A practical method for extending the biuret assay to protein determination of corn-based products

- A modified biuret method was developed for corn-based products in this study.
- The proposed and Kjeldahl methods mostly showed good agreement.
- The proposed method enhanced the accuracy of prediction on zein with BSA as standard.
- The method improved the protein solubility for the thermal processed samples.

A modified biuret method suitable for protein determination of corn-based products was developed by introducing a combination of an alkaline reagent with sodium dodecyl sulfate (reagent A) and heat treatments. The method was tested on seven corn-based samples. The results showed mostly good agreement (P > 0.05) as compared to the Kjeldahl values. The proposed method was found to enhance the accuracy of prediction on zein content using bovine serum albumin as standard. Reagent A and sample treatment were proved to effectively improve protein solubilization for the thermally-dried corn-based products, e.g. corn gluten meal. The absorbance was stable for at least 1-h. Moreover, the whole measurement of protein content only needs 15-20 min more than the traditional biuret assay, and can be performed in batches. The findings suggest that the proposed method could be a timesaving alternative for routine protein analyses in corn processing factories.