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 affec ted the thermal stability of both beta-conglycinin (7S) and glycinin ( 11S) storage proteins when examined by differential scanning calorimet ry used to monitor both denaturation temperature (T(d)) and enthalpy ( DELTAH). As salt ionic strength (mu) increased, the moisture in the hy drated beans decreased. When beans were hydrated with water only, heat stability of both storage proteins increased with moisture decrease. No change in DELTAH was observed. Since all salt treatments showed sim ilar decreases in moisture with increased mu no adjustment for moistur e effects was needed. Except for Na2CO3 all salt hydrations gave incre ased protein thermal stability. Ranking of salts according to ability to stabilize soy storage proteins at mu = 1.2 were: for beta-conglycin in, NaH2PO4 > NaC2H3O2 > NaCl > Na2S2O5 > Na2SO3 > Na2SO4 > Na2CO3 > C aCl2; for glycinin, NaC2H3O2 > NaH2PO4 > NaCl > Na2SO4 > Na2S2O5 > Na2 SO3 > CaCl2 > Na2CO3. The DELTAH's of the first two salts in the 7S se ries and the first three in the 11S series were significantly higher t han either moisture alone or all other salt treatments. When salt trea tment data were evaluated on a molar concentration rather than mu, the neutral salt hydrations followed the lyotropic series for stabilizati on of proteins. Responses of both beta-conglycinin and glycinin differ ed slightly. These differences were attributed to differences in elect rostatic profile and response to water availability for these proteins .