The texture of maize seeds, which is dependent on the proportions of hard and soft endosperm, is an important trait that influences various end-uses of maize such as starch yield and the power required for both wet and dry milling. Maize kernels are divided into general classes based on texture: flint, popcorn, flour, dent, and sweet. Softer textured dent maize is preferred for wet-milling, which is the largest non-feed user of maize in the United States. In the US, most maize starch extraction is done by a wet milling process. The development of softer maize hybrids with higher starch extractability would therefore be of value to maize processors.
Researchers at the Montana State University and Washington State University developed maize varieties with altered maize seed texture and wet milling yield by endosperm-specific expression of puroindoline genes (Pina and Pinb) from wheat. The tryptophan-rich regions in the PIN proteins serve as a non-stick agent enabling PINs to bind to starch granule surface lipids.
Textural analysis of the maize seeds indicated that the expression of PINs decreased adhesion between starch and protein matrix and reduced maize grain hardness significantly. The researchers also found that starch yield was increased by 4.86% on average without negatively impacting starch purity.
The paper published by the Plant Biotechnology Journal is available at http://dx.doi.org/10.1111/j.1467-7652.2009.00438.x