Pomegranate peel yields double the amount of antioxidants than the pulp, and has 'more potential as a health supplement' claim Chinese researchers.
The fruit has commonly been linked to improved heart health, but other varied claims have been made including protecting against prostate cancer and slowing cartilage loss in arthritis.
For example, Pomegreat pomegranate juice is approved by the charity Heart UK, and has seen sales increase ten-fold, to 500,000 litres a month, from mid-2004 to mid-2005.
The majority of research has focussed on the pulp and juice of the fruit. But now scientists from the Institute of Hygiene and Environmental Medicine, Tianjin, China, have reported that the peel offers higher yields of phenolics, flavonoids and proanythocyanidins than the pulp.
Published in the May issue of Food Chemistry (Vol. 96, pp. 254-260), the researchers investigated the method of extraction using a variety of solvents: methanol only; ethanol only; acetone only; and a mixture of methanol, ethanol, acetone and water.
"The mixture of different solvents is more powerful in recovering antioxidants than the individual solvents," reported lead author Yunfeng Li.
The pulp yielded 24 milligrams per gram (mg/g) of phenolics, while the peel yielded a whopping 250 mg/g. Flavonoid content was also significantly greater in the peel than the pulp (59 versus 17 mg/g), as were proanythocyanidins (11 versus 5 mg/g).
Interestingly, the vitamin C content was similar for both the pulp and peel (0.99 versus 0.85 mg/g).
The exact details of the extractions, like the ratios of solvents, was not described by the authors as the extraction procedure has been submitted for Chinese patent protection.
Different measures of antioxidant activity were used, like FRAP (ferric-reducing antioxidant power) assay, the superoxide radical-scavenging activity, the hydroxyl radical prevention activity, and the inhibition of low-density lipoprotein (LDL) oxidation.
Pomegranate peel performed significantly better than the pulp in all of the tests of antioxidant activity - a results that is not so surprising given the relative concentrations of antioxidants in the extracts.
"As compared to the pulp extract, the peel extract acted more dramatically in protecting LDL against oxidation," reported Li.
Oxidation of LDL has been proposed to play a key role in hardening of the arteries (atherosclerosis), which is linked to heart disease - the cause of about 50 per cent of deaths in Europe, and 34.2 percent of Americans (70.1 m people) are reported to have suffered from some form of heart disease in 2002.
The scientists could not conclude if the flavonoids or proanythocyanidins contributed to the antioxidant activity and proposed that the phenolics were the active species.
"We concluded that pomegranate peel extract appeared to have more potential as a health supplement rich in natural antioxidants than the pulp extract and merits further study," said Li.
The study supports previous reports about the heart benefits of pomegranate and pomegranate juice.
Numerous pomegranate extracts are commercially available, some of which are made from whole fruits, including the peel. However, extracts using the peel only, normally a waste product in the juicing process, could offer an alternative source of antioxidants.