Green Labelled Rice Shows a Higher Nutritional and Physiochemical Quality Than Conventional Rice in China

In China, green food refers to a wide array of certified agricultural and processed edible commodities that are produced strictly following defined standard protocols and labelled with a specified “Green Food” logo. The demand for green labelled rice is rapidly growing due to its higher quality and adherence to safety standards compared to conventional rice. Therefore, the physicochemical and nutritional quality of green rice needs to be further investigated for consumers’ benefits. Using Daohuaxiang 2, one of the most famous types of green rice, we found that green rice was significantly superior to conventional rice in terms of thousand kernel weight, chalkiness, amylose content, and rheological properties. Green rice contained lower levels of heavy metals than conventional rice due to a dramatic reduction in chemical inputs during its cultivation. The concentrations of Cr, As, Cd, Pb in green rice decreased, respectively, from 98.7 to 180.1 μg/kg, 49.8 to 62.3 μg/kg, 7.8 to 9.1 μg/kg, and 29.0 to 42.8 μg/kg on average. Gas chromatography coupled with mass spectrometry (GC–MS)-based metabolomics, in combination with multivariate analysis, revealed that 15 metabolites differentially accumulated when comparing green and conventional rice. Among these, 12 metabolites showed a high accumulation in green rice, including seven amino acids, two sugars, and three fatty acids. Overall, our results suggest the superior quality of a type of green rice that is popular in China, which may boost green rice consumption and facilitate the further expansion of green rice production in China.


Introduction
Rapid economic growth in China has been accompanied by the increasing concern of consumers with respect to food quality and safety. In China, there are three levels of certification systems for food, which is indicative of the stringency of the associated standards, namely safe food, green food, and organic food [1]. Green food was first introduced by the Ministry of Agriculture of China in 1990, and it refers to a unique Chinese certification scheme for food, which indicates that the food was produced in accordance with the principle of sustainable development and that standard operational protocols were applied throughout the whole industry chain, as designated by the China Green Food Development Center (CGFDC) [2]. Green food, which is of a relatively lower standard compared with organic food, provides a "middle way" between safe and organic food and is widely accepted in China [3]. At the end of 2019, China already had 13,202 green-certified enterprises, representing 36,345 products and 21.7 million farmers, with 11.1 million hectares being used for the production of 157 million tons of green products. The annual sales and export values were Chinese Yuan (RMB) 455.7 billion yuan and USD 3.21, accounting for 8.20% of the total farmland area in China, and 9.7% of the GDP was from agriculture [4].

Elemental Analysis
The elements in rice were determined using the method described in a previous report [23]. In brief, 500 mg rice samples were placed in a polytetrafluoroethylene (PTFE) digestion container. Nitric acid (6 mL) was added to each container and predigested overnight at 60 • C. Hydrogen peroxide (2 mL) was added after cooling. The heating program was performed in three steps. In the first step, the temperature was increased linearly to 120 • C over a period of 6 min and maintained for 2 min. In the second step, the temperature was increased linearly to 160 • C (1500 W) over a period of 4 min and maintained for 8 min. For the third step, the temperature was increased linearly to 180 • C (1500 W) over a period of 3 min and maintained for 20 min, followed by 30 min of cooling. The essential elements in the rice were determined by inductively coupled plasma-atomic emission spectrometry (ICP-AES) using the Optima 7300DV (Perkin Elmer, Waltham, CO, USA), and the toxic elements were determined using a 7700 Series × ICP-MS (Agilent Technologies, Courtaboeuf, France).

Non-Targeted Metabolomics Analysis
Metabolomic analysis using gas chromatography coupled with mass spectrometry (GC-MS) was performed according to a previous report, with slight modifications [24]. First, 100 mg rice powder was added into 1.0 mL water-methanol-dichloromethane solution (1:3:1) and 40 µL internal standard solution (200 µg/mL, adonitol). The extraction was carried out by sonication for 30 min, and the mixture was then centrifuged for 10 min at 16,000× g. Next, 0.7 mL of the upper layer solution was transferred to a 1.5 mL Eppendorf tube and vacuum-dried in a CentriVap centrifugal vacuum concentrator (Labconco, Kansas City, MO, USA). Sixty microliters of methoxyamine hydrochloride (20 mg/mL in pyridine) was added to each vial and incubated for 30 min at 80 • C. Subsequently, 80 µL BSTFA reagent (1% TMCS, v/v) was added, followed by a reaction time of 1.5 h at 70 • C. GC-MS analysis was conducted using an Agilent 7890 gas chromatograph (Agilent Technologies, Palo Alto, CA, USA) system equipped with a Shimadzu GC-MS QP2010 Plus (Shimadzu, Kyoto, Japan). The instrumental settings followed previous protocols [24].

