Foaming properties of total zein, total kafirin and pre-gelatinized maize starch blends at alkaline pH

The effect of 0.1 M NaOH as a solvent and blending with pre-gelatinized maize starch on the foaming properties of laboratory extracted total zein and total kafirin were determined. Both total zein and total kafirin in 0.1 M NaOH were found to have higher foaming capacity (up to 118% foam volume increase) compared to their non-foaming (0% foam volume increase) properties in water. Blending with pre-gelatinized maize starch reduced the foam volume but increased the foam stability to more than 24 h. Total zein and total zein-pre-gelatinized starch blends had relatively higher foaming capacity than total kafirin and total kafirin-pre-gelatinized starch blends probably because zein was more surface active (more negative zeta potential value) than kafirin. However, total zein and total zein-pre-gelatinized starch blend foams were less stable with time than total kafirin and total kafirin-pre-gelatinized starch blend foams. This is possible because total kafirin, having higher amount of cysteine, can have higher degree of cross linking than total zein to form stronger lamellae. The foam microstructure, bubble size and foam film thickness are related to the foaming capacity and foam stability. Larger bubble size corresponded with higher foaming capacity but smaller bubbles and thicker film lamellae corresponded with lower foaming capacity and improved stability. The improved foam formation of total zein and total kafirin in 0.1 M NaOH solution compared to water could be due to the higher degree of deamidation in 0.1 M NaOH, which in turn would make them more surface-active and could increase their solubility/dispersibility.