Abstract:

The changes in protein structure and water state were studied during tofu gelation process. Results indicated that α-helix, β-sheet and β-turn in soybean protein were not observed before heating treatment of soybean milk and coil was the dominant secondary structure of soybean protein. However, when boiled soybean milk was cooled to 80 ℃ and plaster was added in it, higher level of α-helix was observed. Twenty minutes later, the percentages of α-helix and β-turn structures exhibited a slight increase while the percentage of β- sheet exhibited an obvious decrease; in contrast, the coil structure revealed a significant increase. Fifty minutes later, a stable gel net was formed. Pressed tofu exhibited a declining level of α-helix and an increasing level of β-sheet. Meanwhile, the contents of unfreezable water first decreased and then increased and both the contents of freezable water and balance water exhibited a decreasing trend in the gel net. All of these investigations provide theoretical evidences for further studying gelation mechanisms of soybean protein by plaster and developing new products of soybean protein.

Key words: tofu, gelation, protein, water state, secondary structure