Synergistic effect of supercritical carbon dioxide and peracetic acid on microbial inactivation in shredded Mozzarella-type cheese and its storage stability at ambient temperature

• Study succeeded in preserving shredded Mozzarella cheese (SMC) at 25 °C for 21 d.
• Supercritical carbon dioxide (SCCO2) and peracetic acid (PAA) processing of SMC.
• Combining SCCO2 and PAA led to ≥4.6 log10 inactivation of vegetative microorganisms.
• Higher efficacy for concurrent than sequential (pre-conditioned) hurdle processing.
• Synergistic effects obtained for most SCCO2/PAA-treated microorganism groups.

Supercritical carbon dioxide (SCCO2) in combination with peracetic acid (PAA) could represent an effective decontamination technique to control microorganisms in shredded cheese. Preservation of shredded Mozzarella-type cheese (SMC) was assessed at 25 °C over 21 d, using SCCO2 (9.9 MPa, 35 °C, 30 min) individually and combined with PAA at concentrations of 50 (SCCO2/PAA50), and 100 (SCCO2/PAA100) ppm with optional 30-min pre-conditioning time (SCCO2/PAA100PC). Process efficacy was assessed based on achievable inactivation and treatment synergism reflected in counts of inoculated Escherichia coli, Listeria innocua, Geobacillus stearothermophilus spores and indigenous micro-flora such as total bacteria (TBC) and total yeasts and molds (TYMC). Complete inactivation of E. coli cells (≥7.0 log10) in SMC was achieved with any of the combined treatments, whereas initial reduction of L. innocua was lower when SCCO2/PAA50 and SCCO2/PAA100 combinations were applied (2.9 and 4.6 log10, respectively). G. stearothermophilus spores exhibited the highest resistance, allowing for a reduction of up to 3.8 log10 (SCCO2/PAA100) and indicating no advantage of pre-conditioning. However, PAA concentration significantly affected microbial inactivation, comparing SCCO2/PAA100 to SCCO2/PAA50 in TBC (minimum of 6.6 vs. 4.2 log10, respectively) (P < 0.05) and TYMC (minimum of 7.7 vs. 1.1 log10, respectively) (P < 0.05). The TBC and TYMC were not significantly decreased by stand-alone decontamination techniques (P ≥ 0.05); however, synergistic treatment effects (P < 0.05) occurred for all microorganisms except for E. coli. Overall, the findings demonstrate great potential for a SCCO2/PAA hurdle technology as an alternative to post-processing decontamination strategies for production of shelf-stable SMC at ambient temperatures.