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Rice is a commonly consumed food staple for many Asian and Pacific cultures; thus nutrient enrichment of rice has the potential to increase nutrient intakes for these populations. The objective of this study was to determine the levels of enrichment nutrients (thiamin, niacin, iron, and folic acid) in white rice found in Guam, Saipan (CNMI), and Oahu (Hawaii). The proportion of white rice that was labeled enriched varied by type, bag size, and location. Most long-grain rice was labeled enriched, while most medium-grain rice was not. Bags of either type weighing over 10 pounds were seldom labeled enriched in Hawaii or Saipan. Samples of various types of rice were collected on these three islands (n=19, 12 of which were labeled enriched) and analyzed for their content of the enrichment nutrients. Rice that was labeled enriched in Hawaii and Guam seldom met the minimum enrichment standards for the US. For comparison, three samples of enriched rice from California were also analyzed, and all met the enrichment standards. Nutritionists who are planning or evaluating the diets of these Pacific island populations cannot assume that rice is enriched.
Rice is a primary staple food for many Asian and Pacific cultures including those of Hawaii, Guam (a U.S. Territory in the Pacific), and Saipan (an island within the U.S. Commonwealth of the Northern Mariana Islands (CNMI)). In the U.S. and associated jurisdictions such as Guam and CNMI, commonly consumed refined grains such as white rice are often enriched with the nutrients thiamin, niacin, iron, and folic acid in order to increase intakes of these nutrients. Although enrichment is not mandatory (1), the U.S. Food and Drug Administration (FDA) requires packages of rice that are labeled “enriched” to contain at least the minimum level of enrichment for these nutrients, as specified in the Code of Federal Regulations (CFR)(2). The current standard of identity for rice states that each pound of uncooked rice, if enriched, must contain 2–4 mg thiamin, 16–32 mg of niacin, 13–26 mg iron, and 0.7–1.4 mg folic acid (21 CFR Part: 137.350). The Federal Enrichment Standard for riboflavin in enriched rice has been stayed since 1958, and hence riboflavin is not currently added to enriched rice (2).
Studies in Guam and Hawaii collected information on rice consumption by Filipino, Japanese-American, and Native Hawaiian men and women (3,4). Rice contributes about 18% of the energy in the diets of Filipino and Japanese-American men and 11–14% of energy for Chamorro (indigenous people from Guam) and Hawaiian men. Intakes of rice by women in these ethnic groups are also high, ranging from 9–15% of energy. Enriched rice therefore has the potential to deliver substantial amounts of the four enrichment nutrients. For example, 200 g (1.25 cup) of cooked enriched rice (an amount commonly consumed daily in these cultures) should contain approximately 22% of the Daily Value (5) for thiamin, 30% of the Daily Value for folate, and 15% of the Daily Value for niacin and for iron. Iron and folate are of particular public-health importance in populations consuming diets which are energy-rich but nutrient-poor (6).
In the U.S., the two methods used to enrich rice are coating and dusting (7–9). In the coating method, a fortificant liquid mix is sprayed on to the rice in several layers, forming a rice pre-mix with a waxy layer that prevents micronutrient loss if the rice is washed before cooking. This pre-mix is then blended with retail rice. In the dusting method, retail rice is dusted with the powder form of a micronutrient pre-mix. The assumption is that the micronutrient powder will stick to the rice grain surface because of electrostatic forces. Consumers are advised that rice enriched by dusting should not be rinsed before or after cooking because the enrichment nutrients will be lost (7).
Because washing rice before cooking is a common practice in the Pacific region, the impact of washing on the enrichment nutrients was initially investigated. Samples from one package of enriched rice from Guam were prepared in three ways: 1) according to the label directions (unwashed), 2) washed twice in local tap water, and 3) “superwashed,” that is, rubbed between the hands in tap water, as is the local custom. When laboratory analyses demonstrated no difference in the nutrient composition of washed and unwashed rice samples, the study was modified with the objective of determining the actual levels of enrichment nutrients in white rice in Guam, Oahu (Hawaii) and Saipan.
Staff in Hawaii (Cancer Research Center of Hawaii), Guam (University of Guam), and Saipan (Northern Marianas College) visited a variety of retail stores to collect information on the availability as well as the relative proportion of enriched and unenriched white rice on the shelves. For each product, the brand name, rice type, and the weight of the bag was recorded. Although stores were not chosen at random, an effort was made to include small and large markets, ethnic markets, as well as large discount stores (on Guam and Hawaii). The survey included 8 stores in Saipan, 5 stores in Honolulu, Hawaii, and 7 stores in Guam.
