[Study on mechanism of beer yeast adsorbing copper ion by spectroscopy]

Copper ions adsorption by beer yeast was studied by AAS, FTIR, SEM/EDS etc. The quantity of copper biosorption by NaOH-treated yeast and acetone-treated yeast increased significantly, while the esterification of carboxylate functionalities and the methylation of amino group presented in the cell walls of yeast resulted in a marked decrease in copper adsorption. These results show that amino and carboxylate groups in yeast cell wall play a great role in binding copper. According to IR spectra, the dominating bands near 1 652, 1 539 and 1 237 cm(-1) are assigned to amide I , amide II and amide IlI, the characteristic IR absorption of protein which could be one of the significant components of cell walls. The peak near 1 456 cm(-1) is attributable to the bending stretching of CH2- and CH3-. The changes in the spectra of the copper-exposed yeast biomass were in the stretch of hydroxyl groups or amino groups, which shifted from 3 392 to 3 404 cm' , and in the symmetrical stretch of carboxylate groups, which shifted from 1 405 to 1 383 cm(-1). The components and structure of the exposed-copper biomass remain intact. SEM/EDS analysis shows that the main elements of beer yeast are carbon, oxygen, and magnesium, while the surface of yeast is rough, and the copper-loaded yeast only binds little copper.