29C-12 |
Effect of mechanical energy input and plasticizers on the physical properties of protein-starch extrudates |
C. I. MORARU, M. Gropper, I. Deo, and J. L. Kokini. Dept. of Food Science, Rutgers, The State Univ. of New Jersey, 65 Dudley Rd., New Brunswick, NJ 08901-8520 Mixtures of proteins and starch are frequently used to produce extruded foods. The palatability of such foods depends on their structure and mechanical properties, which are the result of both extrusion conditions and ingredients used in the formulation. This work focuses on understanding the influence of mechanical energy input during extrusion and the addition of plasticizers (water and glycerol) on the properties of protein-starch extrudates. Protein-starch extrudates were produced at different levels of specific mechanical energy (SME) and glycerol, and then stored under controlled environmental conditions. Samples were analyzed for glass transition, mechanical properties, cell size distribution, and microstructure. Increased SME input resulted in extrudates with a higher degree of expansion, larger cells, and a wide cell size distribution. The addition of glycerol decreased the viscosity of the extruded melt, and thus affected expansion. Increasing glycerol content up to 7.5% determined an increase in extrudate expansion, while at higher glycerol concentration the expanded structure started to collapse. Young’s modulus decreased slightly with increased expansion and increased moisture content. At low aw the saw-tooth profile of the force – deformation curves indicated a brittle product, while as aw increased the curves smoothened, since the material became more plastic than brittle. Correlations between mechanical properties and extrudate structure were found. The glass transition temperature of the extrudates did not change with SME, but was significantly depressed by water and glycerol. This work represents a good basis for the understanding of the relationship between processing and functionality for protein-starch extrudates, which can be further used to design products of desired structure and texture.
Session 29C, Food Engineering: Rheology and texture
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