Data Processing and Multivariate Data Analysis
Tentative identification of metabolites was achieved using National Institute of Standards and Technology (NIST) 15 standard mass spectral databases (NIST, Gaithersburg, MD, USA) with a similarity of more than 80%, verified by available reference compounds. Peak areas were normalized to the internal standard and exported to MS Office Excel (version 2019, Microsoft Corporation., Redmond, WA, USA). Principal component analy- sis (PCA) and partial least squares-discriminant analysis (PLS-DA) was conducted using SIMCA-P + software (version 14.0, Umertrics, Umea, Sweden). Statistical analysis was conducted using the SPSS statistical software (version 21; SPSS Corp., Chicago, IL, USA). The Student's t-test was performed to analyze significance of cross-group difference, and p values lower than 0.05 indicated statistical significance. The physical properties, including the thousand kernel weight, bulk density, chalkiness, and percentage of chalky kernels, of the green and conventional rice are reported in Table 1. The thousand kernel weight of rice is an important parameter for the evaluation of rice yield, and green rice showed a significantly higher thousand kernel weight (21.08 g) compared to that of conventional rice (20.21 g). No significant difference in bulk was observed between the green and conventional rice groups. Chalky rice kernels usually cause low eating quality and strongly influence consumer acceptance of products [25]. Green rice had a relatively lower chalkiness (8.31%) and percentage of chalky kernels (22.46%) than conventional rice (9.74% and 26.15%, respectively). Values (± standard deviation) within the same row followed by "a" are significantly higher than those indicated by "b" (p < 0.05) (n = 3).

Results and Discussion
Most inspection guides for rice use chalkiness and the percentage of chalky kernels for grading. The chalky grain rate of first-grade high-quality rice is lower than 10%, while that of inferior rice is higher than 30% in China [26]. Chalkiness is a complex polygenic trait, and nitrogen fertilizers had significant effects on the chalky trait of rice grain. Many studies have reported that nitrogen fertilization significantly increased the percentage of chalky kernels and chalkiness [9,27,28]. Thus, the chalky trait of rice from different production systems may be due to the management of different fertilizers. The adoption of green food production systems, with combined application of organic and inorganic fertilizers, is advisable as a good compromise for chalky rice [6].

Main Chemical Components
The main chemical components of green and conventional rice are shown in Table 1. Protein content is a crucial factor in rice quality. In the present study, green rice exhibited a lower protein content (7.11 g per 100 g) in comparison to conventional rice (7.42 g per 100 g). Amylose content is also an important factor for estimating the cooking or eating quality of rice. Table 1 shows that the amylose content in green rice was higher than in conventional rice. Moisture and fat contents greatly affect the quality of rice. In this study, the results showed no significant difference in moisture and fat contents between the green and conventional rice.
Previous studies have reported that the protein content is negatively correlated to the palatability of rice [29][30][31]. Many studies have reported that a high protein content is associated with a harder cooked rice and may influence its eating quality [32,33]. Similar findings have been reported in an organic rice cropping system, with organic rice showing a lower accumulation of protein than conventional rice [34,35]. It has been observed that the application of a nitrogen fertilizer significantly increases the protein content of rice [27,36]. Previously, a study reported that the combined application of 40% organic fertilizer and 60% chemical fertilizer was the optimal ratio for obtaining the best quality of rice [37].
Low-amylose rice is generally soft and sticky after cooking, whereas high-amylose rice is harder and less sticky. This result, in accordance with previous results, indicate that organic rice shows a higher amylose content than conventional rice [34,38]. A higher amylose content may be associated with fertilizer application. Iqbal et al. reported that the use of an organic fertilizer combined with a chemical fertilizer considerably improved the rice amylase content [39].