A variety of types of rice were collected for analysis, including long-grain, medium-grain, jasmine, and Calrose (a type of medium-grain rice originally developed in California). Rice was purchased in the three island locations in January, 2006. The types of rice to be analyzed were chosen based on the most common brands and sizes of rice packages available. Seventeen rice bags were collected: 8 in Guam (7 labeled enriched, 1 unenriched), 7 in Honolulu (3 enriched, 4 unenriched), and 2 in Saipan (both unenriched). The bags were purchased from more than one store location on each island (two each in Guam and Saipan, and three in Honolulu). Whenever possible, rice bags were purchased as 20-lb or 50-lb units, because the typical family in these areas purchases rice in bulk.
Approximately six months later, five additional rice bags were collected to provide additional information. A bag of long-grain enriched rice was collected in Hawaii because no long-grain bags were included in the initial collection. An enriched rice bag was collected in Saipan because the initial collection included only unenriched bags from Saipan. Finally, for comparison, three enriched rice bags were collected from a single supermarket in northern California. Table 1 lists the purchase location, rice type, enrichment status, and bag weight of the 22 rice samples that were analyzed. Samples A through O were labeled enriched, and samples P through V were not.
Each purchased rice bag was emptied into a large container and stirred so that all contents were distributed uniformly. A three-pound portion from each bag was weighed and packed into an airtight container, and shipped by express mail to the Food Analysis Laboratory Control Center at Virginia Polytechnic Institute and State University (VPI) for preparation. VPI is a collaborator with Agricultural Research Service of USDA for the National Food and Nutrient Analysis Program (NFNAP) (10).
Once at VPI, 450 g samples were taken after the entire three-pound portion was stirred again. These samples were ground in 150-g batches in a Girmi model TR 30 mill. The ground samples were dispensed into 1-oz glass sample jars with Teflon®-lined screw caps, capped under nitrogen, and stored at −60°C.
The samples, along with the appropriate control and reference materials (11), were shipped on dry ice to analytical laboratories that have been prequalified to perform nutrient analyses through the NFNAP. Thiamin was analyzed by a fluorometric method, Association of Official Analytical Chemists (AOAC) 942.23(12). Niacin analyses used a microbiological assay, AOAC 944.13, 940.46 and 985.34. Iron was analyzed by inductively coupled plasma (ICP) atomic emission spectrometry, using AOAC 985.01 and 984.27, Metals in Food by ICP, while folic acid levels were determined by liquid chromatography mass spectrometry (LC-MS) using a trienyzme extraction and methods modified from Doherty and Beecher (13) and Kok et al. (14). Due to cost constraints, folic acid content was determined in a subset of five samples, A, E, G, I, and J (Table 1), that contained relatively high amounts of the other enrichment nutrients. Moisture was analyzed by a gravimetric method, AOAC 964.22.
Reference materials were obtained from the National Institute of Standards and Technology (NIST, Gaithersburg, MD), the American Association of Cereal Chemists (AACC, St. Paul, MN), and quality control materials were prepared by VPI. Because reference materials were included as quality control in each batch of nutrient analyses, duplicate analyses were not performed.
To further investigate the low levels of enrichment nutrients in many of the samples, two additional evaluations were conducted. To ensure that the low values were not due to inadequate mixing of the rice, enrichment nutrients were analyzed in three samples from a single bag: sample L from Saipan. There was little variation across the samples: thiamin ranged from 1.21 to 1.47 mg/100 g, niacin ranged from 5.87 to 6.68 mg/100 g, and iron ranged from 3.30 to 3.98 mg/100 g (in percentages, these differences are 16.5%, 13.8% and 20.6% of the lowest value). Although sample L exceeded the minimum enrichment standards for these nutrients, it was reassuring to note the relatively low within-bag variability.
The second evaluation involved an examination of iron remaining in the rice packaging after the rice had been removed. There was concern that if the “coating” method for enrichment was used, the spraying process might result in a coating of enrichment that could flake off during shipment and storage. Iron was chosen as an indicator of enrichment nutrients remaining on or in the packaging. Four new samples of rice were collected from a supermarket in Maryland. Three were long-grain, one was Calrose, and all were labeled enriched. Three of the bags were plastic, and one was a coated paper. The packaging was rinsed several times in a dilute hydrochloric acid (HCl) solution (0.6 M), and then the HCl rinse was analyzed for iron. Only trace amount of iron were found in the HCl solution, ranging from 0.002 mg of iron for a one-pound bag, to 0.031 mg of iron for a five-pound bag, which was also the paper bag and may have contained small amounts of iron leached from the paper. For comparison, the rice granules were also rinsed in the HCl solution, to ensure that the rice was enriched with iron. The iron levels in this HCl solution were found to be 8 to 250 times higher than the iron levels detected in the HCL solution from the rinsed bags. Thus, it was determined to be unlikely that substantial levels of enrichment nutrients remain in the rice bags.
