Pulsed electric field treatment for the stimulation of microorganisms: Applications in food production


El Kantar S., Koubaa M. (2022): Pulsed electric field treatment for the stimulation of microorganisms: Applications in food production. Res. Agr. Eng., 68: 80–92.

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The pulsed electric field (PEF) technology is a non-thermal processing technique usually used for microbial inactivation in food industries. The application of this technology at sub-lethal levels prior to or during the fermentation processes enhances the mass transfer and cell permeability. It could also cause changes in the genetic, metabolic, and physiological responses of microbial strains leading to an improvement in the fermentation process. Several studies reported the benefits of PEF on microorganisms including growth stimulation, an increase in the fermentation rates and product yields, and improvement in the metabolite extraction. All of these modifications could improve the organoleptic and nutritional properties of fermented food products. The purpose of this review is to summarise and discuss the main findings reported in the literature to date about the effect of PEFs applied at sub-lethal levels on microorganisms in the context of food processing.

Abbas Syed Q. (2017): Pulsed electric field technology in food preservation: A review. Journal of Nutritional Health & Food Engineering, 6: 168–172.
Al Daccache M., Koubaa M., Maroun R.G., Salameh D., Louka N., Vorobiev E. (2020): Pulsed electric field-assisted fermentation of Hanseniaspora sp. yeast isolated from Lebanese apples. Food Research International, 129: 108840. https://doi.org/10.1016/j.foodres.2019.108840
Altuntas J., Evrendilek G.A., Sangun M.K., Zhang H.Q. (2010): Effects of pulsed electric field processing on the quality and microbial inactivation of sour cherry juice. International Journal of Food Science and Technology, 45: 899–905. https://doi.org/10.1111/j.1365-2621.2010.02213.x
Barba F.J., Parniakov O., Pereira S.A., Wiktor A., Grimi N., Boussetta N., Saraiva J.A., Raso J., Martin-Belloso O., Witrowa-Rajchert D., Lebovka N., Vorobiev E. (2015): Current applications and new opportunities for the use of pulsed electric fields in food science and industry. Food Research International, 77: 773–798. https://doi.org/10.1016/j.foodres.2015.09.015
Ben Ammar J., Lanoisellé J.L., Lebovka N.I., van Hecke E., Vorobiev E. (2010): Effect of a pulsed electric field and osmotic treatment on freezing of potato tissue. Food Biophysics, 5: 247–254. https://doi.org/10.1007/s11483-010-9167-y
Ben Ammar J., Lanoisellé J.L., Lebovka N.I., Van Hecke E., Vorobiev E. (2011): Impact of a pulsed electric field on damage of plant tissues: Effects of cell size and tissue electrical conductivity. Journal of Food Science, 76: 90–97. https://doi.org/10.1111/j.1750-3841.2010.01893.x
Bobinaitė R., Pataro G., Lamanauskas N., Šatkauskas S., Viškelis P., Ferrari G. (2015): Application of pulsed electric field in the production of juice and extraction of bioactive compounds from blueberry fruits and their by-products. Journal of Food Science and Technology, 52: 5898–5905. https://doi.org/10.1007/s13197-014-1668-0
Bourdichon F., Casaregola S., Farrokh C., Frisvad J.C., Gerds M.L., Hammes W.P., Harnett J., Huys G., Laulund S., Ouwehand A., Powell I.B., Prajapati J.B., Seto Y., Ter Schure E., Van Boven A., Vankerckhoven V., Zgoda A., Tuijtelaars S., Hansen E.B. (2012): Food fermentations: Microorganisms with technological beneficial use. International Journal of Food Microbiology, 154: 87–97. https://doi.org/10.1016/j.ijfoodmicro.2011.12.030
Chakraborti S., Chakraborti T., Mandal M., Mandal A., Das S., Ghosh S. (2002): Protective role of magnesium in cardiovascular diseases: A review. Molecular and Cellular Biochemistry, 238: 163–179. https://doi.org/10.1023/A:1019998702946
