Chemicals responsible for taints

4.4 Chemicals responsible for taints

  The chemicals listed in the Table 4.4 have been found to cause taint. These compounds have all been associated with taint produced by paper, polymer films, coatings or resins.

  Aldehydes and ketones are two classes of compounds that are often responsible for taints. These include the conjugated unsaturated carbonyl compounds. These compounds are particularly odorous. An excellent evalu- ation of the importance of these compounds was made by Koszinowski and Piringer (1986). These workers synthesised a range of unsaturated car- bonyls and determined the odour thresholds as a function of carbon chain length. They found that the most odorous compounds were those with eight or nine carbon atoms. There are numerous possible reactions that can occur with components in packaging materials that result in the formation of conjugated unsaturated ketones and aldehydes. Isolated double bonds will, if possible, undergo chemical transformation and move into conjugated systems. Once produced, the a- and b-unsaturated compounds are

  76 Taints and off-flavours in food

  Table 4.4 Common tainting compounds Compound

  Jasmine odour

  Impurity in ethyl acetate

  printing ink solvent

  2-Ethyl-5,5-dimethyl-1, Sweet, nutty, woody

  Reaction of 2-propenal with

  3-dioxane

  neopentyl glycol

  3-Isopropyl-2-

  Musty odour

  Suspected formation involving

  methoxypyrazine

  unknown bacteria

  4,4,6-Trimethyl-1,3-

  Musty odour

  Reaction of paraformaldehyde

  dioxane

  with 2-methyl-2,4- pentanediol in a coating

  2,2,6-Trimethyl-1,5-

  Sweet, camphor odour Reaction of acetone with 1,3-

  dioxane

  butanediol

  2,2,4,5-Tetramethyl-1,3- Camphor, liniment

  Reaction of acetone with 2,3-

  2-Ethenyl-2,5-dimethyl- Musty, liniment odour Reaction of methyl ethyl 1,3-dioxane

  ketone with 1,2-propanediol

  4-Methyl-4-

  Catty urine odour

  Hydrogen sulfide adduct of

  mercaptopentan-

  mesityl oxide from

  2-one

  diacetone alcohol with hydrogen sulfide from meats

  4-Phenylcyclohexene

  Synthetic latex odour

  Diels Alder condensation

  product of styrene with butadiene in binder coated paper

  Acetaldehyde

  Pear-like odour taste

  Degradation product

  sometimes formed during processing of PET

  Benzophenone

  Geranium odour

  Photo-initiator in UV inks

  and varnishes

  Aliphatic acids

  Short chain lengths

  Recycled paper

  particularly odorous, Degraded lubricating oil

  e.g. butyric acid has a rancid off odour

  Alkyl acetates e.g.:

  Fruity odour

  Flexo and gravure print solvent

  ethyl acetate propyl acetate butyl acetate

  Alkyl substituted

  Hydrocarbon

  Styrenebutadiene latex binder

  benzenes a-Methyl styrene

  Hydrocarbon plastic

  Styrenebutadiene latex binder, also present in some EVOH grades

  Butyl acetate

  Pear drop odour,

  Printing inks

  fruity taste

  Chlorocresol

  Medicinal odour and

  Disinfectants

  taste

  Cumene (isopropyl

  Hydrocarbon

  Styrenebutadiene latex binder,

  benzene)

  also present at trace level in some EVOH grades

  Packaging materials as a source of taints 77

  Table 4.4 Continued Compound

  Sweet pungent odour

  Screen-printing solvent

  Ditribromophenol

  Medicinal taint

  Bromination of phenol, an

  impurity in polymers, used as wood preservers on pallets

  Ditrichlorophenol

  Medicinal taint

  Wood preservers, herbicides,

  industrial chlorination of natural or synthetic phenols

  Dichlorobenzene

  Medicinal taste

  Disinfectant, drain cleaner,

  fumigants

  Diphenyl sulfide

  Cabbage-like odour

  Photoinitiator for cationic inks

  Glycol ethers e.g.

  Soapy taste

  Printing solvent

  2-butoxyethanol 2-ethoxypropanol

  Guaiacol

  Smoky phenolic

  Lignin derived in kraft paper

  Hexanal

  Boardmown grass

  Lipid degradation commonly

  odour

  associated with paper

  Isophorone

  Pungent brown sugar

  Screen printing inks

  odour

  common cause of taint from promotion toys

  Methyl benzaldehyde

  Almond odour

  Impurity in clarifying agent for

  polypropyelene sheet and containers

  Methyl benzoate

  Pungent herbal odour

  UV inkvarnish unwanted side

  reaction

  n-Propyl benzene

  Hydrocarbon

  Styrenebutadiene latex binder

  Naphthalene

  Petroleum odourtaste Litho print solvent

  p-Cresol

  Phenolic

  Lignin derived in kraft paper

  Pentan-1,2-dione

  Medicinal, chemical

  Present in titanium acetyl

  taint

  acetonoate adhesion promoters

  Propylene glycol

  Chemical taste

  Printing inks

  monobutylether Styrene

  DIY fibre glass car

  Monomer in polystyrene and

  repair odour

  wide range of coatings Migration greater from high

  impact polystyrene (HIPS) than crystal PS

  Thioglycollic acid alkyl Pungent strong stale

  From alkyl tin stabilisers used

  Petroleum odourtaste Litho print solvent

  Tribromoanisoles

  Musty odour

  Bacterial methylation of

  corresponding phenols

  Trichloroanisole

  Musty odour

  Bacterial methylation of

  corresponding phenols

  Trimethylanisole

  Musty odour

  Contaminant in rubber seals

  78 Taints and off-flavours in food chemically very stable owing to the stabilising effect of the conjugation.

  Such compounds tend to persist in the packaging because of a compara- tively low volatility and moderate polarity. The low taint thresholds make the identification of these compounds difficult and sometimes impossible without selective concentration procedures. This class of compounds can produce serious taint problems in food packaging. Aliphatic alcohols and alkanes are rarely the cause of taints. Relatively high concentrations are required before they can be smelt or tasted.