Combination of simple chemical and spectroscopic methods for the identification of Thai Hom Mali rice

Abstract

As the Thai Dawk Mali (KDML105) rice variety is popular due to its high sensory after cook, there is an increase in mixing the KDML105 rice with other rice varieties that leads to unqualified KDML105 milled rice products for export and unqualified unmilled rice seeds for next plants. Instead of using traditional time consuming methods based on the disintegration of the rice kernel in an alkali solution and the inspection of rice cooked in boiling water, this paper proposes to analyze the milled rice powder dissolved in our alkali solution via a spectroscopic method. In our study, 0.1 g, 0.2 g, and 0.3 of milled rice powder from four Thai rice varieties, i.e., KDML105, Pathumthani1, Chainat1, and RD6, are selected. Then each milled rice sample is ground and then dissolved in a 10% potassium hydroxide (KOH) solution. At the specified minutes of dissolution, the relative optical transmission spectrum of the milled rice solution in a 500-800 nm wavelength is measured and only its first derivative is used for the identification of the KDML105 milled rice. We find that the use of 0.10 g of the milled rice powder dissolved in our KOH solution for 10 minutes provides the lowest false rejection rate of 15%, indicating that we have a faster approach with less amount of waste produced. With the 0.2-g milled rice powder, 5 minutes of dissolution is needed but with a slightly higher false rejection rate of 18.3%.