Fingerprinting of Volatile Organic Compounds for the Geographical Discrimination of Rice Samples from Northeast China  
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Footnote 1: email: [EMAIL_ADDRESS] (Z.W.);  
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and high-throughput identification techniques using modern analytical chemistry, which has heightened sensitivity and accuracy, are now more critical than before.  
Whether accidentally or intentionally, adulteration in rice is possible from the crop harvest to the grain arrival to consumers. According to the needs of consumers and to avoid fraud, researchers have proposed different analysis methods, such as targeted and nontargeted analysis, to restrain rice false description, adulteration, or fake origin labeling [7; 8]. The specific origin determines the specific quality of rice. Geographical origin indications have a crucial role in the unique characteristics of rice [9]. Therefore, it has improved the economic return of rice. For the last decade, the geographical indications of rice have been determined according to physical and chemical properties such as morphology (shape, width, and length), amylose, starch, protein content, cooking quality, and element concentration [9; 10; 11].  
In addition to these technologies, DNA-based methods have proven reliable and can detect adulteration and identify geographical indications [12]. However, a recent study reported rice fingerprint identification using spectroscopy, but this technology cannot identify the marker fingerprint [3]. Therefore, metabolomic-based methods have attracted increased focus on solving the defects of the aforementioned method of determining metabolite fingerprinting for geographical identification. Nuclear magnetic resonance spectroscopy and mass spectrometry are the more commonly used analytical techniques in metabolomics [10]. The high chromatographic resolution, assay-specific detection, metabolite quantification, and ability to identify unknown substances of GC-MS make it a suitable tool for fingerprinting studies [13]. Rice is rich in carbohydrates, vitamins, other significant metabolites, and low molecular weight secondary metabolites. In addition, volatile organic compounds (VOCs) are composited during paddy growth and development [1]. Therefore, VOC metabolomics can be utilized to distinguish the peculiarity of rice, the identifiability of rice, and the properties of rice varieties from a specific place of origin. Therefore, it has been applied to evaluate geographical origin [4; 14].  
VOCs are the diagnostic aspects of rice quality that can determine consumers' acceptance. They are also essential indicators of geographical origins. Although VOC metabolites have been studied in various food authenticity studies, such as geographic [1; 4; 14] and botanical origin identification [15; 16; 17], a method for quick identification of the geographic origin of rice from a different region is still lacking. Therefore, in the current study, a non-targeted VOC metabolomics method was applied to study the phenotype of rice from Heilongjiang, Jilin, and Liaoning provinces. Specifically, HS-SPME and GC-MS and multivariate pattern recognition analysis identified the potential variation markers of VOCs in rice. The chromatographic data were analyzed by agglomerative hierarchical clustering (HCA) and principal component analysis (PCA). Partial least squares discriminant analysis (PLS-DA) was applied to develop an estimation model to discriminate samples based on geographical origin. Finally, projection of importance (VIP) scores of variables were calculated to determine the important VOCs of rice.