Taint and odour phenomena in carton-board packaging systems

Unsaturated lipids exist in carton-board and can be the precursors of odorous compounds. Two unsaturated lipids that can be present are oleic acid (cis 9-octadecenoic acid) and linoleic acid (cis, cis 9,12-octadecadienoic acid). These lipids can be present in the free acid form, as alkyl ester derivatives and in the triglyceride form. These lipids are able to undergo oxidation. Such oxidation leads to the formation of a number of odorous compounds. Oxidation proceeds via hydroperoxide intermediates to produce aldehydes, ketones, alcohols, furans, lower fatty acids, alkenes and alkanes, the majority of which are odorous. The aldehydes, in particular, have very low odour and taste detection thresholds, needing to be present only in very small amounts in a packaging material to cause a taint problem. Typically, taints associated with these compounds are described as 'rancid', 'pungent', 'soapy' and 'green'. Static headspace GC/MS analyses have identified a number of odorous compounds formed from oxidation reactions, within standard samples of wood pulp obtained from carton-board manufacturers. These oxidation reactions are affected to various extents, by a number of factors such as the temperature, the nature of the fatty acids, the presence of oxidation catalysts such as transition metal ions, the availability of oxygen, the humidity and the presence of photosensitising agents. Breakdown pathways and reaction schemes are presented in context as are kinetic details of odorous product formation. UV curable inks are commonly used in the printing of carton-board packaging materials. These inks contain photoinitiators which have the potential to affect the oxidation rate and extent of formation of unsaturated lipids, resulting in the formation of odorous compounds within the carton-board matrix. Static headspace analysis, dynamic headspace analysis and vacuum extraction procedures have identified a number of volatile components, that are odorous, in the inks and varnishes. These compounds, which include by-products arising from photoinitiators, amine photoactivators and residual solvents, have the potential to cause 'ink', 'varnishy', 'plasticy' taints in a packaged food system if these components are able to migrate from the carton.