Impact of Irrigation Treatment and Sowing Time on Lipoxygenase Activity and Seed Quality of Australian Sweet Lupin (Lupinus angustifolius L.)

The work aimed to demonstrate the impact of sowing time (2022 trial) and irrigation (2023 trial) on the expression of lipoxygenase (LOX) activity and crude protein and fat contents in five varieties of Australian sweet lupin or narrow-leafed lupin (Lupinus angustifolius L.) and to investigate the relationship of LOX with linoleic acid and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity. The results revealed significant interaction and main treatment effects of lupin varieties and sowing time in expressed LOX activity and crude protein and fat contents in the 2022 trial (p < 0.001). Similarly, the expression of LOX activity and crude protein and fat contents in the 2023 trial was determined by the interaction and main treatment effects of lupin varieties and irrigation treatment (p < 0.001). Among all the significant effects, the expression of LOX activities in both trials was dominated by differences between varieties. However, the expression of crude protein and fat contents in the 2023 trial was primarily influenced by irrigation treatment. The crude fat content in the 2022 trial was primarily governed by the effect of sowing time, whereas the crude protein content was determined by an interaction between variety and sowing time. Lupin LOX was found to positively correlate with linoleic acid and negatively correlate with DPPH radical scavenging activity; to the best of our knowledge, this was demonstrated for the first time in L. angustifolius. This deeper understanding would benefit Australian lupin plant breeders in developing variety-specific planting recommendations or breeding strategies for reduced LOX activity for improved sensory quality when applied to food products.