Inhibition of legume flavor degradation pathways with polyphenols

Abstract: Off-flavors formed by lipid oxidation and Maillard reaction processes are a major impediment to consumer acceptance of sustainable legume proteins in foods. Through their strong antioxidant and protein-binding properties, polyphenols may inhibit these processes, thus prevent off-flavor formation.

Objective: Characterize the abilities of polyphenols to reduce off-flavor formation in legume protein ingredients and a model food.

Aqueous pea (10% w/v) and soy (8% w/v) protein solutions were treated with 0.02% w/w catechin (CAT), green tea extract (GTE), grape seed extract (GSE), or tannic acid (TA). Free polyphenols were quantified with the Folin–Ciocalteu assay. Lipid oxidation was assayed with lipid hydroperoxide for primary products and malondialdehyde via TBARS for secondary products. Free lysine was quantified with spectrophotometric methods; α-dicarbonyls with HPLC; and volatile compounds with GC-MS.

At least 52% of all tested polyphenols were bound to proteins (GSE > TA > GTE > CAT). The polyphenols reduced the secondary lipid oxidation products in both proteins by 50-75%. Polyphenols also reduced free lysine content, thus reduced substrate for Maillard reactions. Purified polyphenols (CAT and TA) showed a higher affinity for α-dicarbonyl trapping than crude extracts (GSE and GTE). Polyphenol addition significantly reduced 2-furanpentyl, benzaldehyde, hexanal, hexanol, and heptanone production. High molecular weight (MW) polyphenols (GSE and TA) were able to inhibit lipid oxidation and Maillard reactions through interactions with proteins, which bound lipoxygenase and also prevented amine groups from reacting with reducing sugars. Alternatively, low MW polyphenols inhibited these processes by binding lysine and trapping α-dicarbonyls. Current work is assessing the sensorial and functional effects of extruded protein-polyphenol ingredients in plant-based burgers.

This work identifies mechanisms by which polyphenols can reduce off-flavors produced during the processing and storage of isolated plant proteins and resulting foods. These findings can promote the sustainability of and increase the market acceptability of protein ingredients.