Understanding the microstructure of a functional meat analogue: Demystifying interactions between fungal hyphae and egg white protein

This study investigated the microstructure and interactions of heat treated concentrated Fusarium venenatum biomass, commonly referred to as 'mycoprotein' (MYC), as well as the impact of 3 wt % egg white protein (EWP) on those interactions – EWP being frequently added as a 'binding agent'. Confocal laser scanning microscopy (CLSM) and cryo-scanning electron microscopy (Cryo-SEM) combined with energy dispersive spectroscopy analysis (EDS) demonstrated the filamentous nature of the MYC, made up of chitin and protein, with a filament aspect ratio typically between 130 and 140. Protein extraction and analysis via SDS-PAGE electrophoresis suggested that the most abundant native protein in the MYC had a molecular weight of 69.2 kDa, probably belonging to the heat shock 70 (HSP70) group. Frequency sweep dynamic shear rheology measurements were performed at combinations of 3 different values of pH (3, 5 and 7), NaCl concentration ([NaCl] = 0, 100 and 200 mM), CaCl2 concentration ([CaCl2] = 0, 50 and 100 mM) and wt. % MYC solids (5, 10, 15 and 20) without added EWP and with added EWP (MYC-EWP). For MYC the storage modulus G′ was seen to increase strongly with increasing wt. % MYC solids but also with [NaCl] and [CaCl2], the latter having greater impact at pH 5 and 7. The opposite trends were observed at pH 3, where G′ decreased with increasing concentration of ions, the highest G′ values for MYC occurring at pH 3 with no added salts. This suggests that electrostatic interactions between the MYC elements are key to the overall texture. On addition of EWP, there was good evidence that EWP completely coats the filaments so that, the hyphal interactions of MYC-EWP are then dominated by the response of EWP to changes in pH and salt composition. Gaining further understanding of the strength and distribution of the loci of these interactions is therefore key to better control of the texture of such meat analogues.