Antioxidants: The rise of polyphenols
In the final part of its series on antioxidants, NutraIngredients looks at the rise of polyphenols and flavonoids, and what still needs to be done.
Data from Leatherhead Food International (LFI) shows that the world functional antioxidants market is increasing year on year by around 3 per cent, and was valued at US$ 400 million in 2004, and US$ 438 million in 2007. Europe, the US, and Japan account for 90 per cent of this market.
With flavonoids and polyphenols reported to be 45 per cent of this functional antioxidant market, equivalent to almost US$ 200 million, it is no wonder that many companies are already offering such ingredients, including Naturex, Burgundy, Chr. Hansen, DSM, Futureceuticals, Danisco, Indena, Frutarom, Genosa, Natraceutical, Cognis, and ADM.
However, while the science is beginning to point to the significant potential and benefits of polyphenols, Ming Hu from the University of Houston recently issued "a call to arms" for more relevant research into the bioavailability and utilisation of the antioxidants, particularly polyphenols, in order to help "the successful development of polyphenols as chemopreventive agents in the future".
Polyphenols are receiving extensive research due to their potent antioxidant activity, their ability to mop-up harmful free radicals, and the associated health benefits. Many have also been implicated in possible protection against diseases such as cancer and cardiovascular disease, while some have been reported to potentially offer protection from Alzheimer's.
A recent study by French researchers using a series of antioxidant assays, including DPPH, ABTS, ORAC, SOD, FRAP of extracts from 30 plants found a “significant relationship between antioxidant capacity and total phenolic content […], indicating that phenolic compounds are the major contributors to the antioxidant properties of these plants” (J. Agric. Food Chem., 2009, Vol. 57, pp. 1768-1774).
Furthermore, according to an editorial in the American Journal of Clinical Nutrition (July 2008, Vol. 88, pp. 12-13), Johanna Geleijnse and Peter Hollman from Wageningen University in the Netherlands stated that the contribution of flavonones to a person's antioxidant capacity was significant.
"More than 6000 different flavonoids in plants have been described, and their total intake could amount to 1 g/d, whereas combined intakes of beta-carotene, vitamin C, and vitamin E from food most often are less than 100 mg/d," they said.
The chemical class refers to compounds called phenylpropanoids, which includes flavonoids, and hydrolyzable tannins such as the gallic acid esters of glucose. Flavonoids can be split into a number of sub-classes, including anthocyanins found in berries, flavonols from a variety of fruit and vegetables, flavones from parsley and thyme, for example, flavanones from citrus, isoflavones from soy, mono- and poly-meric flavonols like the catechins in tea, and proanthocyanidins from berries, wine and chocolate. The non-flavonoids include phenolic acids, lignans, and stilbenes such as resveratrol.
Structure is key
Polyphenols, and flavonoids in particular, are not all created equal. For example, scientists from The Ohio State University reported that the structure of anthocyanins, the antioxidant pigments from a range of fruit and vegetables, is key to the cancer fighting abilities.
According to findings published in the Journal of Agricultural and Food Chemistry (doi: 10.1021/jf8005917), certain types of anthocyanins have greater activity against colon cancer than others.
“The chemical structures of anthocyanins do have a significant impact on their biological activity, and data suggest that non-acylated monoglycosylated anthocyanins are more potent inhibitors of colon cancer cell growth proliferation,” wrote lead author Pu Jing.
The researchers cautioned that more research is necessary to explore the role of anthocyanin structure and the chemo-protective effects.
Much work left to do…
In addition to the potential benefits for reducing the risk of cancer, most of the science has pointed towards a protective role in cardiovascular health. Geleijnse and Geleijnse added, however, that significant study was still needed in this area.
"Substantial evidence for a vasoprotective effect of specific flavonoids is, however, still lacking. Optimal doses of specific flavonoids for cardiovascular protection […] are still beyond the horizon,” they wrote in the American Journal of Clinical Nutrition.
“Flavonoid research has made large progress since the [early days], but, to really advance the field, the step to individual flavonoids must be made now."