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

The influence of L-carrageenan (L-CAR) on the solution, interfacial and emu lsifying properties of 11S globulin Vicia faba at low ionic strength and pH 8 has been investigated before and after high-pressure processing at 200 M Pa for 70 min. The total calorimetric enthalpy (DeltaH) and size exclusion chromatography studies for the: pure 11S indicate that there is subunit dis sociation and extensive aggregation of the protein during or following trea tment. Under the same treatment conditions, 1-anilinonaphthalene-8-sulphona te (ANS) data has shown increased protein surface hydrophobicity. Pressure treatment of 11S gives much lower values of the surface tension, and appare nt surface shear rheology experiments show that the molecules in the film a dsorbed from the pressurised 11S are much more strongly interacting than th ose 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 denaturati on temperature (T-m), the DeltaH value, and protein surface hydrophobicity. Size exclusion chromatography at low ionic Strength is indicative of compl ex formation. Tension measurements at the air-water interface are also cons istent with the presence of a complex. Emulsions made with the simple 1:0.3 3 mixture of 11S + iota -CAR give emulsions with smaller droplets and press ure processing of the biopolymer mixture leads to emulsions with even small er droplets. The presence of iota -CAR at low ionic strength appears to pro tect the globulin against pressure-induced aggregation. (C) 2000 Elsevier S cience Ltd. All rights reserved.