Rheological Properties
The pasting properties, as determined by RVA, are widely accepted indicators for the critical and rapid assessment of the eating and cooking quality of rice [40]. The peak viscosity, final viscosity, breakdown viscosity, and setback viscosity of the green rice and conventional rice are shown in Table 2. The present study shows that the pasting properties of the green rice and conventional rice were significantly different (p < 0.05). Peak viscosity is an indicator of water-binding capacity. The peak viscosity of green rice ranged from 3625 to 4463 centipoise (cP), with a mean value of 4250 cP, while for conventional rice, this ranged from 3417 to 4325 cP, with a mean value of 4055 cP. The final viscosity indicates the ability of the starch to obtain a gel structure after cooking and cooling. The final mean viscosity value of 4353 cP for green rice was high compared to that of conventional rice. Breakdown viscosity is associated with the ease of cooking rice starch, and this value for green rice (1526 cP) was higher than that of conventional rice (1478 cP), but this difference was statistically insignificant (p = 0.5231). Setback viscosity indicates the rate of starch retrogradation, and green rice was found to have lower rates of starch retrogradation compared with conventional rice. Values (± standard deviation) within the same row followed by "a" are significantly higher than those indicated by "b" (p < 0.05) (n = 3).
Cooking quality is an important attribute with respect to consumers' acceptance, and has been found to vary significantly for rice depending on the cultivation system. Overuse of N fertilizers leads to poor eating and cooking quality of the grain [12]. The pasting properties were negatively correlated with the protein content [41]. The green rice with good taste values showed a higher peak viscosity and final viscosity, by contrast, with a lower setback viscosity. A higher peak, final, and setback viscosity was reported in organic rice compared to the conventional product [35,41]. Nonetheless, our study suggested that the cooking and eating quality of green rice was significantly improved due to the adoption of green rice management practice.

Toxic Elements
Four toxic elements of the rice samples were analyzed ( Figure 1). Chromium (Cr) is considered a serious environmental pollutant due to its wide industrial applications. Evidence has demonstrated that Cr can pose serious health risks to humans, causing diarrhea, asthma, and cancer [42]. The Cr concentration in the green rice (98.7 µg/kg) was

Essential Elements
The levels of eight essential elements (P, K, Ca, Mg, Cu, Fe, Na, and Zn) were determined in the rice samples. These micronutrients are important for human health, and a deficiency of these microelements can result in serious diseases. The ANOVA results of each element for the green and conventional rice showed that the P, K, Mg, Fe, and Zn levels were significantly different (p values < 0.05). P and K were the most abundant essential elements in both types of rice, and the P contents of the green rice and conventional rice ranged from 657.3 to 772.0 mg/kg and 671.3 to 995.2 mg/kg, respectively. For K, the content found in green rice ranged from 453.8 to 667.4 mg/kg, which is lower than that in the conventional rice, which ranged from 535.1 to 739.5 mg/kg. Both elements were significantly higher in conventional rice, which may be due to the fact that P and K are contained in synthetic fertilizer and are largely used in conventional rice farming.
Mg is an essential element for the human body. Many studies have reported that an Mg deficiency is associated with a wide range of diseases, including cardiovascular diseases, arrhythmia, osteoporosis, and fibromyalgia [51,52]. The Mg content of green rice (128.1-192.7 mg/kg) was lower that of conventional rice (165.7-248.4 mg/kg). A previous study reported synergistic behavior between the Mg and K concentrations [53].
The iron content of green rice ranged from 1.5 to 2.2 mg/kg, while the range for conventional rice was between 1.7 to 4.9 mg/kg. Previous studies have reported that the application of a nitrogen fertilizer promoted Fe accumulation in rice grain [54]. Iron deficiency was recently listed as a public health problem and the 6th leading cause of disease in developing countries by the World Health Organization (WHO) [55]. The amount of bioavailable iron in rice is low, and the phytic acid present in rice may inhibit the bioavailability of iron [56].
Likewise, the zinc (Zn) concentrations in green rice ranged from 11.6 to 15.2 mg/kg, while the concentration in conventional rice ranged from 13.7 to 17.1 mg/kg. The mean zinc content in green rice was 13.3 mg/kg, and the mean value in conventional rice was 15.3 mg/kg. Zn is one of the most essential elements required for the growth of human beings. The relatively low Zn concentrations found in both types of rice cannot meet the daily dietary requirement [57].
The results of the present study indicate the importance of management practice in contributing to rice element accumulation. Concentrations of all examined toxic (Cr, As, Cd, and Pb) and essential elements (P, K, Mg, Fe, and Zn) in green rice were lower compared to those of conventional rice. Chemical fertilizers promote the absorption of more Arsenic (As) is a ubiquitous metalloid that can cause cancer in humans and enter the food chain mainly from contaminated drinking water [43]. Rice has been reported to contain a more toxic form of arsenic in comparison to other plants [44]. The As content of green rice (42.2-60.7 µg/kg) was lower than that of the conventional rice (44.4-88.9 µg/kg). The As content in this study can be considered low in comparison with that reported in other studies [45,46].
Rice grains around the world are frequently contaminated with cadmium (Cd), which poses a serious threat to human health and has attracted widespread concern [47]. The concentration of Cd in green rice is lower than that in conventional rice. Soil conditions and management practices can significantly influence the Cd content in rice. Previous studies have indicated that the application of organic fertilizer significantly reduces the Cd content in rice plants [48]. Green food reduces chemical nitrogen fertilizer use by 50% compared with the fertilization levels local farmers through supplementation with organic fertilizers [4]. The limit for Cr in rice established by the Ministry of Agriculture is 200 µg/kg. Both types of rice showed very low levels of Cd content, which were well below the prescribed limit.
Lead (Pb) is one of the more frequently studied elements in rice [44,49]. It has been reported that the mean concentration of Pb in rice collected in China is 100 ± 140 µg/kg [50]. In this study, Pb was quantified at concentrations ranging from 17.6 to 40.9 µg/kg for green rice and from 20.1 to 80.6 µg/kg for conventional rice, values which are within the Ministry of Agriculture's maximum permissible limit for this metal (200 µg/kg).

