Effect of copper and iron fortifications on rheological properties of water-in-oil spreads containing κ-carrageenan

Work was undertaken to investigate the effect of copper and Iron fortification (up to 15 mM) on the rheology and firmness of water-in-oil spreads (60 % fat) produced using 0.25 % κ-carrageenan. The apparent viscosity of the aqueous phase (10.9 mPa s) was significantly reduced by fortification with 15mM copper (4 mPa s) or iron (3.2 mPa s) at 60°C. However, inclusion of minerals resulted in gelation of the aqueous phase at 6°C and increased the melting temperature on reheating. Copper addition at 7.5mM levels formed the strongest gel (storage modulus of 7.6 kPa) and increased the melting temperature of the aqueous phase from 21°C (control) to 49°C. At the higher levels of addition (7.5-15 mM), the minerals impaired the firmness at 6°C and rheology of the spreads on heating with copper inclusion resulting in the greatest reductions. The rheological and textural effects observed on fortification were attributed to the pro-oxidant effects of the metallic cations on the oil-phase of the spreads.