Lucerne saponins III.—effect of lucerne saponins on larval growth and their detoxification by various sterols

The role of sapogenins in the antibiological effects exerted by lucerne saponins has been studied. Data are presented, showing that lucerne sapogenins are more toxic towards Tribolium castaneum larvae than their respective saponins, from which they are isolated. Medicagenic acid and to a lesser extent a new, hitherto unidentified sapogenin are the main growth‐depressing factors, the soyasapogenols being almost harmless in this respect. When cholesterol is also included in the diet, the negative influence of the sapogenins is completely abolished. The counteraction found with cholesterol, as well as with various plant sterols, of the growth inhibition of the larvae caused by dietary saponin extracts (SE) was studied quantitatively with different SE: sterol ratios. It is shown that the amount of cholesterol needed to counteract fully the growth impairment depends on the toxicity of the SE preparation and its concentration in the diet. The counteracting property of plant sterols on larval growth depression leads to the conclusion that a built‐in defence mechanism exists in lucerne against the antibiological effects of saponins.