Influence of physicochemical properties of Croatian maize hybrids on quality of extrusion cooking

- Chemical composition and appearance of starch granules of Croatian maize hybrids.
- Expansion index correlated with resistant starch (RS) and amylose content in maize.
- RS in the selected hybrids did not correlate with RS in the corresponding extrudates.

Extrusion cooking of maize grain is widely used in the food and feed industries. While numerous studies have sought to optimise process conditions, few studies have examined the influence of the physical and chemical properties of the raw material. In this study, several commercial maize hybrids of Croatian origin were subjected to extrusion cooking under the same conditions in a laboratory single-screw extruder. The hybrids showed the following ranges for physicochemical characteristics (all in dry matter): total starch, 679-750 g/kg; crude protein, 80.4-111.2 g/kg; crude fat, 36.3-42.8 g/kg; resistant starch, 1.63-3.03%; amylose content, 23.8-27.1% of total starch; average equivalent diameter, 11.1-12.9 μm; and circularity of starch granules, 0.90-0.92. The nutritional value of the various extrudates was assessed using resistant starch content, which varied from 0.28% to 0.40% of dry matter. Quality of the extrudates was assessed based on the expansion index, which ranged from 2.6 to 4.7. This index was higher for hybrids showing lower levels of resistant starch, amylose and crude protein, as well as larger and more spherical starch granules. These results show that selecting hybrids for extrusion can lead to more desirable product attributes.