By Daniel Connor

Summary: Bottled water is usually assumed to be purified or spring water. Another segment of the market making a big splash lately is fortified water. Since most waters are packaged in PET, one chemical company ran some tests to see what effects UV had on waters with different additives. Here are results of the study.  


The growth of enhanced waters has been nothing less than phenomenal. The Beverage Marketing Corp., of New York, reports that enhanced water is the fastest growing segment of the water market, generating $250 million in wholesale sales during 2002 vs. $20 million during 2000.

Plus, this explosive growth continues with an amazing burst of innovation in water formulations that promise to make consumers healthier, “smarter” and more energetic as a result of a broad array of additives. Vitamins A, B-Complex, C and E, St. John’s Wort, chromium, selenium, iron, calcium, magnesium, zinc, ginseng, nicotine (see Newsreel), vegetable flavors and colors, to name just a few, are being added to water in a drive to create unique formulations.

The timing for this innovation appears perfect for today’s consumer. The plastic water bottle has become a natural adjunct to today’s rapid, health-conscience lifestyles, joining the cell phone and the PDA device as essential to urban living. Consumers weary of plain bottled water can select fortified waters that not only hydrate but also promise to enhance one’s life.

Still, there’s a word of caution in this headlong drive to fortified waters. While plain water in PET bottles is safe and secure thanks to well-engineered containers, unique colors, flavors and nutrients added to water aren’t so safe because of potential damage from ultraviolet (UV) rays. Recent research has found many ingredients added to water may cause problems when exposed to UV light in a PET container. While a formulation is ideal when it leaves the bottling plant, its ingredients may degrade because of UV exposure during extended shelf life.

Recent research studies
To learn more about how UV light impacts beverages in PET packaging, an extensive research study was commissioned. Lab tests assessed the impact of various levels of UV light on formulation ingredients common to many of the new enhanced waters including FD&C colors, vitamins and flavor components. The testing was conducted with PET packaging with varying degrees of UV protection.

The goal was to learn more about how UV exposure at different wavelengths can impact color, flavor and nutritional content. The study also was intended to learn more about potential interactions between ingredients when exposed to UV light.

The tests were carried out on water containing a single beverage ingredient. Also tested were ingredients mixed with other common beverage components such as citric acid, vitamin C and trace minerals to examine the “matrix” effect, or interaction of beverage ingredients when formulated together in water.

The following were the test models:

  1. PET control—standard PET container,
  2. Unexposed—standard PET wrapped in aluminum foil,
  3. UV 370—PET container with a UV absorber at the 370 level providing <10 transmission up to 370 nanometers (nm), and
  4. UV 390—PET container with UV protection up to the 390 level providing <5 percent transmission at 390 nm.

Samples were subjected to accelerated UV light exposure in a refrigerated (4°C) chamber equipped with Q-Panel 351 UV bulbs, which were selected to simulate sunlight passing through glass, similar to a retail environment. Although oxygen wasn’t eliminated from test samples in the studies, the structure of tests enabled distinction between purely oxidative effects and photo-oxidative effects. Several important findings emerged from this research.

Pointing out drawbacks
The following are some of the effects UV had on bottled water in PET packaging:

  • UV light has a measurable negative impact on colors, flavors and nutritional content in PET packaging; while PET inherently offers some UV protection, it isn’t sufficient alone.
  • For many ingredients, the impact of UV light is greatly accelerated between 370 and 390 nm.
  • While color is the most easily observed change in beverage quality when exposed to UV light, it isn’t the most sensitive. Taste experiences the greatest impact from UV exposure, followed by nutritional content and then color.
  • The impact of UV exposure on ingredients is extremely complex. While some ingredients are stable in the presence of UV light, they become unstable when exposed to UV rays in certain formulations. This matrix effect can be unpredictable in its outcome.
  • UV protection at the 390 nm level is required to ensure consistent beverage quality over an extended shelf life.

