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

Abstract

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.