Korean earthenware (also known as onggi) has been reported to play an active role in improving the fermentation quality of foods such as fermented soy products, as well as simply serving as a storage container. In this study, we conduct a region-wise analysis of the effects of the onggi shape, chemical composition, and gas-permeation characteristics on the total phenolic content and antioxidant activity of the soy sauce stored in these containers during its fermentation. During the fermentation process, the amount of antioxidant produced in the soy sauce increases with increase in the container diameter relative to the height. The antioxidant amount also increases with decrease in the amounts of alkali and alkaline earth metal oxides in the clay chemical composition and increase in the gas permeability of the onggi. Of all the onggi considered in our experiments, the Gangjin onggi exhibits the widest diameter relative to its height, least amounts of alkali and alkaline earth metal oxide components, and highest gas permeability. The antioxidant power is highest in the soy sauce fermented in the Gangjin onggi, corresponding to a total phenolic content value of 16.6 mg GAE/ml and FRAP of 54.3 mg AAE/ml.

Keywords: Earthenware, Shape, Chemical composition, Gas permeation, Fermentation