Effect of high pressure CO 2 and mild heat processing on natural microorganisms in apple juice

Abstract

Apple juice was pasteurized by high pressure carbon dioxide (HPCD) at 20 MPa with CO 2 concentration of 4.5–5.3% and mild heat (MH) at atmospheric pressure. Microbial inactivation and stability of natural microorganisms in apple juice were investigated. The temperatures were 37, 42, 47, 52, 57 and 62 °C, treatment time was 30 min, and storage temperatures of pasteurized apple juice were 2 and 28 °C. The aerobic bacteria (AB) treated by MH at 62 °C and by HPCD at ≥ 52 °C were almost totally inactivated, the microbial counts were < 10 CFU/mL. The yeasts and moulds (Y&M) treated by MH at ≥ 57 °C and by HPCD at ≥ 42 °C were totally inactivated. HPCD increased the susceptibility of these natural microorganisms to temperature and enhanced their microbial inactivation. The AB in apple juice treated by HPCD at ≥ 52 °C and the Y&M treated by HPCD at ≥ 57 °C, the AB and the Y&M treated by MH at 62 °C showed a better stability during storage at 2 and 28 °C, but apple juice treated by HPCD at ≤ 47 °C was characterized with high microbial counts of the AB ≥ 2.75 × 10 3 CFU/ml. A viable but non-culturable (VBNC) state of the Y&M treated by MH at 57 °C and by HPCD at 42, 47 and 52 °C was observed during storage at 28 °C. Apparently the proper temperature of HPCD treatment of apple juice at 20 MPa and stored at 2 and 28 °C was greater than or equal to 52 °C, while for MH treatment the proper temperature increased to 62 °C in this study.