Abstract
Understanding aggregation in food protein systems is essential to control processes ranging from the stabilization of colloidal dispersions to the formation of macroscopic gels. Patatin rich potato protein isolates (PPI) have promising techno-functionality as alternatives to established proteins from egg white or milk. In this work, the influence of pH and temperature on the kinetics of PPI denaturation and aggregation was investigated as an option for targeted functionalization. At a slightly acidic pH, rates of denaturation and aggregation of the globular patatin in PPI were fast. These aggregates were shown to possess a low amount of disulfide bonds and a high amount of exposed hydrophobic amino acids (S0). Gradually increasing the pH slowed down the rate of denaturation and aggregation and alkaline pH levels led to an increased formation of disulfide bonds within these aggregates, whereas S0 was reduced. Aggregation below denaturation temperature (Td) favored aggregation driven by disulfide bridge formation. Aggregation above Td led to fast unfolding, and initial aggregation was less determined by disulfide bridge formation. Inter-molecular disulfide formation occurred during extended heating times. Blocking different protein interactions revealed that the formation of disulfide bond linked aggregation is preceded by the formation of non-covalent bonds. Overall, the results help to control the kinetics, morphology, and interactions of potato protein aggregation for potential applications in food systems.
Highlights
Published: 8 April 2021Protein aggregates can be used as functional ingredients in different food formulations [1]
The most important covalent bonds are disulfide bonds, which can be formed by the reaction of two thiol-groups or by the reaction of a thiol group with an intramolecular disulfide bond leading to a chain reaction, the thiol-disulfide interchange [2]
This conversion factor was already used by other researchers for potato protein isolates (PPI) [16,24] The patatin content, measured by the relative band intensity (RBI) in a reducing sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE), was found to be around 60% RBI
Summary
Protein aggregates can be used as functional ingredients in different food formulations [1]. The formation of these aggregates can be induced by the unfolding of the globular molecular structure at elevated temperatures. Proteins lose their tertiary and secondary structure, and reactive amino-acid groups get exposed, and the proteins can interact with each other to form aggregates. These interactions can be of covalent or non-covalent nature. Non-covalent interactions comprise hydrophobic interactions and electrostatic interactions. These interactions are weaker than disulfide bonds. The type of protein interaction influences the morphology of the aggregates and is pH and ionic-strength dependent [3]
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