Effect of UHPH on indigenous microbiota of apple juice: a preliminary study of microbial shelf-life.

The effect of ultra high pressure homogenisation (UHPH) at 100, 200 and 300 MPa on apple juice at two different inlet temperatures (4 and 20 degrees C) was studied. Raw and conventional heat treated (PA) apple juice was compared with UHPH treated juice after treatment and during 60 days of storage at 4 degrees C. The microbial quality was studied by enumerating aerobic mesophilic counts (AM), psychrotrophs (PS), moulds and yeasts (MY), lactobacilli (LB), enterobacteriaceae (EB), and faecal coliforms (FC). PA samples were below detection level (< or = -2 log cfu/mL) for all groups, the same as UHPH treated juices at 200 MPa and above but for around 1 log cfu/mL for AM. Those AM counts did not change during 60 days storage at 4 degrees C and proved to be spores. Juices treated at 100 MPa shown little reductions in microbial counts, and surviving microorganisms significantly increased their numbers during storage. This research work showed that non-thermal methods such a UHPH technology may give new opportunities to develop "fresh like" apple juice with a shelf-life equivalent to PA in terms of microbiological characteristics without affecting the product quality.