Hurdle processing of turbid fruit juices involving encapsulated citral and vanillin addition and UV-C treatment.

The aim of this study was to evaluate a hurdle strategy for orange-tangerine (OT) and orange-banana-mango-kiwi-strawberry (OBMKS) juices processing based on UV-C treatment assisted or not by mild heat and the addition of natural antimicrobials. Vanillin and citral emulsions were successfully encapsulated using maltodextrin and HI-CAP (5,18,3) and characterized. The susceptibility of Lactobacillus plantarum ATCC 8014, Escherichia coli ATCC 25922, and Saccharomyces cerevisiae KE 162 to binary mixtures of the encapsulated agents was examined in culture media according to the Berenbaum experimental design. The boundary between growth and non-growth as a function of vanillin and citral concentrations was predicted by means of the probabilistic model using logistic regression. Microbial inactivation achieved by pilot-scale UV-C light (0-390 mJ/cm) on its own, assisted by mild heat (50 °C, UV-C/H) and combined with antimicrobials (1000 ppm vanillin plus 100 ppm citral) addition (UV-C + A/UV-C/H + A) was assessed in OT and OBMKS. Yeast induced damage in a model solution treated by UV-C + A was studied by flow cytometry (FC). All the antimicrobial mixtures resulted in additive effects (FIC = 1), thus offering through the probabilistic models a range of formulation possibilities with antimicrobial capacity encompassing lower vanillin and citral concentrations compared to those required when used alone (V = 0-1875 ppm plus C = 392-0 ppm). UV-C led up to 3.7-3.8, 2.4-3.6 and 1.5-1.6 log-reductions of E. coli, L. plantarum and S. cerevisiae in OT and OBMKS, respectively. A significant increase of 1.7-2.2, 2.1-2.7 and 4.1-5.3 log cycles in microbial inactivation was observed after UV-C/H treatment. Additional inactivation of 0.7-3.1 and 0.5-2.7 log reductions were observed for E. coli and S. cerevisiae, respectively, when UV-C + A and UV-C/H + A were applied in both juices. Therefore, the addition of antimicrobials to the UV-C treated juices, showed additive to synergistic effects on E. coli and S. cerevisiae, respectively along refrigerated storage. A shift from yeast cells with intact membrane and esterase activity in control samples to cells with permeabilized membrane in C + A, UV-C and UV-C + A samples were determined by FC. The shift was more noticeable in UV-C + A samples. Sublethally damaged cells were only detected in C + A and UV-C samples. This study demonstrates that combining a pilot-scale UV-C treatment with the addition of chosen binary mixtures of vanillin and citral, can ensure more than 5 log-reductions of E. coli, L. plantarum and S. cerevisiae in OT and OBKMS juice blends.