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Natural Aromatic Compound Deepens Red Coloring in Apples

Spraying apples with the aromatic compound methyl jasmonate (MJ) before harvest may offer a new way to improve the uniformity of the fruit's red color. That's the implication of studies by Jim Mattheis, an Agricultural Research Service plant physiologist who is exploring new ways to improve the quality and marketability of apples, pears and other fruit grown in the Pacific Northwest.

In jasmine and some other plants, MJ has many functions, including mobilizing antimicrobial proteins. A sweet, flowery aroma also makes MJ a popular cosmetics ingredient, and it is classified by the Food and Drug Administration as a Generally Recognized As Safe substance.

Starting in 1998, Mattheis followed up on earlier research showing that, when apples are exposed to light, MJ activates biochemical processes in the peel that produce anthocyanin pigments. Along with graduate student Dave Rudell and ARS food technologist Xuetong Fan, Mattheis devised a water-based emulsion containing 2 percent or less MJ and a surfactant that can be sprayed directly onto unpicked fruit.

Through lab and orchard trials with Red Delicious, Gala and other varieties, the team discovered timing is crucial; some apples treated too early in the season lost their red color by fall harvest. And too much MJ sometimes harmed the fruit. But at concentrations of 2 percent or less, no adverse effect or significant change in eating quality was apparent, according to Mattheis, at ARS' Tree Fruit Research Station in Wenatchee, Wash.

ARS, on behalf of the U.S. Department of Agriculture, has applied for patent protection on the MJ apple treatment. One particular use may be correcting uneven coloring in Fuji apples that have spent much of their growing season in opaque bags. A more detailed article on the work is in the May issue of Agricultural Research magazine.

ARS is USDA's chief scientific research agency.