Polyphenol interactions with whey protein isolate and whey protein isolate-pectin coacervates

The effects of the interactions between polyphenolic substances (catechin/tannic acid) or plant extracts (grape seed/hibiscus extract), using each in three different concentrations (0.1-0.5%), and preheated whey protein isolate (Pre-HWPI) or Pre-HWPI pectin complexes were studied at different pH (pH 3.2/ 5.2/6.1). Particle size, charge, protein precipitation capacity, and microscopic image were analyzed. The particle diameter (d(43)) in the solution containing polyphenols was slightly affected in a solution of Pre-HWPI at pH 3.2 or 5.2 and clearly increased at pH 6.1. The positive zeta-potential observed at pH 3.2 decreased slightly. The addition of catechin, grape seed extract and tannic acid, excluding hibiscus extract, induced the increase of negative charge at pH 5.2 and 6.1. The presence of polyphenols accelerated the protein precipitation of Pre-HWPI at pH 3.2 and 5.2 rather than at pH 6.1. The different types and concentrations of polyphenols present in Pre-HWPI pectin complexes at pH 3.2 and 5.2 showed a small difference in particle size and charge. The addition of polyphenols to the polymer complexes at pH 6.1 influenced the increasing particle diameter, and the zeta-potential varied from -12.35 to -19.35 mV, depending on the different type and concentration of polyphenol. However, the sedimentation was only clearly observed in the sample containing 0.3 and 0.5% tannic acid. Furthermore, microscopic images depicted the similar structural appearance of the Pre-HWPI and Pre-HWPI pectin complexes in the presence of polyphenols other than tannic acid. In summary, complexation of Pre-HWPI pectin complexes reduces the protein precipitation with polyphenols and allows the use in complex food matrices. (C) 2014 Elsevier Ltd. All rights reserved.