Non-linear pressure/temperature-dependence of high pressure thermal inactivation of proteolytic Clostridium botulinum type B in foods

Abstract

The effect of high pressure thermal (HPT) processing on the inactivation of spores of proteolytic type B Clostridium botulinum TMW 2.357 in four differently composed low-acid foods (green peas with ham, steamed sole, vegetable soup, braised veal) was studied in an industrially feasible pressure range and temperatures between 100 and 120°C. Inactivation curves exhibited rapid inactivation during compression and decompression followed by strong tailing effects. The highest inactivation (approx. 6-log cycle reduction) was obtained in braised veal at 600 MPa and 110°C after 300 s pressure-holding time. In general, inactivation curves exhibited similar negative exponential shapes, but maximum achievable inactivation levels were lower in foods with higher fat contents. At high treatment temperatures, spore inactivation was more effective at lower pressure levels (300 vs. 600 MPa), which indicates a non-linear pressure/temperature-dependence of the HPT spore inactivation efficiency. A comparison of spore inactivation levels achievable using HPT treatments versus a conventional heat sterilization treatment (121.1°C, 3 min) illustrates the potential of combining high pressures and temperatures to replace conventional retorting with the possibility to reduce the process temperature or shorten the processing time. Finally, experiments using varying spore inoculation levels suggested the presence of a resistant fraction comprising approximately 0.01% of a spore population as reason for the pronounced tailing effects in survivor curves. The loss of the high resistance properties upon cultivation indicates that those differences develop during sporulation and are not linked to permanent modifications at the genetic level.

Inactivation of non-proteolytic Clostridium botulinum type E in low-acid foods and phosphate buffer by heat and pressure

“…Below 100 °C, the addition of pressure clearly enhanced spore inactivation, acting synergistically with heat in steamed sole and partially in IPB (for p > 300 MPa). Such synergisms of pressure and temperature on HPT inactivation for several pathogenic and non-pathogenic spore-formers in various buffer and relevant food systems have previously been reported and are basically in line with our observations [ 12 , 21 , 29 , 36 , 41 – 43 ]. However, opposite effects, i.e.…”

“…Therefore, the compression and decompression phase could serve as additional safety margins or directly be integrated into the total lethal effect of HPT treatments. This observed non-negligible impact is in line with previous studies, which investigated the HPT inactivation on spores of several Clostridium and Bacillus species [ 21 , 26 , 29 , 35 , 36 ]. Thereby, the impact of varying compression and decompression rates should also be taken into account, since they can largely affect spore inactivation.…”

“…pressure-protection at certain p/T combinations, have been reported for spores of proteolytic C . botulinum [ 21 , 26 ] and recently, for spores of non-proteolytic C . botulinum strains [ 44 ].…”

“…botulinum type E [ 20 ] [ 18 ]. Growth conditions and spore purification were performed as described previously [ 20 ] [ 21 ]. Briefly, spore production started with inoculating 45 mL of tryptone-peptone-yeast extract-carbohydrates (4 g/L glucose, 1 g/L maltose, 1 g/L starch, 1 g/L cellobiose) (TPYC) broth [ 22 ] [ 20 ] with a -80 °C glycerol stock culture and subsequent incubation in an anaerobic chamber (85% N2, 10% CO2, 5% H2) for 24 h at 28 °C.…”

“…Samples for experiments in RTE foods were basically prepared as previously described [ 21 ]. Briefly, four different heat-sterilized RTE foods ( Table 1 ) were blended into homogeneous pastes, inoculated with spore suspension (spores suspended in deionized water) and thoroughly mixed with a spatula and by vortexing.…”