Effect of pH on the gelling properties of pea protein-pectin dispersions

Phase behavior of protein-polysaccharide mixtures can be controlled by adjusting parameters, such as polymer concentrations and pH. However, the relationships between these interactions and resulting microstructures and textures are not fully understood. The effects of pH (5.5, 7, and 8.5) and low-methoxyl (LM) pectin content (0.5% and 1%) on the rheological properties and microstructures of heat-induced pea protein gels were investigated. At pH 5.5, the addition of LM pectin significantly increased the size of protein aggregates, which is explained by the strong interactions between proteins and LM pectins at that pH; a quartz crystal microbalance revealed the formation of insoluble complexes with reduced solubility. The storage modulus (G′) of pea protein gels at pH 5.5 increased with 0.5% of LM pectin, whereas 1% of LM pectin led to a decreased G′ and the gels water holding capacity. At pHs 7 and 8.5, the addition of LM pectin increased the size of protein aggregates due to the segregative phase separation of negatively charged pea proteins and LM pectins. An increase in G′ with LM pectin concentrations in the gels was also observed at pHs 7 and 8.5. Gel microstructures with phase-separated zones were observed by confocal microscopy. Furthermore, the addition of LM pectin increased the digestibility of pea protein gels prepared at the three pH values under simulated gastrointestinal conditions. Better knowledge of the rheological properties and microstructures of pea protein-LM pectin mixed gels obtained under different pH conditions will allow for optimal use of protein-polysaccharide mixtures in food formulations to attain binary gel products with expected textural and nutritional properties.