Basheer, Aideh

Heller, K.J.

Knøchel, Susanne

Neve, H.

Nielsen, Cecilie Lykke Marvig

Vogensen, Finn Kvist

English

Copenhagen University Research Information System

u n i ve r s i t y  o f  co pe n h ag e n  Københavns UniversitetHeat tolerance of dairy lactococcal c2 phagesNielsen, Cecilie Lykke Marvig; Basheer, Aideh; Neve, H.; Heller, K.J.; Knøchel, Susanne;Vogensen, Finn KvistPublication date:2011Document versionPeer reviewed versionCitation for published version (APA):Nielsen, C. L. M., Basheer, A., Neve, H., Heller, K. J., Knøchel, S., & Vogensen, F. K. (2011). Heat tolerance ofdairy lactococcal c2 phages. Poster session presented at 9th Symposium on Food Microbiology, Helsingør,Denmark.Download date: 02. Feb. 2020Inactivation kinetics followed first order.D70- values of 12 sec and 16.6 min were calculatedfor the sensitive and the resistant phage, respectively.Loss of phage DNA from capsids and disintegrationof phages into head and tail structures were observedafter 15% inactivation. In addition, aggregation ofphage tails was observed after 25% inactivation.Observed percentage of phages with morphologicalchanges correlated with the degree of phageinactivation as measured by pour plate titration.Lactococcus lactis strains are the most importantstarters in the dairy industry and bacteriophageattack is the major cause of fermentation failures. Inspite of this, there is little detailed knowledge on theheat tolerance of different phages.The aim of the present study was to characterize thethermal tolerance and inactivation kinetics of ninelactococcal c2 phages.D E P A R T M E N T   O F   F O O D   S C I E N C EF A C U L T Y   O F   L I F E   S C I E N C E S U N I V E R S I T Y   O F   C O P E N H A G E NHeat tolerance of dairy lactococcal c2 phagesC.L. Marviga, B. Aideha, H. Neveb, K.J. Hellerb, S. Knøchela, F.K. VogensenaaDepartment of Food Science, Faculty of Life Sciences, University of Copenhagen, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark, clmn@life.ku.dkDepartment of Microbiology and Biotechnology, Max Rubner-Institut, Herman-Weigmann Straβe 1, D-24103 Kiel, GermanyPhage TemperatureD-value (min)az-value (°C)aP63565°C 86.4 ±14.06.0 ±0.170°C 16.6 ±0.772°C 8.5 ±0.675°C 2.8 ±0.878°C 0.5 ±0.0CHPC67060°C 20.5 ±1.25.1 ±0.163°C 7.9 ±0.365°C 3.9 ±0.270°C 0.2 ±0.0• Complete inactivation of lactococcal c2 phageswas observed within a temperature span of atleast 10°C.• Many c2 phages will survive pasteurizationtemperatures (72°C, 15 sec).• Thermal inactivation of c2 phages follows first-order kinetics with instant heating.• First step in thermal inactivation of P635 isDNA release and disintegration of head andtails.Part of this work was conducted by CLM at KU-Life for the fulfilment of the M.Sc. in Food Scienceand was supported by The Danisco Foundation. Chr.Hansen A/S is thanked for providing phages and hoststrains.-7-6-5-4-3-2-100 10 20 30 40 50 60 70log (Nt/N0)Time (min)-7-6-5-4-3-2-100 10 20 30 40 50 60 70log (Nt/N0)Time (min)Fig. 2. Inactivation kinetics of a heat sensitive (CHPC670) and heat resistant  c2 phage (P635) after treatment at 60°C (), 63°C (○), 65°C (■), 70°C (Δ), 72°C (●), 75°C (□), and 78°C (▲) in skimmed milk. Error bars represent the standard derivation of triplicate determinations.Table 1: D- and z-values for phages P635 and CHPC670. aValues are given with standard error.012345678910CHPC670 P220 CHPC227 P684 CHPC134 CHPC180 P132 P635 P109Log reduction (log pfu mL-1)Phage65°C70°C75°C80°CFig. 1. Inactivation of nine Lactococcus lactis c2 phages after treatment at 65°C, 70°C, 75°C, and 80°C for 5 min in skimmed milk. When total inactivation was obtained (8-log reductions), higher temperatures were not tested. Error bars represent the standard derivation of triplicate determinations.Fig. 3. Transmission electron micrographs of phage P635before (A+E) and after either 15% inactivation (B-D) or 25%inactivation (F-H) by heat treatment at 65°C. Scale barindicates 100 nm.DBCAFEGHIntroduction and aimMaterials and methodsResultsConclusionAcknowledgementsIn the screening pronounced variation was found.Three phages (P220, CHPC227 and CHPC670)displayed high sensitivity resulting in >8 logreductions after 70°C for 5 min, while the mostthermally resistant phages (P635, P109, CHPC134,CHPC180 and P132) required 80°C for 5 min toobtain the same reduction. One phage with inter-mediate heat resistance was observed (P684).No correlation between thermal resistance and timeperiod of phage isolation was found.Phages: dairy isolates, classified as c2 by electron microscopy and PCR, different host range. Enumeration: double-layer plaque assay method.Suspension medium for thermal inactivations: skimmed milk. Screening for thermal resistance: 1.5 mL screw-capped stainless steel tubes submerged in a water-bath. Heat treatments at 65°C-80°C, holding time 5min.Inactivation kinetics: two phages (P635 andCHPC670) using the coil method (SherwoodInstruments).Transmission electron micrographs were performedon 0, 15 and 25% thermally inactivated phages.P635CHPC670

Heat tolerance of dairy lactococcal c2 phages

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Heat tolerance of dairy lactococcal c2 phages

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