Impacts on Micro- and Macro-Structure of Thermally Stabilised Whey Protein-Pectin Complexes: A Fluorescence Approach

Stability of whey protein-pectin complexes is an essential criterion for their application in different food matrices. The impact of process parameters on microand macro-structural characteristics of thermally stabilised whey protein-pectin complexes was investigated using fluorescence spectroscopy, zeta-potential measurements, dynamic light scattering and phase separation. Complexes prepared from whey protein isolate (WPI) and pectins with different degrees of esterification (HMP, LMP) were generated at different biopolymer concentrations (WPI + pectin: 5.0 % + 1.0 %, chigh; 2.75 % + 0.55 %, c(med); 0.5 % + 0.1 %, clow), heating temperatures (80-90 degrees C) and pH levels (6.1-4.0). Micro-and macro-structural characteristics of the complexes depended on concentration level and degree of esterification, with complexes being more sensitive towards environmental changes at c(low) than at c(med) and c(high). WPI-LMP complexes exhibited sizes < 1 mu m suitable for micro-encapsulation, whereas WPI-HMP complexes at c(med) achieved sizes from 1-10 mu m and at c(high) from 10-200 mu m underlining their potential as fat-replacers and structuring agents, respectively. Slopes and intercepts derived from intensity ratios of fluorescence spectra gave insights into the state of unfolding of beta-lactoglobulin within the complexes and thus about the protective effect of pectin addition.