Technical note: A modified method to quantify prolamin proteins in dry and high-moisture corn

Abstract

Numerous studies have evaluated laboratory methods to quantify prolamin proteins in dry corn; however, the utility of methods to quantify functional prolamins, which impede starch digestibility, in high-moisture corn (HMC) is less defined. As a result, a common rapid turbidimetric (rTM) laboratory procedure was modified (rapid Bradford method, rBM), extracting buffer-soluble proteins before prolamin solubilization in an effort to better quantify functional prolamins in HMC. Twenty samples of dry and HMC were evaluated by rTM and rBM procedures. Prolamin concentration in dry corn, as estimated by rTM or rBM methods, ranged from 6.12 to 2.20g/100 g of DM or 5.46 to 2.41g/100 g of DM, respectively. Dry corn mean prolamin concentrations, as estimated by rTM or rBM methods, were similar at 3.65 or 3.66g/100 g of DM. Prolamin concentration in HMC, as estimated by rTM, ranged from 4.99 to 3.24g/100 g of DM, with a mean prolamin concentration of 4.19g/100 g of DM, but estimation of prolamins in HMC by the rBM method resulted in lower mean (4.19 vs. 3.24g/100 g of DM) prolamin concentration. Prolamin concentration in dry and HMC measured by rTM was negatively related to peak absolute rates (PAR; mL/0.1 g of DM) of in vitro gas production. However, relationships between rTM prolamin concentration and PAR were not homogeneous and were different between dry and HMC. Prolamin proteins as determined by rBM were likewise negatively related to PAR, but corn type did not influence rBM prolamin concentration by PAR relationships. Data suggest that the rBM method defined more similar functional prolamin proteins, which impede starch degradability, in dry and HMC.