Removal of Imidazoles from Caramel Color by Ultrafiltration

Abstract

The ultrafiltration mechanism of the imidazoles from a caramel color through PM-10 and DDS-870 membrane was analyzed.
It was found that some imidazoles were bound irreversibly to impermeable matter in the caramel and thus these imidazoles could not be removed by ultrafiltration.
The following equations estimating the retained imidazoles concentration after various operations of ultra-filtration were obtained :
C= (C₀-KM/V₀) (V₀/V) R_i + KM/V (for single batch operation)
C_n= (C₀-KM/V₀) (V/V₀) ^n(1-Ri) + KM/V₀ (for repeated batch operation)
C= (C₀-KM/V₀) exp {- (1-Ri) V_p/V₀} +KM/V₀ (for fixed-volume operation)
where C [mg/ml] is the concentration of imidazoles in sample, C₀ [mg/ml] is the initial concentration of imidazoles in sample, C_n [mg/ml] is concentration of imidazoles in the sample after n operations of filtration (concentration factor V₀/ V) and dilution (V₀/V-fold), V [ml] is the volume of sample, V₀ [ml] is the initial volume of sample, V_p [ml] is the volume of permeate, n [-] is times of batch operation, R_i [-] is the ideal rejection of imidazoles and KM [mg] is the amount of impermeable imidazoles.
The amount of impermeable imidazoles through the membrane of R_i=0 could be obtained from KM=R_a· C_n · V₀, where R_a [-] is the apparent rejection of imidazoles.
It is expected that the equations obtained above are applicable to ultrafiltration of a solution in which a microsolute binds irreversibly to a high molecular weight solute.