Overview
A rapid, robust, sensitive and specific LC-MS/MS assay has been developed for the simultaneous detection of milk and egg proteins in white wine. The method utilizes a simplified sample preparation protocol, the Eksigent ekspert™ microLC 200, and the AB SCIEX QTRAP® 5500 system with the Scheduled MRM™ algorithm to detect below 0.1 ppm casein in wine.
Introduction
In wine production fining a wine eliminates any appearance of cloudiness by removing sediment. In this process fining agents, such as casein, are stirred into barrels of wine where they act as magnets by picking up the sediment in the wine and depositing it at the bottom of the barrel. Once the wine has been clarified, racking of the wine is done to separate the wine from the sediment. In 2011 EFSA concluded that wines fined with casein, caseinate and milk products may trigger adverse reactions in susceptible individuals following a survey of wine where the detection of casein was reported in trace amounts (<2 mg/L [2 parts-permillion]) in two (out of 32) experimental wines without bentonite treatment and in three (out of 61) commercial wines with unknown treatment.1, 2 This fact together with a new European Union legislation (that states that wine after 30 June 2012 must disclose on the label if fining reagents such as casein and egg ovalbumin have been used in processing)3 has driven the need for methods which are capable of detecting casein products in wine at low levels. Here we present new data using micro flow LC in combination with an LC-MS/MS method developed on an Eksigent ekspert™ microLC 200 and AB SCIEX QTRAP® 5500 system utilizing the Scheduled MRM™ algorithm which detects casein in wine at sub ppm levels. The method utilizes a simple protein digestion of the wine followed by dilution and injection and has been designed to limit extensive sample preparation and perform all protein modification in the same Eppendorf tube. In this paper we will discuss the benefits of micro flow LC over higher flow rate separations.
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