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

Peas (Pisum sativum L.) are increasingly recognized as a valuable source of plant-based proteins, however, their use in food applications is limited by presence of off-flavors, primarily driven by lipid oxidation. This study investigated the influence of fatty acid composition on the formation of primary (oxylipins) and secondary oxidation products (off-notes) during the protein extraction of spring and winter pea varieties. Commercial pea flour and protein isolate were included as references. Linoleic (LA) and alpha-linolenic (ALA) acids were the most abundant fatty acids in all samples. The majority of the oxylipins were found in the esterified form, and their total concentrations increased following protein extraction, especially hydroxy and ketone LA-metabolites, including 9-HODE, 13-HODE, and 13-oxo-ODE. Among the volatile compounds, aldehydes, alcohols, and ketones were the most abundant, with hexanal, 1-octen-3-ol, and 3,5-octadien-2-one being the main compounds detected in the pea protein isolates. Overall, protein extraction process promoted oxylipins and off-notes formation in pea protein isolates. Protein extraction increased total oxylipins by 9-, 11-, 7-fold and hexanal concentrations by 4-, 3-, and 2-fold in spring, winter and commercial pea samples, respectively. Positive correlations among oxylipins and volatiles confirmed the key role of lipid oxidation in off-flavor formation in plant-based proteins. These results underscore the need to optimize extraction conditions and reduce residual lipids in plant protein isolates to improve flavor quality and broaden the use of pea protein ingredients in food products.