A ‘bioactive’ composition that has one or more oligogalacturonans ((1→4)-α-D-galacturonan) or any other oligosaccharides (oligoguluronans) that may present an ‘egg box’ conformation, this conformation being further stabilized by one or more polycationic saccharide(s), preferably either a chitosan oligosaccharide or a chitosan polysaccharide. A method prepares this composition and it is used, in medical, pharmaceutical, agricultural, nutraceutical, food, feed, textile, cosmetic, industrial and/or environmental applications.