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Factors that affect odor and taste of contents due to plastics packaging

The aim of packaging is to minimize sensory changes as much as possible over the shelf lives of these products. Even as plastic packaging protects its contents, it can alter their taste and odor. Taste and odor are very important in packaging of foods, beverages, and other goods sensitive to taste and odor. Preserving the taste and odor of products in plastic packaging is a complex process that extends throughout a package's path from formulation to customer.
In most cases the change in taste and odor is of little consequence, but in some cases, the change can be critical. A glaring example is neutral products like bottled water that are especially susceptible to organoleptic influences. Organoleptic properties, ie additives, processing and storage of products, affect the odor and taste of plastic end products. Given the resources that food, beverage and other manufacturers expend in creating compelling products, it is of prime importance to them to avoid a plastic package alter the taste and odor.

Everyone involved in the chain of the package's creation, including the additive masterbatch suppliers, compounders, molders and extruders, are asked to validate that a package won't cross-contaminate a food or a beverage. This makes it critical to ensure that the materials used and the processing steps followed affect the taste or odor of the contents and their organoleptic qualities as little as possible. Since any packaging raw material can cause organoleptic concerns, masterbatch suppliers and others involved in compound formulation must know how various pigments, resins and additives affect taste and odor.
Taste and odor issues most often occur when a component in the plastic migrates into the contents of the package, although other mechanisms such as “scalping” (chemical interaction between the package and its contents) may also be present. An important initial step is to learn which package ingredients cause off-flavors and aromas so the additive and resin combination chosen has minimal organoleptic impact. Once package prototypes have been developed, the choice of packaging raw materials is often confirmed by taste and odor panels and perhaps by analytical methods. Getting the package formulation right the first time saves time and money in package development, accelerates time to market, and eliminates costly packaging rework and re qualification later on, along with assurance of consumer acceptance.

The ability to make informed choices about components such as pigments, resins and additives, begins with testing of raw materials to create a database of organoleptic properties - based on a company's knowledge of pigments and additives and how they affect taste and odor and the other is empirical and based on how taste and odor panels have evaluated packaging that contains certain colorants and additives. The optimum approach to creating plastics packaging free of taste and odor problems is to choose an “organoleptic-friendly” colorant and avoid the use of functional additives. In general, most FDA-compliant colorants are organoleptically suitable. Still, colorants require careful selection because some have more problematic chemistries than others when it comes to taste and odor. Many formulators avoid colorants that contain either chlorine or sulfur due to their potential to cause sensory issues, and some manufacturers have strict limits on compounds with such colorant content, eg Ultramarine blue pigment, with its residual sulfur content.

Off-tastes can also arise from coatings on mineral pigments, such as rutile titanium dioxide (TiO2), which are often designed to assist dispersion. In fact, only a few of the TiO2 white pigments currently available are suitable, which makes it imperative for those formulating masterbatches for plastic packaging to monitor such pigments from all suppliers. Careful consideration is also required when selecting organic additives used in packaging resins, including slips used for torque reduction in closures or as a mold release, antioxidants for protection against thermal degradation, antistats and dispersion agents that aid in the manufacturing process.

To avoid organoleptic problems, formulators should opt for high-purity additives that contain relatively low concentrations of lower-molecular-weight contaminants that readily migrate out of a plastic. Formulators should also use these additives at the lowest effective dosage. Those made from vegetable sources are generally preferred to those derived from animal sources, which may go rancid over time. Primary slips are a good example, with formulators gravitating to vegetable-based erucamide types over animal-based oleamide slips.
Another key is to minimize or eliminate organic functional groups such as amines, amides, esters, ethers, and hydroxyls, which contain heteroatoms (oxygen, nitrogen, phosphorous, sulfur) that are typically migratory and impact taste and odor. For example, this means avoiding antistats based on amine or ester chemistries and antioxidants that use combinations of phosphates and either hindered phenols or thiol esters.

