Submitted to: Journal of Agriculture and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2009
Publication Date: 9/17/2009
Citation: Woods, K.K., Sessa, D.J., Selling, G.W. 2009. Determination of zein purity by FTIR and circular dichroism. Journal of Agriculture and Food Chemistry. xx.
Interpretive Summary: This research demonstrates that the relative purity of zein samples can be determined using Fourier transform infrared spectroscopy (FTIR). Zein, the dominant protein in corn, is a potentially large co-product of the ethanol production industry. The current focus on bioethanol production has created renewed attention towards zein as a high value co-product. Interest in biodegradable plastics and films has increased significantly due to environmental concerns and zein is an attractive component of such products, due to its excellent film forming properties and ability to be melt-processed. Because of its ability to form a film, zein has been used to coat pharmaceutical tablets and food products such as nuts and candies. While certain applications will be able to utilize commercially available zein, other industries will benefit from a highly purified zein, including the pharmaceutical and food industries. The protein content and purity of commercially available zein can vary widely depending on the source and production method. FTIR, which yields information on protein structure, was used as a quick, inexpensive method to differentiate zein samples of varying levels of purity. Several commercially available zein samples were studied, along with samples that had been further purified. Analysis of the FTIR data showed differences in the commercial and purified samples, which is indicative of a change in structure in the purified proteins. This was attributed to the removal of denatured and contaminant proteins during the purification process. The ratio of two peaks within the same spectrum also changed significantly after purification. This work confirms that FTIR can be effectively used as a simple, inexpensive method to determine zein purity. This straightforward test will help zein producers and customers quickly establish the relative purity of a zein sample.
Technical Abstract: Fourier transform infrared spectroscopy (FTIR) was used as a simple, inexpensive method to determine the purity of zein samples. Several commercially available zein samples, along with those purified using a column chromatography method, were analyzed. Consistent differences were found between the FTIR spectra of purified and commercial zein, with the most obvious differences evident in the ratio of the amide I (1650 cm-1) peak to the C-N stretch at 1445 cm-1, along with the ratio of amide I to the amide III peak at 1240 cm-1. Another significant fingerprint is the ratio of the two dominant peaks in the amide II region (1530 and 1515 cm-1). The ratio of the peaks in this region is strongly dependent on the purity of the zein sample. Circular dichroism results validated the FTIR results, showing increased '-helical content in the purified zein samples. This report illustrates that Fourier transform infrared spectroscopy can be used to differentiate between zeins of different purity.