39D-16

M. E. JARAMILLO-FLORES¹, L. A. González-Ramírez, and H. Hernández-Sánchez. (1) Depto. Graduados Inv. Alimentos, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, Carpio y Plan de Ayala, México, DF, CP. 11340, Mexico

Justification: A knowledge of the structure of the proteins is necessary if the relationship with its activity is to be determined. The crystallization of the proteins is the first step in the determination of their structure by X-ray difraction, and studies on the state of aggregation and solubility are very important in order to obtain adequate protein crystals. Objective: To study the effect of pH and temperature on the aggregation of three proteins important in food science. Methods: Dynamic light scattering was used to follow the aggregation state of the proteins ovoalbumin, hen egg white lysozyme and thaumatin I from Thaumatococcus daniellii. The effect of pH was measured at 18°C and testing pH values of 3,4,5,6,7 and 8. The effect of temperature on aggregation was conducted at 5,10,15,20,25 and 30°C. Results: The aggregation behavior of ovoalbumin is affected at pH values below 4 and above 8, while at pH 6 the protein showed the homogeneous existence of monomers that would allowed to obtain single crystals. On the other hand, the same study in thaumatin and lysozyme did not show any correlation. In the case of ovoalbumin, it formed a dimer when the temperature was between 25 and 30°C and at pH 5. At temperatures below 20°C, this protein exists as a trimer. Thaumatin showed a similar behavior. Lysozyme is a monomer at temperatures between 15 and 30°C and exists as trimer below 15°C. Significance: Dynamic light scattering is a technique with a high sensitivity which is very useful in the prediction of the state of aggregation of different food proteins.