Evaluation of Moisturizing Effect of Metasilicate Extracted from Rice Hull

Abstract

In Japan, where many resources are imported, recycling wastes is one of the most concerning issues. This is consistent with the Sustainable Development Goals (SDGs), which call for the secondary use of agricultural by-products that are regularly generated. Rice hull, particularly, generated during rice production are one of the agricultural by-products. In this study, the utilization of metasilicate which is produced during the extraction of silicic acid present in rice hulls was focused. Metasilicate is mainly a free component of hot springs and is reported to have a moisturizing effect. Thus, the metasilicate extracted from rice hulls would expected also have a similar effect. To examine the use of rice hulls as a moisturizing component, the elution characteristics of metasilicate present in rice hulls in tap water were first evaluated. The concentration of the dissolved metasilicate was determined colorimetrically using the molybdenum yellow method according to the guidelines of the mineral spring analysis method. As a result, 546 mg/kg of metasilicate was eluted from the rice hull in tap water at a water temperature of 40 °C. This value was much higher than 50 mg/kg of metasilicate, which is defined as a mineral spring. Next, the moisturizing effect of metasilicate extracted from rice hulls was evaluated by taking a warm bath in the water in which the hulls were immersed. As a result, the ratio of change of the moisture content of the skin remained higher than the value before the experiment even 30 minutes after the warm bath. In the corresponding t-test at a significance level of 5%, there was no significant difference in the rate of change of the moisture content of the skin 5 and 30 minutes after the warm bath, suggesting that the rice hull may have a moisturizing effect.