곡류의 무기성분 분석 및 비소화학종 분석법 개발

Abstract

Rice, whole grains and grain processed foods account for an important portion of South Koreans’ stable foods. Because of their various nutritive components and diverse physiological activities, their intake is gradually increasing these days. In this study, elemental contents and arsenic species were analyzed in rice, whole grains and grain processed foods via advance analytical techniques. The inorganic elements were analyzed using ICP/OES, ICP/MS, and DMA, and the arsenic species were analyzed using HPLC-ICP/MS. In addition, daily exposure levels were assessed based on the results of the analysis to evaluate the levels of hazards in comparison with the recommended standards. Also using statistical methods the individual grains are identified according to the characteristics of the raw grains.

Ⅰ. Analysis of macro and trace elements in grains and grain processed foods The average contents of macro elements in raw grains were reported in the order of; K: 2421.2 ± 40.6(Mean±SE) mg/kg, P 2420.0±31.9 mg/kg, Mg 752.6±11.1 mg/kg, Ca 114.4±2.8 mg/kg and Na 17.6±0.5 mg/kg. The analyses of nine kinds of raw grains indicated that, although the average contents of macro elements in raw grains were similar in most cases, higher levels were identified in miscellaneous grains such as buckwheat, oats, and adlay. The average contents of macro elements in grain processed foods were found to be; Na 3364.2±301.1 mg/kg, K 1585.5±72.6 mg/kg, P 1192.4±60.0 mg/kg, Mg 273.6±19.5 mg/kg and Ca 218.6±45.3 mg/kg, which were slightly different from those in grain raw materials. The concentrations of trace elements were were found to be varied among samples and were reported higher in whole grains than in polished grains. Among the elements detected with contents not higher than 100 μg/kg, Ga showed significantly higher contents in oat, wheat, and barley while Co showed high contents in millet and buckwheat. The results of analyses of heavy metals (Pb, Cd, As, and Hg) indicated that their contents in raw materials were; As: 0.038±0.001 mg/kg, Cd: 0.016±0.0003 mg/kg, Pb: 0.013±0.001 mg/kg, and Hg: 0.002±0.0001 mg/kg. The heavy metal standards for grains used for comparison were Pb: 0.2 ppm or lower and Cd: 0.1 ppm or lower except for wheat and rice which have the standard of 0.2 ppm or lower. From results it was found that no sample exceeded the standard recommended values. In the case of grain processed foods, the contents of the heavy metals were; As: 0.047±0.004 mg/kg, Pb: 0.020±0.002 mg/kg, Cd: 0.013±0.001 mg/kg, and Hg: 0.002±0.0002 mg/kg, which were similar to those in raw gains. The average contents of Pb and Cd were slightly higher in products containing wheat and the average contents of As were found to be higher in products containing rice compared to other samples. The average contents of Hg were reported to be at the level of natural contents as in raw materials. Based on the results of analyses of heavy metal levels, daily exposures to heavy metals were calculated considering the daily amounts of intake of grains. The daily amounts of intake of white rice, which is taken by South Koreans as the staple food, showed higher levels of exposure to heavy metals compared to other grains. These were as: As (0.226 μg/kg b.w./day), Cd (0.038 μg/kg b.w./day), and Hg (0.006 μg/kg b.w./day). For all four heavy metals, the contribution rates of white rice were reported to be high amounting up to 80%. The human health risks of 12 grain items based on daily exposures to heavy metals were shown to be arsenic: 0.52%, cadmium: 5.49% and mercury: 1.29% compared to the human body exposure safety standards. In the case of lead, the margin of exposure (MOE) values were not higher than 1 for both adults and children. Therefore, the possibility of hazards due to heavy metals resulting from the intake of grains was concluded to be very low and the subject foods were judged to be safe. The statistical techniques were applied for identification of each raw grain using the concentration values of macro and trace elements. From the results it was judged that grains that overlap with each other on the graph have similar characteristics. The LDA statistical analyses of 12 kind of grains showed a discrimination rate of 96%, and it confirmed that the grains were largely divided into rice, barleys, and miscellaneous grains. The LDA statistical analysis of raw materials belonging to the three classified groups, it was identified that they are grouped according to the characteristics of each raw material. However via these analyses, rice (rice, brown rice, glutinous rice) was not easily distinguished because of high variability of samples. The analyses of raw materials of the same variety with and without polishing were judged attributable to elements not affected by polishing.

Ⅱ. Analysis of arsenic species in grains and grain processed foods This study was intended to select the optimal analysis method suitable for the separation of arsenic species in grains by comparing and reviewing elution conditions and extraction solvents in order to analyze arsenic species in samples. In addition, the selected analytical method was applied to miscellaneous grain and rice processed foods to identify the levels of inorganic arsenic and assessing the levels of hazards according to the amounts of intake. To review the analysis method, inorganic arsenic was extracted at 80˚C with a combination of heating extraction and ultrasonic extraction using 1% HNO3 as an extraction solvent and the efficiency levels according to of three elution conditions were checked. When the three elution conditions were compared, the isocratic method using 5 mM malonic acid (pH 5.6) as an elution condition for the analysis of arsenic species in rice was judged to be a very useful analysis method for quantitative analysis of inorganic arsenic in rice. This is because it showed lower baselines and higher sensitivity. To minimize solvent interference, 5 mM malonic acid (pH 5.6) was used as the extraction solvent identically to the mobile phase and the extraction time was set to 120 minutes. As a result of effectiveness validation under the established optimal analysis conditions, the precision was identified as 2.1~4.7%, linearity R2=0.9994, accuracy 96.4~105.6%, detection limits 0.02~0.03 μg/kg, and quantification limits 0.06~0.10 μg/kg. Based on the established analysis method, analyses to separate arsenic species from 135 samples of 12 kinds of raw grains and 135 samples of nine kind of grains processed foods consumed in South Korea were conducted using HPLC-ICP/MS. Inorganic arsenic was detected in all 135 samples of raw grains and the average concentration was identified as 0.028±0.034 mg/kg. By sample, the contents of inorganic arsenic detected in brown rice, white rice, and glutinous rice were 0.084±0.025, 0.059±0.017, and 0.044±0.015 mg/kg, respectively and the ratios of inorganic arsenic to the total arsenic were identified as 24.4%(foxtail millet)~71.89%(brown rice). No samples were found exceeding 0.2 mg/kg, which is the standard for inorganic arsenic in rice, and is currently applied in Korea. Inorganic arsenic was detected in all 135 samples of grain processed foods and the average concentration was 0.055±0.042 mg/kg and the ratios of inorganic arsenic to the total arsenic were shown to be 11.4% (wheat noodles)~65.8% (brown rice snack). High contents of inorganic arsenic were detected in rice and rice-based grain processed foods. It is known that rice has high arsenic contents because it is grown in rice paddies, unlike other crops grown in fields. Risk assessment was conducted using the results of the analysis of inorganic arsenic. According to the results, the level of hazards of 12 kind of grains was identified to be 11.6% compared to the human body exposure safety standard for inorganic arsenic of 9.0 μg/kg bw/week recommended by the Ministry of Food and Drug Safety, indicating that the risk of hazards was very low. Through this study, an analysis method for arsenic species separation was established and the contents of arsenic in grains and grain processed foods consumed in South Korea were monitored to determine the applicability. The analysis method was found practical for analysis and monitoring the safety of inorganic arsenic in grains.