Masao Motoki

Transglutaminase and its use for food processing

Some characteristics and applications of a transglutaminase, derived from a variant of Streptoverticillium mobaraense, namely microbial transglutaminase (MTGase), are considered. MTGase, mass-produced at low cost by fermentation, catalyses the crosslinking of most food proteins through the formation of an e-(γ-glutamyl)lysine bond, in the same way as well-known mammalian enzymes. However, MTGase is remarkable because it is calcium independent and its molecular weight is smaller than that of other known enzymes. The results of many studies suggest that MTGase, as well as other transglutaminases, has many potential applications in food processing and in other areas.

Bacterial cellulose IV. Application to processed foods

Abstract A new form of cellulose, bacterial cellulose (BC), features smooth texture and high water-holding capacity. These properties function positively in food systems: BC functions as a heat-stable suspending agent as well as a filler to reinforce the body of fragile food hydrogels, improved the quality of pasty foods by reducing their stickiness, could be applied to meat products as a fat substitute and to jam as a noncaloric bulking agent. These results show that BC will be widely applicable to processed foods to improve their quality.

Bacterial cellulose II. Processing of the gelatinous cellulose for food materials

Abstract Gelatinous cellulose prepared by fermentation with Acetobacter aceti AJ 12368 consisted of cellulose fibrils (0.9%), bound water (0.3%) and free water (98.8%). The cellulose network absorbed water weakly in capillaries of about 0.5–1.0 microns. When stressed the gel released its water and deformed without fracture. The gel by itself was too tough to bite, but it became edible through processing either with sugar alcohol or with alginate and calcium chloride. The textures resemble fruit, such as grapes and molluscs such as squids, respectively. The mechanism is the immobilization of the water of gelatinous cellulose by viscous or gel-forming material, and accordingly the gel becomes easy to cut off with the teeth. These results show that gelatinous cellulose with its fibrous texture can be a new material for salads, low-calorie desserts, fabricated foods etc.

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.

Bacterial cellulose III. Development of a new form of cellulose

Abstract A new form of cellulose, bacterial cellulose (BC), was developed by disintegrating gelatinous cellulose which was produced by Acetobacter aceti AJ12368. BC is wet (97% water) and paste-like, and comprised of flocks of microfibrils. It swells in water and disperses homogeneously at a level of ≥0.3%. The suspension is a thixotropic fluid, and also shows dilatant flow at a low shear rate. The viscosity of a BC suspension is low compared to common thickeners. As a filler, BC has the highest water-holding capacity among commercial cellulose products. BC is considered as a stabilizer with low viscosity and a low-calorie material as a fat substitute.

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.

Improvement of the pH-solubility profile of sodium caseinate by using Ca2+-independent microbial transglutaminase with gelatin

Abstract Several mixtures composed of sodium caseinate and acid-gelatin were incubated with Ca 2+ -independent microbial transglutaminase (MTGase) of a variant of Streptoverticillium mobaraense. Formation of an e-(γ-Glu) Lys crosslink was observed in all MTGase-treated samples. Several MTGase-treated mixtures showed an improvement in solubility in the pH range 3–5.5 compared with sodium caScinate, mixtures of sodium caScinate and acid-gelatin incubated without MTGase, or mixtures of each MTGase-treated protein.

Determination of molecular weight of agars and effect of the molecular weight on the glass transition.

A novel procedure to determine the molecular weight (MW) and MW distributions for various agars is described. The MW values of commercial agars, an agarose, an agaropectin, and hydrolyzed agaroses were determined by size exclusion chromatography-low angle laser light scattering, using 4.0 M guanidine hydrochloride as eluent to avoid gelation. The MW for the commercial agars was between 106 400 and 243 500 with polydispersity between 1.283 and 6. 600. The MW of the agarose separated from a commercial agar was lower than that of the agaropectin. To prepare agaroses with different MW values, the obtained agarose was hydrolyzed. The MW of the agarose decreased with hydrolysis time, and the polydispersity, on the contrary, increased. The glass transition temperature (T(g)) of agarose with different MW values and that of agaropectin were measured by differential scanning calorimetry. The T(g) of the agarose was higher than that of the agaropectin with higher MW. The T(g) of agarose increased with MW.

Modification of several proteins by using Ca2+-independent microbial transglutaminase with high-pressure treatment

Abstract It was revealed that Ca 2+ -independent microbial transglutaminase (MTGase) of a variant of Streptoverticillium mobaraense could catalyze the acyl transfer reaction between monodansyl cadaverin (MDC) and dimethyl casein (DMC) even after a period (30 min) of high-pressure treatments at 200, 400 and 600 MPa. In the next step, simultaneous application of MTGase and the high-pressure treatments was found to be effective at accelerating the above acyl transfer reaction. Subsequently, it was found that MDC incorporation into several food proteins, e.g. bovine serum albumin (BSA), ovalbumin, γ-globulin and lysozyme, occurred when MTGase and a certain high-pressure treatment were applied to the reaction mixture simultaneously. Self-polymerization of BS A was also caused in the same procedure. Meanwhile, severalpre-treatments with high pressure changed BSA and ovalbumin to being the substrate in MDC incorporation catalyzed by MTGase.

Deamidation of Several Food Proteins Using Free and Immobilized Ca2+-Independent Microbial Transglutaminase

Enzymatic deamidation of αsl-casein was done by using Ca(2 +)-independent microbial transglutaminase (MTGase) of a variant of Streptoverticillium mobaraense. Although the amount of deamidated glutamine residues in αsl -casein was not as high as that of the case using guinea pig liver transglutaminase (GTGase), the improvements in pH-solubility and Ca(2 +)-sensitivity profile of the substrate protein were comparable to it. To do the enzymatic deamidation without chemical acylation of Lys residues of αsl- casein, several immobilized MTGase were prepared with two types of chitosan beads. Although neither αsl-casein nor β-casein was deamidated, dimethyl casein and citraconylated soy 7S globulin were deamidated by using the immobilized enzymes.