Chanos P., Warncke M.C., Ehrmann M.A., Hertel C. (2020): Application of mild pulsed electric fields on starter culture accelerates yogurt fermentation. European Food Research and Technology, 246: 621–630. https://doi.org/10.1007/s00217-020-03428-9
Charles-Rodríguez A.V., Nevárez-Moorillón G.V., Zhang Q.H., Ortega-Rivas E. (2007): Comparison of thermal processing and pulsed electric fields treatment in pasteurization of apple juice. Food and Bioproducts Processing, 85: 93–97. https://doi.org/10.1205/fbp06045
Chaturongakul S., Kirawanich P. (2013): Electropermeabilization responses in gram-positive and gram-negative bacteria. Journal of Electrostatics, 71: 773–777. https://doi.org/10.1016/j.elstat.2013.06.005
Delsart C., Ghidossi R., Poupot C., Cholet C., Grimi N., Vorobiev E., Milisic V., Peuchot M.M. (2012): Enhanced extraction of phenolic compounds from merlot grapes by pulsed electric field treatment. American Journal of Enology and Viticulture, 63: 205–211. https://doi.org/10.5344/ajev.2012.11088
Delsart C., Grimi N., Boussetta N., Miot Sertier C., Ghidossi R., Vorobiev E., Mietton Peuchot M. (2016): Impact of pulsed-electric field and high-voltage electrical discharges on red wine microbial stabilization and quality characteristics. Journal of Applied Microbiology, 120: 152–164. https://doi.org/10.1111/jam.12981
Derom M.L., Sayón-Orea C., Martínez-Ortega J.M., Martínez-González M.A. (2013): Magnesium and depression: A systematic review. Nutritional Neuroscience, 16: 191–206. https://doi.org/10.1179/1476830512Y.0000000044
Djukić-Vuković A., Meglič S.H., Flisar K., Mojović L., Miklavčič D. (2021): Pulsed electric field treatment of Lacticaseibacillus rhamnosus and Lacticaseibacillus paracasei, bacteria with probiotic potential. LWT – Food Science and Technology, 152: 112304. https://doi.org/10.1016/j.lwt.2021.112304
El Darra N., Rajha H.N., Ducasse M.A., Turk M.F., Grimi N., Maroun R.G., Louka N., Vorobiev E. (2016): Effect of pulsed electric field treatment during cold maceration and alcoholic fermentation on major red wine qualitative and quantitative parameters. Food Chemistry, 213: 352–360. https://doi.org/10.1016/j.foodchem.2016.06.073
El Kantar S., Boussetta N., Lebovka N., Foucart F., Rajha H.N., Maroun R.G., Louka N., Vorobiev E. (2018): Pulsed electric field treatment of citrus fruits: Improvement of juice and polyphenols extraction. Innovative Food Science and Emerging Technologies, 46: 153–161. https://doi.org/10.1016/j.ifset.2017.09.024
Ewe J.A., Wan-Abdullah W.N., Alias A.K., Liong M.T. (2012a): Bioconversion of isoflavones and the probiotic properties of the electroporated parent and subsequent three subcultures of Lactobacillus fermentum BT 8219 in biotin-soymilk. Journal of Microbiology and Biotechnology, 22: 947–959.
Ewe J.A., Wan-Abdullah W.N., Alias A.K., Liong M.T. (2012b): Enhanced growth of lactobacilli and bioconversion of isoflavones in biotin-supplemented soymilk by electroporation. International Journal of Food Sciences and Nutrition, 63: 580–596. https://doi.org/10.3109/09637486.2011.641940
Fukada T., Yamasaki S., Nishida K., Murakami M., Hirano T. (2011): Zinc homeostasis and signaling in health and diseases. Journal of Biological Inorganic Chemistry, 16: 1123–1134. https://doi.org/10.1007/s00775-011-0797-4
Galván-D'Alessandro L., Carciochi R.A. (2018): Fermentation assisted by pulsed electric field and ultrasound: A review. Fermentation, 4: 1–12. https://doi.org/10.3390/fermentation4010001
Gilbert E.R, Liu D. (2013): Anti-diabetic functions of soy isoflavone genistein: Mechanisms underlying its effects on pancreatic β-cell function. Food and Function, 4: 200–212. https://doi.org/10.1039/C2FO30199G
Grimi N., Lebovka N.I., Vorobiev E., Vaxelaire J. (2009): Effect of a pulsed electric field treatment on expression behavior and juice quality of Chardonnay grape. Food Biophysics, 4: 191–198. https://doi.org/10.1007/s11483-009-9117-8
