Generic behavior of pulse proteins in 2D and 3D food systems

Summary

Foam, emulsions and gels are common food systems often stabilized by animal proteins (e.g., meat, dairy and egg proteins). Since producing animal proteins is resource-intensive and generates high greenhouse gas emissions, there is an urgent need for animal protein alternatives, where plant proteins have caught a lot of attention. Among numerous plant protein sources, pulses are cheap, diverse, widespread and rich in proteins. Pulse proteins have shown great potential in replacing animal proteins, but their mechanisms in stabilizing food structures are still poorly understood. Compared to animal proteins, pulse proteins are generally much more complex in molecular structure and composition, and their physicochemical properties are susceptible to extraction and heating processing. Therefore, how pulse proteins stabilize complex food systems is largely unclear, which makes it difficult to utilize them robustly for food production. This thesis aims to understand the functionalities of pulse proteins in stabilizing 2D structures in foam and emulsions and 3D structures in gels. We chose three mainstream pulses: lentil, faba bean and chickpea, and systematically studied the foaming, emulsifying and gelling properties of the whole protein extracts and two main protein fractions, i.e., globulins and albumins, on nano, micro and macro scales. This project found that pulse albumins tend to form stiffer structures which allow better fabrication and stabilization of those food systems, especially for foam, than the globulin fractions. This is due to their smaller size and more flexible molecular structure rich in -SH groups in comparison to globulins. Of the globulins, vicilin proteins tend to have higher foam stabilities, emulsifying activities and gel stretchability than legumin proteins. Legumins, instead, tend to be disruptive to the 2D structures formed in foam and emulsions and 3D structures in gels, likely due to their compact and large molecular structures compared to other pulse protein components. In the last research chapter (chapter 8), we investigated the influence of the coexistence of native and thermally denatured faba bean globulins (Fg) on gelation. We found that the denatured Fg with a low aggregation level had significantly improved gelation properties due to a considerable increase in surface hydrophobicity, forming stiffer, more stretchable, more connected, and less heterogeneous self-supporting gel structures. The denatured Fg with a high aggregation level tends to increase the overall heterogeneity of the gel systems and in turn weaken the gels, especially when coexisting with native Fg. This thesis provides deep insights into the performances of pulse proteins in stabilizing 2D and 3D food structures. The findings could guide a broader utilization of pulse proteins in food applications as animal protein replacers and promote the transition to a more sustainable food production system.