# Impact of Ageing on Pea Protein Volatile Compounds and Correlation with Odor
## 1 Introduction  
The demand for plant-based proteins is increasing due to their numerous positive effects [1; 2; 3]. Many studies are dealing with the sensory aspects of these proteins [4; 5], especially the 'beany' off-flavor, as it is limiting the consumer's acceptance [6; 7; 8]. Numerous works are done on the off-flavor characterization, and on the impact of various processes on the profile in volatile compounds [9; 10; 11; 12; 13]. The typical 'beany' off-flavor, associated with 'green' and 'earthy' attributes, is a combination of different volatile compounds belonging to various chemical families like aldehydes, ketones, or alcohols [7; 10]. These compounds are typically found in pulses or other legumes and are generated through different pathways, like enzymatic and non-enzymatic degradation of lipids, amino-acids and peptides [6; 14]. Lipid oxidation starts early and rapidly after the harvest and during the first stages of the production of pea protein isolate (PPI) [6; 10]. The 'beany' off-flavor is generated in early phases and can evolve during the storage. Especially, this off-flavor can evolve quickly in PPI powder, becoming detrimental to the product. From the humidity/water activity (a\({}_{w}\)) relation to oxidation sensitivity, powders are highly sensible to lipid oxidation [15]. The lipid oxidation is very fast and can start since the harvest of the raw material. Lipids are rapidly converted into fatty acid hydroperodes (HPOD), leading to the formation of volatile and non-volatile compounds [16]. The primary products (HPOD) appear as early as seven days after the start of the cells breaking, and secondary products (volatile compounds) generally appear after the 15 th day [17]. In this way, just after fabrication, PPI we used in the present studyalready contained all the volatile compounds resulting from lipid oxidation, originating from the harvest, the fabrication of PPI and the first months of storage. The first substrates, the lipids, generated the profile in volatile compounds of the product, by enzymatic and non-enzymatic oxidations. A\({}_{\text{w}}\) changes during the storage could also impact the oxidation sensitivity. Scheme 1 presents the different phenomena affecting PPI. Optimal storage conditions are required to limit the off-flavor worsening and the product deterioration. Some studies have already dealt with the evolution of volatile compounds (responsible for the 'beany' off-flavor) during the storage [21; 22]. As an example, [PERSON] et al. (2011) analyzed the impact of transformation processes on the preservation of PPI under good storage conditions, and [PERSON] et al. (2011) the impact of the storage temperature on different cultivars of raw peas. The present paper comes as a complementary study, by focusing on the impact of two important parameters of storage on a PPI: light and temperature. This paper investigated the evolution of volatile compounds, of the odor, and of color of PPI during two storage treatments. The aim was to link the evolution of the volatile compounds with the odor deterioration and to observe the impact of storage parameters. The change of color of the PPI was also investigated as an external indicator of the conservation of the product. The storage conditions selection was guided towards abnormal storage conditions where environmental parameters were poorly controlled. Thus, treatment A was selected, with the product stored at 20 \({}^{\circ}\)C [22] and exposed to ambient light, mimicking a lack of control on the light exposition. Secondly, treatment B was selected, with the product stored at 30 \({}^{\circ}\)C in the dark, mimicking control over the light exposition but a lack of control over the temperature (increase in the storage temperature). Firstly, the evolution of the volatile compounds, of the odor, and of color during the two storage treatments, were investigated. Then, hypotheses on the mechanisms involved in this evolution were proposed. Nine volatile compounds of interest were subsequently semi-quantified in the PPI.