The present invention allows a plant seed that contains at least galacturonic acid and rhamnose as constituents to be reduced in a general bacterial count to a cosmetically acceptable level by placing the plant seed under reduced pressure, subsequently exposing the plant seed in bacteriocidal gas atmosphere with higher pressure than atmospheric pressure, and then placing the plant seed under reduced pressure. The plant seed of the present invention can form a pectic coat in water upon soaking in the water. The bacteriocidal in the present invention can be selected from any combination of ethylene oxide, ethylene glycol, ethylene chlorohydrin, and inert gas.
