FIELD: postharvest treatment of grain before laying for storage with the use of organic preservatives. SUBSTANCE: method involves treating grain, before laying for storage, in electromagnetic superhigh frequency field with propionic acid including additive of chitosan; using specific preparation as chitosan source, said preparation being produced by sequential extracting of Mortierella nigrescens micromycet biomass with the use of non-polar extractant in above-critical state, water, alkaline, water, acid, water, alkaline, and water, followed by joining of first extract with solid residue. EFFECT: reliable storage of grain upon secondary contamination. 2 ex
