Impact of process conditions and type of protein on conjugate formation with pectin by vacuum drying

Abstract

Plant proteins exhibit low solubility and functionality, limiting their use as emulsifiers. Maillard reaction-based conjugation with polysaccharides, e.g. pectin, is a strategy to improve their functionality. The commonly applied batch process involves economically unviable freeze-drying as a pre-treatment. Vacuum drying was therefore investigated as a novel approach combining the drying process and conjugate formation.First, the process parameters (time and temperature) were altered to determine the optimum conditions for conjugation between potato protein and high methoxylated pectin. Then, the conjugation between the pectin and various plant proteins (soy, pea, rapeseed) was tested to assess the impact of protein type. Conjugate samples were analysed by dry matter, decrease in free amino groups, browning index and molecular weight. Emulsifying properties were evaluated by oil droplet size and emulsion stability. Process parameters of 100 °C and 3 h were identified to favour conjugation. Corresponding potato protein conjugates had high molecular weight and improved emulsion stability at the pI of the protein. Soy protein conjugates showed the highest decrease in free amino groups and enhanced emulsion stability with prevented coalescence. Rapeseed protein conjugates exhibited the most stable emulsions with narrow oil droplet size distribution but were hampered by their inherent colouration.The results confirm that all plant proteins can be used for conjugation with pectin and the obtained conjugates are suitable as emulsifiers for food systems. However, differences in the amino acids content, chemical structure, and overall composition of plant proteins affect conjugation and must be considered in process design.