Étude de l'impact des traitements électriques à hauts voltages sur les propriétés fonctionnelles et l'hydrolyse enzymatique de la beta-lactoglobuline

Authors: Agoua, Enongande Kokou Rock-Seth
Advisor: Mikhaylin, Sergey; Bazinet, Laurent
Abstract: Due to increasingly severe legislative restrictions on environmental pollution, dairy industries have faced over the past few years a crucial challenge of valuing the large quantities of whey generated. Thus, thanks to recent technological and scientific progress as well as the important growth of the biofunctional ingredients market, a more efficient and promising way of whey valorization has emerged. Indeed, in recent years, several studies have demonstrated that the nutritional and biofunctional attributes of whey are particularly linked to its proteins, which constitute an optimal source of functional food ingredients and bioactive peptides. Therefore, -lactoglobulin (ß-lg), a major whey protein is an additive frequently used in a wide range of food products due to its excellent biofunctional properties, its high nutritional value and its low cost. These biofunctional properties of ß-lg can be improved by different treatment methods, including physical, chemical and enzymatic ones. However, due to its compact globular structure, ß-lg in its native form is relatively resistant to modifications. Although conventional treatments are effective in improving the structural and functional properties of proteins as well as the production of biologically active peptides, they are nonetheless resource intensive and can negatively affect the quality of final products. Therefore, the application of emerging nonthermal physical treatment methods is necessary. Thus, in the frame of this doctoral project, sustainably high-voltage electrical treatments (HVET), namely pulsed electric fields (PEF) and electric arcs (ARC) were used as pretreatment method of ß-lg. Thermal pretreatment of ß-lg was performed in order to compare the efficiency of HVET pretreatments with the conventional approach. Therefore, the preheated ß-lg samples were considered as positive control and those of the native one as negative control. The effect of pretreatments on the functional properties of ß-lg was evaluated. Likewise, the impact of HVET and heat pretreatments on the structure of ß-lg and its susceptibility to tryptic and chymotryptic hydrolyses was investigated. Ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS) was used to analyze and characterize the peptide fractions from the various hydrolysates of ß-lg. In addition, the eco-efficiency (EE) scores of peptide generation after tryptic and chymotryptic hydrolyses were calculated in order to determine which of the performed pretreatment methods was the most efficient. The results demonstrated an improvement in the functional properties (foaming, emulsifying and hygroscopicity properties) of ß-lg promoted by the positive impact of HVET on its secondary structure. Indeed, structural analyzes have shown that HVET induced a partial modification of the conformation of ß-lg. Such structural modification resulted in almost 2-times increase in the degree of hydrolysis (DH) after HVET pretreatments compared to the native protein. In the case of the conventional heating pretreatment, the increase in DH was approximately 1.2-times compared to native protein. These results were confirmed by the improvement in the kinetic parameters of ß-lg at steady state after HVET. Furthermore, a significant difference was observed between trypsin and chymotrypsin with regard to DH and the catalytic efficiency of the two enzymes. Indeed, the catalytic efficiency constants of chymotrypsin were higher than those of trypsin, suggesting a better affinity of chymotrypsin with the protein compared to trypsin. In addition, the UPLC-MS MS analysis of pretreated samples demonstrated that the application of HVET led to the release of peptides from ß-lg molecules even before the addition of trypsin and chymotrypsin to the reaction media. Additionally, the HVET have generated in average 37-50% more peptides than native and preheated proteins. Finally, the EE analysis revealed that HVET were the most efficient pretreatment method than the conventional one as their EE scores were higher for both hydrolysis processes and bioactive peptides generated from performed hydrolyses. This thesis highlights new understanding elements regarding the multidirectional valorization of whey proteins
Document Type: Thèse de doctorat
Issue Date: 2021
Open Access Date: 20 September 2021
Permalink: http://hdl.handle.net/20.500.11794/70399
Grantor: Université Laval
Collection:Thèses et mémoires

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