Inactivation of spoilage microorganisms in apple cider using a continuous flow pulsed electric field system

Abstract

The effect of pulsed electric field (PEF) in inactivating naturally occurring microorganisms (yeast and molds) in freshly squeezed apple cider was investigated in a continuous flow system. The microbial count decreased with an increase of applied pulses (17.6–58.7 total) and treatment temperature (45–50 °C), and a decrease of flow rate (3–10 l/h). At field strength of 27–33 kV/cm (3 mm electrode gap in a concentric chamber), 200 pulses/s, 3 l/h flow rate, and 50 °C process temperature, there was a 3.10 log reduction in microbial counts. By PEF treatment in the presence of a mixture of nisin and lysozyme (27.5 U/ml for nisin and 690 U/ml for lysozyme), there was an increase in the microbial count from 1.12 to 1.78 log reductions for 10 l/h flow. When cider samples were treated in the presence of clove oil (3 or 5 ml/100 ml), an additive reduction of 1.99 log cycles in microbial counts was observed.