Structural and quantitative changes of saponins in fresh alfalfa compared to alfalfa silage

Alfalfa (Medicago sativa) is an important legume used in animal feed. The primary objective of the present study was to analyze and trace the individual saponins in fresh and ensiled alfalfa of ten varieties, with the aim of evaluating the structural changes that saponins undergo during ensiling. A secondary objective was to examine whether any of the changes in saponin content were associated with changes in the basic nutrient composition of the ensiled alfalfa.

The total saponin concentration increased when the fresh alfalfa was processed into silage. Three of the zanhic acid glycosides were degraded substantially, whereas the other two increased in all the tested varieties. Five of the seven medicagenic acid glycosides were not changed, whereas the remaining saponins completely disappeared. Finally, two glycosides of soyasapogenol B displayed an inverse relationship to each other.

The nutrient content of fresh material and silages remained relatively constant, with some variations in the crude protein content of the selected alfalfa varieties. The total concentration of saponins increased two- to three-fold after ensilation over the levels present in fresh alfalfa material. The increases in saponin concentration showed a negative linear relationship between protein on a dry matter basis and saponin content. These findings are significant because no known published data have shown this transformation in the ensiling of alfalfa. © 2018 Society of Chemical Industry.