Heat tolerance of dairy lactococcal c2 phages

Nine Lactococcus lactis c2 phages propagated on different hosts were screened for thermal resistance in skimmed milk. Pronounced variations in thermal resistance were found. Three phages displayed high sensitivity towards heat resulting in >8 log reductions after 70 degrees C for 5 min, whereas the most thermal resistant phages required 80 degrees C for 5 min to obtain the same reduction. Inactivation kinetics were determined for a thermo-sensitive and a thermo-resistant phage at 60-70 degrees C and 65-78 degrees C, respectively, using a submerged-coil system with extremely short heating-up times. Inactivation followed first-order kinetics with correlation coefficients of 0.96-0.99. D70-values of 12 s and 16.6 min were calculated for the most sensitive and resistant phage, respectively. Release of phage DNA from capsids, and disintegration of phage heads and tails were among the first morphological changes observed for moderately thermal inactivated lysates (15% phage inactivation) of the heat tolerant phage P635. (C) 2011 Elsevier Ltd. All rights reserved.