Technical note: Quantification of zeins from corn, high-moisture corn, and corn silage using a turbidimetric method: Comparative efficiencies of isopropyl and tert-butyl alcohols
Zeins are corn endosperm storage proteins that encapsulate starch granules into a protein matrix, which can act as a barrier to starch accessibility and digestion. Laboratory methods to quantify zein are seldom used because they are considered arduous and time-consuming. A recently published rapid turbidimetric method (mTM) was reinvestigated by changing the solution originally used for the zein solubilization step. In particular, the aim was to explore whether, and to what extent, the use of tert-butyl alcohol (t-BuOH-mTM) in lieu of isopropyl alcohol (i-PrOH-mTM) was able to improve the quantification of zeins from dry corn, high-moisture corn, and corn silage samples. The nature of the alcohol influenced the zein extraction values, and t-BuOH-mTM gave higher zein values in corn (3.6 vs. 3.3g/100g of dry matter) and corn silage samples (1.2 vs. 0.9g/100g of dry matter) compared with i-PrOH-mTM. In contrast, similar zein extraction values were obtained for high-moisture corn (2.1 vs. 1.9g/100g of dry matter, respectively). Sodium dodecyl sulfate-PAGE analysis revealed no contamination by nonzein proteins with the use of tert-butyl alcohol. Overall, these findings indicated that tert-butyl alcohol has a greater ability to solubilize zein compared with isopropyl alcohol and thus the t-BuOH-mTM allowed greater extraction of zeins. Considering the growing interest of animal nutritionists in zein proteins, such results should provide useful information for routine laboratory analysis.