Analytical nutrient values from the laboratories were received electronically as Excel spreadsheets, and combined into a single spreadsheet for statistical analyses. For each enrichment nutrient in each of the 11 rice samples labeled “enriched”, a t-test was performed in Excel to determine if the analytical value for the sample was statistically different (p < 0.05) from the minimum enrichment standard for rice (2) (converted to a 100-g basis) and from the unenriched rice value (average of 7 samples). Variability for these tests was computed from the variability among samples within nutrient. Because the variability among samples should exceed the variability within a sample, this assumption leads to a conservative test for statistically significant differences.
The rice available in stores on the three islands revealed differences in the enrichment labeling of rice bags (Table 2). Of the largest bags (20–50 lb), none from Hawaii and only 3 from Saipan were labeled as enriched. However, most of the smaller bags of rice (2–10 lb) in these two locations were labeled as enriched. Enrichment labeling also tended to vary by type of rice, with Calrose rice less likely to be labeled enriched than long-grain rice. In Guam, a majority of the bags were labeled enriched, regardless of size or type.
All samples were uncooked when analyzed. Nutrient values reported were per one-hundred grams of raw, uncooked rice, which yields approximately 1 cup of cooked rice. The average moisture content for the samples of uncooked rice (15 enriched and 7 unenriched) was 12.8 g/100 g. The nutrient values per 100 g for the seven unenriched rice samples were (mean, mg/100 g ± SD): thiamin, 0.05 ± 0.02; niacin, 1.22 ± 0.34; and iron, 0.38 ± 0.14. Because folic acid in unenriched rice is very low (less than 5 ug/100g) (6), it was not measured.
Figure 1 shows the results of the nutrient analyses of the 11 enriched rice samples collected in Honolulu and Guam. The minimum enrichment standards are based on the standard of identity for enriched rice in the CFR, Title 21, Part 137.350 (2). On a 100-gram basis, the minimum levels are 0.44 mg for thiamin, 3.5 mg for niacin, 154 μg for folic acid, and 2.9 mg for iron.
Sample L, the 12th enriched rice sample, was from Saipan and was the only sample with values that exceeded the minimum enrichment standards for iron, thiamin, and niacin (folic acid analyses were not performed for this sample). To avoid distorting the scale, it is not shown in the figure, but the nutrient values are given in a footnote. Values for all other samples (A through K) were significantly below the standard (p < 0.05) except samples A, J and K for thiamin, samples E, G, I, J, and K for niacin, and sample J for iron. All five samples analyzed for folic acid yielded values significantly below the minimum enrichment standard. Among the 11 samples from Hawaii and Guam that were labeled enriched, only sample J did not fall significantly below the minimum enrichment levels for all three nutrients (thiamin, niacin and iron).
All three packages of rice that were purchased in California were labeled enriched, and values for three of the enrichment nutrients exceeded the minimum enrichment standards. For samples M, N, and O, respectively, thiamin content was 0.65, 1.76, and 0.74 mg/100 g, niacin content was 5.78, 19.50, and 7.80 mg/100 g, and iron content was 3.01, 15.50, and 3.63 mg/100 g. The nutrients in sample N, a Calrose rice, greatly exceeded the maximum levels in the CFR by 0.88 mg/100 g over the maximum for thiamin, 7.0 mg/100 g over the maximum for niacin, and 5.8 mg/100 g over the maximum for iron. Sample M was from a package that was identical to sample L from Saipan, but the enrichment nutrients still varied: the thiamin level was 0.65 mg/100 g in the California sample and 1.36 mg/100 g in the Saipan sample; niacin values were 5.78 and 6.37 mg/100 g, respectively, while iron values were 3.01 and 3.50 mg/100 g. Similarly, sample O from California was from a package that was the same as that for sample K from Honolulu, but the levels of enrichment were over twice as high in the California sample.
Findings suggest that most rice in these islands was not enriched at the time of this study even when labeled as enriched. In Hawaii and Saipan, very few of the commonly purchased larger bags were labeled as enriched. In Guam, the larger bags were frequently labeled enriched, but analyses show that the levels of the four enrichment nutrients were usually well below the minimum standards. All three locations are U.S.-affiliated, so the food labels are under FDA jurisdiction. These data have been provided to the FDA for follow-up.
