Although Hom Mali rice is considered the highest quality rice in Thailand, it is susceptible to adulteration and substitution. There is a need for rapid, low-cost and efficient analytical techniques for monitoring the authenticity and geographical origin of Thai Hom Mali rice. In this study, two infrared spectroscopy techniques, Fourier-transform infrared spectroscopy with attenuated total reflection (FTIR-ATR) and near-infrared (NIR) spectroscopy, were applied and compared for the differentiation of Thai Hom Mali rice from two geographical regions over two production years. The Orthogonal Projections to Latent Structures Discriminant Analysis (OPLS-DA) model, built using spectral data from the benchtop FTIR-ATR, achieved 96.97% and 100% correct classification of the test dataset for each of the production years, respectively. The OPLS-DA model, built using spectral data from the portable handheld NIR, achieved 84.85% and 86.96% correct classification of the test dataset for each of the production years, respectively. Direct NIR analysis of the polished rice grains (i.e., no sample preparation) was determined as reliable for analysis of ground rice samples. FTIR-ATR and NIR spectroscopic analysis both have significant potential as screening tools for the rapid detection of fraud issues related to the geographical origin of Thai Hom Mali rice.
Thai Hom Mali rice is an economic crop of Thailand and well-known as a premium rice in the world trade. In this research, Thai Hom Mali rice samples were collected from the paddy fields in the northern and northeastern regions of Thailand for verifying the authenticity of rice origin. Multi-element and stable isotopic compositions in rice samples were determined by inductively coupled plasma mass spectrometry (ICP-MS) and isotope ratio mass spectrometry (IRMS), respectively. A radar plot was applied to discriminate the origin of rice. Thai Hom Mali Rice from both regions had similar pattern of isotopic composition. The two regions clearly displayed different distribution of elemental patterns. Therefore, Thai Hom Mali rice can be differentiated from each region using multi-element combined with a radar plot.
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