Novel technologies: study for application to fresh dairy sector

Ricotta is a potential growth medium for a wide range of microorganisms and it is an easily perishable food, characterized by a short shelf life (2-3 days), even under refrigerated conditions. Heat-based treatments can provoke microbial reduction, but alteration of the chemical and sensory profile can also occur. Therefore, in this Ph-D research alternative non-thermal technologies were tested on artisanal and industrial ricotta cheese to optimize parameters that promote quality preservation. The technologies tested were summarized in the figure 1 reported below (X-rays, Ultraviolet (UV-C) and Near Ultraviolet visible light (NUVL), Pulsed Light (PL) and Cold plasma). Specifically, artisanal and/or industrial ricotta were adopted for testing the effects of the above-mentioned techniques. In the first test artisanal and industrial ricotta samples were irradiated at 0.5, 2.0 and 3.0 kGy. At the two highest intensities (2.0 and 3.0 kGy), the artisanal product remained acceptable for more than 20 days, while the untreated samples became unacceptable after only 3 days of storage. The shelf life of the product irradiated at 0.5 kGy was limited to 14 days, due to the appearance of sensory defects. The industrial product irradiated at all X-rays intensities recorded a significant extension of the shelf life up to 84 days compared to the control which was discarded after 40 days due to sensory defects. As regard PL treatments at increasing fluence (1.3, 3.1, 7.5, 15.0 J/cm2) it was observed that PL at 1.3 and 3.1 J/cm2 allowed to delay microbial spoilage during storage, but higher fluences favored microbial growth and odor formation, possibly due to the surface nature of the PL technology. The analyses carried out on the product demonstrated that PL induced the formation of small protein particles, capable of interacting with lipids and carbohydrates and reorganizing into larger aggregates. Aggregation reduced protein solubility and occurred after exposure to hydrophobic protein groups. The photoreaction of proteins was confirmed by the formation of melanoidins and 8 carbonyls. Ricotta cheese artificially inoculated with Pseudomonas fluorescens was also tested by UV-C and NUVL. Results highlighted that the control samples became unacceptable after less than 5 days, while treated samples remained acceptable for more than 6 days. Finally, two different plasma-assisted approaches were assessed to extend the shelf life of artisanal ricotta cheese. In one test the plasma is applied indirectly, with plasma ignited in a controlled atmosphere (91% of N2 plus 9% of O2 supply gas) and the gaseous effluents (no plasma) directed to flow through small sterile tubes containing the cheese. In the other test product was directly exposed to the effects of the plasma. Treated and untreated samples were stored at 4 °C for a period of 8 days, during which microbiological, sensory and pH measurements were carried out. The results of the two approaches were similar: the concentrations of viable cells in the treated samples remained lower than those recorded in the control cheese, thus making the product more stable. From a sensorial point of view, the properties of ricotta in treated cheeses have been better preserved. Therefore, also cold plasma was effective in prolonging ricotta cheese shelf life.