High-Intensity Pulsed Electric Field Variables Affecting Staphylococcus aureus Inoculated in Milk

Abstract

Staphylococcus aureus is an important milk-related pathogen that is inactivated by high-intensity pulsed electric fields (HIPEF). In this study, inactivation of Staph. aureus suspended in milk by HIPEF was studied using a response surface methodology, in which electric field intensity, pulse number, pulse width, pulse polarity, and the fat content of milk were the controlled variables. It was found that the fat content of milk did not significantly affect the microbial inactivation of Staph. aureus. A maximum value of 4.5 log reductions was obtained by applying 150 bipolar pulses of 8 mus each at 35 kV/cm. Bipolar pulses were more effective than those applied in the monopolar mode. An increase in electric field intensity, pulse number, or pulse width resulted in a drop in the survival fraction of Staph. aureus. Pulse widths close to 6.7 micros lead to greater microbial death with a minimum number of applied pulses. At a constant treatment time, a greater number of shorter pulses achieved better inactivation than those treatments performed at a lower number of longer pulses. The combined action of pulse number and electric field intensity followed a similar pattern, indicating that the same fraction of microbial death can be reached with different combinations of the variables. The behavior and relationship among the electrical variables suggest that the energy input of HIPEF processing might be optimized without decreasing the microbial death.

Review: Potential of High-Intensity Pulsed Electric Field Technology for Milk Processing

“…In fact, equipotential lines concentrate in the cavity of the bubble, distorting the electric field within the gap, and developing voltage potentials that get higher as the gap distance gets shorter and/or the bubble gets bigger [21]. The unexpected electrical gradient gives rise to one of two possibilities: (1) the sample is undertreated and the effectiveness of the treatment is reduced if breakdown is disregarded [21] or (2) there is an immediate breakdown and subsequent arcing. Since the breakdown strength of gases is much lower than that for liquids [21], arcs may cause the coagulation and/or evaporation of milk and the formation of solid deposits on stainless steel surfaces.…”

“…Though, treatments of mild or moderate pulsed-electric field intensity are currently under study to prospect their potential of permeabilising tissue structures, thus allowing the implementation in the context of already existing operations such as extraction or drying [2]. Moreover, pumpable media containing solid particles, such as juices, milk products, chocolate milk [3] or starch solutions [4], and even viscous liquids, such as yoghourt, syrups, soup stuff and liquid eggs [5], are susceptible of being treated by pulsed electric field.…”

Combination of Pulsed Electric Fields with Other Preservation Techniques

“…Although solid foods are susceptible to be processed by PEF (Puertolas et al 2010;De Vito et al 2008), this nonthermal technique as preservation method has mainly been assayed in liquid foods, such as juices (Hodgins et al 2002;Liang et al 2002;Mosqueda-Melgar et al 2008;Sampedro et al 2009;Zhang and Mittal 2005), fermented beverages (Iu et al 2001;Liang et al 2006;Ulmer et al 2002), liquid egg (CalderonMiranda et al 1999b;Pina-Pérez et al 2009), milk (Smith et al 2002;Sobrino-López et al 2006b;Sobrino-López and Martín-Belloso 2010;Walkling-Ribeiro et al 2009a) and dairy products (Gallo et al 2007). PEF also exhibits antimicrobial activity against: gram-positive bacteria, such as Spahylococcus aureus (Sobrino-López et al 2006b), Listeria innocua (Calderon-Miranda et al 1999a), Micrococcus luteus (Dutreux et al 2000) and Bacillus cereus (Pina-Pérez et al 2009); gram-negative bacteria, such as Escherichia coli (Iu et al 2001) and Salmonella typhimurium (Liang et al 2002); spores when they are submitted to a pre-germination treatment, such as Bacillus subtilis (Shin et al 2010); yeasts (McNamee et al 2010;Zhang and Mittal 2005); and moulds (Evrendilek et al 2008).…”

“…PEF also exhibits antimicrobial activity against: gram-positive bacteria, such as Spahylococcus aureus (Sobrino-López et al 2006b), Listeria innocua (Calderon-Miranda et al 1999a), Micrococcus luteus (Dutreux et al 2000) and Bacillus cereus (Pina-Pérez et al 2009); gram-negative bacteria, such as Escherichia coli (Iu et al 2001) and Salmonella typhimurium (Liang et al 2002); spores when they are submitted to a pre-germination treatment, such as Bacillus subtilis (Shin et al 2010); yeasts (McNamee et al 2010;Zhang and Mittal 2005); and moulds (Evrendilek et al 2008).…”

Influence of Certain Pulsed Electric Field Conditions on the Growth of Lactobacillus acidophilus LA-K

“…They achieved 3.5 log reductions using 29 kV/cm, 4 µs, and 71.3 µs of total treatment time. Sobrino-López et al [6] reached a 4.5 log reduction in Staphylococcus aureus by applyingAlthough there is extensive literature on use of PEF conditions to kill pathogens, there is scanty literature on PEF conditions to modulate growth of desirable bacteria. Just as high temperatures are used to kill pathogens and mild temperatures are used to grow culture bacteria, it is not known if pulsed electric field can have a similar effect.…”