Taste Styrene

Odor and taste Polystyrene, styrene-acrylonitrile, polyethylene, acrylic, ABS, polysulfone, EVA, polyphenylene oxide, and many other TPs are examples of satisfactorily odor-free. FDA approvals are available for many of these plastics. Food packaging and refrigerating conditions will also eliminate certain plastics. There are TPs and melamine as well as urea compounds that are suitable for this service. 

Clear, colorless, watery liquid with a penetrating or pungent rubber-like odor. Becomes yellow to yellowish-brown on exposure to air. Experimentally determined odor threshold concentrations in air for inhibited and unhibited styrene were 0.1 and 0.047 ppmv, respectively (Leonardos et al., 1969). Experimentally determined detection and recognition odor threshold concentrations were 220-640 pg/m (52-150 ppbv) and 64 pg/m (15 ppbv), respectively (Heilman and Small, 1974). At 40 °C, the average odor threshold concentration and the lowest concentration at which an odor was detected were 65 and 37 pg/L, respectively. At 25 °C, the lowest concentration at which a taste was detected was 94 pg/L, respectively (Young et al., 1996). The average least detectable odor threshold concentrations in water at 60 °C and in air at 40 °C were 3.6 and 120 pg/L, respectively (Alexander et al., 1982). 

Marchsan and Morran (2002) found that flavor descriptions varied between chlorinated and nonchlorinated water in contact with PE and PP with stronger tastes frequently found in chlorinated samples. "Plas-tic/rubber" terms were used for chlorinated and nonchlorinated waters stored in PP and PE as well as in nonchlorinated waters from acryloni-trile/butadience/styrene (ABS). "Plastic/chemical" descriptors were used for chlorinated and nonchlorinated waters in PP and PE and polyurea materials, and in ABS materials for chlorinated waters only. Polyurethane materials contributed chemical tastes to chlorinated waters and medicinal flavors to nonchlorinated water. The "chemical" term also was applied to chlorinated water stored in PP, PE, and ABS and nonchlorinated water stored in ABS. "Medicinal" also was used to describe both nonchlorinated and chlorinated waters stored in PP. 

Taste threshold levels for styrene monomer in foods... 

The residual styrene monomer remaining in the finished material can cause taints by transferring to the packed product in amounts that exceed the taste threshold concentration level in that particular food. Each food matrix has a characteristic styrene concentration (threshold concentration) above which the styrene taint becomes evident (Chapter 13). A series of sensory taste threshold concentrations taken from the literature for different foods are shown in Table 14-2. 

Ethylbenzene is commonly used as a solvent diluent during the polystyrene polymerization process. It can be found in the finished material and can be a source of taints as well. As seen in Table 14-2 the sensory taste threshold concentrations for ethylbenzene are 2 to 3 times higher than those for styrene. 

Based on taste threshold s published in the literature as well as food industry experience, an average acceptable taste threshold level of styrene monomer in a variety of food products ranges around 0.3 ppm. 

Table 14-2 Taste thresholds for styrene and ethylbenzene in foods.

From experience it has been established that the sensory threshold for coffee creamer and condensed milk products is on the order of 0.1 mg/kg (ppm) of styrene in the product. This observation is only partly supported by threshold values from the literature in Table 14-2 where values range from 0.2 ppm for 3 % yogurt, 1.2 ppm for 3.8 % fat milk and 2-5 ppm for condensed milk. This points out two problems with threshold concentration values caused by the way they are determined (e.g. experimental methods) and the definition of the threshold value being the value at which the substance is correctly identified by 50 % of the panelists (versus other possible ways of measur-ing/defining the taste threshold). 

Assuming complete migration of styrene at this styrene monomer level in the PS, the taste of styrene monomer will be readily detected in the product based on a threshold of 0.1-0.3 ppm. 

The effect of the partition coefficient on the transfer of styrene into an aqueous product is dramatic, the estimated potential migration is reduced by 60 times compared to Example 14-1, However, the taste threshold for styrene in low fat products is lower (around 0.40 mg/kg). 

