Rheological characteristics of high pressure treated dispersions of waxy maize starch in skim milk

The effects of high pressure treatment on the rheology of waxy maize starch-skim milk dispersions were investigated. Starch was gelatinised by heating dispersions at 90°C, before high pressure treatment. Measurements of skim milk light reflectance indicated that this pre-treatment significantly increased milk protein particle size and hence also their effective volume fraction, Φ, compared to unheated pressurized milk. In oscillation tests to assess viscoelasticity, starch-skim milk dispersions, high pressure treated at 200, 400 or 600 MPa, had significantly increased storage modulus, G' and decreased loss tangent, tan δ, indicating increased elastic contribution to the rheology, consistent with increased effective Φ. Measurements from strain sweep tests showed that high pressure treatment significantly increased the stress required to cause the starch-skim milk dispersions to flow. Measurements of consistency index, K and flow behaviour index, n in continuous shear showed that high pressure treatment significantly increased K, suggesting increased flocculation and significantly decreased n, indicating increased shear thinning of the starch-skim milk dispersions. Such changes would potentially allow products having a specified rheological performance to be prepared using less starch.