Spatial characterisation of eye-growing kinetics in semi-hard cheeses with propionic acid fermentation

An important characteristic of semi-hard cheeses with propionic acid fermentation is the eyes. However, growth mechanisms of the eyes are only qualitatively understood. In this study, X-ray computed tomography was used to monitor eye growth inside cheeses during ripening without disrupting any mechanism. Chemical and rheological analyses carried out in two different zones of the cheeses revealed a spatial-dependency, with the position the eyes significantly correlated to their final volume, and a different CO2 production by CO2-producing propionic acid bacteria with 27.7 mmol kg−1 in the centre and 18.7 mmol kg−1 in the outer zone. Furthermore, the present study allowed quantification using image processing: the overall cheese porosity grew from 0.03% at the beginning of ripening up to 4.60% at the end. Moreover, the porosity was 10 times lower, and the volume of eyes 13 times lower, in the outer zone than in the centre of the cheese.