Effect of Variety of Soybean Seeds and Processing of Soy Milk on the Isoflavone Content of Tofu

Abstract

Soy milks were produced by the heat-squeezing method and the non heat-squeezing method from four varieties of soybean seeds, Suzuyutaka, Tohoku 126, Tohoku 135 (variety lacking lipoxygenase activity), and Tohoku 139 (variety containing small amount of allergen). Contents of isoflavone and relating compounds were then compared to find the processing way of soy milk containing large amounts of isoflavone. (1) Large amounts of isoflavone were detected in the seed of Tohoku 126 and the content was 437mg / 100g seed. While the isoflavone content in the seed of Tohoku 139 was only 107mg / 100g seed. (2) Most of isoflavone in the soybean seeds was malonyl type, and malonylgenistin was the most predominant isoflavone. Ratio of malonyl type in total isoflavone in the soybean seeds was 66.7-91.6%, and that of aglycon type was only 0.82.5%. (3) Total isoflavone content in soy milk varied with the varieties of soybean seed, and its content in each soy milk was 1 / 6-1 / 8 as much as in the corresponding soybean seed. Isoflavone content in soy milk (Y) and that in soybean (X) were correlated with 1% level of significance under the formula of y = 0.1348x + 0.5626 (r = 0.993). (4) Total isoflavone content in Tofu confected by the heat-squeezing method from whole soybean and hulled soybean was higher than that in Tofu by the non heat-squeezing method. (5) When soy milk was produced by the heat-squeezing method from whole soybean and hulled soybean, isoflavone in soy milk from whole soybean was efficiently extracted after adding water until six-fold volume of soybean used as materials. Total isoflavone content in soy milk from hulled soybean increased in response to the volume of adding water. Total isoflavone content in Okara milk from hulled soybean was not changed by the volume of additional water. (6) Ratio of the content of malonyl type, glycosyl type, and aglycon type of isoflavone in Tofu from whole soybean and hulled soybean confected by the heat-squeezing method and the non heat-squeezing method was almost the same. (7) Contents of protein and solid matter in Tofu produced from Okara milk were higher than that in Tofu from whole soybean and hulled soybean. Moreover, dietary fiber was detected in the Okara Tofu.