Enrichment, folate

While the fluid mosaic model of membrane stmcture has stood up well to detailed scrutiny, additional features of membrane structure and function are constantly emerging. Two structures of particular current interest, located in surface membranes, are tipid rafts and caveolae. The former are dynamic areas of the exo-plasmic leaflet of the lipid bilayer enriched in cholesterol and sphingolipids they are involved in signal transduction and possibly other processes. Caveolae may derive from lipid rafts. Many if not all of them contain the protein caveolin-1, which may be involved in their formation from rafts. Caveolae are observable by electron microscopy as flask-shaped indentations of the cell membrane. Proteins detected in caveolae include various components of the signal-transduction system (eg, the insutin receptor and some G proteins), the folate receptor, and endothetial nitric oxide synthase (eNOS). Caveolae and lipid rafts are active areas of research, and ideas concerning them and their possible roles in various diseases are rapidly evolving. 

Folate Enrichment of Foods May Put Some People at Risk... 

Folate deficiency is associated with the increased risk of neural tube defects (spina bifida, anencephaly), cardiovascular diseases, megaloblastic anemia, and some cancers (Bailey et al., 2003 Finglas et al., 2006 Scott et al, 1999). Unfortunately, folate intake is suboptimal in most of the world s populations, even in developed countries (Scott et al., 2000). Therefore there is an urgent need to increase folate content and bioavailability in staple foods. Because of its large consumption worldwide, potato is an appealing target for enrichment. 

Oatpla3 consists of two variants (Oat-kl and Oat-k2) in the kidney (69,70). Oat-k2 lacks 172 amino acids at the amino terminal (70). The localization of Oat-kl has been suggested to be brush border membrane of the renal tubules since polyclonal antibody detected Oat-kl only in the brush border membrane-enriched fraction from the kidney (71). In contrast to other Oatps, Oat-kl mediates facilitated transport since the uptake by Oat-kl was insensitive to an ATP depleter (sodium azide) (69). Oat-kl accepts only folate derivatives such as MTX and folate, while the substrates of Oat-k2 include TCA and prostaglandin E2 in addition to these folate derivatives (69,70). 

When foods have been enriched with vitamins, because of the requirement for the food to contain the stated amount of vitamin after normal storage, manufacturers commonly add more than the stated amount - so-called overage. One of the problems in the debate concerning folate enrichment of flour (Section 10.12) is the relatively small difference between the amount that is considered desirable and the amount that may pose a hazard to vulnerable population groups, and the precision to which manufacturers can control the amount in the final products. In pharmaceutical preparations, considerable latitude is allowed the U.S. Pharmacopeia permits preparations to contain from 90% to 150% of the declared amount of water-soluble vitamins and from 90% to 165% of the fat-soluble vitamins. 

Although folate is widely distributed in foods, dietary deficiency is not uncommon, and a number of commonly used drugs can cause folate depletion. Marginal folate status is a factor in the development of neural tube defects and supplements of 400 fj,g per day periconceptually reduce the incidence of neural tube defects significantly. High intakes of folate lower the plasma concentration of homocysteine in people genetically at risk of hyperhomo-cysteinemia and may reduce the risk of cardiovascular disease, although as yet there is no evidence from intervention studies. There is also evidence that low folate status is associated with increased risk of colorectal and other cancers and that folate may be protective. Mandatory enrichment of cereal products with folic acid has been introduced in the United States and other countries, and considered in others. 

It is unlikely that an increase in folate intake equivalent to 400 /rg of free folic acid per day could be achieved from unfortified foods. Women who are planning a pregnancy are advised to take supplements. As discussed in Section 10.12, enrichment of cereal products with folic acid is now mandatory in some countries, mainly to reduce the incidence of neural tube defects. 

Modern functional foods became available in the 1920s, when iodine was added to salt to prevent goiter. This was followed by vitamin D milk. Today, many Americans start their day with calcium-fortified orange juice (to strengthen their bones). Then, they spread a margarine that lowers cholesterol on folate-enriched toast (to protect their hearts and prevent birth defects). 

Folic acid is easily lost during storage of fresh vegetables at room temperature and through many heat processes. Oxidative destruction of 50-95% of the folate can occur with protracted cooking or canning. Currently in the United States folate is added to all enriched or fortified cereal and flour products in order to increase this nutrient to prevent neural tube defects and to reduce coronary disease and some cancers. Thus, the processed, fortified product will have more folate. 

