Discrimination of haymilk and conventional milk via fatty acid profiles

Milk produced by feeding silage-free feed has become popular in Europe. This kind of milk has recently been recognized as "traditional speciality guaranteed" by the European Union. As a consequence, an analytical discrimination of this silage-free produced milk quality has become necessary. In this study, discrimination of "haymilk" (HM) from conventional milk (CM) in retail samples was attempted taking in consideration all feeding seasons. For analytical discrimination, a partial least square discriminant analysis (PLS-DA) to fatty acids methyl esters (FAMEs) obtained from analysis by gas chromatography was applied. All groups of long-chain fatty acids, including saturated, odd chain fatty acids, mono- and polyunsaturated fatty acids of both cis/trans configuration, contributed to discrimination of the two types of milk, where alpha linolenic acid (+ 37% in HM) and conjugated linoleic acid (C18:2c9t11-+ 22% in HM) were the most relevant for calibration. Applying PLS-DA was successful in discriminating CM and HM from retail milk in all seasons. From 48 identified fatty acids, 18 showed different levels in CM and HM samples and could be used for discrimination of the two groups. The method was able to discriminate HM and CM produced in the cold season, but showed unclear results in the warm season due to a higher scattering of both groups. These higher deviations were attributed to the fact that most dairy cows are able to consume fresh grass during summer. Although it is not possible to discriminate HM and CM produced in warm season, the fatty acid pattern of HM can be taken as a reference, from which a properly produced HM should not deviate. A separate calibration for each season is recommended for optimal results.