, Aida (2017) A study of flavonols in bok choy and their anti-cancer properties. PhD thesis, Victoria University.

Abstract

Phytochemicals are defined as biologically active, non-nutrient (i.e. not essential for the maintenance of life), plant compounds. They are present in all fruits, vegetables, grains, and other plant foods, and have been shown to be beneficial to human health. Flavonols are a group of phytochemicals present in a variety of different vegetables including broccoli, Brussels sprouts, cabbage, cauliflower, kale and bok choy. Flavonols have been shown to exhibit powerful antioxidant activity as well as possess potential protective properties against certain cancers. The aim of this research was to measure the levels of the major flavonols in bok choy and to assess the antiproliferative activity of crude bok choy extracts, selected fractions, and individual flavonol compounds on human colon cancer cells (HT-29) in vitro. The flavonol composition of three bok choy cultivars (Sumo, Karate, and Miyako) was determined after acid hydrolysis by HPLC-PDA/ESI-MSn . Kaempferol (85.5 – 122 mg/100 g DW), isorhamnetin (38.3 – 66.7 mg/100 g DW), and quercetin (10 – 20.6 mg/100 g DW) were the main flavonols present. The Miyako variety contained the highest levels of both quercetin and isorhamnetin, however, the levels of kaempferol were comparable in all three cultivars. The total flavonol aglycone content in the three bok choy cultivars did not vary significantly (183.3 mg/100 g DW, 159.9 mg/100 g DW, and 197.3 mg/100 g DW for Sumo, Karate, and Miyako respectively), therefore, no conclusions were made as to whether one bok choy cultivar may contain more health-promoting flavonols than another. Several glycoside and hydroxycinnamic acid derivatives of quercetin, isorhamnetin, and kaempferol were identified in the alkaline and hydroalcoholic bok choy extracts by HPLCPDA/ESI-MSn . Two flavonol-3-sophoroside-7-glucosides and three flavonol-3,7-diglucosides were identified in the bok choy after alkaline hydrolysis, and six complex flavonol glycosidehydroxycinnamic acid derivatives, two flavonol di-glycosides, and one flavonol mono-glucoside were identified in the hydroalcoholic extracts. Kaempferol-3-O-sophoroside-7-O-glucoside was purified by preparative HPLC and SPE and fully characterised by NMR, UV and MSn . The ability of crude bok choy extracts, selected fractions, and individual flavonol compounds to inhibit cell proliferation of the human colon adenocarcinoma cell line, HT-29, in vitro was assessed using the MTT assay. The antiproliferative effects on HT-29 cells was evident for all extracts/fractions/compounds examined, however, the crude bok choy extracts were found to be the most potent. The IC50 values for the three bok choy cultivars ranged between 1.58 – 4.01 mg/L after 72 hours of exposure. Preliminary results suggested that bok choy has the potential to positively influence human health, both from a chemopreventive perspective as well as a chemotherapeutic.

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