Shintaro Pang and Dr. Michael Dunn, NDFS
Introduction
Rice is the main staple in many people’s diet, accounting for 80% of the daily caloric intake of 3 billion people. Studies also show that folate intake is insufficient worldwide (Schoenlechner et al 2010). This is of much concern because folate deficiency is linked to many serious disorders, such as megaloblastic anemia and neural tube defects in newborns (Steur et al 2010). In order to remedy this problem, folate concentrations in many foods, including rice has been well analyzed. However, the stability of folic acid in rice is less known. This information is of interest because folic acid is very sensitive to light, air, heat and extreme pH conditions (Keagy 1985). Furthermore, rice is stored and prepared in different ways before it is consumed.
Without a study of the stability of added folic acid in rice after various storage and cooking conditions, there will be uncertainty as to how much added folic acid should be incorporated into rice in order for it to serve its purpose – to eliminate folate deficiency. This research serves to unfold this particular information, thus allowing suppliers and government officers to determine the actual folic acid concentration available in folic acid-fortified rice.
Method
In order to determine the effects of common preparation, storage and cooking techniques on the folate concentration of rice, we conducted folate analysis on folate enriched rice treated under 5 different conditions (i.e. dry (uncooked), washed (uncooked), cooked, microwaved and fried). For the washed rice, 1 cup of dry rice and 3 cups of water was stirred by hand for 30 s, and drained with a No. 35 sieve. This process was then repeated once more. For the cooked rice, 2 cups of water was added to 1 cup of rice and steamed in a Salton rice cooker. A portion of the cooked rice was then kept in a closed-lid container for 2 days after which, it was used for the microwaved and fried rice. For the microwaved rice, a portion of the refrigerated rice was microwaved for 30 s. For the fried rice, a portion of the refrigerated rice was stir-fried on a heated oil pan for 2 mins. Two separate lots of the same brand/type were procured in order to determine batch to batch consistency.
Folates and folic acid (reported as total folates) concentrations were analyzed using the trienzyme extraction method (AOAC 2004.05) with some modifications as described by Chapman et al (2010). In order to allow results to be reported on a dry-weight basis, the moisture content of all samples were analyzed gravimetrically using the American Association of Cereal Chemists (AACC) 44-15A method. Statistical analysis was conducted using XLSTAT software.
Results and Discussion
The table below (Table 1) shows the total folate concentration measured in rice that underwent different treatments. Lot-to-lot variation was also measured. Calculations showed there was a significant difference in folate concentration between treatment-to-treatment (p<0.05) except between dry vs. steamed (p=0.146) and microwaved vs. fried (p=0.271). The significant difference suggests that folates are either lost or gained after each treatment. The lost in folate after treatment supports the fact that folic acid is very sensitive to external conditions. The gain in folate after treatment however is surprising. One possible explanation could be that folateproducing bacteria are present in rice, similar to that of oat and rye (Herranen et al 2010), and that could have caused the increase in folate concentration among the microwaved and fried rice (both of which were refrigerated for two days before their last treatment). A noteworthy result was the huge differences in folate concentration between dry (80. 01μg/100g) and washed (18.20μg/100g) rice, suggesting that most of the water-soluble folate vitamin was drained away with the drained water. Another noteworthy result was that steaming (i.e. cooking) the rice did not affect its folate concentration. This brand of rice also did not meet the minimum folic acid requirement of 150μg/100g.
Conclusion
We can learn from this study that folic acid-enriched rice should not be washed in order to prevent the loss of folic acid. This could be explicitly stated on the packaging to inform consumers since many Asian cultures practice washing their rice before steaming them. When evaluating the amount of folic acid to add in rice, government officers and suppliers should take into account the final folate concentration in rice that is being consumed as our study shows marked difference between most treatments. Lastly, further studies could be conducted to explain the increase in folate concentration in microwaved and fried rice.
References
- Chapman, J.S., Steele, F.M., Eggett, D.L., Johnston, N.P., and Dunn, M.L. 2010. Stability of native folate and added folic acid in micronutrient-fortified corn masa and tortillas. Cereal Chem 87(5):434-8.
- De Steur, H., Gellynck, X., Storozhenko, S., Ge, Liqun., Lambert, W., Van Der Straeten, D., and Viaene, J. 2010. Health impact in China of folate-biofortified rice. Nat Biotechnol. 28(6):554- 556.
- Herranen, M., Kariluoto, S., Edelmann, M., Piironen, V., Ahvenniemi, K., Iivonen, V., Salovaara, H. and Korhola M. 2010. Isolation and characterization of folate-producing bacteria from oat bran and rye flakes. Int J. Food Micro. 142(3):277-285
- Keagy, P. M. 1985. Folacin: microbiological and animal assays. In: Methods of vitamin assay, J. Klein, B. P. Klein, & P. B. Venugopal, 4th ed. John Wiley and Sons: New York, NY.
- Schoenlechner, R., Wendner, M., Siebenhandl-Ehn, S., and Berghofer, E. 2010. Pseudocereals as alternative sources for high folate content in staple foods. J Cereal Sci. 52(3):475-479.