Study on the Preparation of Transparent Whey Protein Isolate at Isoelectric Point by Maillard Reaction
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Abstract:
Whey protein isolate (WPI) was used as the raw material for this study. The solubility, emulsifying activity index (EAI), emulsifying stability index (ESI), thermal stability, and other functional properties of WPI and its Maillard reaction products (MRPs) around the isoelectric point were studied, to lay a basis for their application in transparent-type beverages. The MRPs of WPI and L-lactose were formed by the reaction between WPI and L-lactose at a relative humidity of 79% and a temperature of 70 ℃. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) results suggested that the molecular weights of α-lactalbumin and β-lactoglobulin were increased by about 2~3 ku. The o-phthalaldehyde (OPA) results showed that the free amino acid content in WPI was reduced by about 35% after the Maillard reaction for 12 h. The solubility, EAI, ESI, and thermal stability were enhanced remarkably (EAI and ESI were 0.35 m2/g and 20 min, respectively, which were 1.5 times and 1.7 times as much as those of WPI). Zeta-potential and particle size analysis indicated that the enhancement of the solubility and thermal stability of the MRPs was induced by the steric hindrance of the saccharides introduced to the protein surface, instead of the electrostatic interactions.
