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Important notes:Do NOT write outside the grey boxes. Any text or images outside the boxes will be deleted. Do NOT alter the structure of this form. Simply enter your information into the boxes. The form will be automatically processed -if you alter its structure your submission will not be processed correctly.Do not include keywords -you can add them when you submit the abstract online. Title Abstract:Whey is used as an ingredient in long shelf life sports drinks due to its high nutritional value. However, some liquid Whey Protein Isolate (WPI) based products develop insoluble material during shelf time; a phenomenon referred to as "unwanted protein aggregation". In many cases this deterioration can be avoided, by increasing the heat treatments from 95⁰C/180s to 120⁰C/20s. A fluorescence amine assay that monitors the level of free amino terminals (Larsen et al., 2004) has shown that the products subjected to the mild heat treatment have an increase in amino terminals during storage which is more than twice as high as the increase observed in the more harsh heat treated products. This indicates a presence of proteolytic activity from heat stable proteases in products having undergone both types of heat treatments, but also a heat treatment dependent inactivation of the respective proteases. Therefore a mass spectrometry (MS) based peptidomic approach was initiated to characterize the peptide fraction of the WPIs, with the aim of identifying a relation between the peptide profiles and the product quality of the re-dissolved WPIs during storage and furthermore to deduce information about the proteolytic activity and the identity of the proteases. Redissolved WPIs were adjusted to pH 3 to simulate the sports drinks conditions and subsequently subjected to heat treatments. After two weeks of storage at room temperature the peptide fractions of the samples were isolated using centrifugal filter units with a cutoff of 10kDa and 3kDa and the permeates were desalted and concentrated on handmade chromatographic columns as described by Gobom et al, (1999). By means of MALDI-TOF-TOF, this peptide fraction was subjected to MS/MS and mass searches were carried out using the SwissProt database.