Fermentation of grass pea (Lathyrus sativus L.): an ancestral approach with impact in grass pea's quality

Lathyrus sativus (grass pea) is a legume highly resilient to adverse environmental conditions (e.g., drought). Able to thrive in varying climate and soil conditions, demonstrating good adaptation to both dry and waterlogged environments, the grass pea seeds are characterized by diverse morphology (colour and size). Grown worldwide, in southern, central, and eastern Europe, Asia and Africa, this neglected crop is among the most affordable forms of dietary protein in developing countries, especially when all other crops fail due to adverse environmental conditions.1 Being one of the cheapest legumes in the world, grass pea has been traditionally relegated, particularly in developing countries, to the poor classes. Its consumption associated with a very restrictive non-diversified diet, like the one practiced in famine periods, has been linked to the development of lathyrism. The accumulation of the neurotoxin β-N-oxalyl-L-α, β-diaminopropionic acid (β-ODAP), a non-protein amino acid which accounts for 95% of total ODAP, in the context of a poor unbalanced diet has been pointed as the main reason for the disease onset.2 Notwithstanding this drawback, grass pea has undeniable nutritional value, not only as a remarkable source of protein but also as a dietetic source of L-homoarginine, L-hArg, a non-proteinogenic amino acid proposed as a novel cardioprotective biomarker as suggested by the promising effects in several animal models.3 The studies reporting the influence of ancestral processing techniques, such as fermentation, on the nutritional, antinutritional and volatile composition of grass pea, and their fermented derivatives are still very scarce, therefore and within the European DIVINFOOD project, the miso and tempeh fermented products obtained by the action of Aspergillus oryzae, Rhizopus oligosporusand starter cultures on the cooked grass pea were compared to the corresponding cooked and raw grass pea seeds in terms of their amino acid composition, antinutritional (e.g., phenolic compounds, saponins, trypsin inhibitors) content and volatile composition. Their antioxidant activity was also evaluated following in vitro assays, such as hydroxyl radical scavenging capacity, HOSC, and oxygen radical absorbance capacity, ORAC. The volatile composition was assessed by Gas chromatography Mass Spectrometry – Triple Quadrupole, GCMS-TQ, and the compounds’ tentative identification made by comparison with Willey and NIST libraries, considering a similarity index higher than 80%. The analysis of the raw and processed grass pea showed a clear separation between raw and fermented samples. Compared to the raw seeds, the fermented samples stood out by their higher in vitro antioxidant activity and lower trypsin inhibitor activity. These differences support the consumption of fermented legumes as a potential source of beneficial antioxidant compounds in the human diet. For the identification of compounds with potential antioxidant activity high resolution mass spectrometry will be applied. The presence of flavoring compounds such as alpha-angelica lactone, produced as a secondary metabolite of the fungi applied in miso preparation or the tetramethylpyrazine, produced in tempeh, during the fermentation process, enhance the value of fermented legume products for the food industry focused in developing tastier plant-based alternatives. In conclusion, the fermentation is an ancestral processing approach that should be applied to legumes namely, to grass pea with positive impact not only in the protein digestibility through the reduction of trypsin inhibitors activity, but also in the flavour and acceptance of the derived food products.