PEF based hurdle strategy to control Pichia fermentans, Listeria innocua and Escherichia coli k12 in orange juice

The combination of pulsed electric fields (PEF) and bacteriocins in a hurdle approach has been reported to enhance microbial inactivation. This study investigates the preservation of orange juice using PEF in combination with nisin (2.5 ppm), natamycin (10 ppm), benzoic acid (BA; 100 ppm), or lactic acid, (LA; 500 ppm). Pichia fermentans, a spoilage yeast frequently isolated from orange juice, Escherichia coli k12 or Listeria innocua were inoculated into sterile orange juice (OJ) with, and without, added preservatives. The antimicrobial activity over time was evaluated relative to an untreated control. The effect of PEF treatment (40 kV/cm, 100 μs; max temperature 56 °C) was assessed on its own, and in combination with each antimicrobial.The acidic environment of OJ inactivated E. coli k12 (1.5 log reduction) and L. innocua (0.7 log reduction) slightly but had no effect on P. fermentans. PEF caused a significant decrease (P < 0.05) in the viability of P. fermentans, L. innocua and E. coli k12 achieving reductions of 4.8, 3.7 and 6.3 log respectively. Nisin combined with PEF inactivated L. innocua and E. coli k12 in a synergistic manner resulting in a total reduction to 5.6 and 7.9 log respectively. A similar synergy was shown between LA and PEF in the inactivation of L. innocua and P. fermentans (6.1 and 7.8 log reduction), but not E. coli k12. The BA–PEF combination caused an additive inactivation of P. fermentans, whereas the natamycin–PEF combination against P. fermentans was not significantly different to the effect caused by PEF alone. This study shows that combining PEF with the chosen preservatives, at levels lower than those in current use, can provide greater than 5 log reductions of E. coli k12, L. innocua and P. fermentans in OJ. These PEF–bio–preservative combination hurdles could provide the beverage industry with effective non-thermal alternatives to prevent microbial spoilage, and improve the safety of fruit juice.