Vitamin E in Cereal Germs (Whole Grains) Thiamine (Bi) inWhole Grain and Enriched Produ (B2), Folate in EnricI Foods, Niacin in Enr Fortified Products ... 

FIG. 5. Isotopic enrichment of urinary folate in an adult female subject during chronic ingestion of a low-folate diet supplemented with d2-folic acid. The value of 0.284 enrichment represents the labeling (i.e., isotopic enrichment) of ingested folate from dietary and supplemental sources. In this figure, the data were fit to the two-pool, one-output model depicted in Fig. 3, which yielded the solid regression line (Gregory el aL, 1994). 

FIG. 7. Isotopic enrichment of urinary folate in an adult male subject. In addition to dietary folate, the subjects received the following daily supplement Days 1S-7S, 100 ju.g d4-folic acid + 100 /ig nonlabeled folic acid Days 76-126,200 /rg nonlabeled folic acid (no d4-folic acid) (Stites el al., 1994). The solid line represents enrichment as predicted using the model shown in Fig. 6. 

Laino, J.E., del Valle, M.J., de Giori, G.S., and LeBlanc, J.G. (2013) Development of a high folate concentration yogurt naturally bio-enriched using selected lactic acid bacteria. LWT Food Sci. Technol, 54, 1-5. 

The validated method has been successfully applied to determine folates in real rice samples. 5-Methyltetrahydrofolate was the predominant natural folate form in both wild-type (60%) and transgenic (90%) rice. The analysis of the distribution and levels of folates in wild-type and folate-biofortifled rice showed up to 50-fold enrichment in biofortified rice, with total folate levels of up to 900 Xg/100 g rice. Figure 10.7 shows the UPLC-MS/MS chromatogram for the folates in the two different samples. Some biofortified lines yielded folate levels of up to 900 (xg/lOO g, whereas levels in wild-type rice were around 20 g/100 g [108]. 

Vitamin-enriched corn has been derived from a South African white corn hybrid (M37W). The new corn has bright orange kernels that have 169 times more beta carotene, 6 times more vitamin C, and twice the folate content of the regular corn. Rice, a major staple in Asian countries, has been modified by the introduction of three new genes, two from daffodils and one from a bacterium, to create Golden Rice, which is high in beta carotene, a precursor to vitamin A. 

Reference Intakes for folate have been reported (Food and Nutrition Board 1998) (Table 44.2). The high frequency of folate deficiency has led the Food and Drug Administration in the United States to require folic acid fortification of all enriched cereals and grain products since January 1998. Folate deficiency is a major public health concern both northern and southern countries, and affects both industrialized and non-industrialized nations. In non-industrialized countries, it is particularly accentuated by poverty, limited access to food resources, and infectious diseases (Change and Abdennebi-Najar, 2011). 

The liver rapidly absorbs from 10 to 20% of dietary folate, with a preference for non-methylated and non-reduced derivatives, while peripheral tissues are enriched in reduced and methylated functional derivatives. Folate is mainly stored in the liver. Hepatic folates are partly excreted into the bile enterohepatic circulation and reabsorbed (Steinberg et al. 1979). This is one of the mechanisms involved in the recirculation of folate. Regarding renal elimination, folate is filtered by the glomerulus and reabsorbed into the proximal tubule. The daily urinary excretion of intact folates is between 1 to 12 pg. When the serum plasma folate concentration is very high, it is possible to overwhelm the renal reabsorption capacity in this case, folate derivatives are excreted in the urine. Due to the possible production by the gut microflora, fecal folate levels are quite high. 

In Apo E null mice increased Hey by a diet enriched with methionine but depleted in folate, Bg, and B12 increased atherosclerotic lesion area and complexity and enhanced expression of receptor for advanced glycation endproducts (AGE), VCAM-1, TF, and MMP-9 in the vasculature. These effects were suppressed in parallel with decreased plasma Hey levels upon dietary supplementation with folate, Bg, and B12 (7- 5). Also, methionine load increased vWF in patients with arterial or venous occlusive disease with or without hyperhomocysteinemia, suggesting endothelial dysfunction (146). 

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