An application method of 1-monopropionine compound and its isoform 3-monopropionine being used as preserving agents in animal feeds, corns, grains, and other food materials. The monopropionine compounds are obtained by esterification reaction of propionic acid and glycerol. The product is a translucent viscous liquid composition comprising monopropionine compounds and other components, such as free acid, or certain salt forms of propionate. The generated composition can be further distilled in glycerol. The final product can take a liquid form or a powder form. 1-monopropionine compound and its isoform 3-monopropionine function as preserving agent at a low effective dosage of about 0.05 to 1% (by weight), and preferably 0.1 to 0.3% (by weight). A preferable application condition of this method is to preserve animal feeds and corns under a low (about 2% to 12%) moisture condition.