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.