Purification of immunostimulatory glucose homopolymer from broccoli (Brassica oleracea var. italica)

We prepared broccoli ( Brassica oleracea var. italica) neutral polysaccharides (flow-through fractions of anion exchange column chromatography from hot water extracts) from different broccoli cultivars and compared their immunostimulatory effects in the silkworm muscle contraction assay. The cultivars showed a wide range of activity, with the cultivar ‘Winter dome’ showing the highest specific activity (more than 100 times higher than curdlan). Furthermore, the active substance was purified by gel filtration column chromatography. The active substance showed heterogeneous molecular weights of more than 270 kDa. Sugar composition analysis of the purified fraction revealed that more than 95% of its sugar component was glucose, suggesting that the immunostimulatory neutral polysaccharide from broccoli cultivar ‘Winter dome’ was a homopolymer of glucose. The purified fraction also induced TNFα production in cultured mouse macrophage cells. These results suggest that the glucose homopolymer in broccoli has an immunostimulatory effect on both arthropod and mammalian immune system. * ABEE : 4-aminobenzoic acid ethyl ester PP : Paralytic peptide DEAE : Diethylaminoethyl TNF : Tumor necrosis factor HPLC : High performance liquid chromatography