Influence of the polyethylene packaging on the adsorption of odour-active compounds from UHT-milk

Application of an Aroma Extract Dilution Analysis (AEDA) on distillates prepared from two UHT-milks either packed in polyethylene (PE-M) or glass (G-M), respectively, revealed delta-decalactone and gamma-dodecalactone as the most odour-active constituents among the 37 odour-active constituents in the PE-M. delta-Decalactone was also the most odour-active among the 32 odorants detected in G-M, followed by delta-octalactone, gamma-dodecalactone, (Z)-6-gamma-dodecenolactone and vanillin. To detect a possible adsorption of odorants at the packaging, the AEDA was also applied on solvent extracts obtained from both, the glass and the polyethylene bottles, in which the two milks were supplied. The results confirmed the high tendency of polyethylene to adsorb odorants, while the affinity of the aroma compounds to glass were weak. A comparative quantification of selected key odorants in the polyethylene packaging as well as in the milk, allowed the calculation of adsorption ratios. The results demonstrated a strong influence of the chemical structure on the extent of adsorption. For instance, aldehydes, such as (E)-2-nonenal and (E,Z)-2,6-nonadienal, had a much higher affinity to polyethylene than lactones and acids. The results indicated that the overall aroma of UHT-milk packed in polyethylene can be changed during storage by adsorption as well as by permeation processes of milk aroma compounds to and through polyethylene packaging.