Grimi N., Mamouni F., Lebovka N., Vorobiev E., Vaxelaire J. (2011): Impact of apple processing modes on extracted juice quality: Pressing assisted by pulsed electric fields. Journal of Food Engineering, 103: 52–61. https://doi.org/10.1016/j.jfoodeng.2010.09.019
Guo J., Ma R., Su B., Li Y., Zhang J., Fang J. (2016): Raising the avermectins production in Streptomyces avermitilis by utilizing nanosecond pulsed electric fields (nsPEFs). Scientific Reports, 6: 1–10. https://doi.org/10.1038/srep25949
Góral M., Kozłowicz K., Pankiewicz U., Góral D. (2018): Magnesium enriched lactic acid bacteria as a carrier for probiotic ice cream production. Food Chemistry, 239: 1151–1159. https://doi.org/10.1016/j.foodchem.2017.07.053
Góral M., Pankiewicz U. (2017): Effect of pulsed electric fields (PEF) on accumulation of magnesium in Lactobacillus rhamnosus B 442 cells. Journal of Membrane Biology, 250: 565–572. https://doi.org/10.1007/s00232-017-9986-6
Góral M., Pankiewicz U., Sujka M., Kowalski R. (2019): Bioaccumulation of zinc ions in Lactobacillus rhamnosus B 442 cells under treatment of the culture with pulsed electric field. European Food Research and Technology, 245: 817–824. https://doi.org/10.1007/s00217-018-3219-9
Hunt R.W., Zavalin A., Bhatnagar A., Chinnasamy S., Das K.C. (2009): Electromagnetic biostimulation of living cultures for biotechnology, biofuel and bioenergy applications. International Journal of Molecular Sciences, 10: 4515–4558. https://doi.org/10.3390/ijms10104515
Ivey M., Massel M., Phister T.G. (2013): Microbial interactions in food fermentations. Annual Review of Food Science and Technology, 4: 141–162. https://doi.org/10.1146/annurev-food-022811-101219
Jacka F., Overland S., Stewart R., Tell G., Bjelland I., Mykletun A. (2009): Association between magnesium intake and depression and anxiety in community-dwelling adults: The Hordaland health study. Australian and New Zealand Journal of Psychiatry, 43: 45–52. https://doi.org/10.1080/00048670802534408
Jalté M., Lanoisellé J.L., Lebovka N.I., Vorobiev E. (2009): Freezing of potato tissue pre-treated by pulsed electric fields. LWT – Food Science and Technology, 42: 576–580. https://doi.org/10.1016/j.lwt.2008.09.007
Jemai A.B., Vorobiev E. (2006): Pulsed electric field assisted pressing of sugar beet slices: Towards a novel process of cold juice extraction. Biosystems Engineering, 93: 57–68. https://doi.org/10.1016/j.biosystemseng.2005.09.008
Joo D.H., Jeon B.Y., Park D.H. (2013): Effects of an electric pulse on variation of bacterial community and metabolite production in kimchi-making culture. Biotechnology and Bioprocess Engineering, 18: 909–917. https://doi.org/10.1007/s12257-013-0098-6
Kanafusa S., Uhlig E., Uemura K., Gómez Galindo F., Håkansson Å. (2021): The effect of nanosecond pulsed electric field on the production of metabolites from lactic acid bacteria in fermented watermelon juice. Innovative Food Science and Emerging Technologies, 72: 102749. https://doi.org/10.1016/j.ifset.2021.102749
Koubaa M., Roselló-Soto E., Šic Žlabur J., Režek Jambrak A., Brnčić M., Grimi N., Boussetta N., Barba F.J. (2015): Current and new insights in the sustainable and green recovery of nutritionally valuable compounds from Stevia rebaudiana Bertoni. Journal of Agricultural and Food Chemistry, 63: 6835–6846. https://doi.org/10.1021/acs.jafc.5b01994
Lebovka N.I., Praporscic I., Vorobiev E. (2003): Enhanced expression of juice from soft vegetable tissues by pulsed electric fields: Consolidation stages analysis. Journal of Food Engineering, 59: 309–317. https://doi.org/10.1016/S0260-8774(02)00472-7
Lebovka N.I., Shynkaryk N.V., Vorobiev E. (2007): Pulsed electric field enhanced drying of potato tissue. Journal of Food Engineering, 78: 606–613. https://doi.org/10.1016/j.jfoodeng.2005.10.032
Lee N. (2017): A review of magnesium, iron, and zinc supplementation effects on athletic performance. The Korean Journal of Physical Education, 56: 797–806. https://doi.org/10.23949/kjpe.2017.
