Oligosaccharides, phytate and trypsin inhibitors in sweet lupine seeds (Lupinus angustifolius L.) and commercial products derived from them

Lupine seeds (Lupinus angustifolius) are increasingly recognized as a valuable source of plant-based protein for human nutrition. Similar to other legumes, lupines contain antinutrients. This study analyzed the content of raffinose family oligosaccharides (RFO), phytate and trypsin inhibitors for the first time in raw lupine seeds and in a bunch of commercially available lupin products made from them. In the seeds, RFO content ranged from 46 to 49 mg total RFOs/kg (dry weight), with approximately 30 mg/kg attributed to stachyose. Phytate levels ranged between 1.2 and 2.2 g/100 g (dry weight), and trypsin inhibitors were found to be between 0.75 and 0.90 TUI/mg (dry weight). The concentrations of these compounds in the flakes, grist, and flour were comparable to those in the seeds. The conditions applied in coffee surrogate and wort production resulted in a significant reduction in RFO and trypsin inhibitor activity. However, phytate levels remained relatively stable. Germination reduced RFO, while phytate and trypsin inhibitor activity showed only marginal reduction. This study highlights irrelevant changes of RFO, phytate and trypsin inhibitors of lightly processed lupine products like flour. In contrast, the decrease in RFO content was substantial in intensively processed lupine products like wort or coffee surrogate and in germinated seeds, while phytate and trypsin inhibitor activity are either unaffected or only partially diminished in these products compared to lupine seeds. These findings underline the varying impact of different processing steps on RFO and the relative stability of phytate and trypsin inhibitor activity.