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Do Not Eat - What's That Packet In My Food or Medicine?
Do Not Eat
You may have opened a vitamin bottle or maybe a package of pepperoni and noticed a small packet or canister that was marked ‘Do Not Eat.’ It can be disconcerting to find an inedible object mixed in with your food or medicines. But not to worry, the part that comes in contact with food or medicine must be made from materials that are generally recognized as safe (GRAS) per the FDA. These packets and canisters are put into food and drug products to extend their shelf lives as well as to protect the natural flavors of food.
But what are they exactly? Collectively, they are called sorbents. Depending on the need of the product, the sorbent could be a desiccant, used to keep a product dry or control the moisture in the package; it could be an oxygen absorber, used to prevent oxidation of the product or to prevent aerobic microbial growth or mold growth; or it could be a volatile adsorber used to adsorb strong odors.
The outside material of the packet is most often made from permeable Tyvek® and the canisters are made from a permeable plastic material. The permeability allows ingress of small moisture and oxygen molecules and prohibits the active material inside the packet or canister to leak out. The material Inside these packets and canisters are chemicals or a mix of chemicals that help to achieve the desired function.
Desiccants used in food and drug applications are typically made from silica gel, molecular sieve, and to a lesser degree, clay, or a mixture of these. These work by physical adsorption. Basically stated, the water vapor molecule adheres to the surface of the material; however, under high temperatures the moisture can be released - the desiccant can be regenerated and reused in some circumstances. Oxygen absorbers undergo a chemical change and cannot be regenerated.
Silica gel is the most widely used desiccant and has existed for more than 300 years. However, the wide use seen today wouldn't have been possible if it weren't for Walter Patrick, whose 1912 doctoral research focused on a method for making silica gel in large quantities. Silica gel was used on a large scale in gas masks during WWI and introduced for industrial applications by Patrick in 1921. By WWII, it was being used to protect penicillin from moisture. This was the beginning of its use for protecting medicines.
Silica gel is synthetically manufactured from sodium silicate. Typically, it takes the form of small beads and is not a gel as the name implies. Through the control of certain manufacturing processes, such as washing and drying, physical characteristics of the silica gel (e.g., pore size and surface area) can be altered depending on the intended use.
Sometimes cobalt chloride (II) is added to the silica gel as a moisture indicator. It turns from blue to pink as a visual indication that the silica gel has been fully saturated. These are typically found in industrial applications because cobalt chloride is considered a probable carcinogen by the World Health Organization. Other non-cobalt color indicators are used as well, such as those that change from orange to green.
Molecular sieves can be either naturally occurring or synthetically produced zeolites. It has been known for more than two centuries that naturally occurring zeolites had the ability to adsorb moisture and release it when heated. In the 1950s, Union Carbide developed the first synthetic zeolites. Synthetic zeolites are manufactured under closely controlled conditions from sodium silicate, aluminum trihydrate, and sodium hydroxide.
Zeolites are compounds with well-defined crystalline structures that adsorb particles according to molecular size. The pore size of the molecular sieve can be controlled during manufacturing, allowing it to selectively adsorb molecules. For example, a molecular sieve with 3Å pore diameter will adsorb molecules below that size. Water vapor is less than 3Å in size and would be readily adsorbed.
Clay is a naturally occurring desiccant material. It is excavated by strip-mining, field dried, crushed, and dried further to obtain the desired moisture content. Because it is naturally occurring, manufacturers must be careful of compatibility issues caused by mineral impurities. Another issue with clay is that it will release moisture at a rather low temperature -120°F, which could be an issue in hot climates.
Oxygen absorbers were well established in the food industry before they were used with pharmaceuticals. There were early reports in the 1920s of oxygen being removed from enclosed food components using iron containing mixtures. In the 40s more work was done with closed food packages, but there was little commercial success. The first major commercial success was an iron based oxygen permeable packet produced my Mitsubishi Gas Chemical Company in the 1970s.
In the early 1980s and 1990s, the pharmaceutical industry was starting to consider the use of oxygen absorbers as there were a few Japanese patents issued for use of oxygen absorbers with pharmaceuticals. Oxygen absorber use was fairly new and prior to their common use, medications were simply over desiccated to prevent oxidation that was caused by moisture. By the mid 2000s, advancements in oxygen absorbers made them more popular for this use.
Oxygen absorbers are usually iron based. Oxygen in the presence of moisture (from food/drug or chemically pre-activated) will oxidize the iron, much the same way that metal rusts. This can achieve a fairly low oxygen level in the package or bottle - provided oxygen ingress is prohibited through use of proper materials and seals.
If a child or pet accidentally eats a packet or canister, you should call the poison control center or your vet. Desiccants and oxygen absorbers used in food and pharmaceutical applications are much higher quality than the ones you might find in your shoe box, but in many cases you really have no way of knowing what is in the packet, so its better to be safe than sorry.
© 2014 Lisa Benson