Foods and beverages, personal care products and household cleaners packaged in clear polyethylene terephthalate (PET) bottles face a threat to their formulations and ingredients from ultraviolet (UV) light.

Exposure to sunlight and artificial light sources during warehousing, distribution, retail display and post-purchase storage can degrade the color, flavor, fragrance and nutritional value of consumer products. In particular, UV light can cause color fading and shifting, create off-flavors and aromas, and reduce vitamin potency. Ultimately, lower product quality and shorter shelf life resulting from UV damage can impact profitability and brand reputation.

The traditional solutions to UV light protection for PET bottles, including using opaque or dark-colored plastics or covering the bottle with graphics to block UV radiation, may not appeal to consumers. These methods prevent consumers from seeing what they are buying. Many people prefer clear packaging, which offers visibility and connotes purity and safety.

The other approach – incorporating UV stabilizers, preservatives and other additives in the product itself – has drawbacks as well. It runs counter to the current clean label trend, which emphasizes natural, simple ingredients, and speaks to a desire for quality, trust and transparency. These additives also can raise the cost of the product.

Blocking High UV Wavelengths

The most effective strategy for combatting UV degradation is incorporating a UV blocker in clear PET packaging to protect against wavelengths above 320 nanometers (nm), the limit of inherent PET resistance. However, most of these additives only block UV wavelengths up to 370 nm. Therefore, if an ingredient degrades under exposure to light at a higher wavelength, a UV 370 absorber will not help (Fig. 1).

A few UV absorbers protect ingredients from damaging UV light at wavelengths up to 400 nm. They address the susceptibility of certain colors, fragrances and vitamins to high UV wavelengths. These ingredients include Blue #1 colorant, various lavender fragrances, and a variety of vitamins such as vitamin A, B2 (riboflavin), B6, B12 and folic acid. In some cases, such as vitamin B2 and B12, protection may even require the addition of a colorant since the ingredient is susceptible to wavelengths in the visible portion of the light spectrum. As a result, products such as milk, beer and wine commonly necessitate the incorporation of Keyplast Blue KR, Keyplast Yellow 4GL and Keyplast Red 60 into the PET material, as these colorants contain unique UV properties.

Adding Value to UV Absorbers

When selecting a high-wavelength UV absorber for PET, converters, packaging manufacturers and brand owners can gain additional value from those offering a polymer-bound formulation, which means they do not leach out of the plastic and potentially contaminate the product. Another desirable attribute of these types of UV absorbers is their non-interference with the crystal clarity of PET, enabling consumers to enjoy a clear view of the contents of the container. Finally, the UV absorber should be food contact compliant.

Strategic Benefits of UV Blockers

A high-performance UV additive for PET can:

  • Protect UV-sensitive foods and beverages to extend shelf life
  • Sustain the integrity of brand elements such as color (Fig. 2)
  • Support the clean label trend and sustainability efforts

Other considerations include the following:

Extending shelf life: Without proper UV protection, foods and beverages can degrade on store shelves or in consumers’ homes. A slight change in the molecular structure of a nutrient can render it biologically ineffective. As mentioned earlier, many vitamins are known to be specifically vulnerable to degradation by UV light. Light also accelerates the destructive interaction between vitamins. For example, the degradation of both folic acid and citric acid (vitamin C) is accelerated by the combined presence of riboflavin (vitamin B2) and light. So, when milk is exposed to light, vitamin C begins to degrade. Shorter shelf life can increase costly waste and cause consumer dissatisfaction.

Degradation also can cause a product to become non-compliant with food labeling regulations such as the U.S. Food and Drug Administration’s 21 CFR Part 101, which requires Class I nutrients (vitamins, minerals and other ingredients added to fortified food products) to remain at or above the declared value on the label. Class II nutrients – those occurring naturally in food – must be present at 80 percent or more of the value declared on the label. [1] Otherwise, the product may be considered misbranded.

Some food and beverage makers deliberately overload Class I ingredients as a hedge against future degradation. This may seem like a simple fix, but additional amounts of particular ingredients can lead to changes in taste, aroma or color, and sometimes are more expensive and complex than incorporating the necessary protection into the packaging in the first place. Selecting an effective UV absorber can remove the need to overdose Class I nutrients.

