Phase transition of triglycerides during semi-hard cheese ripening

Sixteen semi-hard cheeses varying by their protein (20.2-24.1%), fat (23.7- 31.1%) and dry matter (50.2-57.9%) contents were manufactured and ripened i n controlled conditions. Fluorescence (vitamin A) and mid-infrared (2780-30 00 cm(-1) region) spectra were collected on the 16 different cheeses at 1,2 1, 51 and 81 days of ripening. The data tables containing the mid-infrared and fluorescence spectra of the different cheeses were analyzed by principa l component analysis and canonical correlation analysis methods. The obtain ed similarity maps showed that it was possible to discriminate the cheeses at the four different ripening times from the infrared and fluorescence spe ctra. In addition, the interest to combine the two spectroscopies was demon strated since a better discrimination of the four stages was obtained using canonical correlation analysis. The examination of the spectral patterns a ssociated with the principal components and the canonical variates showed t hat the structure of triglycerides acyl chains in fat globules was modified during cheeses ripening. The shift of the methylene bands in the infrared region and the changes of the shape of vitamin A fluorescence spectra agree with partial crystallization of triglycerides from 21 to 81 days of storag e. (C) 2000 Elsevier Science Ltd. All rights reserved.