Study of the physicochemical and functional properties of vegetable proteins used in the formulation of a UHT industrial product

Abstract

For several decades, following changes in consumption patterns, food industries have been aiming to replace animal protein with vegetable protein. Moreover, as a result of population growth, it is essential to identify new non-conventional sources of protein. Among these sources, pea is currently booming. In addition to health, environmental and political interest, this legume is highly appreciated by food industries for its techno-functional properties such as foaming, emulsifying and gelation capacities. Nevertheless, the use of pea proteins in foodstuff formulation is hindered by the heterogeneity of their techno-functional properties. Therefore, this master thesis aimed to study the chemical, physical and functional characteristics of various pea protein isolates. Firstly, a chemical characterization revealed a standardization of dry matter and protein contents. However, significant differences where observed between the ash, lipid and carbohydrate contents. Secondly, several SDS-PAGE electrophoreses revealed variations between the different protein profiles. While the albumins, legumins and vicilins were common to all samples, some of them were distinguished by the presence of convicilins and an unidentified 80 kDa protein fraction. Moreover, qualitative analyses showed significant differences between the samples and highlighted a link between the albumin and legumin contents. The lower the albumin content, the higher the legumin content. It led to the establishment of classes of protein isolates but independently of the previous chemical characterization. Afterwards, several DSC experiments demonstrated the partial denaturation of proteins in relation to the protein profile. Indeed, the lower the albumin content and the higher the legumin content, the higher denaturation degree. In addition, the results showed the impact of the UHT treatment, carried out during the industrial process, on the denaturation degree. Then, significant differences were revealed between exposed SH and total SH contents, regardless the legumin content. Some physical characteristics of protein isolates, such as particle size and colour parameters were also determined. More specifically, the study of the particle size distributions revealed significant differences between the samples and suggesting a variation of grinding parameters during the industrial process. Regarding the colouring parameters, the observed differences suggested a heterogeneity related to the isolate composition or a variation of industrial process conditions. Lastly, first two functional properties such as solubility and water retention capacity were measured. The results did not reveal any link with the chemical and physical characteristics. Nevertheless, they showed the complexity of the interactions between all these characteristics.