Sunday, May 8, 2011

Fruit Olympics: Study Analyses Antioxidant and Total Phenolic Content of 62 Fruits

Did you ever want to know how your favorite fruit would perform in the most prestigious disciplines of the "Fruit Olympics", i.e. antioxidant capacity and phenolic content? Yes? Well, I guess a group of researchers from China has just done you a favor...

Xu et al. (Xu. 2011) analysed the antioxidant capacity by Ferric-reducing antioxidant power (FRAP) assays and the free radical scavenging capacities by Trolox equivalent antioxidant capacity assays (TEAC) and found:
Seven fruits had the strongest antioxidant activities among 62 tested fruits [...] they were Chinese date, pomegranate, guava, sweetsop, persimmon, Chinese wampee and plum (sanhua). In addition, olive showed the strongest free radical scavenging ability, and cherry and pineapple also had high antioxidant capacities. Because of their high antioxidant activities, it could be speculated that these fruits will be beneficial for the diseases caused by oxidative stress.
An interesting observation is that the total antioxidant capacity measured by FRAP and the radical scavenging capacities directly assessed by Trolox show only a weak correlation of R² = 0.0337 (0<1; R = 1 would indicate 100% correlated), which would "suggest that the compounds capable of reducing oxidants could be different from those scavenging free radicals in these fruits". By removing the four fruits with the highest antioxidant capacity, however, the correlation increases to R²=0.7169, which makes me think that the lack of correlation might be explained by artifices of the measuring process at high antioxidant concentrations. It is nevertheless an interesting thought that, after all, the amount of antioxidants (measured by FRAP) would only partly explain the free-radical scavenging capability of a certain food.
Figure 1: The Chinese or red date (also known as Jujuba), an antioxidant powerhouse with an abundance of polyphenols (photo by Marco Schmidt, Wikipedia)
Next to antioxidants, the "perfomance" in terms of total phenolic content, constitutes the second most prestigious discipline of the "Fruit Olympics". Xu et al. used the Folin–Ciocalteu method, "which relie[s] on the transfer of electrons from phenolic compounds to the Folin–Ciocalteu reagent in alkaline medium, and is a simple and widely used method" and found that
[...] the total phenolic contents varied from 11.88 to 585.52mg GAE/100 g with the difference of 49-fold, and the mean value was 71.80 mg GAE/100 g for 62 fruits.Chinese date (585.52    +/-18.59 mg GAE/100 g) had the highest total phenolic content, followed by sweetsop (405.41 +/-16.70 mg GAE/100 g), guava (194.11+/-7.01 mg GAE/100 g), pomegranate (146.94+/-0.04 mg GAE/100 g), Chinese wampee (116.10+/-7.48 mg GAE/100 g), cherries (114.56+/-4.72 mg GAE/100 g), persimmon (112.09+/-4.60 mg GAE/100 g) and plum (sanhua) (102.43    2.83 mg GAE/100 g), but pear (honey) had the lowest total phenolic content (11.88    0.11 mg GAE/100 g) among the tested fruits.
Another result is that olive oil had the highest content of gallic acid (50.25 ± 4.87 mg/100g), followed by wax apple and Chinese date. The latter also had the highest content of cyanidin-3-O-galacoside (13.5 ± 0.11 mg/100g, while one of my personal favorites, the pomegranate, outperformed the competition in terms of  quercetin-3-glucoside (11.1 ± 0.60 mg/100g). If you are looking for hesperitin, a natural COX-2 inhibitor (anti-inflammatory), lemons should be your "fruit athlete" of choice.
Figure 2: Although he is not among the "top athletes", a recent study has shown that "an apple a day [in fact] keeps the doctor away" (photo by Firr2000)

In view of all this data, don't forget the motto of the original Olympic Games: "Its taking part that counts!" Or, in other word, get your daily serving of healthy fruits and if you cannot stand Chinese dates, or Jujuba's as they are commonly called, as well, eat something less exotic - remember: A recent study validated the old saying "an apple a day will keep the doctor away".