Inactivation of Bacillus spores in reconstituted skim milk by combined high pressure and heat treatment

Abstract

Aims: To determine the resistance of a variety of Bacillus species spores to a combined high pressure and heat treatment; and to determine the affect of varying sporulation and treatment conditions on the level of inactivation achieved. Methods and Results: Spores from eight Bacillus species (40 isolates) were high pressure–heat treated at 600 MPa, 1 min, initial temperature 72°C. The level of inactivation was broad (no inactivation to 6 log10 spores ml−1 reduction) and it varied within species. Different sporulation agar, high pressure equipment and pressure‐transmitting fluid significantly affected the response of some isolates. Varying the initial treatment temperature (75, 85 or 95°C) shifted the relative order of isolate high pressure–heat resistance. Conclusions: The response of Bacillus spores to combined high pressure–heat treatment is variable and can be attributed to both intrinsic and extrinsic factors. The combined process resulted in a high level of spore inactivation for several Bacillus species and is a potential alternative treatment to traditional heat‐only processes. Significance and Impact of the Study: Sporulation conditions, processing conditions and treatment temperature all affect the response of Bacillus spores to the combined treatment of high pressure and heat. High levels of spore inactivation can be achieved but the response is variable both within and between species.

Strong and Consistently Synergistic Inactivation of Spores of Spoilage-AssociatedBacillusandGeobacillusspp. by High Pressure and Heat Compared with Inactivation by Heat Alone

“…This degree of resistance was dissimilar to those of the other two strains of B. coagulans examined (3.7 and 5.4 log 10 reduction) by Scurrah and others (26), indicating that FRR B2723 may be peculiarly HPT resistant. In this study, when processed in either Bolognese or cream sauce in the pilot The observation of variability in HPT resistance within a species noted for B. coagulans (26) has also previously been observed among strains of proteolytic C. botulinum (17) and B. subtilis (18); however, for the several B. amyloliquefaciens strains examined to date by others (1,17,18,23), all have been shown to produce similarly highly HPT-resistant spores in comparison to those of other species examined. In particular, strain TMW 2.479 (Fad 82) has received attention as a potential HPT nonpathogenic surrogate for proteolytic C. botulinum since its resistance to HPT processing was first assessed by Margosch and others (17).…”

“…Indeed, spores of B. coagulans were shown to be significantly protected from inactivation in cream sauce during HPT processing. The HPTresistant nature of this strain of B. coagulans, FRR B2723, was established by Scurrah and others (26), who demonstrated an average 0.5 log 10 CFU/ml reduction in skim milk processed at 600 MPa for 1 min at an initial temperature of 72°C (estimated T max , ϳ95°C). This degree of resistance was dissimilar to those of the other two strains of B. coagulans examined (3.7 and 5.4 log 10 reduction) by Scurrah and others (26), indicating that FRR B2723 may be peculiarly HPT resistant.…”

“…The HPTresistant nature of this strain of B. coagulans, FRR B2723, was established by Scurrah and others (26), who demonstrated an average 0.5 log 10 CFU/ml reduction in skim milk processed at 600 MPa for 1 min at an initial temperature of 72°C (estimated T max , ϳ95°C). This degree of resistance was dissimilar to those of the other two strains of B. coagulans examined (3.7 and 5.4 log 10 reduction) by Scurrah and others (26), indicating that FRR B2723 may be peculiarly HPT resistant. In this study, when processed in either Bolognese or cream sauce in the pilot The observation of variability in HPT resistance within a species noted for B. coagulans (26) has also previously been observed among strains of proteolytic C. botulinum (17) and B. subtilis (18); however, for the several B. amyloliquefaciens strains examined to date by others (1,17,18,23), all have been shown to produce similarly highly HPT-resistant spores in comparison to those of other species examined.…”

“…In comparison, strains of the aerobic mesophilic species Bacillus amyloliquefaciens, which produces spores with intermediate heat resistance, have been shown to produce highly HPTresistant spores (1,17,18,23) that under some conditions appear to be stabilized by high pressure against thermal inactivation (16). B. amyloliquefaciens is closely related to Bacillus subtilis and Bacillus licheniformis, but to date, the spores of these related bacteria have been found to be relatively sensitive to HPT processing (17,18,26). A number of B. amyloliquefaciens strains have been proposed as relevant target spoilage organisms for 18) and even as potential surrogates to assess the efficacy of HPT processes with respect to proteolytic C. botulinum (23).…”

Compression Heating and Temperature Control for High-Pressure Destruction of Bacterial Spores: An Experimental Method for Kinetics Evaluation

“…However, bacterial spores are highly resistant to pressure destruction (Sale et al 1970;Mills et al 1998). HP sterilization of low-acid foods is more difficult and complex but may be achieved by combining HP with elevated temperatures (Furukawa et al 2003;Reddy et al 2006;Scurrah et al 2006).…”