Advanced high-wavelength UV absorbers available today for PET, such as Milliken Chemical’s ClearShield® 390B UV absorber, have been shown to protect vitamin A’s shelf life 30 times better than when packaged in standard PET. Studies also indicate that they improve the shelf life of vitamin B6, riboflavin, folic acid and vitamin B12 (Table 1).

Reinforcing brand identity: Brand identity is often associated with a signature color and flavor, such as the yellow-green color and lemon-lime flavor of a well-known sports beverage. When the distinctive color of a beverage, shampoo, dish soap or other product fades or shifts due to UV exposure, consumers can spot the change immediately. Inconsistent color can imply uneven quality and reflect poorly on the brand’s image, which in turn negatively affects repeat purchases and customer loyalty.

In the United States, seven synthetic dyes are approved for general food use and more than 30 for general use in cosmetics. Although many of these dyes independently exhibit favorable stability to UV light, they have been shown to be unstable to light when formulated with certain ingredients. For example, citric acid is frequently added to beverages for nutritional value and to scavenge dissolved oxygen that can attack certain flavor components. When citric acid in beverages containing certain synthetic colorants is exposed to UV light, rapid fading of the colorant can result. The ClearShield technology has been shown to substantially increase the stability of several U.S. Food, Drug, & Cosmetic Act (FD&C Act) colorants, including Blue #1, Red #40 and Yellow #5, in the presence of citric acid (Graph 1).

Returning to the sports drink example, one of the significant contributors to lemon flavor, and one of the most photosensitive, is citral. When exposed to UV light, citral ingredients degrade into several byproducts, including photocitral-A, photocitral-B and another compound that exhibits a strong off-flavor at levels that are hard to detect through analytical methods. Testing of a high-wavelength UV absorber in clear PET using sensory panels demonstrated that the plastic packaging preserved the integrity of a citrus-flavored beverage to a much greater extent than PET with a UV 370 absorber, green PET or standard PET.

In 2016, sales of sports and energy drinks in the United States totaled $25 billion[2] If these customers suddenly stopped purchasing their favorite beverage because of an off-taste, color shift or unpleasant aroma, the negative effects on brand loyalty and revenues could far outweigh the costs of UV protection.

Supporting the clean label movement: Although the definition of clean label can vary, in general, it refers to consumers’ desire for products containing mostly recognizable ingredients. This can mean all-natural or organic ingredients, no artificial preservatives and colors, and the elimination of hormones and antibiotics. 

To protect against UV light damage and extend shelf life, preservatives such as sodium benzoate and citric acid are often added. Removing preservatives and other synthetic ingredients from product formulations to support a clean label requires an alternative method to block UV radiation. A high-wavelength UV blocker ensures that the PET bottle will protect sensitive ingredients without the need to add preservatives to the food, beverage or other product.

To address consumer concerns about purity and safety, it is important to use a polymer-bound UV absorber that will not leach from the packaging into the contents. Non-polymer-bound formulations can migrate to the surface of the PET bottle, leaving residue on the inside of the packaging or even contaminating the product itself.

Migration of the additive can also occur during the high heat of processing, causing plate-out. Conventional UV absorbers can extract out of the PET and create residue on the mold (Fig. 3). This residue could contaminate other bottles. It also requires frequent cleaning of the machinery, which can add costs and cause production delays.

Enhancing sustainability: Opaque and intensely colored PET materials that are produced to block UV light can darken the recycle stream, causing processing difficulties and lessening the value of the reclaimed plastic. By supporting the use of clear, uncolored PET, UV absorbers help to facilitate effective recycling.

High Performance, High Value

Natural or artificial UV light can damage products, profitability and brand reputation. The ideal way to protect against UV degradation, while meeting consumer demands for clean labels, transparent packaging and recyclability, is to use clear PET bottles containing a UV absorber designed for high wavelengths up to 400 nm. These additives provide an effective shield that helps avoid impacts to color, flavor, aroma and nutrients in package contents. A polymer-bound product formulation can deliver additional benefits, including avoidance of additive migration that can impact packaging and product quality and processing efficiency. 

[1] Code of Federal Regulations, Title 21, Food labeling

[2] Packaged Facts news release, May 16, 2017