Thermal Stability of Soy Storage Proteins in Cracked Beans Hydrated with a Variety of Salts

Abstract

Various salt solutions used to hydrate full-fat cracked soybeans affected the thermal stability of both β-conglycinin (7S) and glycinin (11S) storage proteins when examined by differential scanning calorimetry used to monitor both denaturation temperature (Td) and enthalpy (ΔH). As salt ionic strength (μ) increased, the moisture in the hydrated beans decreased. When beans were hydrated with water only, heat stability of both storage proteins increased with moisture decrease. No change in ΔH was observed. Since all salt treatments showed similar decreases in moisture with increased μ no adjustment for moisture effects was needed. Except for Na2CO3 all salt hydrations gave increased protein thermal stability. Ranking of salts according to ability to stabilize soy storage proteins at μ = 1.2 were: for β-conglycinin, NaH2PO4 > NaC2H3O2 > NaCl > Na2S2O5 > Na2SO3 > Na2SO4 > Na2CO3 > CaCl2; for glycinin, NaC2H3O2 > NaH2PO4 > NaCl > Na2SO4 > Na2S2O5 > Na2SO3 > CaCl2 > Na2CO3. The ΔH's of the first two salts in the 7S series and the first three in the 11S series were significantly higher than either moisture alone or all other salt treatments. When salt treatment data were evaluated on a molar concentration rather than μ, the neutral salt hydrations followed the lyotropic series for stabilization of proteins. Responses of both β-conglycinin and glycinin differed slightly. These differences were attributed to differences in electrostatic profile and response to water availability for these proteins.