Asparagus Roots: From an Agricultural By-Product to a Valuable Source of Fructans

Asparagus roots are by-products from asparagus cultivation and they could be considered one of the best sources of fructans. These polymers are interesting food ingredients for their prebiotic and immuno-stimulating characteristics. The aim of this work is to characterize the fructan profile from the roots of several asparagus varieties grown at different locations and pickled at three vegetative statuses in order to valorize these by-products as fructan source. Fructans were extracted with hot water and fractionated into three pools according to their molecular weight (MW). Their average MW was studied by HPSEC and their degree of polymerization by HPAEC. The fructan content was up to 12.5% on fresh weight basis, depending on variety and sampling date. The relative abundance of the three pools also depended on the picking moment as after the spear harvest period their total content and MW increased. The average MW of the three fractions was similar among varieties with 4.8, 8.4 and 9 sugar units, although fructans up to 30 units were identified by HPAEC. These characteristics make them similar to the commercialized Orafti^®-GR inulin, a common additive to food products. Therefore, the concept of asparagus roots as cultivation waste must be changed to a new feedstock for sustainable agriculture and industry.