A simple and efficient system for green note compound biogenesis by use of certain lipoxygenase and hydroperoxide lyase sources

Six-carbon (C₆) aldehydes and alcohols are important components of the aroma and flavor of fruits and vegetables. Soybean lipoxygenase (LOX) isozyme LOX 3 was reported not only to produce less 13-hydroperoxides, precursors of C₆ aldehydes, but also to convert them to ketodiene products. Here, we examined the effects of LOX 3 on hexenal formation from linolenic acid homogenized with watermelon 13-hydroperoxide lyase (HL)-overexpressing Nicotiana tabacum leaves and soybean acetone powder. Compared to the wild type, which contains LOXs 1, 2, and 3, the elimination of LOX 3 in LOX 1 + 2 facilitates greater production of hexenals. The use of LOX 2 alone yielded the highest hexenal production, while a two-step conversion was required for LOX 1 to produce hexenals at high levels due to different pH optima of the enzymes involved. These results clearly demonstrate that the soybeans lacking LOX 3 in combination with watermelon HL-overexpressing leaf tissues greatly enhance hexenal formation.