Relationship between Sublethal Injury and Inactivation of Yeast Cells by the Combination of Sorbic Acid and Pulsed Electric Fields

Abstract

The objective of this study was to investigate the occurrence of sublethal injury after the pulsed-electric-field (PEF) treatment of two yeasts, Dekkera bruxellensis and Saccharomyces cerevisiae, as well as the relation of sublethal injury to the inactivating effect of the combination of PEF and sorbic acid. PEF caused sublethal injury in both yeasts: more than 90% of surviving D. bruxellensis cells and 99% of surviving S. cerevisiae cells were sublethally injured after 50 pulses at 12 kV/cm in buffer at pHs of both 7.0 and 4.0. The proportion of sublethally injured cells reached a maximum after 50 pulses at 12.0 kV/cm (S. cerevisiae) or 16.5 kV/cm (D. bruxellensis), and it kept constant or progressively decreased at greater electric field strengths and with longer PEF treatments. Sublethally PEF-injured cells showed sensitivity to the presence of sorbic acid at a concentration of 2,000 ppm. A synergistic inactivating effect of the combination of PEF and sorbic acid was observed. Survivors of the PEF treatment were progressively inactivated in the presence of 2,000 ppm of sorbic acid at pH 3.8, with the combined treatments achieving more than log 10 5 cycles of dead cells under the conditions investigated. This study has demonstrated the occurrence of sublethal injury after exposure to PEF, so yeast inactivation by PEF is not an all-or-nothing event. The combination of PEF and sorbic acid has proven to be an effective method to achieve a higher level of yeast inactivation. This work contributes to the knowledge of the mechanism of microbial inactivation by PEF, and it may be useful for improving food preservation by PEF technology.

Relationship between Sublethal Injury and Microbial Inactivation by the Combination of High Hydrostatic Pressure and Citral or tert -Butyl Hydroquinone

“…The extent of sublethal injury after HHP treatment was also greater at pH 4.0 than at pH 7.0 in E. coli and L. monocytogenes, whereas in S. cerevisiae, injury did not depend on the treatment medium pH. As with pressure, the occurrence of sublethal injury in yeast after PEF has been shown to be independent of the treatment medium pH (54). The similarity in the effect of pH on inactivation and injury by HHP and PEF may perhaps be related to the fact that the cytoplasmic membrane is a major target for damage in both processes (40).…”

“…Both bacterial species were more sensitive to pressure at acidic pHs, as expected, but there was no difference in the resistance of S. cerevisiae when the yeast was pressurized at pH 7.0 or pH 4.0. This might be regarded as unexpected, though survival of S. cerevisiae during pulsed electric field (PEF) treatment was similarly unaffected by pH (54). The extent of sublethal injury after HHP treatment was also greater at pH 4.0 than at pH 7.0 in E. coli and L. monocytogenes, whereas in S. cerevisiae, injury did not depend on the treatment medium pH.…”

Volatile compounds and microbial development in sonicated cloudy apple juices: preliminary results

“…The raw juice was inoculated with a mix of both strains (3 log 10 CFU/ mL). The evaluation of yeast sublethal injury was conducted according to the plate methods proposed by Somolinos et al (2007). In order to assess the cell injury, OGYE medium was added with 5% w/v NaCl and 12% w/v NaCl, respectively.…”

“…However, only C. parapsilosis showed a significant level of sublethally-injured cells in sonicated juices (Mann-Whitney test: p = 0.01; Figure S3). In general, sublethally-injured cells became sensitive to many selective compounds due to the damage of their membranes and modification of their permeability (Jasson et al, 2007;Somolinos et al, 2007). Furthermore, other studies demonstrated the presence of sublethally-injured yeasts after non-thermal processing, such as pulsed electric fields (Somolinos et al, 2007).…”

“…To better understand the yeast development, two spoilers (Rhodotorula glutinis and Candida parapsilosis) were inoculated in the juices (challenge test); moreover, the appearance of sublethally injured cells was also evaluated (Somolinos, Garcia, Condón, Maňas, & Pagán, 2007;Jasson, Uyttendaele, Rajkovic, and Debevere (2007)). The strains tested for the spoilage inoculum had been previously isolated and characterized during preliminary experiments as the dominant yeast species that were resistant to weaker sonication treatments (300 s/100 mL and amplitude of 100%; in apple juice (Montemurro et al, 2014)).…”