Control the formation of secondary flavor compounds.

Most volatile flavor compounds are esters, alcohols, aldehydes, ketones, lactones and sulfur-containing compounds. Aldehydes are generally formed enzymatically or oxidatively and are seldom considered endogenous in intact fruit.

Lipoxygenase catalyzes the formation of such aldehydes as hexanal,(E)-2-hexenal, (E,Z)-2,6-nonadienal and (E)-2-nonenal. These compounds, although not considered endogenous to fruit, are known to be important in how they impact flavor in the tomato and cucumber.

The induction or presence of secondary volatiles in stored processed fruits might affect the products' flavor attributes. The goal of USDA-ARS scientists was to compare endogenous and secondary aldehyde production in cantaloupe, honeydew, mango and watermelon by sampling unprocessed tissue and fruit blended using different protocols.

Investigators used a lipoxygenase inhibitor, n-propyl gallate (nPG), and oxygen exclusion technology. Various techniques were used to isolate and identify target compounds. In cantaloupe and honeydew, scientists recovered esters, alcohols and aldehydes. They found a few aldehydes present in cantaloupe, mango or watermelon tissue.

The use of oxygen exclusion and nPG techniques had similar results in blocking the formation of most aldehydes during cantaloupe sampling. Levels of hexanal, (E,Z)-2,6-nonadienal and (E)-2-nonenal were reduced 89%, 97% and 94%, respectively, in nPG-blended honeydew. In mango, mostly terpenes were recovered. However, hexanal and (E,Z)-2,6-nonadienal were also recovered and were completely inhibited by nPG blending.

In watermelon, the researchers recovered aldehydes, alcohols and ketones. Levels of hexanal, (E)-2-hexenal and (E)-2-nonenal were reduced by 90%, 68%, and 95%, respectively, when blended with nPG. Lipoxygenase-generated compounds were present in the blended samples. Their levels were reduced substantially by inhibitors. These compounds are believed to have a significant impact on the flavor and aroma attributes of these fruits.

Like tomato and cucumber, the researchers' data indicate that some flavor-important secondary compounds are not formed until fruit is macerated or its tissue disrupted. Evaluating processing aids that inhibit aldehyde production, and analyzing secondary compounds after fruit is processed and during its fresh-cut fruit storage, could help the industry deliver products that would better satisfy consumers. Further information. Jeanne Lea, Food Processing and Sensory Quality Unit, USDA-ARS Southern Regional Research Center, 1100 Robert E. Lee Blvd., New Orleans, LA 70179;phone: [phone]; email: [e-mail].