Leroy F., De Vuyst L. (2004): Lactic acid bacteria as functional starter cultures for the food fermentation industry. Trends in Food Science and Technology, 15: 67–78. https://doi.org/10.1016/j.tifs.2003.09.004
Liu C., Grimi N., Bals O., Lebovka N., Vorobiev E. (2021): Effects of pulsed electric fields and preliminary vacuum drying on freezing assisted processes in potato tissue. Food and Bioproducts Processing, 125: 126–133. https://doi.org/10.1016/j.fbp.2020.11.002
Liu C., Pirozzi A., Ferrari G., Vorobiev E., Grimi N. (2020): Effects of pulsed electric fields on vacuum drying and quality characteristics of dried carrot. Food and Bioprocess Technology, 13: 45–52. https://doi.org/10.1007/s11947-019-02364-1
Loginova K., Loginov M., Vorobiev E., Lebovka N.I. (2011): Quality and filtration characteristics of sugar beet juice obtained by "cold" extraction assisted by pulsed electric field. Journal of Food Engineering, 106: 144–151. https://doi.org/10.1016/j.jfoodeng.2011.04.017
Lye H.S., Karim A.A., Rusul G., Liong M.T. (2011): Electroporation enhances the ability of lactobacilli to remove cholesterol. Journal of Dairy Science, 94: 4820–4830. https://doi.org/10.3168/jds.2011-4426
Lye H.S., Khoo B.Y., Karim A.A., Rusul G., Liong M.T. (2012): Growth properties and cholesterol removal ability of electroporated Lactobacillus acidophilus BT 1088. Journal of Microbiology and Biotechnology, 22: 981–989. https://doi.org/10.4014/jmb.1201.12073
Maruo T., Gotoh Y., Nishimura H., Ohashi S., Toda T., Takahashi K. (2012): Oral administration of milk fermented with Lactococcus lactis subsp. cremoris FC protects mice against influenza virus infection. Letters in Applied Microbiology, 55: 135–140. https://doi.org/10.1111/j.1472-765X.2012.03270.x
Mattar J.R., Turk M.F., Nonus M., Lebovka N.I., El Zakhem H., Vorobiev E. (2014): Stimulation of Saccharomyces cerevisiae cultures by pulsed electric fields. Food and Bioprocess Technology, 7: 3328–3335. https://doi.org/10.1007/s11947-014-1336-4
Mattar J.R., Turk M.F., Nonus M., Lebovka N.I., El Zakhem H., Vorobiev E. (2015): S. cerevisiae fermentation activity after moderate pulsed electric field pre-treatments. Bioelectrochemistry, 103: 92–97. https://doi.org/10.1016/j.bioelechem.2014.08.016
Maza M.A., Martínez J.M., Hernández-Orte P., Cebrián G., Sánchez-Gimeno A.C., Álvarez I., Raso J. (2019): Influence of pulsed electric fields on aroma and polyphenolic compounds of Garnacha wine. Food and Bioproducts Processing, 116: 249–257. https://doi.org/10.1016/j.fbp.2019.06.005
McDonald C.J., Lloyd S.W., Vitale M.A., Petersson K., Innings F. (2000): Effects of pulsed electric fields on microorganisms in orange juice using electric field strengths of 30 and 50 kV/cm. Journal of Food Science, 65: 984–989. https://doi.org/10.1111/j.1365-2621.2000.tb09404.x
Min H.R., Jeon B.Y., Seo H.N., Kim M.J., Kim J.C., Kim J.K., Park D.H. (2009): Effect of low intensity pulsed electric field on ethanol fermentation and chemical component variation in a winemaking culture. Food Science and Biotechnology, 18: 1358–1364.
