Cranberry juice is best known for its ability to prevent urinary tract infection because it inhibits the adhesive ability of Escherichia coli bacteria responsibly for the infection. Cranberry juice is able to do this because it contains proanthocyanidins, a group of chemicals that belong to the flavonoid family (here). Cranberry is an excellent source of flavonoids and phenolic acids and contains a wide variety of different compounds, that give the fruit some very important health benefits (figure 1). Analysis of cranberry fruits have shown that over 75 % of the flavonoid content is made up of quecetin. In addition cranberry fruit is an excellent source of anthocyanins. The main anthocyanins are cyanidin and peonidin. Cranberries also contain proanthocyanidin dimmers, trimers and oligimers made up of repeating units of the flavon-3-ols epicatichin with varying linkages.
Figure 1. The main flavonoids in cranberry fruit. A is cyanidin (anthocyanin). B is peonidin (anthocyanin). C is quercetin (flavonol). D is myricetin (flavonol).
Flavonoids are excellent reducing agents which are able to scavenge free radicals in plasma and cells by donating electrons. The phenolic ring structure of the flanonoids then delocalises the unpaired electrons to stabilise the molecule. This antioxidant role means that flavonoids are protective of cardiovascular disease because they are able to inhibit the oxidation of LDL and prevent damage to the endothelium of the blood vessels. The wide variety of flavonoids in cranberry fruit also is known to work synergistically in multiple ways to inhibit and kill cancer cells in vitro, suggesting that cranberry consumption is anti carcinogenic. Quercetin is known to have potent anti-inflammatory effects. It is therefore not surprising that cranberry fruit has been shown to inhibit inflammation by inhibition of the cyclooxygenase enzyme necessary for activation of inflammatory prostanglandins (here).
If you have read my previous article on berries (here), you will already be aware that regular consumption of a variety of fruit berries provides some important health benefits. Cranberries are an excellent berry food to incorporate into the diet because they have such a wide range of flavonoids and are a rich source of quercetin. Attempting to replicate the flavonoid intake of cranberries with supplements would be expensive. Drinking fruit juice made from cranberries can be beneficial and studies have analysed the flavonoid contents of commercial juice and found they do contain high concentration of flavonoids. However, fruit juice can contain added sugar and so it is important to read labels carefully. Frozen berries are known to maintain their flavonoid content, and this is an excellent way to incorporate cranberries into your diet.
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