The consumption of “enriched rice” that is not actually enriched is cause for concern by public health professionals in these locations. Intakes of thiamin, niacin, iron, and folate are probably lower than has been previously estimated because food-consumption surveys have generally used food-composition values for enriched rice. The Food and Nutrient Database for Dietary Surveys that is used for the U.S. national nutrition surveys, assumes enrichment of all white rice except Thai “sticky” rice (15). Furthermore, institutional feeding programs such as the School Lunch Program in Guam, Saipan, and Hawaii may also be unknowingly serving unenriched rice to their participants, and thus not delivering the assumed level of the enrichment nutrients. Because rice is a primary staple food on these islands, the prevalence of nutrient inadequacy may be undesirably higher than that of the general U.S. population. It would be useful to re-evaluate estimated nutrient intakes from U.S. dietary surveys under the assumption that white rice is unenriched. Further, washing rice is a common practice among many Asian and Pacific cultures, in spite of the package directions to the contrary. This would further remove enrichment nutrients in white rice.
There is no explanation for the low levels of enrichment nutrients in rice that is labeled “enriched” in Guam and Hawaii. Although the labels do not indicate how the enrichment is performed, powder “dusting” or liquid “coating”, the current regulations require the following statement for powder enrichment: “To retain vitamins do not rinse before or drain after cooking.” Five of the 12 bags of enriched rice from the islands bore that statement. One bag labeled as enriched stated “washing not necessary.” Another one of the enriched bags, as part of the cooking directions, included “wash under cold running water.” Of the three bags from California, two gave the required statement for powder enrichment, and the third said that washing was not necessary. Thus, it seems likely that powdered enrichment was more commonly the process used for the rice analyzed in this study.
There was no indication that iron enrichment particles were left in the packaging. If coating-type enrichment was used, then it might result in low enrichment values if the sample did not include enough of the liquid coated rice kernels. However, little variation was found across multiple samples from a single bag, indicating that the contents were relatively uniform. A more complete investigation of the types of enrichment that are commonly used for rice, and the reasons for the low levels that were found, was beyond the resources available for the current study.
This is one of the first studies to examine rice enrichment in these three Pacific island locations. The results demonstrated that dietary intake estimates of thiamin, niacin, iron and folate for people consuming substantial amounts of rice in these Pacific Islands may be inaccurate. Food composition tables generally don’t contain nutrient values for location, brand, type of rice, and package size and there was considerable enrichment level variability by these variables. Entries on the National Nutrient Database for Standard Reference are often representative averages of analytic values from food items obtained in multiple locations in the U.S. (5). However, it may be important to increase the specificity of the entries to include different representative values for different locations (such as California vs. the Pacific islands). It may also be useful to ask survey participants for information on the brand, type, and package size of rice that is typically purchased and consumed. Until better data are available, dietitians, nutritionists, and others who plan or evaluate the diets of these Pacific Island populations should not assume that rice is enriched, even when it is so labeled.
Because the data are based upon a convenience sample, the true prevalence of low rice enrichment levels for this region is not known. Rice is a staple food for many cultures in this area and the nutrients delivered through rice enrichment are of public health importance. Given the results presented in this paper, a comprehensive sampling and nutrient analysis of enriched rice in the Pacific Islands is warranted to determine the true extent of the problem.
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Rachael T. LeonGuerrero, College of Natural & Applied Sciences, University of Guam, UOG Station, Mangilao, Guam 96923, Telephone: 671-735-2026; Fax: 671-734-6842.
Susan E. Gebhardt, Beltsville Human Nutrition Research Center, USDA, 10300 Baltimore Ave., Bldg. 005, Beltsville, MD 20705, Telephone: 301-504-0644; Fax: 301-504-0632.
Joanne Holden, Beltsville Human Nutrition Research Center, USDA, 10300 Baltimore Ave., Bldg. 005, Beltsville, MD 20705, Telephone: 301-504-0630; Fax: 301-504-0632.
Mary J. Kretsch, Nutrition, Food Safety/Quality Program, Agricultural Research Service, USDA, 5601 Sunnyside Avenue, GWCC-BLTSVL, Beltsville, MD 20705, Telephone: 301-504-4788; Fax: 301-504-5467.
Karen Todd, General Clinical Research Center, University of California, San Francisco, Box 0126, Moffitt 1202, San Francisco, CA 94143, Telephone and Fax: 775-425-1543, (address at the time of the study; now retired)
Rachel Novotny, Kaiser Permanente, Center for Health Research Hawaii, 501 Alakawa St., Suite 201, Honolulu, Hawaii 96817, Telephone: 808-432-4782; Fax: 808-432-4785, and University of Hawaii, 1955 East-West Road, Agricultural Science 216, Honolulu, Hawaii 96822, Telephone: 808-956-3848; Fax: 808-956-4024.
Suzanne P. Murphy, Cancer Research Center of Hawaii, 1236 Lauhala Street, Suite 407, Honolulu, HI 96813, Telephone: 808-564-5861; Fax: 808-586-2982.