Thermal degradation of flavonol glycosides in Noni leaves during roasting processes


Shixin Deng,, Brett J West,, Jarakae C. Jensen, and Afa K Palu, Research and Development Department, Tahitian Noni International, 737 East, 1180 South, American Fork, UT 84003
Noni is a tropical plant prevalent in south Pacific islands. Traditionally, noni leaves have been used for a variety of health benefits, including arthritis, diabetes, headaches, inflammation, pain, etc. Noni leaf tea, a commercial product made by a roasting process, is increasingly attracting more attention and becoming one of the most promising health drinks. Flavonoids appear to be some of predominant constituents in noni leaves. As well-recognized antioxidants, flavonoids are widely present in natural resources, such as vegetables, fruits, and herbs, mostly in the forms of glycosides or polymers. Degradation to corresponding metabolites is usually needed for bio-absorption. This study investigates the effects of non-aqueous roasting processes on flavonoids in noni leaves. The results showed that thermal processes have significant impacts on noni leaf flavonoids. As roasting time and/or temperature increased, the contents of quercetin and kaempferol glycosides dropped dramatically, and more quercetin and kaempferol were produced, accordingly. Quercetin and kaempferol in the roasted leaf tea were found to be 2.5 and 4.3 times more than those in raw leaves, respectively. These findings indicate that the roasting processes could induce the degradation of flavonol glycosides, and produce their aglycone metabolites, which in turn, may lead to more beneficial bioactivities and bioavailability. Furthermore, a quantitative comparison of noni leaves collected from Tahiti, Tonga, Panama, and Saipan showed that the noni leaves from Tahiti contain the highest amount of flavonoids.

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