Formation of Volatile Compounds in Model Experiments with Crude Leek (Allium ampeloprasum Var. Lancelot) Enzyme Extract and Linoleic Acid or Linolenic Acid

Three continuous assays are described for lipoxygenase (LOX), hydroperoxide lyase (HPL) and alcohol dehydrogenase (ADH) in leek tissue. The catalytic activity of LOX showed significant difference (significance level 5%) between linolenic acid (9.43 × 10-4 katals per kg protein) and linoleic acid (2.53 × 10-4 katals per kg protein), and the pH-optimum of LOX was 4.5−5.5 against linoleic acid. The catalytic activity of HPL was statistically the same for 9-(S)-hydroperoxy-(10E,12Z)-octadecadienoic acid (1.01 × 10-2 katals per kg protein) and 13-(S)-hydroperoxy-(9Z,11E)-octadecadienoic acid (7.69 × 10-3 katals per kg protein). ADH showed a catalytic activity of 5.01 × 10-4 katals/kg of protein toward hexanal. Model experiments with crude enzyme extract from leek mixed with linoleic acid or linolenic acid demonstrated differences in the amount of produced aroma compounds. Linoleic acid resulted in significantly most hexanal, heptanal, (E)-2-heptenal, (E)-2-octenal, (E,E)-2,4-decadienal, pentanol, and hexanol, whereas linolenic acid resulted in significantly most (E)-2-pentenal, (E)-2-hexenal, (E,Z)-2,4-heptadienal, (E,E)-2,4-heptadienal, and butanol. Leek LOX produced only the 13-hydroperoxide of linoleic acid and linolenic acid. Keywords: Leek; flavor; lipoxygenase; hydroperoxide lyase; alcohol dehydrogenase; enzyme assays