PURPOSE: A method of preparing fermented soy products containing the fermented liquid of Opuntia ficus-indica var. Saboten Makino by adding brown sugar to an Opuntia ficus-indica fruit, inoculating the mixed liquid of lactic bacteria and yeast thereinto is provided. By various enzymes and flavorings produced during the fermentation process, soy products such as fermented soybean paste, soy sauce and red pepper paste have improved taste and functionality. CONSTITUTION: About 3%(w/v) brown sugar is added to washed Opuntia ficus-indica to give a mixture, 10%(v/v) of mixed liquid of lactic bacteria(10¬9 cells/ml) and yeast(10¬4 cells/ml) in a ratio of 9:1 is inoculated into the mixture and then fermented in a thermostatic bath at 35 to 45deg.C for 7 to 12 days to produce fermented liquid. A steamed and defatted soybean is mixed with wheat flour and the fermented liquid in a weight ratio of 10:10:1, followed by inoculation with Aspergillus oryzae to produce fermented soybean Koji. The fermented soybean paste con
