Water Vapor Sorption by Soy Proteins, Proteinates and Hydrolysates

155 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1981.Sorption data were obtained using the Proximity Equilibration Cell to equilibrate a sample to the water activity (a(,w)) of a saturated salt slush or by equilibrating a calibrated reference material to the a(,w) of a sample. Soy isolate dispersed in water, heated for 10 and 30 minutes at 100(DEGREES)C or 121(DEGREES)C and then freeze dried showed no statistically significant changes in the amount of water sorbed. Differences between isolates dried with a freeze drier, a spray drier or a drum drier were also not significant. Thus, water sorption by soy isolate is independent of heat induced structural changes. Soy protein isolates prepared by precipitation at different pH and subsequently neutralized showed significantly different amounts of water sorbed. Increased ash content was thought to be responsible for the increased water sorption. Isoelectric isolate was dispersed in water and adjusted to pH levels between 4.5 and 11 with NaOH or KOH. The amount of water sorbed was a linear function of the amount of alkali ions added. This indicated the increase in sorption with pH was due to the added ions and not a pH effect. Both sodium and potassium ions were found to sorb less water in the presence of protein than they did alone. This was attributed to ionic interactions that reduce the ability of an ion to sorb water. Enzyme hydrolysis increased water sorption. Each hydrolysed peptide bond increased water sorption by the same amount. The total amount of water sorbed by a hydrolysate was the sum of the water sorbed by the substrate, by the added Na ions, and by the hydrolysed peptide bonds. NaCl was found to adsorb less water in the presence of soy isolate than it did alone. This was attributed to salt binding by the isolate. An equation was developed to calculate the amount of salt bound at various a(,w) and salt levels. Salt binding was a function of salt to isolate ratio and the amount of water added to the mixture during preparation. Salt binding was independent of a(,w) between 0.75 and 0.91 and of temperature between 7 and 30(DEGREES)C.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD