Oxygenation of lipids during the processing soybeans affects the flavor properties of soy products. We prepared tofu under anaerobic conditions and then evaluated its sensory properties and the compositions of volatiles and oxidized lipids. Anaerobic processing resulted in tofu with less intense richness (kokumi) concomitant with reductions in the amounts of oxidized lipids and volatile compounds.Key words: soybean (Glycin max L. Merril) seed; tofu; flavor; anaerobic process; lipoxygenase A variety of health claims for soy products have increased the consumption of soybeans, but currently available soy products continue to exhibit flavor problems, characterized as beany, green, and grassy, especially for European and US consumers.1-3) Oxygenation of fatty acids during processing produces the compounds responsible to such soybean-like flavors. n-Hexanal and n-hexan-1-ol among others are undesirable compounds that reduce acceptance of soy products by many consumers, who prefer a bland flavor. On the other hand, sensory evaluation by Japanese panelists suggested that tofu rich in n-hexanal had deeper richness. 4) These flavor compounds are formed from linoleic acid, mostly through oxygenation by lipoxygenases (LOXs) and the cleavage of the resulting linoleic acid 13-hydroperoxide (HPO) by HPO lyase.5) The formation of these compounds independently of soybean seed LOXs is also evident, and hence, introduction of the LOX-free soybean lines settled the flavor problems only partly. 6,7) It was expected that spontaneous oxygenation also proceeds during the processing soybean seeds, and that anaerobic processing suppresses lipid oxygenation, but no effect of anaerobiosis during tofu processing on the flavor properties of tofu has been reported. In this study, we prepared tofu in an anaerobic way, and examined its sensory properties as well as the compositions of volatile and lipid peroxide.Normal soybeans (Fukuyutaka) and the LOX-less soybean (L-Star) were grown at the National Institute of Crop Science, Tsukuba, Japan during the summer of 2006. Soybean seeds (120 g) were soaked in tap water at 20 C for 18 h and the water was drained off. Tap water was added to make the total weight of 720 g, and then the seeds were ground with a mixer (NB-780, Nakasa, Osaka, Japan) for 2 min. The slurry was boiled for 3 min, and then filtrated with cheesecloth. After degassing under a vacuum for 20 min, the slurry was mixed with gluconodeltalactone (Maglactone-70) to make 0.3% w/w, and the mixture was poured into a polypropylene tube (7 cm i.d.). After sealing of the tube, coagulation was done at 80 C for 40 min. In order to prepare the tofu anaerobically, the air in the water for imbibition and grinding was expelled with N 2 gas prior to use, and every step before degassing was performed under an N 2 atmosphere. After cooling to 25 C, the edges of the tofu block were removed, and a piece (7 cm i.d. Â 2 cm) was submitted to sensory evaluation. Sensory training was done with tofu made aerobically from Fukuyutaka and L-Star, and then eigh...