Eduardo Morales Sánchez

Optical techniques coupled to ohmic heating to study heat-induced changes in biological systems

Solutions of bovine serum albumin protein were heated from 30 to 85°C in a temperature-controlled optical cell equipped with air-convective and ohmic heating systems. A polarized laser beam passed through a photo-elastic modulator was used to measure system changes in optical rotation. Results using both the air-convective and the ohmic heating systems showed that when the protein system was heated, an increase in absolute value of optical rotation occurred close to the temperature of denaturation of the protein. Both heating systems were compared, evaluating data points spread and variation in calculated temperature of denaturation for the replicates. Although no improvement in these parameters was obtained with ohmic heating when compared to those obtained with the air-convective system, the optical change related to protein denaturation was more clearly observed. Because ohmic heating strongly interacts with the sample under study, samples with low polarity and not susceptible to electrolysis should be used to avoid electrical effects; regardless, ohmic heating coupled to optical systems could also be a useful tool for the evaluation of interaction of electric field with biological systems optically active.

Optical properties of a heated cornstarch mixture

In this study, the objective was to evaluate optical properties of a corn starch-water mixture as descriptors of its behavior under processing conditions. A solution of corn starch in water was prepared and heated from 25 to 85°C in a temperature-controlled optical cell. For the measurement of optical properties, a polarized laser beam modulated through a photoelastic modulator and an analyzer, was used as optical probe. It was possible to measure transmitted light, along with optical rotation. Optical measurements showed changes related to temperature dependent phenomena such as starch granule swelling and gelatinization, in the ranges 25 to 60°C, 60 to 85°C. Above 80°C transmission values were higher, due to the solution clarification caused by corn starch gelatinization. Regarding optical rotation, it was difficult to obtain reliable measurements at low temperatures due to the high turbidity of the system. However, once gel was formed at higher temperatures, optical rotation and light transmission increased. This study demonstrated that optical techniques are suitable for the study of the behavior of water-starch mixtures under processing conditions such as heating, revealing a promising future for the monitoring of such phenomena in the production line to lower costs and improve product quality.