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Absorbing the vitamin B-12 that is naturally in food requires a complex series of steps (Fig. 10.12). Natural vitamin B-12 is bound to animal protein that prevents its absorption. When the food enters the stomach, the vitamin is released from the protein, primarily by the actions of hydrochloric acid (HCl) in gastric juice. Synthetic vitamin B-12 in dietary supplements or fortified foods is not bound to food protein, so it does not need stomach acid to release the protein. Thus, synthetic vitamin B-12 is more readily absorbed than the natural form of the micronutrient; In the small intestine, vitamin B-12 binds to intrinsic factor (IF), a compound that is produced by parietal cells of the stomach. Eventually, the vitamin B-12/intrinsic factor complex reaches the ileum of the small intestine, where the vitamin complex is absorbed. Within the absorptive cells, vitamin B-12 is separated from intrinsic factor and attached to transport molecules. The transport molecules enter the bloodstream and travel to the liver via the hepatic portal vein. The liver removes vitamin B-12 from many of the carrier molecules and stores about 50% of the vitamin. A healthy liver has enough vitamin B-12 reserves to last 5 to 10 years.35 Therefore, a healthy person who decides to follow a diet that completely lacks vitamin B-12 is not likely to experience signs and symptoms of the vitamin's deficiency disorder for as long as 10 years. Even though vitamin B-12 is stored in the liver, no UL has been established for the micronutrient, because no adverse effects have been observed with excess intakes; 1. HCL separates B12 from animal protein 2. stomach secretes intrinsic factor 3. B12 binds to IF 4. The IF/B12 complex enters the cells and the complex breaks apart 5. B12 binds to carrier molecule for transport in the blood
The intestinal tract absorbs the ferrous (Fe2+) form of iron more efficiently than the ferric (Fe3+) form (Fig. 12.3). Under acidic conditions, ferric iron can be converted to ferrous iron. Thus, medications that decrease stomach acidity, such as antacids, may reduce iron absorption.1 Calcium and iron compete for absorption in the small intestine, so a meal with high calcium content can inhibit iron absorption. Therefore, people should consume a variety of food sources of iron throughout the day.

Some plant foods, such as spinach, contain nonheme iron, but oxalic acid in spinach binds to the mineral, reducing its absorption. Other naturally occurring compounds that reduce iron absorption include polyphenols, phytic acid (or phytates), and soy protein. Polyphenols are present in tea, coffee, wine, and some fruits and vegetables. Phytates are in several foods, including whole grains, rice, and legumes. Absorption of iron from phytate-containing legumes, such as soybeans, black beans, lentils, and split peas, may be as little as 2%.1 Soy protein, including the kind used to make tofu, also reduces iron absorption.

Certain dietary factors can enhance iron absorption, especially of nonheme iron. Foods that are high in vitamin C increase intestinal absorption of the trace mineral. Adding a source of vitamin C to meals can increase the absorption of nonheme iron by 20%.5 People can also increase their absorption of nonheme iron by combining a small amount of heme iron (from meat) with foods that contain nonheme iron. In addition to heme iron, meat, fish, and poultry contain a factor (sometimes called "MFP factor") that enhances the intestinal tract's ability to absorb nonheme iron. Enhance: Vit C, Heme Iron, Leavening of bread, fermentation, soaking beans or grains; Inhibit: High intake of calcium with iron-containing food, medications that reduce stomach acidity, oxalic acid from foods such as spinach, phytic acid from foods such as whole grains, soy protein such as tofu, polyphenols from foods and beverages, such as tea
transferring of pathogens from a contaminated food or surface to an uncontaminated food or surface

Ex. Using the same cutting board to cut raw meat and raw fruits and vegetables
Transporting cooked meat on the same plate used to transport raw meat.
Using the same utensils to handle raw meat and raw produce.

*To prevent cross contamination be sure to wash:
Hands (20 seconds)
Surfaces
Cutting boards
FDA recommends using nonporous material such as plastic, marble, or glass.
Wooden cutting boards should be nonabsorbent with no cracks or seams.
Utensils and other equipment*

Hands
Wash hands thoroughly with very warm, soapy water for at least 20 seconds before and after touching food. If clean water for hand washing is not available, use sanitizing hand wipes.

If you are preparing more than one type of food, such as cutting up chicken and dicing carrots, wash hands in between.

Use a fresh paper towel or clean hand towel to dry hands. Reserve dish towels for drying pots, pans, and cooking utensils that are not washed and dried in a dishwasher.

Surfaces
Before preparing food, clean food preparation surfaces, including kitchen counters, cutting boards, dishes, knives, and other food preparation equipment, with hot, soapy water.

Sanitize food preparation surfaces and equipment that have come in contact with raw meat, fish, poultry, and eggs as soon as possible. Sanitizing is a process that uses heat or chemicals to destroy pathogens. Most pathogens on surfaces can be killed by using a sanitizing solution made by adding a tablespoon of bleach to 1 gallon of cool water.17 However, avoid getting bleach solution on colored fabrics or surfaces that can be damaged by bleach (granite, for example).

Cutting boards
The FDA recommends using cutting boards with unmarred surfaces made of easy-to-clean, nonporous materials, such as plastic, marble, or glass. If you prefer to use wooden cutting boards, make sure they are made of a nonabsorbent hardwood, such as oak or maple, and have no obvious seams or cracks.

Replace cutting boards when they become streaked with cuts, because these grooves can be difficult to clean thoroughly and may harbor bacteria.

If possible, have a cutting board reserved for meats, fish, and poultry; another cutting board for fruits and vegetables; and a third board for breads.

Utensils and other equipment

Do not reuse cooking utensils such as tongs, knives, or spoons that have previously touched raw meat, fish, poultry, or eggs unless they have been sanitized first.

Sanitize kitchen sponges and wash kitchen towels frequently.
Food selection guidelines emphasize selecting unexpired foods, purchasing fresh produce, and keeping cold or frozen foods at the proper temperature during transport home. To reduce the risk of food-borne illness:

Packaged and fresh perishable foods
Check "best by" dates on packaged perishable foods. Choose meats and other animal products with the latest dates.

Do not buy food in damaged containers; for example, avoid cans that leak, bulge, or are severely dented, or jars that are cracked or have loose or bulging lids.

Dairy and eggs
Open egg cartons and examine eggs; do not buy cartons that have cracked eggs.

Purchase only pasteurized milk and cheese, as well as fruit and vegetable juices (check the label).

Store whole eggs in their cartons, even if the refrigerator has a place for storing eggs. Egg cartons are designed to keep eggs fresh longer than a refrigerator's egg compartment.

Meats, fish, and frozen foods
When shopping in a supermarket, select frozen and cold foods last, especially potentially hazardous foods such as meats, poultry, dairy, or fish.

Pack meat, fish, and poultry in separate plastic bags, so their drippings do not contaminate each other and other groceries.

After shopping for food, take groceries home immediately. Refrigerate or freeze meat, fish, egg, and dairy products promptly.

*selecting unexpired foods
purchasing fresh produce
keeping cold or frozen foods at the proper temperature during transport home
do not use foods from containers that have damaged safety lids
do not taste or use food that spurts liquid or has a bad odor
carefully wash foods under running water
avoid eating moldy foods
when in doubt, throw the food away*