Color is one of many defining attributes for some of the new enhanced water, and many UV absorbers incorporated into PET packaging today are designed to address color stability. Although many of today’s commonly used dyes are stable in the presence of UV light, they have been shown to be unstable to light when formulated with certain ingredients. For example, ascorbic acid (vitamin C) is frequently added to beverages for nutritional value and to scavenge dissolved oxygen that can attack certain flavor components. The presence of ascorbic acid in beverages containing certain synthetic colorants, however, can result in rapid fading when exposed to UV light. The presence of trace metals can also have a destabilizing effect on the synthetic colorants.

UV exposure testing was conducted on the FD&C colorants Blue #1, Red #40 and Yellow #5. In these tests, the matrix effect was simulated by the addition of citric acid to a pH of 3.5 and 1 part per million (ppm) of iron. Over an exposure period of 14 hours, each of the colors showed substantially increased stability in PET bottles enhanced with 390 protection, and to a lesser extent with 370 protection.

Impact on vitamins
A key component in many of the new enhanced waters is vitamins, which we know are generally sensitive to the effects of temperature, oxygen and light. A slight change in the molecular structure of a nutrient can render vitamins biologically ineffective, i.e., they no longer serve a nutritional role in the body.

Many vitamins are known to be specifically vulnerable to degradation by UV light including Vitamin A, B2 (riboflavin), B6, B12 and folic acid. Light also accelerates the destructive interaction between vitamins.

To meet label declarations during anticipated shelf life, product formulators typically include an excess amount of nutrients based on the required shelf life. From a practical perspective, excessive amounts may introduce added cost and product quality concerns. Excessive levels of vitamins, or formation of their degradation products, may also result in off-flavors or shifts in the color of products.

UV testing was conducted on several vitamins, and they generally showed substantial sensitivity to UV. Each was significantly more stable in PET bottles enhanced with 390 coverage.

Effects on taste buds
Many of the newly enhanced waters offer unique flavors, created through the addition of components that may be sensitive to UV exposure. The degradation of these ingredients can lead to the formation of unpleasant qualities detectable by taste and smell at low concentrations. To establish an initial focal point in this area, the lemon aroma complex was investigated. A significant contributor to lemon flavor, and also one of the most photosensitive, is “citral.” When exposed to UV, citral degrades into by-products including “photocitral-A” and “photocitral-B,” which are readily detectable in the lab. Another compound is also formed that exhibits a strong off-flavor at levels not easily detectable by analytical methods.

Photocitral-A and photocitral-B were measured as indicators  for the degradation of the lemon flavor package. Formation of photocitral-A occurred rapidly in standard PET and green PET bottles while samples with 370 protection generated only slight levels of photocitral-A. Samples with 390 protection didn’t generate significant levels of photocitral-A.

Research has documented a complex matrix effect of ingredients and UV light. While some ingredients in isolation are stable when exposed to UV light, they become unstable when in combination with other ingredients. On the other hand, some ingredients that are inherently unstable to UV become stabilized by the presence of other components. The only way of determining matrix effects is through testing.

Conclusion
PET packaging is well established as the ideal container for bottled water, and there’s no reason it cannot continue to play this role with enhanced waters. The one caveat is that beverage companies must not only fortify their waters, they must also fortify their PET packaging with UV protection at the 390 level. This additional step will assure that promises of nutrition, energy and good taste will be delivered to the consumer each and every time.

About the author
Dr. Daniel Connor is a senior research and development chemist for Milliken Chemical, a division of Milliken & Company in Spartanburg, S.C. He earned a bachelor’s degree in chemistry and a doctorate in organic/polymer chemistry from the Georgia Tech. For four years, he has performed polymer additives research for Milliken while focusing on design and synthesis of colorants and UV absorbers, effects of light on food ingredients and design and synthesis of nucleating agents for polymers. This contributed to Milliken’s ClearShield® UV absorber technology, the subject of this article. Connor holds eight patents in amorphous polyester resin compositions, novel chromophores for thermoplastics, and colorless UV absorbers for PET. He can be reached at (864) 503-6084, email: [email protected] or website: www.millikenchemical.com

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