Monitoring the effect of transglutaminase in semi-hard cheese during ripening by hyperspectral imaging

Semi-hard cheese samples made from pasteurized 3.5% and 5% fat cow's milk were partly enzyme treated with microbial transglutaminase (mTG). Cheese colour and yield was greatly affected by mTG at both fat levels. The cross-linking effect of mTG also led to improved protein content and hardness in cheese. As Texture Profile Analysis (TPA) could only distinguish according to enzyme treatment we studied hyperspectral imaging (HSI) to differentiate also according to fat level and ripening status. HSI was used on a weekly basis during 4-10 weeks period of ripening time. In case of uneven surface, using the spatial information and making proper normalization on the spectra of ROI pixels, the hyperspectral method can provide even better signal-to-noise ratio then the conventional spectrophotometric method. Statistical analysis with Partial Least Squares (PLS) regression and Monte Carlo Cross Validation (MCCV) led to determination of significant wavelengths both for the detection of enzyme treatment (1387 nm) and for fat content (1190, 1234 nm) independent of the actual age of examined semi-hard cheese. Hyperspectral measurement method allowed remote inspection of the product through transparent vacuum foil. The spectrum normalization allowed the elimination of effects originating from inhomogeneous illumination caused by cheese holes. (C) 2016 Elsevier Ltd. All rights reserved.