Min S., Zhang Q.H. (2003): Effects of commercial-scale pulsed electric field processing on flavor and color of tomato juice. Journal of Food Science, 68: 1600–1606. https://doi.org/10.1111/j.1365-2621.2003.tb12298.x
Mosqueda-Melgar J., Raybaudi-Massilia R.M., Martín-Belloso O. (2008): Non-thermal pasteurization of fruit juices by combining high-intensity pulsed electric field with natural antimicrobials. Innovative Food Science and Emerging Technologies, 9: 328–340. https://doi.org/10.1016/j.ifset.2007.09.003
Najim N., Aryana K.J. (2013): A mild pulsed electric field condition that improves acid tolerance, growth, and protease activity of Lactobacillus acidophilus LA-K and Lactobacillus delbrueckii subspecies bulgaricus LB-12. Journal of Dairy Science, 96: 3424–3434. https://doi.org/10.3168/jds.2012-5842
Nowosad K., Sujka M., Pankiewicz U., Miklavčič D., Arczewska M. (2021): Pulsed electric field (PEF) enhances iron uptake by the yeast Saccharomyces cerevisiae. Biomolecules, 11: 850. https://doi.org/10.3390/biom11060850
Ohba T., Uemura K., Nabetani H. (2016): Moderate pulsed electric field treatment enhances exopolysaccharide production by Lactococcus lactis subspecies cremoris. Process Biochemistry, 51: 1120–1128. https://doi.org/10.1016/j.procbio.2016.05.027
Ojha K.S., Mason T.J., O'Donnell C.P., Kerry J.P., Tiwari B.K. (2017): Ultrasound technology for food fermentation applications. Ultrasonics Sonochemistry, 34: 410–417. https://doi.org/10.1016/j.ultsonch.2016.06.001
Ostermeier R., Giersemehl P., Siemer C., Töpfl S., Jäger H. (2018): Influence of pulsed electric field (PEF) pre-treatment on the convective drying kinetics of onions. Journal of Food Engineering, 237: 110–117. https://doi.org/10.1016/j.jfoodeng.2018.05.010
Oziembłowski M., Kopeć W. (2005): Pulsed Electric Fields (PEF) As an unconventional method of food preservation. Polish Journal of Food and Nutrition Sciences, 14: 31–35.
Pankiewicz U., Jamroz J. (2010): Effect of pulsed electric fields upon accumulation of magnesium in Saccharomyces cerevisiae. European Food Research and Technology, 231: 663–668. https://doi.org/10.1007/s00217-010-1317-4
Pankiewicz U., Jamroz J. (2011): Effect of pulsed electric fields upon accumulation of zinc in Saccharomyces cerevisiae. Journal of Microbiology and Biotechnology, 21: 646–651. https://doi.org/10.4014/jmb.1101.01030
Parniakov O., Bals O., Lebovka N., Vorobiev E. (2016): Pulsed electric field assisted vacuum freeze-drying of apple tissue. Innovative Food Science and Emerging Technologies, 35: 52–57. https://doi.org/10.1016/j.ifset.2016.04.002
Paul Ross R., Morgan S., Hill C. (2002): Preservation and fermentation: Past, present and future. International Journal of Food Microbiology, 79: 3–16. https://doi.org/10.1016/S0168-1605(02)00174-5
Peng K., Koubaa M., Bals O., Vorobiev E. (2020): Recent insights in the impact of emerging technologies on lactic acid bacteria: A review. Food Research International, 137: 109544. https://doi.org/10.1016/j.foodres.2020.109544
Pothakamury U.R., Vega H., Zhang Q., Barbosa-Canovas G.V., Swanson B.G. (1996): Effect of growth stage and processing temperature on the inactivation of E. coli by pulsed electric fields. Journal of Food Protection, 59: 1167–1171. https://doi.org/10.4315/0362-028X-59.11.1167
Praporscic I., Lebovka N., Vorobiev E., Mietton-Peuchot M. (2007): Pulsed electric field enhanced expression and juice quality of white grapes. Separation and Purification Technology, 52: 520–526. https://doi.org/10.1016/j.seppur.2006.06.007
Pudenz M., Roth K., Gerhauser C. (2014): Impact of soy isoflavones on the epigenome in cancer prevention. Nutrients, 6: 4218–4272. https://doi.org/10.3390/nu6104218
Puértolas E., Luengo E., Álvarez I., Raso J. (2012): Improving mass transfer to soften tissues by pulsed electric fields: Fundamentals and applications. Annual Review of Food Science and Technology, 3: 263–282. https://doi.org/10.1146/annurev-food-022811-101208
Salehi F. (2020): Physico-chemical properties of fruit and vegetable juices as affected by pulsed electric field: A review. International Journal of Food Properties, 23: 1036–1050. https://doi.org/10.1080/10942912.2020.1775250
Sampedro F., Rivas A., Rodrigo D., Martínez A., Rodrigo M. (2007): Pulsed electric fields inactivation of Lactobacillus plantarum in an orange juice-milk based beverage: Effect of process parameters. Journal of Food Engineering, 80: 931–938. https://doi.org/10.1016/j.jfoodeng.2006.08.013
Shayanfar S., Chauhan O., Toepfl S., Heinz V. (2014): Pulsed electric field treatment prior to freezing carrot discs significantly maintains their initial quality parameters after thawing. International Journal of Food Science and Technology, 49: 1224–1230. https://doi.org/10.1111/ijfs.12421
Short M.W., Domagalski J.E. (2013): Iron deficiency anemia: Evaluation and management. American Family Physician, 87: 98–104.
