Functionality of native and denatured cashew nut kernel protein isolates at isoelectric pH as a function of salt concentration

The reduced solubility of proteins near the isoelectric pH limits their use in food formulations whose pH lies in the range 5.0-6.0 because of poor functionality. In the present study, the effect of salt on the functionality of native and denatured cashew nut kernel protein isolates at the isoelectric pH was investigated. Both isolates showed improvement in their functional properties, but the improvement was greater for the denatured protein isolate. The solubilities of denatured and native protein isolates at the isoelectric pH increased from 26.4 g l^-1 and 64 g l^-1, respectively, without salt to maxima of 363 and 308 g l^-1, respectively, at 0.75 M salt concentration. The water binding capacity of the isolates increased with increase in NaCl concentration from 1.70 ml g^-1 to 1.77, 1.82, 1.92 and 2.2 ml g^-1 for denatured protein isolate and from 1.45 ml g^-1 to 1.65, 1.69, 1.82 and 1.97 ml g^-1 for native protein isolate at 0.25, 0.50, 0.75 and 1.0 M salt concentrations, respectively. When the properties of the isolates in 0.75 M NaCl solutions were compared with those in salt-free water there were 15% and 116% increases in emulsifying capacity, 40-fold and 45-fold increases in emulsifying activity and 4.6-fold and 40-fold increases in emulsion stability for native and denatured protein isolates, respectively, whilst the corresponding foaming capacities increased from 4 to 5.5 and 0 to 8.9 ml g^-1 protein. Statistically, no difference in the foaming capacity of either of the isolates was observed above 0.5 M NaCl. The foam stability also exhibited similar behaviour.