Influence of high pressure on interactions of 11S globulin Vicia faba with ι-carrageenan in bulk solution and at interfaces

The influence of L-carrageenan (L-CAR) on the solution, interfacial and emulsifying properties of 11S globulin Vicia faba at low ionic strength and pH 8 has been investigated before and after high-pressure processing at 200 MPa for 70 min. The total calorimetric enthalpy (DeltaH) and size exclusion chromatography studies for the: pure 11S indicate that there is subunit dissociation and extensive aggregation of the protein during or following treatment. Under the same treatment conditions, 1-anilinonaphthalene-8-sulphonate (ANS) data has shown increased protein surface hydrophobicity. Pressure treatment of 11S gives much lower values of the surface tension, and apparent surface shear rheology experiments show that the molecules in the film adsorbed from the pressurised 11S are much more strongly interacting than those adsorbed from the native 11S. However, emulsions prepared with pressure processed 11S give substantially bigger droplets than those made with the untreated pure protein. Addition of iota -CAR to 11S reduces the denaturation temperature (T(m)), the DeltaH value, and protein surface hydrophobicity. Size exclusion chromatography at low ionic Strength is indicative of complex formation. Tension measurements at the air-water interface are also consistent with the presence of a complex. Emulsions made with the simple 1:0.33 mixture of 11S + iota -CAR give emulsions with smaller droplets and pressure processing of the biopolymer mixture leads to emulsions with even smaller droplets. The presence of iota -CAR at low ionic strength appears to protect the globulin against pressure-induced aggregation. (C) 2000 Elsevier Science Ltd. All rights reserved.