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

Various salt solutions used to hydrate full-fat cracked soybeans affected the thermal stability of both f)-conglycinin (75) and glycinin (115) storage proteins when examined by differential scanning calorimetry used to monitor both denaturation temperature (Td) and enthalpy (LiH). As salt ionic strength (fL) 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 LiH was observed. Since all salt treatments showed similar decreases in moisture with increased fL no adjustment for moisture effects was needed. Except for Na2C03 all salt hydrations gave increased protein thermal stability. Ranking of salts according to ability to stabilize soy storage proteins at fL = 1.2 were:for f)-conglycinin, NaH2P04 > NaC2H30 2 > NaCI > Na25205 > Na2503 > Na2504 > Na2C03 > CaCl2;for glycinin, NaC2H30 2 > NaH2P04 > NaCI > Na2504 > Na25205 > Na2503 > CaCl2 > Na2C03' The LiH's of the first two salts in the 75 series and the first three in the 115 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 fL, the neutral salt hydrations followed the lyotropic series for stabilization ofproteins. Responses of both f)-conglycinin and glycinin differed slightly. These differences were attributed to differences in electrostatic profile and response to water availability for these proteins.