Hiroko Sakamoto

Changes caused by microbial transglutaminase on physical properties of thermally induced soy protein gels

Abstract Two types of soy protein product, soy protein isolate (SPI) and soy protein concentrate (SPC), were incubated with a Ca 2+ -independent microbial transglutaminase to prepare thermally induced gels. Polymerization of soy protein molecules in the gels were shown on SDS-polyacrylamide gel electrophoresis. In the appropriate range of enzyme concentration several physical properties of the thermally induced gels were substantially enhanced. The impairment of physical properties due to the addition of NaCl as well as the reduction of solid content were well compensated by the enzyme treatment. Thus, the transglutaminase treatment was very useful for the improvement of heat induced gel of soy proteins.

Filler effects of oil droplets on the viscoelastic properties of emulsion gels

Abstract Filler effects of oil droplets on the viscoelastic properties of emulsion gels were investigated by small deformation mechanical measurements. The emulsions were made with soya oil and soy 11S globulin (15 wt% oil, 1.5–7% protein concentrations). The emulsion and soy 11S globulin solutions were gelled using Ca ++ -independent transglutaminase from a microorganism. The shear storage modulus (G′) and loss modulus (G″) of the proteinous gels and emulsion gels depended on the protein concentration. The concentration dependence of the modulus was approximated by an exponential function of the form: G ∝ C n , n = 4 and n = 2 being found in the cases of the proteinous gels and the emulsion gels, respectively. Shear moduli of the emulsion gels were much higher than those of the proteinous gels. Gels made from a fine emulsion (containing smaller oil droplets) exhibited higher G′ and G″ values than corresponding gels from a coarse emulsion. Addition of Tween 20 was found to reduce G′ and G″ of emulsion gels even when the protein matrix was not significantly displaced from the oil—water interface by the surfactant.

Retort-resistant tofu prepared by incubation with microbial transglutaminase

Abstract Addition of Ca 2+ -independent microbial transglutaminase with glucono- δ -lactone before a coagulation step of packed tofu manufacturing process made the tofu retort-resistant. The enzyme treatment effectively suppressed retort-induced water-release and hardening of the tofu sample pieces packed with water in a retort-pouch. The occurrence of polymerized soybean proteins in the enzyme-treated tofu was found.

Calcium — Independent Transglutaminase Derived from a Microorganism : Its Characteristics and Capability in Protein Crosslinking and Gel Formation

Characteristics of a novel trans glutaminase which was derived from a microorganism thought to belong to Streptoverticillium sp. were observed. The molecular weight of the purified enzyme was found to be about 40,000 on SDS-polyacrylamide gel electrophoresis, the isoelectric point 8.9 and the optimum pH of the reaction 6 ~ 7. The enzyme requires no calcium ions for its activity.

Gelation Mechanism of 11s Globulins of Soybeans by Ca+ 2 -Independent Transglutaminase

In this study, Ca+ 2-independent transglutaminase, isolated from culture filtrate of Streptoverticillium sp., was used to enzymatically crosslink 11S globulin of soybean. In the case of native glycinin, 70% of its acidic subunits participated in the reaction, while most of the basic subunits did not. For pre-heated glycinin, both the acidic and basic subunits were susceptible to the reaction. In the presence of N-Ethylmaleimide(NEM), pre-heated glycinin formed a better crosslinked network structure and had the higher values of storage and loss modulus as compared to the case or native glycinin. In the absence of NEM, only loss modulus values of pre-heated glycinin were significantly higher than those of native one.

Filler Effects of Oil Droplets on Physical Properties of Emulsion Gels

Filler effects of oil droplets on viscoelastic properties of emulsion gels were investigated by small deformation mechanical measurements. Emulsions were made with soya oil and soy l1S globulin(15 wt % oil, 1.5 - 7 % protein concentrations). Emulsions and soy 11S globulin solutions were gelated by Ca++-independent transglutaminase from microorganism. The shear storage modulus (G’) and loss modulus (G”) of proteinous gels and emulsion gels depended on the protein concentration. The concentrate-dependence of modulus was approximately by an exponential function of the form G ∞ cn, in which n=4 and n=2 was found in the case of the proteinous gel and the emulsion gel, respectively. Shear moduli of emulsion gels were much higher than those of proteinous gels. The gel made from fine emulsion (containing smaller size oil droplets) exhibited higher G’ and G” than the gel from coarse emulsion. Addition of Tween 20 was found to reduce G’ and G” of emulsion gel even if the protein matrix is not significantly displaced from the oil-water interface by the surfactant.