PURPOSE: To obtain an inexpensive natural material for food having high safety, having bactericidal and antibacterial action and suitable as preservatives for food, oxidation and putrefaction-preventing agent, freshness-retaining agent, etc., by crushing seed of grape fruit and extracting effective ingredients contained in the seed.

CONSTITUTION: Seeds of grape fruit is crushed and then treated by a method such as heat distillation method, hydrolysis method, alcohol extraction method or squeezing method and liquid effective ingredient contained in seeds is extracted to provide the natural material for food. When used, the extract liquid is blended with natural dispersing agent (e.g. natural glycerol) and the blend is diluted into desired magnification by water and the diluted liquid is applied to a food such as marine product, livestock product, agricultural product or processed food by a method such as spraying, immersing, coating or mixing to carry out preservation of food, retention of freshness, prevention of putrefaction or prevention of oxidation.