Kasper Hettinga, Dept. of Dairy Science and Technology, Wageningen University, The Netherlands
Kasper Hettinga1, Bob Comstock2, Bethany Michele Henrick3, Erika von Mutius4, Bruce German3, and Markus Ege4
1. Food Quality & Design group, Wageningen University, The Netherlands;
2. Tamarack Biotics, Fresno, CA;
3. Department of Food Science and Technology, University of California, Davis;
4. Dr. von Hauner Children’s Hospital, Ludwig Maximilians University Munich, Germany
At the IMGC-2014, data was presented on the difference in the breast milk proteome of allergic versus non-allergic mothers, which was subsequently published (Hettinga et al, 2015). The major outcome of that study was that protease inhibitors were increased in milk of mothers with house dust mite allergy, one of the main allergies in the Western world. Hence, protease inhibitors may play a causal role in the development or prevention of house dust mite allergy; therefore, they have been patented by pharmaceutical industry. Besides breast milk, also bovine milk contains protease inhibitors. The aim of the present study was to determine the heat damage to immuneactive bovine milk proteins in general and protease inhibitors in particular.
Bovine milk was heat-treated at different temperatures (from low pasteurization to ultra-high temperature sterilization). Also a non-thermal treatment (UV-C irradiation) was tested as a comparator to thermal treatment of milk. After these milk treatments were done, non-native proteins were removed according to Zhang et al. (2016), followed by LC/MSMS-based proteomics according to Hettinga et al. (2015). Heat damage was calculated as percentage of the protein concentration / activity lost due to heat or UVC treatment, in comparison to the original raw milk. The remaining activity of immuneactive proteins was assessed by bacteriostatic assays in both heat and UVC treated milk.
Around 300 proteins were identified in the thermal and UVC treated milk samples combined. Heat damage to the immune-active proteins ranged from around 10% for low pasteurization to 90% for UHT sterilization, showing decreasing proteins concentrations with increasing heating intensities. Protease inhibitors decreased more after low pasteurization (-40%) than other immune-active proteins (-10%), whereas the decrease after UHT sterilization was similar for all immune-active proteins (-85 to -90%).
UVC also damaged proteins, however with different physical-chemical characteristics, as determined by chromatography profiles. Both immune-active proteins (-10%) as well as protease inhibitors (-48%) show a similar decrease after UVC treatment compared to low pasteurization (-10% and -40%, respectively). The bacteriostatic assays corroborated the findings from the proteome analyses.
Damage to immune-active proteins and protease inhibitors depends on the treatment applied to bovine milk. The effect of heat treatment depends strongly on heating intensity, with pasteurization showing relatively high retention of immune-active proteins. UVC treatment is an interesting alternative to heat pasteurization. The physical-chemical nature of the damage by UVC to the proteome remains to be elucidated.
Hettinga KA, Reina FM, Boeren S, Zhang L, Koppelman GH, Postma SD, Vervoort JJM Wijga AH. Difference in the Breast Milk Proteome between Allergic and Non-Allergic Mothers. PLoS One 2015; 10(3): e0122234; Zhang L, Boeren S, van Hooijdonk ACM, Vervoort JJM, Hettinga KA. 2016. Proteomic study on the stability of proteins in bovine, camel, and caprine milk sera after processing. Food Research International 82: 104–111Download PDF