Tomoo Mihori

Moisture diffusion in a dry soybean seed measured using pulsed-field-gradient NMR

Abstract Moisture diffusion coefficient in a dry soybean seed was measured by a pulsed field gradient NMR method using stimulated echoes. A constant diffusion coefficient of 4·3 × 10 −10 m 2 s −1 was obtained for diffusion times ranging from 18·5 ms to 28·5 ms. This value is 10 times larger than literature values measured by a gravimetric method of seed hydration, and is 100 times larger than that calculated using absorption and desorption data. With the aid of NMR imaging, it was revealed that a dry soybean seed had considerable freely movable water which was centred at the intercotyledon face surrounded by an oil layer. The discrepancy in diffusion coefficients between those measured by NMR and by the gravimetric method is discussed. When the diffusion time was extended over 38·5 ms to 113 ms, a clearly restricted feature of diffusion was observed.

An on-line method for predicting freezing time using time/temperature data collected in the early stages of freezing

Abstract Existing methods of estimation of freezing time require data on thermal properties of the product and any relevant heat transfer coefficients. This paper describes a new procedure for estimating freezing time; a procedure that does not require the knowledge of thermal data of the food being frozen. This procedure collects time/temperature data from the early stages of cooling, analyzes these data to determine system parameters associated with the heat conduction equation and predicts the time/temperature profile in the remainder of the freezing process using these system parameters. This system has been validated via experiments on freezing fish meat as well as wheat flour dough.

Thermal and rheological properties of pressurized carp meat

Abstract In order to make clear the thermal and rheological changes in meat from high pressure treatment, we discussed volume changes, enthalpy changes from measurement of DSC, molecular weight changes from SDS-PAGE, and dynamic viscoelastic measurement on the pressurized samples. Carp meat was pressurized from 98MPa to 490MPa for 13h at 1°C. Although pressurized meat paste under 294MPa produced a gel by heating, meat paste pressurized at not less than 392MPa gave a brittle structure. A comparison of the results from other measurements suggested that there was a similar denaturation mechanism in both heating and pressurizing treatments.

Fracture Stress of Frozen Soybean Curd

Fracture stress of soybean curd (tofu) was measured in a wide range of low temperature by compression tests. Fracture stress of frozen soybean curd increased as the temperature decreased from -20°C. At -65°C, fracture stress of soybean curd reached to that of pure water ice, and it continued to increase as temperature decreased until it reached a characteristic temperature (-80°C); below this temperature the fracture stress was constant (35MPa). Soybean curd with less moisture content, prepared by dehydrating before freezing, showed larger fracture stress. When a soybean curd was dehydrated from 9.93 g H2O/g DM to 1.0 g H2O/g DM, its fracture stress increased up to 2.5 times large. The measured fracture stress was successfully analyzed using a mathematical model, a two component system consisting of pure water ice and concentrated amorphous solution (CAS). The estimated value of fracture stress of CAS was nearly five times larger than that of pure water ice.

Moisture Diffusion in Fresh and Dehydrated Fish Flesh Measured by PFG-NMR

Diffusion coefficient of moisture in codfish was measured using PFG–NMR. Intact as well as processed (minced with and without NaCI, fresh and heated, freeze-dried) sample were examined. The effect of diffusion time ranging from 28 ms to 100 ms was examined. Intact flesh showed unrestricted feature of moisture diffusion while minced flesh showed restricted moisture diffusion. Dependence of moisture content on diffusion coefficient was obtained.