Lipid oxidation in dairy products

An important factor for the shelf life and aroma formation in dairy products is lipid oxidation. The aim of this project is to characterize minor amounts of oxidation products by using HPLC (primary oxidation produts) and dynamic headspace GC/MS (secondary oxidation products) and to implement the knowledge into the production. The project is established in cooperation with the industry (MD Foods and the Danish Dairy Board).
During the first part of the project the methods were optimized for the new applications. Then storage experiments with processed cheese and feta cheese were carried out. The products were stored at 5, 20 and 37 °C for up to one year, half of the processed cheeses were stored in light and the rest i darkness. The changes were followed by determination of secondary volatile products by GC/MS. A general increase in the content of volatile compounds was found during storage of the processed cheeses. The formation of some compounds (eg. 2-hexanone and 2-heptanone) were mainly dependent of the temperature whereas others (eg.octane, hexanal and octanal) were mainly dependent of light. These findings were confirmed by multivariate statistic evaluation.
In 1999 a storage experiment on sliced Havarti cheese was performed. The influence of light on lipid oxidation was examined by analysing the volatiles produced by dynamic headspace GC/MS. Only small differences due to light exposure wereg observed. A general increase in the content of volatiles was found.
Similar examinations, but for shorter periods and at lower temperatures, were conducted on fish oil/ rapeseed oil containing dairy spreads.
Another part of this project is carried out at Department of Dairy and Food Science, The Royal Veterinary and Agricultural University, where radical formation is studied.