Interactions between hydrolysed high methoxyl pectin and heat-treated egg white protein: impact on emulsifying properties

Abstract In this study, the interactions between hydrolysed high-methoxyl pectin (HMPH) and heat-treated egg white (HEW) were investigated. Firstly, the hydrolysis of high-methoxyl pectin (HMP) was carried out by heating HMP solutions at concentrations ranging from 1% to 5% at 80–100 °C for 2 hr. The intrinsic viscosity [η] of HMPH decreased linearly with the heating temperature, whereas the HMP concentration had no effect. Additionally, molecular weights decreased from 137 kDa for native HMP to 117–41 kDa for HMPH. The interactions of HMPH with HEW, at a 1:1 mass ratio, were then analysed in terms of zeta potential, turbidity, and colloidal stability through visual assessment after 24 hr. Zeta potential vs. pH profiles remained unaffected by hydrolysis and were primarily governed by the pectin. According to the turbidity vs. pH results (absorbance at 600 nm), the critical pH (pH𝑐) values were 5.7 for HEW-HMP and ~6.1 for HEW-HMPH, while the phase separation onset pH (pH${}_\varphi$) was 3.5 for HEW-HMP and between 3.1 and 3.6 for HEW-HMPH. Visual inspection of the systems after 24 hr showed macroscopic phase separation at pH < 3. The emulsifying properties, including the emulsifying activity index (EAI) and stability, of the 1:1 HEW-HMPH system were evaluated across a pH range of 3–7 by preparing emulsions with corn oil at an oil volume fraction of 0.1 and a total biopolymer concentration of 2%. In general, the EAI of HEW-HMP systems increased compared to HEW, while the EAI of HEW-HMPH decreased relative to HEW-HMP. Furthermore, the most stable emulsions were observed for the HEW-HMP system.