The effect of salt ion on the freeze-thaw stability and digestibility of the lipophilic protein-hydroxypropyl methylcellulose emulsion

The effect of salt ion on the freeze-thaw stability of protein-polysaccharide emulsions remains controversial. In this study, we investigated the effects of two salts, CaCl2 and NaCl, on the freeze-thaw stability and digestion characteristics of soybean lipoprotein-hydroxypropyl methyl cellulose (LP-HPMC) emulsions. Analysis of the particle size, protein adsorption, and zeta-potential showed that addition of salt ions led to an increased extent of interfacial protein adsorption. The best oxidation stability and emulsification were observed when 100 mM salt was added. Analyses of the microstructure, creaming index, oiling off, and coalescence degree revealed that the presence of salt ions significantly improved the freeze-thaw stability of the emulsion, and addition of monovalent ions of NaCl to the emulsion to showed better interface protein crack resistance performance during the freezethaw cycle, low oiling off (8.75 +/- 0.5 %), and coalescence degree (43.67 +/- 2.5 %) compared to adding divalent ions of CaCl2. Moreover, Fourier infrared spectroscopy data revealed that the alpha-helix content in the secondary structure of LP was closely related to the freeze-thaw stability of the emulsion. Addition of salt ions delayed the release rate of internal oils in the LP-HPMC emulsion. These results provide a foundation of producing new emulsified foods with favorable freeze-thaw stability.