Type of pectin affects the functionality of potato protein-pectin conjugates in emulsions

• Published in: Food hydrocolloids 2024-11, Vol.156, p.110251, Article 110251
• Main Authors: Eichhorn, Marina, Sankowski, Larissa Vivienne, Drusch, Stephan, Kastner, Hanna
• Format: Article
• Language: English
• Subjects: Amidated pectin; Degree of methoxylation; Emulsifier; Maillard reaction; Pectin degradation; Solubility
• ISSN: 0268-005X
• DOI: 10.1016/j.foodhyd.2024.110251

This study investigated the effect of the molecular structure of pectin on conjugate formation and its functionality in plant protein-based emulsions. For this purpose, high-methoxylated, low-methoxylated, amidated citrus pectin and their mixtures with potato protein were vacuum-dried at defined process conditions. The change in free amino groups, colour and molecular weight distribution assessed conjugation. The side reaction, such as pectin degradation, was monitored by the degree of methoxylation, galacturonic acid content and intrinsic viscosity. In addition, FT-IR and hydrophobicity measurements were performed to determine the changes in chemical structure due to the occurring reactions. The ζ-potential, solubility and oil droplet size reflected the functionality of the conjugated samples. The results confirm that, apart from the conjugation of protein and pectin, where the most significant decrease in free amino groups was obtained with an increasing degree of methoxylation or presence of amide groups, undesirable degradation of pectin occurring, resulting in a broad molecular weight distribution of the conjugate samples. The conjugate formation was the highest with amidated pectin. The FT-IR measurements confirmed the formation of Maillard conjugates. The FT-IR spectra showed a decrease in the intensity signals of amide I and amide II and the formation of new C–N bond maxima. In addition, the conjugation caused the shift of the protein's isoelectric point to the acidic environment, resulting in higher solubility and improved emulsion stability at the isoelectric point of the protein. Regarding emulsion stability, the conjugates with amidated pectin performed best and achieved the narrowest oil droplet size distribution over a wider pH range. Emulsion-stabilising properties of conjugates with high- and low-methoxylated pectin differed only slightly. To better understand the underlying mechanisms for emulsion stabilisation, future research will focus on the interfacial properties of the conjugates as determined by interfacial shear rheology and pendant drop analysis. [Display omitted] •Pectin samples are degraded to a different extent under thermal conditions during conjugation.•Pectin degradation leads to a broad molecular weight profile of conjugates.•Conjugation improves the protein's functionality at the isoelectric point.•Amount of methoxylated groups in protein-pectin conjugates only slightly affects the emulsion stability.•Pectin's amide groups