Essential Elements
The levels of eight essential elements (P, K, Ca, Mg, Cu, Fe, Na, and Zn) were determined in the rice samples. These micronutrients are important for human health, and a deficiency of these microelements can result in serious diseases. The ANOVA results of each element for the green and conventional rice showed that the P, K, Mg, Fe, and Zn levels were significantly different (p values < 0.05). P and K were the most abundant essential elements in both types of rice, and the P contents of the green rice and conventional rice ranged from 657.3 to 772.0 mg/kg and 671.3 to 995.2 mg/kg, respectively. For K, the content found in green rice ranged from 453.8 to 667.4 mg/kg, which is lower than that in the conventional rice, which ranged from 535.1 to 739.5 mg/kg. Both elements were significantly higher in conventional rice, which may be due to the fact that P and K are contained in synthetic fertilizer and are largely used in conventional rice farming.
Mg is an essential element for the human body. Many studies have reported that an Mg deficiency is associated with a wide range of diseases, including cardiovascular diseases, arrhythmia, osteoporosis, and fibromyalgia [51,52]. The Mg content of green rice (128.1-192.7 mg/kg) was lower that of conventional rice (165.7-248.4 mg/kg). A previous study reported synergistic behavior between the Mg and K concentrations [53].
The iron content of green rice ranged from 1.5 to 2.2 mg/kg, while the range for conventional rice was between 1.7 to 4.9 mg/kg. Previous studies have reported that the application of a nitrogen fertilizer promoted Fe accumulation in rice grain [54]. Iron deficiency was recently listed as a public health problem and the 6th leading cause of disease in developing countries by the World Health Organization (WHO) [55]. The amount of bioavailable iron in rice is low, and the phytic acid present in rice may inhibit the bioavailability of iron [56].
Likewise, the zinc (Zn) concentrations in green rice ranged from 11.6 to 15.2 mg/kg, while the concentration in conventional rice ranged from 13.7 to 17.1 mg/kg. The mean zinc content in green rice was 13.3 mg/kg, and the mean value in conventional rice was 15.3 mg/kg. Zn is one of the most essential elements required for the growth of human beings. The relatively low Zn concentrations found in both types of rice cannot meet the daily dietary requirement [57].
The results of the present study indicate the importance of management practice in contributing to rice element accumulation. Concentrations of all examined toxic (Cr, As, Cd, and Pb) and essential elements (P, K, Mg, Fe, and Zn) in green rice were lower compared to those of conventional rice. Chemical fertilizers promote the absorption of more elements from the soil by the rice. There were no significant differences found in Ca, Cu, and Na between the green and conventional rice. The synthetic N, P, and K compound fertilizers are applied at high concentrations in conventional rice, so the associated elements are accumulated at higher levels. With strict regulations and regular inspection, green rice contained significantly lower levels of toxic elements than conventional rice. These results are useful as scientific evidence of the greater safety of green rice in comparison with conventional rice in terms of toxic metal levels. In a study by Xiao et al. in China, the range of Cr, As, Cd, and Pb contents in rice increased from 0 to 200 µg/kg, 100 to 200 µg/kg, 0 to 150 µg/kg, and 0 to 100 µg/kg, respectively [58]. When comparing these results with ours (Figure 1), all of the toxic elements are well within the acceptable range. Indeed, Cd was much lower than the average in China, which may be due to the low Cd accumulation in the soil in northern China compared to the other areas [59]. Additionally, the content of toxic elements in both types of rice was well below the prescribed limit, indicating that the twenty brands of rice sold in Beijing markets can be considered as very safe. Consumer demand for healthier and safer rice that contains a lower content of toxic elements is growing. In our study, green rice was demonstrated to be safer than conventional rice. However, it is also worth noting that the levels of essential elements were observed to be lower in green rice than in conventional rice, suggesting that greater efforts should be made toward improving the content of essential elements in green rice by biofortification in the future.

