Effect of Water Addition on the Microstructure, Lipid Incorporation, and Lipid Oxidation of Corn Extrudates

Lipid oxidation is a major cause of quality deterioration during the production and storage of fat containing extrudates, which is a result of the high‐specific surface of the matrix with increased oxygen access. During the extrusion process, corn starch gelatinizes and forms an amorphous matrix that incorporates lipids. To estimate the effect of incorporation on oxidative stability of lipids a model extrudate of corn meal, water, and a mixture of sunflower‐ and rapeseed oil is developed. The extrusion process is conducted on a laboratory twin screw extruder with varying moisture contents, affecting in turn process parameters such as the specific mechanical energy. A fractionated extraction protocol serves to obtain surface lipids, inner surface lipids, and lipids incorporated in the starch matrix. Oxidation is analyzed at different points in time during storage at 40 °C in the three lipid fractions. Furthermore, the microstructure of the extrudates is analyzed by computerized microtomography (µCT). The results show that increasing fat inclusion decreases the rate of lipid oxidation. A compact structure with low expansion is achieved by high‐water contents. These extrudates in turn exhibit an increased amount of incorporated lipids less susceptible to oxidation. Practical Applications: The presented work investigates extrusion technology, widely used by industry. Lipid oxidation covers an important topic, as stable products are necessary in order to avoid waste. The stabilization of lipids in extrudates against oxidation is therefore of great interest. With the model extrudate used in this study and a newly developed lipid fraction extraction protocol, it is possible to define the regions in terms of oxidation status. The results of this study provide the basis for products with an enhanced stability against lipid oxidation because of their structural characteristics considering the principles of green chemistry. The aim of the present study is to investigate the relationship between the microstructure and lipid oxidation in corn extrudates. Therefore, a new fractionated lipid extraction protocol is developed. Increasing feed water extrudates expand less and thicker cell walls are formed. Increasing the degree of lipid inclusion results in lower degree of oxidation.