Purpose: This research was aimed to investigate native flora as well as some inoculated microorganisms (Escherichia coli ATCC 35218; Listeria innocua ATCC 33090, Salmonella Enteritidis MA44 and Saccharomyces cerevisiae KE162) evolution in the following fresh squeezed juices: apple (pH: 3.4; 12.7°Brix), orange (pH: 4.3; 10.4°Brix), and strawberry (pH: 3.6; 9.8°Brix), after being exposed to PL and during refrigerated storage.
Methods: For each PL treatment (Xenon lamp; 3 pulses/s; 60 s; 71.6 J/cm2), 0.1 ml of inoculum (~5x108 CFU/ml) was added to the juice (4.9 ml) contained in a Petri dish refrigerated with ice flakes (T < 20°C). PL treated samples were collected in 10 ml caramel jars and kept under refrigerated conditions (5 ± 1°C) for 12 days. At periodic time intervals they were analyzed for survivors. Non inoculated juices were used for the shelf-life study. Experiences were performed in quintuplicate.
Results: PL treatment produced 1.4 - 2.6-log reductions in apple juice depending on the strain; while 0.3 - 0.8-log reductions were obtained in orange and strawberry juices. A significant decrease of 5.0 - 8.0 log cycles was determined at the end of storage for S. Enteritidis and L. innocua in all PL treated juices. Non growth was observed for E. coli and S. cerevisiae, except in apple juice, where the yeast was able to recover starting from day 9 of storage . PL reduced up to 1.4 and 1.5 log cycles molds and yeasts and aerobic mesophilic counts, respectively; however it did not prevent their recovery along storage.
Significance: PL was effective providing microbiological stability regarding relevant microorganisms along refrigerated storage but it did not improve juice shelf life, suggesting the requirement of its combination with other hurdles in order to reach the desired storage stability.