Extraction and structure-function properties of lentil protein, and its applications as an egg replacer in baked goods

• Author / Creator

  Jarpa, Marcela A

• Consumption of lentils relates to several health benefits. Lentils are also a good protein source that is waiting for exploitation of their full potential. This is largely due to the unknown relationship between its molecular structure and functionalities and the lack of knowledge of the impact of the extraction and environmental conditions on those properties. Therefore, the objective of this thesis research was to achieve a more complete knowledge of the lentil proteins and use this knowledge in the potential development of value-added food products. The first goals were to develop a protein extraction protocol to prepare a lentil protein isolate or concentrate, and to understand lentil protein functionalities. The optimized conditions for protein extraction were determined to be pH 9.0 with a solid/solvent ratio of 1:10 (w:v). SE-HPLC and SDS-PAGE results showed that globulins were the major proteins in the protein concentrate. Environmental pH influenced protein solubility and surface charge, and subsequently the gelling and foaming properties. Excellent foaming capacity was identified for lentil proteins, which motived us to study their air-water interfacial behavior. Once the lentil legumin-like protein fraction was isolated, its structure and functional properties were characterized in detail. This protein was capable of forming long-life foams at pH 5.0 and 7.0. The latter were especially stable because the combination of the α-helix secondary structure, medium molecular size, and balance between solubility/hydrophobicity contributed to building strong protein networks at the interface. At pH 5.0, the protein formed a dense and thick network composed of randomly aggregated protein particles at the interface. At pH 3.0, the unordered structure increased intra-protein flexibility, producing a less compact interface that reduces the elasticity modulus with time and reduced foam resistance against collapse. Polysaccharides were then added to the lentil legumin-like protein system to investigate the feasibility of further improving foaming properties. When the protein was mixed with guar gum, xanthan gum, and pectin, foam stability (FS) was remarkably increased at pH 5.0. This stability was closely related to the adsorption of aggregates on to the interface to form strong interfacial networks, avoiding coalescence and coarsening of the foams. Aggregates also plugged the junctions of the Plateau borders, thus slowed down the drainage by a jamming effect. Similarly, the polysaccharides improved the FS at pH 3.0, in which associative interactions dominated and a coacervation phenomenon was observed. The coacervates may have stabilized the foams against collapse because they increased the foam viscosity and formed a coacervate network that might have a gel-like network behavior. At pH 7.0, the FS of the mixtures was poor, reducing the mean life of the original foam. Thermodynamic incompatibility phenomena at pH 7.0 produced a phase separation of polymers in the bulk and at the interface. Phase separation induced a disruption of this interfacial membrane making it weaker and easier to break, thus reducing FS. This phenomenon might be a result of a partial displacement of the protein by the polysaccharides through an orogenic mechanism. Finally, the feasibility of using lentil protein to partially replace egg white in angel food cake and completely replace egg/milk protein in muffin was evaluated in terms of physical properties and sensory analysis. Using lentil protein did not change the final volume of the cakes, but it contributed to holding the crumb structure after baking by the formation of an entangled network structure that did not affect the dough network formation. Sensory evaluation by a consumer panel showed that the use of lentil protein increased compressive stress, chewiness, and density of the cakes. Yet, angel food cake formulation with 50% replacement had a “nutty”flavor and a higher moistness that was appreciated by the consumers. In fact, lentil protein showed a strong water holding capacity that reduced the baking loss in the cakes. Additionally, a 100% replacement of egg and milk protein by lentil protein produced a muffin that was preferred by the consumers. With this thesis, a deeper understanding of lentil protein functionalities was gained, in relation to molecular structures as impacted by environmental conditions (pH and presence of polysaccharides), which established a good foundation for applying this knowledge in developing lentil protein as a food ingredient and product applications

• Subjects / Keywords

  • Structure-function relationship
  • Lentil protein
  • Extraction of protein

• Graduation date

  Fall 2015

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3KP7V03G

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.