More carotenoids from warmer watermelon, says study
and beta-carotene, increases if stored at room temperature, says a
study from US Department of Agriculture researchers.
The results could have implications for both the natural products market and the functional beverage market.
"The ability of some watermelon cultivars to accumulate lycopene and beta-carotene when held at 21 degrees Celsius after harvest may be useful for processors wishing to obtain these carotenoids for the natural products market," wrote the researchers, Penelope Perkins-Veazie and Julie Collins from the South Central Agricultural Research Laboratory.
Lycopene, a potent antioxidant that gives the fruit its characteristic red colour, is the main carotenoid in watermelon, while others, such as beta-carotene, lutein and phytofluene are also present.
Eighty percent of the lycopene intake in the average US diet is said to come from tomato products, with watermelon number five in the source rankings.
A 180 gram serving of watermelon is said to contribute between eight and 20 mg of lycopene, making it a rich source of the carotenoid.
Recent studies have linked tomatoes and, in particular, lycopene to reducing the risk of several diseases, such as prostate cancer, and lowering inflammation that may cause hypertension and heart disease.
The new research, published on-line ahead of print in the Journal of Agricultural and Food Chemistry (doi: 10.1021/jf0532664 S0021-8561(05)03266-8), looked at the effect of storage on the carotenoid levels of three types of watermelon (open-pollinated seeded, hybrid seeded, and seedless) at 5, 13, and 21 degrees Celsius for 14 days.
Perkins-Veazie and Collins report that watermelons stored at 21 degrees Celsius had increased levels of carotenoids, compared to fresh fruit.
Compared to fresh fruit, the watermelons stored at this temperature gained between 11 to 40 percent in lycopene, but the increase was only significant for the seedless ('Sugar Shack') and hybrid seeded ('Summer Flavor 800') cultivars.
Beta-carotene content increased by between 50 and 139 percent for all three cultivars, with the biggest increase for the 'Summer Flavor 800' cultivar. Fruit stored at 13 degrees Celsius had relatively small carotenoid content changes.
"The increased lycopene, beta-carotene, and phytofluene contents of fruit held at 21 degrees Celsius but not at five degrees Celsius indicate temperature sensitivity and enhancement of carotenoid pathway enzymes in watermelon," wrote the researchers.
Lycopene is said to be produced by increased conversion of geranyl-geranyl diphosphate (GGPP) to phytoene by the enzyme, phytoene synthsase, which is then turned into lycopene by the enzyme, phytoene desaturase.
The researchers point out that the watermelon cultivars were "selected by commercial growers as fully ripe when harvested."
The results could be of great interest to processors who may wish to extract these carotenoids for the natural products market, or also for those who produce functional beverages.
US sales for functional fruit and vegetable juices rose from $2.2bn in 2002 to $2.4bn in 2005, according to Euromonitor International. The growth in market share for these products was even larger, albeit from a lower base, in Europe over the same period - rising from $1.5bn to $2.4bn.
