MECHANISM OF DEVELOPMENT OF BEANY FLAVOR DURING PROCESSING OF SOYBEAN

大豆香精的主要成分之一己醛在大豆中的形成机理如下。大豆含有三种类型的脂氧合酶同工酶（l-1, l-2, l-3）。在这些同工酶中，在通常的条件下（pH值6-7），L-2同工酶主要与亚油酸反应生成亚油酸的13-和9-氢过氧化物。生成的13-氢过氧化物（13-hpo）通过13-hpo裂解酶裂解成己醛。该项目在大豆中发现了该酶的存在。通过对两步酶促反应的动力学分析，得出了亚油酸生成己醛的速率决定步骤是脂氧合酶l-2同工酶生成13-hpo的步骤，而不是13-hpo裂解酶裂解13-hpo的步骤。研究了脂氧酶缺陷突变体大豆（l-1、l-2、l-3、l-1、-3）的食品品质。大豆的水分、粗蛋白质、粗脂肪和碳水化合物组成以及蛋白质的氨基酸组成和脂肪的脂肪酸组成与普通大豆（铃丰）非常相似。大豆种子中蛋白质的相对乳化活性也与正常大豆相似。这些结果表明，缺乏脂氧酶的大豆是有用的食物资源。

THE MECHANISM OF DEVELOPMENT OF HEXANAL, ONE OF MAJOR ELEMENTS OF SOYBEAN FLAVOR, IN SOYBEAN WAS REVEALED AS FOLLOWS. SOYBEAN CONTAINS THREE TYPES OF LIPOXYGENASE ISOZYMES (L-1, L-2, L-3). OF THESE ISOZYMES, UNDER THE USUAL CONDITIONS (pH 6-7), L-2 ISOZYME PREDOMINATLY REACTS WITH LINOLEIC ACID TO FORM 13- AND 9-HYDROPEROXIDES OF LINOLEIC ACID. THE RESULTING 13-HYDROPEROXIDE (13-HPO) IS CLEAVED TO HEXANAL BY 13-HPO-LYASE. THE PRESENCE OF THE ENZYME IN SOYBEAN WAS FOUND ON THIS PROJECT. FROM KINETIC EXAMINATION OF THE TWO STEPS OF ENZYMATIC REACTIONS, IT IS CONCLUDED THAT A RATE-DETERMINIG STEP OF HEXANAL FORMATION FROM LINOLEIC ACID IS A STEP OF 13-HPO FORMATION BY LIPOXYGENASE L-2 ISOZYME, NOT A STEP OF 13-HPO CLEAVAGE BY 13-HPO-LYASE.FOOD QUALITY OF LIPOXYGENASE DEFICIENT MUTANT SOYBEANS (L-1 NULL, L-2 NULL, L-3 NULL, L-1,-3 NULL) WAS ALSO INVESTIGATED. FOOS OOMPOSITION (MOISTURE, CRUDE PROTEIN, CRUDE FAT AND CARBOHYDRATE) OF THE SOYBEANS AND AMINO ACID COMPOSITION OF PROTEINS AND FATTY ACID COMPOSITION OF FAT FROM THEM WERE VERY SIMILAR TO THOSE OF NORMAL SOYBEAN (SUZUYUTAKA). RELATIVE EMULSIFYING ACTIVITY OF PROTEINS FROM THE SEEDS WAS ALSO SIMILAR TO THAT OF THE NORMAL SOYBEAN. THESE RESULTS SUGGEST THAT LIPOXYGENASE DEFICIENT SOYBEANS ARE USEFUL AS FOOD RESOURCES.