Effect of Grain Coating by Natural Materials on the Aroma Quality of KDML105 Rice

This study evaluated the effectiveness of different coating formulas in preserving the aroma quality of Khao Dawk Mali 105 (KDML 105) rice grains, particularly focusing on the key aroma compound, 2-acetyl-1-pyrroline (2AP). Initially, thirteen coating formulas were tested, and gum arabic was found to be the most effective in maintaining rice appearance and preventing mold growth during storage. In a subsequent experiment, rice coated with carnauba wax, gum arabic, and a 1:1 mixture of both was analyzed for 2AP content over 10 weeks using SHS-GC, under storage conditions of ambient temperature (25 °C) and 4 °C in polyethylene and laminated bags. The 10% gum arabic coating was the most effective at retaining 2AP after 10 weeks. Additionally, the study included a comparison with a 5% rice gel coating and a mixture of 5% gum arabic and 5% rice gel. The results indicated rice stored at 4 °C in laminated bags exhibited a 2-3% reduction in 2AP content after 6 weeks, while at ambient temperature, a reduction of 44-64% was observed. After 10 weeks, the 2AP contents in the 10% gum arabic coated rice were the highest at an average of 38-40% compared to those of the control group. Furthermore, the rancid compounds, including hexanal, heptanal, octanal, nonanal, and 2-pentylfuran, increased significantly in all coated rice samples at ambient temperature, with the highest hexanal content found in rice coated with a mixture of 5% gum arabic and 5% rice gel, showing approximately 22-55% increase compared with those of the uncoated rice. Overall, gum arabic coating was the most effective in preserving 2AP for at least 10 weeks, and storage at 4 °C provided the best conditions for aroma retention and rancid prevention.