C03 | Evaluation of the shelf life of homogenized buffalo ricotta cheese supplemented with protective indigenous cultures: preliminary study

M. Di Paolo¹, M. Egidio¹, R. L. Ambrosio¹, T. Cardellicchio², O. Di Maro², F. Capano¹, R. Marrone¹. | ¹Dip. di Medicina Veterinaria e Produzioni Animali, Univerità degli Studi di Napoli Federico II, Napoli, Italia; ²Dip. di Coordinamento della Sicurezza Alimentare, Istituto Zooprofilattico Sperimentale del Mezzogiorno, Portici, Italia.

Purpose: In recent years, the use of protective cultures (PC) in foods has increased significantly, representing a natural alternative to chemical preservatives. Ricotta cheese is a suitable matrix for the delivery of PC such as lactic acid bacteria (LAB). The aim of the study was to evaluate the shelf life of homogenized buffalo ricotta made with three PC isolated from milk (Lactiplantibacillus plantarum; LC44 and LC11) and buffalo whey (Leuconostoc mesenteroides ssp. mesenteroides; SS14). Materials and methods: The isolated strains were characterized through an in vitro study of their probiotic, antimicrobial, and antioxidant properties. For the production of ricotta cheese, in collaboration with a buffalo milk processing plant, the optimal inoculum concentration to be used during production was evaluated to ensure a minimum LAB 30° concentration of 10⁶ CFU/g. Four experimental groups of ricotta cheese were produced from a single production batch: a control without CP (CTR) and three with LC44 (BRM44), LC11 (BRM11), and SS14 (BRW14). The production technology involved a modification of the company flow chart for the cooling phase (35±2°C) for the inoculation of the CP. The ricotta cheeses were analyzed for their nutritional, chemical-physical, sensory, and microbiological characteristics during storage at 4±1°C. The analyses were conducted at T0 (1 d), T1 (8 d), T2 (15 d), T3 (18 d), T4 (22 d), and T5 (25 d). Results: The CP isolated from milk showed greater survival in simulated gastric juice at pH 2.5 and in simulated intestinal juice with bile salts. The supernatants of the PC showed antimicrobial activity against all indicator microorganisms, with Listeria monocytogenes being the most sensitive species. The milk strains proved to be more effective than the whey strains. All strains showed significant antioxidant activity due to their ability to neutralize free radicals. The application of CP in ricotta cheese confirmed the greater resistance and adaptability of strains isolated from milk compared to those from whey. Although the initial concentration of LAB at 30°C in BRW14 was below the minimum threshold, it increased to suitable values during storage. The samples with CP showed lower pH values than CTR, contributing to the inhibition of microbial population growth. The addition of CP did not cause any changes in nutritional composition and did not affect the oxidative state of the ricotta cheeses. The cheeses with added CP showed a more intense lactic aroma and a more yellow color, as also confirmed by colorimetric analyses. Starting from T2, the emergence of excessive acidity and bitterness compromised the acceptability of the product. Conclusions: The study demonstrated the potential of CP to enrich buffalo ricotta with functional, antimicrobial, and antioxidant properties. However, preliminary data show that the shelf life of this type of product requires a specific production process that balances the microbial dynamics of the matrix and the logistical and economic needs of companies. Future studies will make it possible to obtain probiotic dairy products with specific technological protocols and suitable shelf life studies.