Chotika Viriyarattanasak

Ice nucleation and supercooling behavior of polymer aqueous solutions

We determined the homogeneous nucleation temperature depression, DeltaT(f,hom), the equilibrium melting point depression, DeltaT(m), and the value lambda, which can be obtained from the linear relationship DeltaT(f,hom)=lambdaDeltaT(m), for aqueous solutions of PEG (200-20,000 g mol(-1)), PVP (10,000, 35,000, 40,000 g mol(-1)), and dextran (10,000 g mol(-1)) in the concentration range 0-40 wt% using the emulsion method. The molecular weight dependence of T(f,hom), T(m), and lambda in PEG aqueous solutions was found to change in the vicinity of Mw 600-1540 at all concentrations. In addition, it was confirmed that for all of the polymers studied, there was a good linear relationship between lambda and the logarithmic value of the self-diffusion coefficient D(0) of the solute molecule. These results indicate that the parameters that describe non-equilibrium freezing, such as T(f,hom) and lambda, are dependent on solution properties such as viscosity and self-diffusion of solute molecules.

Equations for spectrophotometric determination of relative concentrations of myoglobin derivatives in aqueous tuna meat extracts

The percentage of metmyoglobin (%metMb) in aqueous meat extracts of bigeye and bluefin tuna and beef samples were estimated using previously reported equations derived from the absorption spectra of horse Mb. The results demonstrate that in an aqueous extract, the difference in %metMb estimated by the different equations was negligible for beef samples. Conversely, in an aqueous tuna extract, different %metMb values were obtained with the different equations. The discrepancy in the tuna sample results might be due to differences in absorption spectra for horse and tuna Mb. Therefore, a new set of equations derived from the absorption spectra of bigeye tuna Mb, reported by Matsuura and Hashimoto (1955), was established. The accuracy of the proposed equations was compared with the cyanmetmyoglobin (cyanmetMb) method. The results show that the total Mb concentrations estimated by our proposed equations were in good agreement with the results obtained by the conventional cyanmetMb method (R(2)=0.984). Therefore, the new set of proposed equations is valid for the spectrophotometric determination of the relative proportions of Mb derivatives and total Mb concentration in aqueous tuna meat extracts.

Prediction Approach to the Glass Transition Temperature of Amorphous Carbohydrate Polymer

Most of carbohydrate polymers exist, at least partially, in an amorphous state, and thus, glass transition occur during dehydration/rehydration and cooling/heating processing. Since various physical properties are changed drastically by the glass transition (Levine and Slade 1988; Roos 1995; Le Meste et al. 2002), it is important to understand the glass transition temperature (Tg).

Effects of fatty acid and emulsifier on the complex formation and in vitro digestibility of gelatinized potato starch

ABSTRACT The effects of fatty acid, monoacylglycerol, and polyglycerol fatty acid ester with varying chain length in their acyl chains on the extent of complex formation (complex index) and in vitro enzymatic digestibility of gelatinized potato starch were investigated. The complex index increased with increase in the concentration of the ligands (fatty acid, monoacylglycerol, and polyglycerol fatty acid ester), with the plateau in the complex index value depending on the type of ligands. In comparison of complex index among fatty acid-samples, the complex index maximum increased as the chain length increased up to octanoic acid and then decreased. In comparison of complex index among fatty acid-, monoacylglycerol-, and polyglycerol fatty acid ester-samples at each acyl chain, the complex index maximum followed the order polyglycerol fatty acid ester > monoacylglycerol > fatty acid. Fatty acid, monoacylglycerol, and polyglycerol fatty acid ester with long acyl chains greatly reduced the enzymatic hydrolysis of starch. Polyglycerol fatty acid ester with palmitic acid chains was the strongest inhibitor of starch hydrolysis, suggesting that further complex formation may occur during the hydrolysis of gelatinized starch (enzyme-annealing).