Synergistic effects of alkaline and heat treatments on structural and functional properties of mung bean protein isolate: improving physicochemical stability of plant-based emulsions

Plant-based meat alternatives often require fat replacers to mimic the texture of traditional products. This study aimed to develop plant-based emulsion gels using mung bean protein isolate (MBPI) as a potential fat substitute. However, creating these gels via heat setting requires a high protein concentration, which demands modification of the MBPI structure to enhance emulsifying properties. This study investigated synergistic effects of alkaline treatment (0.3 or 3.5% Na₂CO₃) and heat treatments (40 or 70 °C) on the functional properties of MBPI at high protein levels, for potential application as a plant-based emulsion. The combined treatments reduced the zeta potential of protein suspensions from −9 to −19 mV and altered the protein conformation to form smaller particles (from 426 to 166 μm) with increased β-sheet content. These treatments improved dispersibility of 8% MBPI suspension (58 to 86%), emulsifying activity index (6.34–10.89 m² g⁻¹), and stability coefficient (43 to 96%). Notably, MBPI samples treated with 0.3% Na₂CO₃ at 40 and 70 °C exhibited excellent emulsifying properties, forming stable monolayers at the oil–water interface, likely due to the increased surface activity of MBPI. Increasing protein concentration to 11% facilitated heat-set gel formation; however, addition of 3.5%-Na₂CO₃ induced premature gelation, limiting its application in emulsions. At 0.3%-Na₂CO₃, increasing the protein content from 8% to 11% and the oil content from 10% to 30% further reduced emulsion droplet size, especially for MBPI treated with 0.3% Na₂CO₃ at 70 °C (MB-0.3%-70 °C) from 5.10 to 2.61 μm, likely due to decreased coalescence. This treatment yielded superior MBPI-stabilised emulsion gels with enhanced penetration, fluid retention, and stability by possibly reducing protein aggregation. These findings demonstrate the potential of MBPI modified by combined addition of 0.3% Na₂CO₃ and heat treatment, particularly MB-0.3%-70 °C, as a promising ingredient for producing plant-based emulsions.