| Summary: | 碩士 === 中國文化大學 === 生活應用科學系 === 100 === This study is going to investigate the effect of different storage condition of soy protein isolate (SPI) and the quality of paiyen tofu. SPI was stored in 7 different conditions which were the room temperature treatment (25℃, Aw 0.25), the high temperature treatment (45℃, Aw 0.25), the low temperature treatment (5℃, Aw 0.25), the high humidity treatment (25℃, Aw 0.75), the light treatment (12hours daylight exposure, 25℃, Aw 0.25), the vacuum treatment (vacuum packaging, 25℃, Aw 0.25) and the high temperature-high humidity treatment (45℃, Aw0.75).
The experiment was 224 days totally, every 28 days sampling once and totally 8 sampling times. SPI sample was examined the following items：color, nitrogen solubility, hydrophobicity, pH, functional properties (including gelation, emulsification, foaming ability, viscosity, water holding capacity) and electrophoresis. Then paiyen tofu was made and determined its color, density and texture and the viscosity of half product.
The result found：(1) The color of the SPI has changed to reddish yellow in the high temperature - high humidity treatment sample and to yellowish green in the high humidity treatment sample. (2) The longer the storage time, the lower the nitrogen solubility. The phenomenon is especially obvious in the high temperature treatment and the high temperature - high humidity treatment samples. (3) The highest degree of hydrophobicity is found in the high temperature - high humidity treatment sample. (4) All the samples become more acid after being stored. (5) The functional properties of SPI sample are decreased significantly in the high humidity treatment and the high temperature - high humidity treatment samples. (6) Electrophoresis result found after storage, the protein molecule weight of SPI significantly decreased and the charge of the protein molecule has migrated. (7) The viscosity of half product of paiyen tofu and the texture of paiyen tofu declined significantly in the high humidity treatment and the high temperature - high humidity treatment samples. (8) The inside color of paiyen tofu become dark reddish yellow in the high temperature - high humidity treatment sample. (9) The longer the storage time, the greater the density of paiyen tofu.
In conclusion, the temperature and the humidity are most two important factors affecting SPI quality during storage. On the other hand, low temperature and vacuum packaging are the best way to preserve SPI.
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