Fate of pulse globulin proteins molecular Structure and composition on high moisture extrusion
Smriti Shrestha, Leonie van ‘t Hag, Victoria S. Haritos, Sushil Dhital
Abstract
Mungbean and lentil proteins are gaining attention for the production of high moisture extrusion (HME)-based meat- and dairy-analogues. However, understanding the mechanism of fibrous structure formation and molecular and higher-order changes in HME remains limited. Globulin protein isolated from mungbean (MBPI), green lentil (GLPI) and yellow pea (YPPI) along with commercial soy (CSPI) and yellow pea (CPPI) protein isolates were investigated for pasting properties using high-pressure rapid visco analyser (RVA), and formation of anisotropic structures and molecular changes at a constant HME condition. Vicilin-rich MBPI showed higher viscosity on RVA, consumed higher specific mechanical energy (SME) on extrusion, and developed extrudates with higher textural strength and cutting force than proteins with both legumin and vicilin-like globulins, i.e. GLPI and YPPI. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and size-exclusion chromatography (SEC) of extrudates' soluble proteins showed dissociation of vicilin-like globulins into their smaller subunits. In contrast, legumin-like globulins were reaggregated into higher molecular weight (Mw) soluble macromolecules. Further, SDS-PAGE of extrudates’ total protein revealed the involvement of legumin-like globulin in the macrostructure network of the extrudates. Due to HME, native unfolded structures were destroyed with conversion, predominately driving changes in the tertiary structure (thermal denaturation) and secondary structure with loss of helical structure to formation of random coil and beta-sheet. Protein extractability in different solvents was greatly reduced, with covalent and non-covalent interactions being majorly involved in the stabilisation of extrudates structure. Protein composition, and in particular vicilin-legumin ratio and protein conformation, determined the structural development and molecular changes in HME.