As long as the initial concentration, cpo, of styrene in the material is not larger than the largest QMcalc value calculated from Eq. (14-8) or (14-9) the taste threshold in the product will not be exceeded. 

Figures 14-1 and 14-2 show estimations of shelf life in a 7.5 g PS containing portion pack before two different taste threshold concentrations (2 and 0.1 mg/kg) of styrene are exceeded in the product. In each graph the diffusion coefficients from Linssen et al. (1992) for a 1 1 PS HIPS polymer blend at room temperature (23 °C) and refrigeration temperature (4 °C) are used. The estimation using Eq. (14-5) at 23 °C and 4 °C and an calculated apparent diffusion coefficient for PS/PE and PS/EVOH/PE structures (see Table 14-3) are used in Eq. (14-4) (see example 14-5) to calculate the days before a styrene taint is detected in the product. The shelf life is decreased by a factor of the square of the increase in the material s residual styrene content. As seen in Figures 14-1 and 14-2 a reduction in the taste threshold by a factor of ten means almost a 100 times decrease in the shelf life.

Linssen, J., Janssens, A., Reitsma, H., Bredie, W., Roozen, J. 1993. Taste Recognition Threshold Concentrations of Styrene in Oil-In-Water Emulsions and Yogurts. J. Sci. Food Agric. 61 457-462. 

ANs are those that contain a majority of nitrile polymers. They provide good gas barrier, chemical resistance, and low taste and odor transfer with good impact properties when modified with rubber. Extruded sheet is used extensively in food packaging and rigid packaging applications. This crystalline TP is most useful in copolymers. Its copolymer with butadiene is nitrile rubber. Acrylonitrile-butadiene copolymers with styrene (SAN) exist that are tougher than PS. It is also used as a synthetic fiber and as a chemical intermediate. 

According to Winter et al. (1976e), at a concentration of 0.5 ppm in a syrup base, it has a styrene-like, aromatic taste. 

Polystyrene is made by bulk or suspension polymerization of styrene. Polystyrene is very low cost and is extensively used where price alone dictates. Its major characteristics [19,20] include rigidity, transparency, high refractive index, no taste, odor, or toxicity, good electrical insulation characteristics, low water absorption, and ease of coloring and processing. Polystyrene has excellent organic acid, alkali, salts, and lower alcohol resistance. It is, however, attacked by hydrocarbons, esters, ketones, and essential oils. 

Classification Polymer Definition Sodium form of a sulfonated divinylbenzene-styrene copolymer cation exchange resin Empirical (CsHsOsS Na)x Properties Golden brn. fine powd., odorless, char, taste insol. in water anionic Toxicology LD50 (oral, rat) > 8 g/kg, (oral, mouse) > 10,125 mg/kg mildly toxic by ing. irritant experimental reproductive effects TSCA listed... 

Strong acid anionic resins such as sulphonated styrene-divinyl benzene copolymers can be used to mask the taste of basic drugs with a bitter taste. They can be used almost throughout the entire physiological pH range above... 

Di-t-butyl peroxide (125°C) is useful for the high-temperature finish of styrene polymerization to reduce residual styrene monomer content and thus improve modulus, HDT, taste, and odor. 

Commercial PSs are normally rather pure poljmers. The amount of styrene, ethylbenzene, styrene dimers and trimers, and other hydrocarbons is minimized by effective devolatilization or by the use of chemical initiators (30). Polystyrenes with low overall volatile content have relatively high heat-deformation temperatures. The very low content of monomer and other solvents, eg, ethylbenzene, in PS is desirable in the packaging of food. The negligible level of extraction of organic materials from PS is of crucial importance in this application because of taste and odor issues. 

Some foods packaged in PS are extremely sensitive to taste (eg, chocolate chip cookies). These sensitive applications reqnire PS having residnal styrene monomer levels below 200 ppm. It is not feasible to consistently lower the styrene level to <200 ppm withont special techniqnes. 

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