Evolution of volatile compounds from milk to curd during manufacturing of Mozzarella

The aim of this study was to investigate the evolution of the volatile compounds (VOC) from milk to curd during mozzarella manufacturing, in connection with the technique used for curd acidification (traditional = natural whey starter fermentation; industrial = direct acidification by citric acid addition). Overall, 40 compounds were identified from the entire set of samples, belonging to different chemical classes. All compounds detected in milk were also found in the curd, but at much higher concentration. In addition, many other compounds formed during curd production. By comparison of the samples from the 2 acidification techniques, and analysing the scientific literature to explain the source of the volatile compounds, it was found that microbial activity played a main role in VOC formation. In fact, the curd obtained by natural whey starter fermentation showed the most complex profile, whereas that of the curd obtained by direct acidification was much simpler. The most important odour-active compounds that could contribute to flavour of the curd made by traditional technology were 3-methylbutanal, ethyl acetate and 2,3-butanedione, responsible for ethereal, fruity and buttery odour. For direct acidification they were 3-methylbutanal (at lower level), nonanal and decanal (herbal/fruity odour). The PCA analysis showed clear clusterization of the three types of samples: milks and direct acidified curds were rather close in the bi-plot graph, whereas traditional curds were spread all along the space. The research is currently in progress, for assessing the evolution of the volatile compounds during the next technological steps of mozzarella manufacturing.