PURPOSE: To provide a method for retaining quality of a food without emitting any malodor and offensive smell remaining in the interior and causing discoloration of the food itself in placing the food containing much sulfur in a hermetically sealed container and carrying out thermal sterilization treatment.

CONSTITUTION: The subject method for improving quality of a food is a method characterized as follows. The food, together with a synthetic resin material containing zinc oxide, is arranged in a hermetically sealable container and hermetically sealed and thermal sterilization treatment is then carried out.