Examining polyphenols to reduce off-flavors associated with protein-rich plant ingredients

Justification
Protein-rich plant ingredients are associated with significant off-flavors, which are primarily products of lipid oxidation and the Maillard reaction, occurring throughout processing and storage. Utilizing protein-polyphenol interactions may reduce undesirable products. 
 
Objective  
We aim to identify if and how polyphenols may interrupt lipid oxidation and Maillard reactions to reduce the production of off-flavors in pea protein ingredients.
 
Methods
Pea protein solutions (10% w/v) were heated for 30 min at 90˚C, then treated with 0.02% w/w catechin, tannic acid (TA), or grapeseed extract (GSE). FRAP was used to measure the antioxidant activity of polyphenols. The Folin-Ciocalteu method was used to quantify free polyphenols. Melanoidin production was quantified by measuring absorbance of protein-polyphenol solutions at 420 nm. Resulting primary (peroxide) and secondary (TBARS) lipid oxidation products were quantified using a modified IDF method and TBARS assay, respectively. Volatile Maillard reaction and lipid oxidation compounds were quantified using GC-MS. 
 
Results
Quantification of free polyphenols showed that at least 64% of all tested polyphenols were bound to proteins (catechin < TA < GSE). Catechin, TA, and GSE significantly reduced melanoidin production by 39%, 43%, & 48%, respectively. Because GSE had the highest amount of polyphenol-bound protein, thus fewest amine groups available to react with reducing sugars, it was able to reduce the Maillard reaction products most effectively.  Catechin, TA, and GSE reduced TBARS by 39%, 76%, & 75%, respectively, and LOOH by 21%, 50%, & 51%, respectively. Polyphenol addition significantly reduced hexanal, furan, hexanol, and heptanone production. Likely, TA and GSE more effectively reduced lipid oxidation products than catechin because their larger structures presented more hydroxyl groups and hydrophobic regions able to interact with proteins, such as lipoxygenase. 
 
AOCS Significance
Expanding the knowledge of protein-polyphenol interactions could enable solutions to reduce undesirable oxidative and Maillard reaction products found in lipid and protein systems.