# Presence and Impact of Aldol Condensation Products as Off-Notes in Plant-Based Protein Sources

## TL;DR

This paper identifies a new source of old soap odors in plant-based proteins, caused by chemical reactions during processing.

## Contribution

The study identifies and characterizes α,β-unsaturated aldehydes formed via aldol condensation in plant-based protein isolates.

## Key findings

- Old soap odors in pea protein isolates are caused by α,β-unsaturated aldehydes from aldol condensation.
- Aldol condensation products are present in rice, soy, and hemp proteins but not in whey protein.
- Manufacturing processes influence the formation of these odor-active compounds in plant-based proteins.

## Abstract

Off-notes in plant-based
sources of protein are mainly formed via
the lipid oxidation of unsaturated fatty acids. During gas chromatography–olfactometry
analysis of pea protein isolate, previously uncharacterized old soap
odors were detected. These were found to arise from a family of α,β-unsaturated
aldehydes formed from the aldol condensation of pentanal and hexanal
during the protein extraction process. These compounds were synthesized,
and it was confirmed that they are highly odor-active and contribute
to the old soap odor in pea protein isolates at very low concentrations.
Comparison with rice, soy, and hemp protein isolates showed that they
all contained at least one such aldol condensate, whereas they were
not detected in whey protein. We suggest that the main factor determining
the formation of these compounds is the manufacturing process used
to isolate and dry the pea protein biomass.