Untargeted Metabolomics
Untargeted metabolomics was used to provide comprehensive information for comparing green rice and conventional rice. In this study, the metabolites from rice grains were identified by GC-MS. Metabolite identification was performed through a comparison of the results with authentic standards, fragmentation patterns, and database references. In total, 64 metabolites, including amino acids, organic acids, sugars, sugar alcohols, and amines, were identified in the rice samples. The relative intensities were normalized based on the intensities of the internal standards and were used to perform multivariate statistical analyses. PCA and PLS-DA were used to analyze the metabolomics datasets for green and conventional rice. The PCA score plots exhibited clear differentiations between the green and conventional rice for PC1 (28.1%) and PC2 (12.2%) (Supplementary Materials Figure  S1). A similar separation pattern was observed using PLS-DA, including 23.8% of the first and 15.3% of the second principal components (Figure 1), and 15 significantly different metabolites were selected, with a variable importance for projection (VIP) > 1.0 and p < 0.05 (Figure 2). These significant differing metabolites served as characteristic compounds that could be used for differentiating green rice and conventional rice.
paring green rice and conventional rice. In this study, the metabolites from rice grains were identified by GC-MS. Metabolite identification was performed through a comparison of the results with authentic standards, fragmentation patterns, and database references. In total, 64 metabolites, including amino acids, organic acids, sugars, sugar alcohols, and amines, were identified in the rice samples. The relative intensities were normalized based on the intensities of the internal standards and were used to perform multivariate statistical analyses. PCA and PLS-DA were used to analyze the metabolomics datasets for green and conventional rice. The PCA score plots exhibited clear differentiations between the green and conventional rice for PC1 (28.1%) and PC2 (12.2%) (Supplementary Materials Figure S1). A similar separation pattern was observed using PLS-DA, including 23.8% of the first and 15.3% of the second principal components (Figure 1), and 15 significantly different metabolites were selected, with a variable importance for projection (VIP) > 1.0 and p < 0.05 (Figure 2). These significant differing metabolites served as characteristic compounds that could be used for differentiating green rice and conventional rice. The 15 differential metabolites included seven amino acids, five sugars, and three fatty acids. The heatmap shows the abundance of metabolites in different clusters from each sample (Figure 3). In green rice, seven (proline, serine, asparagine, lysine, threonine, L-glutamine, and L-isoleucine) out of 18 amino acids accumulated to significantly higher levels than in conventional rice. Sugars are important for the taste and quality of the grain. Sucrose and lactose were found to be highly expressed in green rice. In contrast, higher levels of myo-inositol, mannose, and glucitol were found in green rice compared to the conventional rice. Three fatty acids, including oleic, linoleic, and palmitic acid, were significantly differentially expressed between the green and conventional rice, with expression higher in green rice. The 15 differential metabolites included seven amino acids, five sugars, and three fatty acids. The heatmap shows the abundance of metabolites in different clusters from each sample (Figure 3). In green rice, seven (proline, serine, asparagine, lysine, threonine, L-glutamine, and L-isoleucine) out of 18 amino acids accumulated to significantly higher levels than in conventional rice. Sugars are important for the taste and quality of the grain. Sucrose and lactose were found to be highly expressed in green rice. In contrast, higher levels of myo-inositol, mannose, and glucitol were found in green rice compared to the conventional rice. Three fatty acids, including oleic, linoleic, and palmitic acid, were significantly differentially expressed between the green and conventional rice, with expression higher in green rice. levels than in conventional rice. Sugars are important for the taste and quality of the grain. Sucrose and lactose were found to be highly expressed in green rice. In contrast, higher levels of myo-inositol, mannose, and glucitol were found in green rice compared to the conventional rice. Three fatty acids, including oleic, linoleic, and palmitic acid, were significantly differentially expressed between the green and conventional rice, with expression higher in green rice.  The results of untargeted metabolomics in this study revealed that the metabolic variations between green and conventional rice were significantly different. Amino acids are essential nutritional components in rice. The difference in amino acid contents between green and conventional rice may be due to their different production systems. The green rice was produced with a limited amount of chemical fertilizers in combination with organic fertilizers. In a previous study, the combined application of organic and chemical fertilizers significantly increased the nitrogen use efficiency, soil matter, microbial activity in the soil, and rice yield [15,16,60]. Significantly increased total essential amino acid contents have also been found when using combined chemical and organic fertilizers [61,62]. However, organic rice has shown a lower or similar level of amino acids than conventional rice [63,64]. 15N-labeled tracer techniques showed that combined application of chemical and organic fertilizers significantly increased the percentages of organic N and amino acid N [65]. The release of N from organic fertilizers partially contributed to increased amino acid accumulation.
We noted that the contents of sucrose and lactose were significantly higher in green rice than in conventional rice, with p-values of less than 0.001. It was reported that nitrogen overfertilization significantly inhibited sugar biosynthesis and lower its accumulation with the application of K [66]. However, three other sugars, including myo-inositol, mannose, and glucitol, were present in higher amounts in conventional rice compared to green rice. The reason for this phenomenon remains unanswered at present. Oleic, linoleic, and palmitic acid are the major fatty acids, accounting for more than 90% of the total fatty acids in rice [67]. All of the three fatty acids were significantly higher in the green rice than in the conventional rice, and this is an important consideration for future research. Fatty acids are highly associated with fungi, and the addition of organic fertilizers significantly increased the fungal population [68]. It has been reported that these fatty acids contribute to the prevention of several diseases, such as cardiovascular disease, inflammatory disease, and cancer [69].
In our study, most metabolites were highly accumulated in green rice. Most probably, the production systems of green rice involved chemical fertilizers combined with organic fertilizers, which can improve the utilization rate of fertilizers and the microbial activities in soil and alter metabolic pathways to certain extent within the plant, thus, enhancing the accumulation of beneficial metabolites in rice.