Shynkaryk M.V., Lebovka N.I., Vorobiev E. (2008): Pulsed electric fields and temperature effects on drying and rehydration of red beetroots. Drying Technology, 26: 695–704. https://doi.org/10.1080/07373930802046260
Sotelo K.A.G., Hamid N., Oey I., Pook C., Gutierrez-Maddox N., Ma Q., Ying Leong S., Lu J. (2018): Red cherries (Prunus avium var. Stella) processed by pulsed electric field – Physical, chemical and microbiological analyses. Food Chemistry, 240: 926–934. https://doi.org/10.1016/j.foodchem.2017.08.017
Timmermans R.A.H., Nierop Groot M.N., Nederhoff A.L., van Boekel M.A.J.S., Matser A.M., Mastwijk H.C. (2014): Pulsed electric field processing of different fruit juices: Impact of pH and temperature on inactivation of spoilage and pathogenic micro-organisms. International Journal of Food Microbiology, 173: 105–111. https://doi.org/10.1016/j.ijfoodmicro.2013.12.022
Toepfl S., Heinz V., Knorr D. (2007): High intensity pulsed electric fields applied for food preservation. Chemical Engineering and Processing: Process Intensification, 46: 537–546. https://doi.org/10.1016/j.cep.2006.07.011
Turk M.F., Vorobiev E., Baron A. (2012): Improving apple juice expression and quality by pulsed electric field on an industrial scale. LWT – Food Science and Technology, 49: 245–250. https://doi.org/10.1016/j.lwt.2012.07.024
Vorobiev E., Lebovka N. (2008): Pulsed-electric-fields-induced effects in plant tissues: Fundamental aspects and perspectives of applications. In: Vorobiev E., Lebovka N. (eds): Electrotechnologies for Extraction from Food Plants and Biomaterials. Food Engineering Series. New York, Springer-Verlag New York Inc.: 39–81.
Wang M.S., Wang L.H., Bekhit A.E.D.A., Yang J., Hou Z.P., Wang Y.Z., Dai Q.Z., Zeng X.A. (2018): A review of sublethal effects of pulsed electric field on cells in food processing. Journal of Food Engineering, 223: 32–41. https://doi.org/10.1016/j.jfoodeng.2017.11.035
Wang S., Wang Y., Pan M.H., Ho C.T. (2017): Anti-obesity molecular mechanism of soy isoflavones: Weaving the way to new therapeutic routes. Food and Function, 8: 3831–3846. https://doi.org/10.1039/C7FO01094J
Wiktor A., Schulz M., Voigt E., Witrowa-Rajchert D., Knorr D. (2015): The effect of pulsed electric field treatment on immersion freezing, thawing and selected properties of apple tissue. Journal of Food Engineering, 146: 8–16. https://doi.org/10.1016/j.jfoodeng.2014.08.013
Yeo S.K., Liong M.T. (2013): Effect of electroporation on viability and bioconversion of isoflavones in mannitol-soymilk fermented by lactobacilli and bifidobacteria. Journal of the Science of Food and Agriculture, 93: 396–409. https://doi.org/10.1002/jsfa.5775
Yu J., Bi X., Yu B., Chen D. (2016): Isoflavones: Anti-inflammatory benefit and possible caveats. Nutrients, 8: 1–16.
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