Natural Compound Improves Apples’ Red Colour

Methyl jasmonate (MJ) has many functions. The natural compound derived from plant oils – especially jasmine and honeysuckle oils – helps plants muster pest-defence proteins. Incorporated into cosmetic products, it produces a sweet, flowery aroma. Now, spraying MJ onto apples before harvest may improve uniformity and depth of red colouring in the fruit’s peel, new research suggests.

“Applying MJ increases the total percentage of the crop having uniform red colour, and important grading issue for domestic and export markets,” says Agricultural Research Service plant pathologist James Mattheis.

The approach draws on published research showing that when apples are exposed to natural or artificial light, MJ activities processes in the peel that produce anthocyanin pigments. MJ also breaks down the peel’s green chlorophyll, though light isn’t required.

“Application timing is important; treat too early in the season, and the colour can face by harvest,” says Mattheis, who heads ARS’ Tree Fruit Research Laboratory in Wenatchee, Washington, a state forecast to produce 88.8 million boxes of fresh-market apples this year.

Through research is ongoing, ARS in May 2002 applied for patent protection (10/146,687) on the treatment, since no similar products are currently marketed, notes Mattheis, whose research team includes graduate student Dave Rudell and food technologist Xuetong Fan.

One particular use for MJ may be ensuring a more uniform red colour on Fugi apples that have spent much of the growing season enclosed within opaque bags. In the United States and Japan, where Fujis originated, bagging is practiced to enhance the apple’s red colour or close to harvest. Starting in late June, more than a month after a Fuji’s flowers have bloomed, two overlapping bags are placed around the immature fruit by hand and keep in place until a few weeks before harvest (late September to early October in Washington). Even after the bags are removed, the red colour continues to develop, albeit unevenly. Spraying MJ helps correct for this by promoting red colour development on all sides of the apple, Mattheis notes.

MJ also works on such popular varieties as Red Delicious and Gala. “We didn’t see any significant change in eating quality compared to untreated fruit,” says Mattheis of lab and orchard studies in which apples were treated with a water-based emulsion containing a sufficient and 2 percent or less MJ.

Other positives: MJ also works on harvested fruit for degreening, and is already classified by the Food and Drug Administration as a generally Recognized As Safe substance. Despite its promise, MJ needs further evaluation. Too much can harm he fruit, and at about $43 an ounce, the economics of orchard-scale treatments are uncertain.

“We’re still not totally there in terms of minimizing the variability,” Mattheis says, “We’re still trying to improve MJ formation and timing and better understand the factors that influence success with this treatment.”

But if the approach bears fruit in terms of consistency and cont, apple growers could get a head-start on improving their crop’s marketability.