Several other factors can weigh in on the organoleptic integrity of a package. Among them is the choice of carrier resins used in masterbatches. These should be neat resins that are free of low-molecular-weight components. Even when formulating with a high level of organoleptic awareness, problems can arise during processing. To safeguard against cross-contamination, packaging manufacturers should consider using dedicated equipment whenever possible for applications sensitive to taste and odor. There are a few standard ASTM methods that have been developed that evaluate & measure organoleptic properties. They are:

ASTM E1870-04, “Standard Test Method for Odor and Taste Transfer from Polymeric Packaging Film,” provides test methods for evaluating monolayer, coextruded, and laminated films in terms of perceived odor and the transfer of package-related odors and flavors.
ASTM D1292-05, “Standard Test Method for Odor in Water,” offers a test method for determining odor intensity with regard to effluents, which may carry a myriad of compounds that contribute to odor problems.
ASTM E460-04, “Standard Practice for Determining Effect of Packaging on Food and Beverage Products During Storage,” addresses the detection of changes in the sensory attributes of foods and beverages stored in various packaging materials and systems.
ASTM STP 434, “Manual on Sensory Testing Methods” and ASTM STP 758, “Guidelines for Selection and Training of Sensory Panel Members,” are publications that are out of print but available in some libraries.

Shelf life is also an issue with masterbatches designed for an organoleptic-sensitive application, because additives can degrade as they age. Such masterbatches usually have shelf lives of six months or less, as opposed to two years for conventional masterbatches. The shorter shelf lives prevent migratory components in the masterbatch from traveling to the pellet surfaces. Good manufacturing practices regarding inventory turnover is a requirement to ensure product viability.

Molders and extruders need to keep processing temperatures from rising so high that the resin degrades and creates species that cause offensive odors and tastes. The rest of the supply chain can also create organoleptic problems. For example, sterilization by ultraviolet light or ozone can affect some of the organic additives in a plastic to create off-tastes and odors. Even distribution and storage can alter taste and odor if the package shelf life is exceeded or storage temperature goes too high.
Taste and odor are psychophysical phenomena that vary from person to person. As subjective perceptions, they are best evaluated by panels of carefully selected individuals trained to detect them. Packagers of beverages like wine, liquor, coffee, and water, as well as foods, drugs, perfumes, cosmetics, and other fragrant health and beauty aids, have a long history of reliance on taste and odor panels to assess aroma and flavor.

Molders and manufacturers often use such panels to screen prototype packaging to see if the organic and inorganic ingredients and processing method used affect the organoleptic integrity of the contents. Testing panels are also used in quality-control programs during production to evaluate incoming raw materials or respond to customer complaints. Panels also come into play after a package is reformulated.
Much thought has been given to how to gain dependable results from taste and odor panels. Their use typically involves blind studies in which test samples are evaluated against a control. Panels may simply rate the difference between samples and a control as pass or fail or, they may rank the taste and odor intensity of samples based on set descriptions e.g., no difference, slight difference (acceptable), moderate difference (problematical), and pronounced differences (rejected). Such descriptors are often assigned numerical values—e.g., zero for no difference, 0 to 1 for a slight difference, and so forth. Panel members rate samples along the spectrum defined by the scale so the results can be analyzed statistically.

Taste and odor panels contain 4 to 15 or more individuals selected from the local community who represent a cross section of age and gender. The overall goal is to have all panel members assess samples in the same way. Recruits are tested for sensitivity to tastes and odors using standard odorants to ensure they are not hypersensitive or lack sensitivity to odors. They cannot be smokers and they must be free of physical conditions that affect smell or taste, such as colds, allergies, and asthma. Those accepted are trained in sensory awareness, the descriptors to be used, and how to behave on the panel (such as to avoid biasing others on the panel with one's perceptions during testing).

Panels operate in a controlled environment free of odors, noise, and other distractions, and are asked not to chew gum or eat just before or during testing, to not wear perfume and other scented items, and to keep their hands and clothes clean and free of odors. All samples are prepared and presented to panel members in the same way.
Data from taste and odor panels is often all that is needed to ensure a product is suitable for its intended use. Such panels remain the most consistent and practical method for determining if a package is suitable for a food or beverage application.

At times there is a need to identify offending substances in a package so the source of the problem can be found and corrected. Characterizing such substances is a daunting and time-consuming task. While gas chromatographs (GC) and mass spectrometers (MS) provide objective measurement of specific chemicals, this approach is limited because flavor involves trace levels of a great many compounds interacting with the human sensory apparatus.

An effective approach to identifying compounds that cause odor quality defects combines conventional gas chromatograph and mass spectroscopy (GC-MS) methods with olfactometry and multidimensional GC separation techniques.

(Source Courtsey: Plastics Technology)

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