Comparison of characteristics of carbonized rice straw from various rice varieties and parts of rice straws as a source for natural black colorant

This study compared the characteristics of carbonized rice straw (CRS) made of a whole straw and merang (the half of the upper part of the rice stem until the panicle without leaves) of three different rice varieties. The yield, mineral components, carbon content, color, pH, and stability for heat and light were analyzed. The results showed that the yield of CRS ranged from 16.73 to 21.80% and there was no significant yield difference of CRS from different parts of straw and varieties of rice. The carbon content of merang was higher than that of rice straw, regardless rice varieties. The CRS of black glutinous rice had the highest carbon content, and the lowest silica content (31.69%) compared to the other rice varieties studied. The pH of the CRSs was ranging from 10.53 to 11.08. Exposed in light at 40 °C, the color and pH of the CRS filtrates were stable for 15 days of storage. The CRS from the merang of black glutinous rice had the darkest color due to its high carbon content and the low mineral content.