A review of polyphenol and whey protein-based conjugates

Abstract

Proteins act as a primary food component obtained from different food sources. In contrast, polyphenols are metabolites and are abundantly present in plants, so their combination plays a crucial role in defining the functional properties of a food product. In the current review, the protein-polyphenol interactions have been briefly reviewed, along with the changes that occur because of their interaction. The mechanisms and the factors affecting the functionalities of the protein-polyphenol conjugates, e.g., the solubility, antioxidant, and gelling properties, have also been briefly reviewed. In addition, the interaction of polyphenols with whey proteins was been reviewed with various applications within the food industry, e.g., emulsifiers, foaming agents, and antioxidants. To end the review, future challenges were also highlighted.

Full Article

A Review of Polyphenol and Whey Protein-based Conjugates

Diana Tazeddinova,^a Abduvali Djaraovich Toshev,^a Aizhan Abylgazinova,^b Md. Rezaur Rahman,*^,c Md. Mahbubul Matin,^d Muhammad Khusairy Bin Bakri,^c and Orazov Ayan ^e

Proteins act as a primary food component obtained from different food sources. In contrast, polyphenols are metabolites and are abundantly present in plants, so their combination plays a crucial role in defining the functional properties of a food product. In the current review, the protein-polyphenol interactions have been briefly reviewed, along with the changes that occur because of their interaction. The mechanisms and the factors affecting the functionalities of the protein-polyphenol conjugates, e.g., the solubility, antioxidant, and gelling properties, have also been briefly reviewed. In addition, the interaction of polyphenols with whey proteins was been reviewed with various applications within the food industry, e.g., emulsifiers, foaming agents, and antioxidants. To end the review, future challenges were also highlighted.

DOI: 10.15376/biores.17.4.Tazeddinova1

Keywords: Protein; Polyphenols; Whey protein; Functional properties; Conjugates; Interactions

Contact information: a: Department of Technology and Catering Organization, South Ural State University, Chelyabinsk 454080 Russian Federation; b: Zhangir Khan Agrarian Technical University, Uralsk Kazakhstan; c: Faculty of Engineering, Universiti Malaysia Sarawak, Jalan Datuk Mohammad Musa, Kota Samarahan, Sarawak, Malaysia; Composite Materials and Engineering Centre, Department of Civil and Environmental Engineering, Washington State University, Pullman 99164 WA USA; d: Department of Chemistry, University of Chittagong; e: Zhangir Khan West Kazakhstan Agrarian – Technical University, Uralsk, Kazakhstan

* Corresponding author: Md Rezaur Rahman, Email: rmrezaur@unimas.my

INTRODUCTION

With more than 8000 different compounds, phenolic compounds are secondary metabolites with the same structure, i.e., an aromatic ring bonded to a hydroxyl group, and they are classified according to their number of carbon atoms (Kroll et al. 2003). Some examples of phenolic compounds are as follows: phenolic acids, flavonoids, lignans, and stilbenes in plants, which can react with protein molecules and undergo chemical change during food processing and even after consumption, as shown in Figs. 1a and 1b (Parada and Aguilera 2007; Crozier et al. 2009). The important factors determining polyphenol-protein interactions include the structural flexibility, molecular weight of the polyphenol, the side chain type, and the hydroxyl group number, as polyphenols with a higher molecular weight and abundant hydroxyl groups have greater protein affinity (Frazier et al. 2010; Xiao et al. 2011; Czubinki and Dwiecki 2017; Buitimea-Cantú et al. 2018). Protein-polyphenol interaction is classified into covalent interactions (irreversible) and noncovalent interactions (reversible), which are further reported as five groups, including electrostatic interactions, hydrogen bonds, pi (π) bonds, hydrophobic interactions, and van der Waals (Prigent et al. 2003; Frazier et al. 2010; Rawel and Rohn 2010; McRae and Kennedy 2011).

Fig. 1a. Major phenolic acid structures

Fig. 1b. Major flavonoid compounds

Hydrolysis causes modification to the functional properties of proteins. However, moderate hydrolysis of whey proteins increases their heat stability as a result of the reduced secondary structure. This development does not always translate directly to more complex systems such as emulsions made using hydrolyzed whey protein, where heat stability has been shown to be adversely affected by hydrolysis of whey protein. Conjugation of proteins with polyphenol reaction has been shown to be effective in altering protein functionality (Liu et al. 2012; Costa et al. 2021). Widespread research supporting the beneficial effects of protein modification through conjugation is available in the scientific literature; improved functional properties of proteins including solubility, emulsification, encapsulation, emulsion stability, and thermal stability as a result of conjugation are well documented (Akhtar and Dickinson 2003; Buamard and Benjakul 2017, 2018).

A protein can interact through hydrophobic interactions with polyphenols. Hydrogen bonds and hydrophobic interaction are the primary noncovalent interactions regulating protein-polyphenolic interactions and involved amino acids. Examples include valine, leucine, isoleucine, alanine, phenylalanine, methionine, tryptophan, glycine, cysteine, and tyrosine. Phenolic compounds form a hydrogen bond with the protein carboxyl group, as they are hydrogen donors, so a hydrogen bond is ultimately formed between the oxygen/nitrogen molecule of amino acids and a phenolic hydroxyl group (Prigent et al. 2003; Rawel and Rohn 2010; Xiao et al. 2011; Mulaudizi et al. 2012; Jongberg et al. 2015; Tang et al 2021; Xiong and Guo 2021). The mechanism of the protein-polyphenol reaction is illustrated in Fig. 2. Phenolic compounds can produce a quinone radical via covalent bond formation, and in the presence of oxygen and an alkaline environment, a quinone radical is generated via enzymatic/non-enzymatic reactions (Jongberg et al. 2015; Czajkowska–González et al. 2021; Zhao et al. 2021). In the second step, a quinone forms a dimer via a condensation reaction, known as tannins (which are brown-colored, with a high molecular weight), by reacting with the polypeptide amino acid chain via covalent bonding, and are re-oxidized and react with another polypeptide chain in the third step (Felton et al. 1989; Arts et al. 2001; Buchner et al. 2006). Examples of covalent and noncovalent protein-polyphenol interactions are explained in Table 1 (Fig. 3 and Fig. 4).

Fig. 2. Phenolic acid compound reactions with polypeptide amino acid side chains

Fig. 3. Protein-polyphenol noncovalent conjugation and cross-linking of proteins via hydrogen bonding (a); hydrophobic-hydrophobic interaction (b); and ionic interaction (c)