Combined use of natural antimicrobial based nanoemulsions and ultra high pressure homogenization to increase safety and shelf-life of apple juice

The present research was aimed to investigate the potentialities of ultra high pressure homogenization (UHPH) to produce stable natural antimicrobial based nanoemulsions. Initially, the nanoemulsions were characterized for their size, stability over time and antimicrobial properties against several pathogenic and spoilage microorganisms. After that nanoemulsions were tested to increase the safety and shelf-life of apple juice deliberately inoculated with pathogenic (Listeria monocytogenes Scott A, Staph. aureus SR231, Escherichia coli 555) and spoilage microorganisms (Saccharomyces cerevisiae SPA, Lactobacillus plantarum 82) and treated with different high pressure homogenization treatments. The analyses performed by dynamic laser light scattering showed that the hexanal and trans-2-hexenal based nanoemulsions were characterized by an average size of 86 and 100 nm, respectively while they were characterized by a stability, over time, of 14 months without separation. Moreover, the nanoemulsions resulted, after the UHPH treatment, colourless. The pathogenic species deliberately inoculated in apple juice decreased their cell loads with different kinetics in relation to the use of hexanal and trans-2-hexenal and high pressure homogenization treatment applied. Regarding spoilage microorganisms, S. cerevisiae cell loads decreased under detection limit (1 log CFU/mL) in juice containing nanoemulsions and treated at 200 MPa for 2 cycles. The data of the present research contribute to support the application of natural antimicrobial based nanoemulsions into complex food system, enlarging the experimental evidence for their use in food sector. In particular, the obtained hexanal and tran-2-hexenal based nanoemulsions have demonstrated great application, due also to their organoleptic compatibility, to the fruit juice sector, promoting also an increase of quality of apple juice.