Abstract:

In the colloidal chemistry part of physical chemistry course, the original experiment is the preparation of iron hydroxide colloid and the determination of electrophoresis rate, which are confirmatory experiments. Furthermore, the resulting characterization of colloids is limited to electrical properties with no consideration of particle size or optical properties. In this paper, the preparation, characterization, and aggregation of soybean protein colloids were studied and the experiments were improved from the original confirmatory experiment to a comprehensive, exploratory experiment. Soybean protein colloids were prepared using the physical dispersion method, and the resulting particle size was then characterized, as well as the optical and electrical properties. Next, the aggregation and precipitation conditions were explored, and finally, tofu was produced. The particle size of the soybean protein colloids was found to be between 20–120 nm, with the most probable distribution of 51 nm, and an average charge of −41.8 mV. According to the Dindal effect, scattered blue light is observed in the direction perpendicular to the incident light, whereas the transmitted light is orange and red. By exploring the effects of counter ion types, temperature, and pH value, a deeper understanding of the colloidal precipitation process of plant protein was developed. The experiment introduces modern Zeta potential and particle size analysis, and considers protein aggregation and precipitation to extend the application of book knowledge. The final product, tofu, is closely related to life, highlighting the charm of chemistry and demonstrating the crucial role it plays in the manufacture of everyday items.

Key words: Innovation experiment, Colloid, Tofu, Soybean protein, Aggregation