Light induced off-flavors (LIOFs) can be an issue when milk is packaged in high density polyethylene (HDPE) plastic jugs instead of glass bottles. In this study, we used solid-phase microextraction (SPME) followed by GC/MS to investigate the effectiveness of a range of plastic materials as barriers to the production of offflavors. Headspace SPME with a Carboxen®/PDMS (CAR/PDMS) coated Nitinol fiber retains low molecular weight analytes which can be detected from samples at concentration levels of less than 1 ng/mL (ppb) allowing accurate analysis of these small flavoring analytes.
Light induced off-flavors (LIOFs) in milk became an issue when dairies began to package milk in high density polyethylene (HDPE) plastic jugs instead of glass bottles. There are several types of LIOFs with the most common coming from oxidation of lipids and degradation of sulfur containing amino acids. Light induced lipid oxidation occurs from free radicals reacting with unsaturated fatty acids in milk. The free radical reaction cleaves the double bond and forms hydroperoxides that degrade predominately to aldehydes and, to a lesser degree, ketones and alcohols. The most common light activated analytes in this class are hexanal and pentanal primarily induced from linoleic acid.
The mechanism for the breakdown of sulfur containing amino acids in whey protein is not fully understood, but most common breakdown products in this class are dimethylsulfide (DMS), methanethiol (MT) and dimethyldisulfide (DMDS). Due to the high volatility of DMS and MT, this study focused primarily on DMDS.
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