The invention relates to a method for obtaining an active ingredient having an immediate anti-wrinkle and skin-tensioning effect, by extracting and purifying high molecular weight polysaccharides from oat bran, fibers and/or grains, and solubilizing and stabilizing the polysaccharides in water. The invention also relates to the product thus obtained, to uses thereof, and to cosmetic compositions containing this active ingredient. The oat bran polysaccharides include alpha-glucans having a molecular weight of between 25 kDa and 300 kDa.