Inactivation of naturally occurring microbiota in cucumber juice by pressure treatment

The inactivation effects of high hydrostatic pressure (HHP) (350 MPa/10 min, 400 MPa/4 min and 500 MPa/2 min) with homogenization (20 MPa/2 min), nisin (100 IU/mL) and decompression time (< 3 s and 7–8 s) on naturally occurring microbiota in cucumber juice were investigated. Initial concentration of yeasts and molds (Y&M) was 5.6 × 103–2.4 × 104 CFU/mL, and total plate count (TPC) was 1.0 × 105–3.5 × 105 CFU/mL. Y&M were inactivated below the detection level (≤ 10 CFU/mL) in all cases. The reduction of TPC in non-homogenized cucumber juice (NHCJ) was 2.5–3.0 log cycles, which was significantly higher than 1.0 log cycle in homogenized cucumber juice. The combination of nisin with HHP had a synergistic effect on the inactivation of TPC. The reduction of TPC in NHCJ with a decompression time of < 3 s was approximately 4.5 log cycles, which was significantly higher than a decompression time of 7–8 s. Five non-linear models including the biphasic, Weibull, modified Gompertz, log-logistic and Baranyi models were fitted to TPC inactivation curves for the NHCJ at 300, 350 and 400 MPa for 2–15 min and 500 MPa for 2–8 min at a decompression time of < 3 s. The biphasic model provided the best fit for the data.