Microbial inactivation by ultra high-pressure homogenisation on fresh apple juice

Abstract

The effect of ultra high-pressure homogenisation (UHPH) on the microbial shelf life of fresh apple juice immediately after treatment and storage at 4 °C was studied and compared with fresh raw apple juice and a conventional heat treatment (pasteurised apple juice (PA)) used at industrial level (90 °C for 4 min). Apple juice samples were processed using an ultra high-pressure homogeniser (model FPG11300, Stansted Fluid Power Ltd., Essex, UK), applying treatments of 100, 200 and 300 MPa (single stage) at an inlet temperature of 4 °C. The microbial quality was studied by enumerating total counts (TC), psychrotrophs (PS), moulds and yeasts (MY), lactobacilli (LB), enterobacteriaceae (EB) and faecal coliforms (FC). UHPH samples at 200 and 300 MPa and PA samples reached reductions on PS, MY, LB, EB and FC of at least 3.9, 3.5, 2.4, 3.2 and 3.0 log cycles, respectively, whereas on TC reductions were of 2.6 and 3.6 log cycles on UHPH samples at 200 and 300 MPa, respectively, and at least 4.3 log cycles (not detected) on PA samples. Hence, alternative methods such as UHPH may give new opportunities to develop fresh apple juice with an equivalent shelf life to PA in terms of microbiological characteristics.