Determination of mTG Activity in Low-Fat Semi-Hard Cheese Using Fluorescent Labelling

A method to directly determine enzyme activity in cheese has not been published yet despite the fact that mTG mediated gel strength or hardness modification may be unpredictable and unfavorable during ripening and/or storage. The present study was performed to determine enzyme activity of semi-fat semi-hard Hungarian Trappist cheese. The widely known hydroxamate method was not suitable to even detect enzyme treatment, because of the disturbing effect of milk proteins. However incorporation of a dansylated glutamine dipeptide into milk protein contributed to monitoring the enzyme activity. The fluorescent measurement reflected mTG activity by increasing fluorescence intensity at 532 nm in a 5-min continuously running assay. The presented dipeptide assay allows the determination of enzyme activity after 2 min measurement by the manufacturing stage: cutting and up-heating. This assay can be used to monitor mTG activity during manufacture of low-fat semi-hard cheese type, in case if it was produced according to general recommendation of enzyme preparation providers (enzyme dosage: 0.1%, v/w). According to the preliminary calibration this assay can define mTG activity in the range of 0.05–0.3 U/g.