Food processing by pulsed electric fields. II. Biological aspects

Abstract

Investigations on the biological effects of high voltage electric pulses primarily concern membrane permeabilization and microbial inactivation. Electroporation resulting from increased transmembrane potential is probably the main cause for membrane permeabilization. Equations are presented for this phenomenon. Results from several studies on the inactivation of microorganisms by pulsed electric fields are summarized in tables that relate the rate of inactivation to process conditions. The influence of three sets of parameters is discussed: 1) type and physiological state of the microorganism; 2) chemical composition and electrical resistivity of the microorganism-containing food or medium; 3) process conditions such as field intensity, duration and number of pulses, dissipated energy, final temperature, type of pulse and of treatment chamber. Data can be used to select conditions which produce a 5-6 log cycle inactivation for many yeasts or vegetative bacteria. Bacterial spores generally resist inactivation. Pulsed electric fields of relatively low intensity may be used to permeabilize larger cells from plant or animal tissues in order to facilitate the 182 BARSOTTI AND CHEFTEL extraction of specific constituents or to increase the drying rate. Little is known concerning the possible chemical or physico-chemical modifications of food constituents by high voltage electric pulses. Some enzymes appear to be inactivated, even at low temperatures, while others are more resistant. The sensorial characteristics of a number of foods subjected to electric fields do not appear to be significantly altered. Potential food applications are numerous and mainly related to liquid foods (fruit juices, milk, sauces, liquid egg) or to pumpable food pastes (fruit or vegetable purées, minced meat, etc.). Both neutral and acidic foods are likely candidates. The main objectives of microbial inactivation by electric pulses are food sanitation and/or extension of chilled storage. The process should be nonthermal (maximum T of ~30°C) to preserve food freshness and quality. A low operating cost, estimated at 0.4-0.8 US cents per liter of food (capital investment not included) and continuous operation at high flow rate (>1000 L/h) represent significant industrial advantages for this new technology.

Inactivation of Alkaline Phosphatase and Shelf Life Extension of Milk Processed by Hurdle Technology

“…This is due to the hurdles (PEF and mild heat) applied to the milk samples. The electric field strength, pulse duration of PEF treatment, mild heat influenced the inactivation of alkaline phosphatase and resulted in shelf life extension (Barsotti and Cheftel, 1999). The Duncan's analysis was carried out to find homogeneous subsets.…”

Mass Transfer Enhancement by Means of Electroporation

“…Recently, the interest in electropermeabilization has considerably grown, as it offers the possibility to develop different non-thermal alternatives to the traditional processing methods of the food industry requiring the disintegration of cell membrane. For example, the complete damage of the microbial cell membrane induced by the application of intensive PEF process conditions has been intensively studied in the last twenty years as a new nonthermal method of food preservation (Barsotti and Cheftel, 1999;Mosqueda-Melgar et al, 2008;Pataro et al, 2011). More interestingly, it has been also reported by several research teams that the application of a pulsed electric fields pre-treatment of moderate intensity to biological tissue may considerably increase the mass and heat transfer rates between plant cells and the surroundings, making it suitable for enhancing the efficiency of the pressing, extraction, drying and diffusion processes of the food industry (Angersbach, 2000;Vorobiev et al, 2005;Vorobiev and Lebovka, 2006;Donsì et al, 2010b).…”

Modelling of n-Stage Blumlein Stacked Lines for Bipolar Pulse Generation

“…Short duration high voltage pulses with fast rise and fall times and flat top are required for many applications such as: medical treatment, food and water sterilization and exhaust gas discharge [1][2][3]. A practical way of getting high voltage, almost, rectangular pulses, with width less than one microsecond, are with the help of PFL.…”