Compared with floury or high-moisture
corns, dry corn with a greater percentage of vitreous endosperm has been demonstrated to be negatively related to
starch digestibility and milk yield of lactating dairy cows.
Starch granules in corn are encapsulated by hydrophobic
prolamin proteins that are innately insoluble in the rumen environment. Corn
prolamin proteins are named
zein, and laboratory methods to quantify
zein exist but are seldom employed in ruminant nutrition because of their arduous nature. In this study, advances in cereal chemistry were combined with rapid turbidimetric methods yielding a modified turbidimetric
zein method (mTZM) to quantify
zein in whole corn. Ten dry
corns containing unique endosperms were evaluated using the mTZM.
Corns with flint, dent, floury, or opaque endosperms were found to contain 19.3, 11.3, 5.8, and 4.9 g of
zein/100 g of
starch, respectively. The ability of mTZM to differentiate corn endosperm types as defined by least significant difference was 2.6 g of
zein/100 g of
starch. Ten high-moisture
corns of varying moisture content were also evaluated using the mTZM.
Zein content of high-moisture
corns as defined by mTZM ranged from 8.3 to 2.8 g of
zein/100 g of
starch with a least significant difference of 1.2 g of
zein/100 g of
starch. The mTZM determined that
zein contents of high-moisture, floury, and opaque
corns were markedly less than those of flint and dent dry
corns, indicating that mTZM has the ability to quantify
starch granule encapsulation by hydrophobic
prolamin proteins in whole corn.