Killing of microorganisms by pulsed electric fields

Abstract

Lethal effects of pulsed electric fields (PEF) on suspensions of various bacteria, yeast, and spores in buffer solutions and liquid foodstuffs were examined. Living-cell counts of vegetative cell types were reduced by PEF treatment by up to more than four orders of magnitude (> 99.99%). On the other hand, endo- and ascospores were not inactivated or killed to any great extent. The killing of vegetative cell types depends on the electrical field strength of the pulses and on the treatment time (the product of the pulse number and the decay time constant of the pulses). For each cell type, a specific critical electric field strength (Ec) and a specific critical treatment time (tc) were determined. Above these critical values, the fractions of surviving cells were reduced drastically. The "limits" Ec and tc depend on the cell characteristics as well as on the type of medium in which the cells are suspended. Especially in acid media living-cell counts were sufficiently decreased at very low energy inputs. In addition to the inactivation of microorganisms, the effect of PEF on food components such as whey proteins, enzymes and vitamins, and on the taste of foodstuffs was studied. The degree of destruction of these food components by PEF was very low or negligible. Moreover, no significant deterioration of the taste of foodstuffs was detected after PEF treatment. Disintegration of cells by PEF treatment in order to harvest intracellular products was also studied. Yeast cells, suspended in buffer solution, were not disintegrated by electric pulses. Hence, PEF treatment is an excellent process for inactivation of microorganisms in acid and in thermosensive media, but not for complete disintegration of microbial cells.

Continuous raw skim milk processing by pulsed electric field at non-lethal temperature: effect on microbial inactivation and functional properties

“…It can therefore be concluded that PEF processing of milk may involve modifications of its structure because functional properties such as cheese-making properties are modified by the treatment. These results are not in agreement with some other studies reporting that PEF treatment preserves the nutritional components and minimizes physical and chemical changes in food products [9,14,24]. Michalac et al [21] measured that total solids, protein, pH, electrical conductivity, viscosity and density of milk were not affected by PEF processing.…”

“…Color and particle sizes of the milk were not changed significantly by this processing. Only Grahl and Märkl [14] measured some PEF-induced destruction of milk components, but only at high energy inputs (Q > 200 kJ·kg -1 ) for the enzyme lipase and vitamin C (ascorbic acid). Other food components that were analyzed (alkaline phosphatase, peroxidase, vitamin A and whey protein) did not show any large-scale inactivation.…”

Amplitude Modulated Waves as a Promising Tool for Food Preservation

“…Additionally, electromagnetic waves induced great reduction in viable cells of microorganisms depending on the wave frequency, time of exposure and/or the exposed organism (Grahl and Markl, 1996). Such reduction might be due to breakdown of cell membrane (Calderon-Miranda et al, 1999;Schoenbach et al, 2000;Dunne, 2000;Oshima and Sato, 2004;Aronsson et al, 2005).…”

Avaliação em escala laboratorial da utilização do processo eletrolítico no tratamento de águas

“…8 Nas reações que ocorrem com a passagem da corrente elétrica nos eletrodos são gerados vários componentes tóxicos à viabilidade celular. 9 O objetivo deste trabalho foi utilizar o tratamento eletrolítico na água proveniente do Rio das Cinzas, Bandeirantes -PR, avaliando a possibilidade da retirada do gás cloro utilizado no pré-tratamento da água bruta, na ETA do Serviço Autônomo de Água e Esgoto (SAAE), onde numa primeira fase foram testados o processo eletrolítico e coadjuvantes do tratamento tradicional de água. Finalmente, buscou-se avaliar a geração de substâncias tóxicas pelo processo eletrolítico aplicado através de testes de biotoxicidade aguda com o microcrustáceo Daphnia similis.…”