lupin debittering

An EFSA scientific opinion states that bitter lupin seeds have traditionally been debittered by soaking them in brine and then washing them. It also reports that water treatment and boiling remove 89–97% of the quinolizidine alkaloids (QA) in the seeds. However, the individual studies underlying this 89–97% figure, including the species and conditions studied, could not be traced from the opinion.

A 2016 review describes biological, chemical, and water-based methods, such as soaking, for detoxifying (debittering) bitter lupins, and states that the shortest process can be completed in 1 hour. The review does not go into the details of the processes; its description only indicates that debittering methods range from traditional brine soaking to faster methods.

The progress of debittering has also been recorded in stages. Soaking and heating alone reduced alkaloids to about 50–65% of their initial level. Subsequent solid-state fermentation with the mold used to make tempeh (Rhizopus oligosporus) was reported, depending on the study, to reduce them by an additional 9% to 43% of their initial level. Yet a test with another bitter species found no detectable reduction at the fermentation stage. Results are inconsistent across mold strains, bean types, and the presence or absence of an acidic environment.

Within the scope of the abstract, washing Lupinus albus seeds with a 0.5% or 1% sodium chloride or citric acid solution has also been tested. Compared with conventional water soaking as the control, treatment with a 1% citric acid solution saved 88 hours and 65 L of water per 1 kg of dried lupins, while lowering alkaloid content to the level of commercial standards (0.31–1.03 g/kg dry matter). An electronic-tongue measurement of taste profiles placed the experimental and commercial samples in distinct clusters, and bitter and umami responses correlated well with alkaloid content. Specific electronic-tongue response values and details of statistical tests could not be confirmed from the abstract.