Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/20/2006
Publication Date: 5/23/2006
Citation: Lee, K., Bean, S., Alavi, S., Herrman, T.J. 2006. The physical and biochemical determinants of maize hardness and extrudate properties. Journal of Agricultural and Food Chemistry. 54:4260-4269. Interpretive Summary: For people that cannot eat wheat-based food products, like persons with celiac disease, high quality cereal grain food products are limited. The production of wheat-free cereal food products is challenging as only wheat is capable of being made into a visco-elastic dough. One technique available for producing wheat free food products, is extrusion processing. Extrusion uses a combination of high temperature, shear, and pressure to produce food products; this is commonly used to produce snack products for example. Cereal grains such as maize and sorghum can be extrusion processed into wheat-free food products relatively easily. However, the biochemical factors governing extrusion processing of non-wheat cereal grains is not completely understood. This study investigates the relationships between maize kernel hardness and protein properties to extrudate quality as a model to understanding the extrusion of non-wheat cereal grains. Such information will be useful in selecting maize and sorghum samples for extrusion processing and to improve the quality of wheat-free extruded products.
Technical Abstract: The biochemical determinants of maize kernel hardness and their roles during extrusion processing were explored in an attempt to improve maize hybrid selection criteria for breeders, producers, and end-users. Physical maize kernel properties were evaluated using a tangential abrasion dehulling device, Stenvert grinding test, pycnometer density, test weight, and spectral analysis to characterize grain hardness. These methods were significantly correlated with one another and also with the endosperm protein and zein contents. Maize hybrids were clustered into groups based on hardness-associated properties by using multivariate statistical techniques. A representative hybrid from each cluster was selected for extrusion experiments. Maize hybrids representing each hardness cluster showed unique RP-HPLC chromatograms depending on endosperm texture. Maize kernel hardness significantly affected both the physical and textural properties of extrudates, including expansion ratio (ER), specific mechanical energy (SME), water absorption index (WAI), water solubility index (WSI), and oil absorption capacity (OAC). Extrudates from harder grits had lower protein solubility and greater protein aggregation after extrusion. Proteins in extrudates made from softer grits were more easily dissociated and degraded into smaller molecules as screw speed increased, which resulted in higher protein solubility and greater WAI, WSI, and OAC.