Does milk treatment before cheese-making affect microbial and chemical traits of ripened cheese? Grana Trentino as a case study

The aim of this study was to evaluate the influence of different storage temperatures and delivery system of the milk on the microbiological and physicochemical characteristics of a long ripened hard cooked Italian cheese like Grana Trentino. In particular, the milk was kept and delivered to the dairy at 18 °C or at 12 °C or in the traditional way without milk temperature control and using churns. Milk, natural whey starter and cheeses after 18 months of ripening were sampled and plate counts, physico-chemical analysis, proteolysis evaluation and study of cheese volatile compounds through Solid Phase Micro Extraction (SPME) GC-MS technique were performed. All these results were also elaborated by Principal Components Analysis which allowed to relate the experimental data to technological parameters in order to characterize and distinguish the cheese obtained from the different treated milk. At the end of ripening, cheeses produced in the traditional way without temperature controlling varied significantly in the microbial, chemical, free aminoacids (FAA) and volatile organic compounds (VOC) analysis. In addition, different behaviours of nitrogen fractions in cheese were detected. In fact, lower temperatures of milk storage involved a higher soluble nitrogen fraction and favoured a higher cheese proteolysis. On the other hand, the FAA amounts normalised to the soluble nitrogen showed no differences between samples probably because the lactic acid bacteria, involved in AA production, were not affected during ripening by the milk treatment. Free fatty acids (FFA) and esters contents were significantly higher in cheeses from milk without temperature controlling. This is probably due to a higher release of fat after the fat globule membrane break during the transport in churns that involve a deeper lipolysis. The results obtained in this work allow a better understanding of ripening dynamics in an important Protected Designation of Origin (POD) cheese like Grana Trentino.