Production of protein based functional ingredient through the modification of protein primary structure with the phenolic compounds

Proteins are vital food ingrediens due to their nutritional value and functional properties. Changing the protein structure with modifications is important in terms of providing food safety, corresponding nutritional demands and palatability with the obtained new raw material. Polyphenols, which are well known to have anti carcinogenic and anti mutagenic effects as well as scavenging free radicals and reactive oxygen species, have high affinity for binding with proteins. The polyphenols found in the most of foods are highly reactive considering their chemical structure and they are easily oxidized by enzymatically or non-enzymatically. At the beginning of these reactions, quinones are formed and accordingly, polyphenol molecule becomes electrophilic. Therefore, nucleophilic addition of the oxidized polyphenols to the side chains in protein structure give rise to modification in the protein structure. Oxidation of polyphenols may vary depending on pH, temperature or interaction time, and investigation of the effects of these factors is an important issue in terms of modification of protein. To date, proteins are known to covalently bind with polyphenols under alkaline condition. In this study, it is aimed to obtain protein or protein based food with induced antioxidant potential as well as reduced reactivity of amino group resulting in limited glycation potential through modification of proteins with gren tea polyphenols. For this purpose, in order to obtain modified proteins, casein (CN), ovalbumin (OVA) and gluten (GLU) proteins were firstly treated with green tea extract (GTE) under alkaline condition (pH 8, 10, 12). Treatment were performed at 25ºC and 50ºC for 30, 60 and 120 minutes. In this way, polyphenols are aimed to be oxidized and form quinones, thus becoming reactive. Total antioxidant capacity (TAC) and amino acid amount of both control and modified protein samples was measured to confirm the formation of quinone and covalent binding of the formed quinones to amine residues of proteins. In order to confirm the modification of the modified proteins, amino acid analysis was performed in the control and modified proteins, and then lysine contents were determined. As a result of the reaction of CN, OVA and GLU and green tea extract solution at pH 10, it has been shown that lysine amounts can be modified 94% modified casein and ovalbumin samples, and 71% for modified gluten samples compared to the control. According to the results, TAC of treated proteins samples was significantly higher than control proteins samples (p<0,05). The highest increase in TAC was observed in the samples treated at pH 10. The results indicated that both treatment temperature and time was not as effective as alkaline conditions in terms of binding. Following this, in order to investigate the effect of modification on glycation potential of modified proteins, model reactions were prepared from modified proteins having highest TAC value. Model systems prepared with either control or treated proteins and glucose in varying concentrations (1-5-10-20-100 μmol) were heated in an oil bath at 100ºC for 15 minutes. Then glycation products such as furosine and N-ε-carboxymethyllysine (CML) were measured as indicators of early and advanced glycation. The amount of furosine formed by heating the modified protein complexes in the dry system was significantly lower than in the heated control model systems (p<0,05). However, there was no significant difference in CML amounts of both heated modified protein and control model systems (p>0,05). In some protein based food samples; (skim milk, sugarless soy milk, egg, wheat flour, rye flour and oat flour) reaction was performed with GTE under optimum conditions and the changes in the TAC were observed. The TAC results obtained with modified protein based food samples are significantly higher than the control samples (p<0,05). These results shows that modified protein-based foods can be used as functional food additives with increased antioxidant properties. Consequently, this study offers that the treatment of CN, OVA and GLU proteins with green tea phenolics has a great potential for obtaining functional protein with increased antioxidant potential and limited glycation potential.