Unveiling the role of oxylipins in the formation of off-flavor in pea protein isolates

Peas (Pisum sativum L) have increasingly been recognized as a valuable source of alternative plant-based protein. However, the presence of off-flavors, often described as "beany" or "grassy," has limited their application in food products. These undesirable flavors can be generated from primary and secondary residual lipid oxidation products, such as oxylipins and volatiles compounds. This study aimed to understand how fatty acid composition drives the formation of oxylipins and volatile compounds during pea protein extraction and isolation. Spring and winter pea flours, along with their corresponding protein isolates were analyzed for fatty acid composition, free and total oxylipins, and volatile profiles. Commercial pea protein flour and protein isolate were used as reference samples. Fatty acid composition was determined by gas chromatography coupled to flame ionization detection (GC-FID), free and total oxylipins were determined using liquid chromatography coupled to mass spectrometry (LC-MS/MS), and the volatile profile was evaluated by gas chromatography coupled to mass spectrometry (GC-MS). Linoleic (LA) and alfa-linolenic (ALA) acids were the most abundant fatty acids in the pea flour and protein isolates. The majority of oxylipins were present in the esterified form, with an increase in concentration of total oxylipins following the protein extraction, especially of the hydroxy and ketone LA metabolites such as the 9-hydroxy-10E,12Z-octadecadienoic acid (9-HODE), 13-hydroxy-9Z,11E-octadecadienoic acid (13-HODE), and 13-oxo-9Z,11E-octadecadienoic acid (13-OxoODE). Aldehydes and alcohols, such as hexanal and 1-nonanol, were the most abundant volatile compounds identified in the pea samples. Protein isolates had around 5 times more hexanal compared to the flour, evidencing the oxidation throughout the extraction process. Overall, protein extraction increased the formation of total and free oxylipin and volatile compounds. Further investigation of processing conditions and strategies to reduce residual lipids in plant protein isolates should be addressed to enhance the sensory quality of pea protein-based products.