title: Protection by sucrose against heat-induced lethal and sublethal injury of Lactococcus lactis: an FT-IR study.
abstract: The heat inactivation of Lactococcus lactis was studied by determination of cell counts, and by FT-IR spectroscopy recording the average structure of cell proteins. Cell counts were measured after incubation milk buffer or milk buffer with 1. 5 M sucrose, and FT-IR spectra were recorded in (2)H(2)O or (2)H(2)O with 1. 5 M sucrose in the range of 6-75 degrees Celsius. Sucrose protected L. lactis against heat inactivation. The cell counts differed by up to 6-log cycles after treatment in milk buffer as compared to milk buffer with sucrose. The (1)H/(2)H exchange in proteins, and secondary structure elements were detected by the analysis of amide I', amide II and amide II' bands. A reduced (1)H/(2)H exchange as well as a lower content of disordered structural elements was observed when sucrose was present. Conformational fluctuations of native proteins as indicated by the (1)H/(2)H exchange were apparent already at sublethal temperatures. The loss of viability of L. lactis occurred in the same temperature range as the loss of the protein secondary structure. These results demonstrate that sucrose protects L. lactis against heat inactivation, and that the increased heat stability of proteins in the presence of sucrose contributed to this enhanced heat resistance.
authors.affiliation: Lehrstuhl für Fluidmechanik und Prozessautomation, Technische Universität München, Weihenstephaner Steig 23, D-85350 Freising, Germany.
authors.forename: Klaus V
authors.initials: KV
authors.lastname: Kilimann
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Doster
authors.forename: Rudi F
authors.initials: RF
authors.lastname: Vogel
authors.forename: Christoph
authors.initials: C
authors.lastname: Hartmann
authors.forename: Michael G
authors.initials: MG
authors.lastname: Gänzle
mesh_terms: D000577:Amides / Q000737:chemistry; D001426:Bacterial Proteins / Q000737:chemistry; D002462:Cell Membrane / Q000737:chemistry / Q000187:drug effects; D015169:Colony Count, Microbial; D005227:Fatty Acids / Q000737:chemistry; D006358:Hot Temperature; D013294:Lactococcus lactis / Q000187:drug effects* / Q000254:growth & development; D008055:Lipids / Q000737:chemistry; D050296:Microbial Viability / Q000187:drug effects*; D044367:Phase Transition / Q000187:drug effects; D011487:Protein Conformation; D011489:Protein Denaturation / Q000187:drug effects; D017433:Protein Structure, Secondary; D017550:Spectroscopy, Fourier Transform Infrared; D013395:Sucrose / Q000494:pharmacology*; D013696:Temperature
chemical_list: D000577:Amides; D001426:Bacterial Proteins; D005227:Fatty Acids; D008055:Lipids; D013395:Sucrose