Conclusions
Currently, the growing concern of consumers as regards food safety and the environment is gaining strength. The current agricultural system in China heavily depends on the use of chemical N, which negatively affects N use efficiency and soil health, the environment, and food safety. This paper investigated and compared the quality and metabolomics of rice grown in green-certified versus conventional production systems. The physicochemical and rheological properties were higher for rice grown under the green-certified system than under the conventional farming system. The toxic elements in both types of rice were very low, indicating that the investigated rice sold in Beijing markets can be regarded as very safe, although the green rice was found to be safer than the conventional rice, as it had a lower toxicity. However, the essential elements (P, K, Mg, Fe, and Zn) were present at lower levels in green rice compared with conventional rice. Through untargeted metabolomics analysis using GC-MS, we found that 15 of the 64 detected metabolites were more highly expressed in green rice, and three metabolites were more highly expressed in the conventional rice. The differences between the two types of rice in terms of metabolites may be mainly due to the reductions in the use of synthetic fertilizers and the combined use of organic and chemical fertilizers. Thus, the green rice production system is a potential alternative to the conventional system, which allows for a reduction in chemical fertilizer use, producing safer rice of a higher quality and, thus, is financially attractive to farmers. The results of this study could be useful in the further development of green rice production in China.

Supplementary Materials:
The following are available online at https://www.mdpi.com/article/10 .3390/foods10050915/s1, Table S1: The information of rice samples from green rice and conventional rice. Figure S1: PCA score plots derived from non-targeted metabolite profiling of three different treatments analyzed by GC-MS.

Conflicts of Interest:
The authors declare no conflict of interest.