Application of electron spin resonance spectroscopy and spin probes to investigate the effect of ingredients on changes in wheat dough during heating.

The change in microviscosity of the aqueous and lipid phases of wheat flour dough, during heating and subsequent cooling, has been measured using novel spin probes based on the isoindolin-yloxyl structure. The spin probes, water and/or lipid soluble, were used with combinations of dough ingredients: diacetyl tartaric acid ester of monoglycerides (DATEM), salt, yeast, and sodium ascorbate. The lipid soluble probe showed that DATEM does not produce a homogeneous phase with endogenous lipids but is found in a separate, less mobile phase. Also, the lipids were shown not to be involved in the baking process, although DATEM may be incorporated into the gelled starch matrix. The water soluble probe enabled starch gelatinization to be investigated in detail and showed that gelatinization produces a reduction of dielectric constant. The technique is appropriate for the detailed examination of the behavior of different ingredients during baking and also potentially to examine interactions between ingredients and flour components in dough.

Microstructural effects on microbial survival: phase-separating dextran solutions.

Evolving microstructure in a model dextran solution is shown to exert a major influence on the survival of Escherichia coli K-12 frag 1 and Salmonella typhimurium LT2. The microstructure results from microscopic phase separation, which develops over several hours resulting in hardening of the solution into a glassy state. The microstructure is characterized by an array of physical methods including image analysis, electron spin resonance and bulk rheology, and it is shown that bacterial survival depends on the formation of microscopic. water-rich domains and not primarily on bulk water activity or hardness.

Green tea polyphenols react with 1,1-diphenyl-2-picrylhydrazyl free radicals in the bilayer of liposomes: direct evidence from electron spin resonance studies.

Free radical scavenging reactions of green tea polyphenols (GTP) were investigated with electron spin resonance (ESR) spectroscopy in the phospholipid bilayer of liposomes, using 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical as a model. The results showed that (1) GTP reacts with DPPH radicals in the bilayer of liposomes of both 1-hexadecanoyl-2-[(cis,cis,cis,cis,cis,cis)-4,7,10, 13,16,19-docosahexaenoyl]-sn-glycero-3-phosphocholine (DHAPC) and 1, 2-di[cis-9-hexadecenoyl]-sn-glycero-3-phosphocholine) (DPPC); and (2) GTP protects DHAPC liposomes effectively from the oxidation initiated by DPPH radicals. These results provide direct evidence that GTP reacts with free radicals in the model membrane and support the hypothesis that GTP protects unsaturated phospholipids from oxidation by reacting directly with the radicals.

Selected spin probes for the electron spin resonance study of the dynamics of water and lipids in doughs.

New water-soluble and lipid-soluble spin probes suitable for the ESR investigation of the physical states and interactions of components of dough have been developed. This paper reports some preliminary findings on the suitability of these probes for this type of investigation. Rotational correlation times have been measured for the spin probes in water, dough, oil, and a starch/water mixture. An increase in rotational correlation time of the spin probe corresponds to an increase in microviscosity of the medium. Changes observed in correlation times of the water-soluble spin probes in doughs and in water/starch mixtures clearly correspond to a gelatinization process when the mixtures are heated above 60 degrees C. These irreversible changes, clearly important in the baking process, were monitored by following the change of mobility of a spin probe in doughs over a wide temperature range. The similarity of the results from the two sets of experiments suggests that the phenomenon of the increase of correlation times with temperature in doughs is attributable to the starch component. The lipid-soluble spin probe was found to be located preferentially in the lipid phase of the dough.

The design of spin probes for electron magnetic resonance spectroscopy and imaging.

The problems that have to be addressed in designing suitable spin probes are manifold. In this article it will be shown that some the properties the probes need to possess are (i) a simple EMR spectrum (in some types of imaging or oximetry a single line is desirable), (ii) sharp lines with no unresolved splittings, to provide maximum sensitivity to detection, (iii) chemical, metabolic and thermal stability, (iv) easy possible synthesis to permit substitution with isotopes, prosthetic groups or groups to control the partition coefficients in lipid/water systems, and (v) electronic anisotropy, if rotational correlation times are to be determined, for example for the measurement of local viscosity.

Calcium ionophore enhances the electron spin resonance signal from isolated skeletal muscle.

Electron spin resonance studies of the free radical signal from isolated skeletal muscle during experimental damage have shown that elevation of muscle intracellular calcium with the calcium ionophore A23187 induced an average 61% increase in the amplitude of the signal of g value 2.0047 compared to paired, untreated control muscles, accompanied by a large efflux of intracellular creatine kinase to the external medium. Inhibitors of the calcium-induced loss of cell viability leading to enzyme efflux, i.e., chlorpromazine, phenidone and nordihydroguaiaretic acid had variable effects on the signal, suggesting that the free radical signal obtained from skeletal muscle by electron spin resonance techniques is stimulated by intracellular calcium overload, but is not directly related to the mechanisms by which calcium overload leads to a loss of cell viability leading to intracellular enzyme efflux.