Preparation Of W/O And W/O/W Emulsion Coagulants And Their Improvement To The Quality Of Traditional Bittern-solidified Tofu

Bittern-solidified tofu is very popular for its soybean flavor and special sweet taste. However, when bittern or bittern solution is used as the tofu coagulant, the quick and intense solidification will result in several negative effects, including low water content, low yeild, high hardness, loose gel network, and loss of nutrients. The rapid solidification on the local scale also causes the coagulation process difficult to control. In this thesis, traditional bittern solidified tofu was selected as the research object and the study tried to find the solutions to the quick solidification in tofu process by the approach of adopting emulsification and controlled-release technique, in whick, water in oil (W/O) and water in oil in water (W/O/W) emuslsions as the delivery system were prepared to embed and slowly release the bittern solution, finally, to improve the quality of traditional bittern solidified tofu. Main conclusions were as follows:1. After examing the preparation parameters and characteristic of W/O emulsions, it was found that parameters including the mass ratios between water phase and oil phase, bath temperature, emulsifier (818SK) concentration, and homogeneous pressure played the key role in the emulsion preparation. The selected preparation conditions were:used mass ratio at4:6or5:5, with the818SK concentrtion from0.6%to1.0%, then kept warm in water bath at60℃for15min, finally, underwent the high pressure homogenization at60MPa for once after a2-min high speed shearing at the speed of13000r/min. Following the above processes, W/O emulsions with good particle size distribution, fine viscosity, high embedding ratio of magnesium, and good stability were prepared. These W/O emulsions also had the expected controlled-release property which was affected by the temperature, shearing strength, and the components of emulsions.2. After investigating the factors affecting the preparation of W/O/W emulsions and their stability, particle size distribution, and controlled release effect, the results showed that the higher of818SK concentration in the oil phase and the mass ratio beteween W/O emulsion and the external water phase were set, the smaller and more uniform of the emulsion particle size would be, and the better of the stability that the emulsions would have. The818SK concentration from1.2%-1.6%and the mass ratio of6:4was selected. Both of the excessive higher emulsifier concentration and the mass ratio would cause the increase of viscosity. Moreover, neither excessive strong nor excessive weak homogenization strength was benefit for the emulsion stability. Hence, sheraing speed at11000r/min for120s was chose. As the hydrophilic emulsifier, Q12S in the external water phase had the positive effect on the stability of W/O/W emulsions. When the concentration of Q12S approached to0.8%, W/O/W emulsions with good properties could be abtained. It was also found that, when bull serum albumin (BSA) or whey protein isolate (WPI) was added into the internal phase, the W/O/W emulsions with much smaller particle size and much better stability could be prepared. Under these circumstance, the W/O/W emulsions had the expected controlled-release property which was affected by the temperature, shearing strength, and the component of emulsions. 3. Both the W/O and W/O/W emulsion coagulants could postpone the solidification process, which made the tofu with greater water content, higher yield, finer macrostructure, microstructure and texture, and more acceptable color compared with the tofu solidified by the traditional coagulant.4. When W/O or W/O/W emulsion coagulants were used, results also indicated that the loss of protein and soy isoflavones during tofu preparation was decreased, and the yield of protein and soy isoflavones was increased.