Inactivation of Bacillus spores in batch vs continuous heating systems at sterilisation temperatures

This study was performed to assess the heat resistance of spores of Bacillus species in batch and continuous heating systems under commercial sterilisation conditions. Spores of thermophilic Bacillus smithii and mesophilic Bacillus amyloliquefaciens were found to be highly heat resistant in the batch system. They were able to withstand typical sterilisation temperatures. B. amyloliquefaciens showed tailing in the batch system and, before the onset of the tailing, a higher inactivation rate than in the continuous system at low temperatures. The reason for the tailing might be the presence of spore aggregates which are disrupted in the continuous system.     

Control of Alicyclobacillus spp. vegetative cells and spores in apple juice with rosemary extracts

In this study, we initially investigated the antimicrobial activities of two commercial rosemary extracts (V20, V40) against Alicyclobacillus strains, with the ultimate purpose to determine whether these can be used in apple juice for the control of growth of alicyclobacilli. Minimum inhibitory concentrations (MICs) were first determined, and put through sensory analysis. Addition of the rosemary extracts to apple juice at their MICs did not change the colour, odour, taste or opacity of the apple juice. Growth kinetics studies with these rosemary extracts indicated a reduction in vegetative cells for Alicyclobacillus acidoterrestris, Alicyclobacillus hesperidum and Alicyclobacillus cycloheptanicus in Bacillus acidoterrestris broth and in apple juice. Further studies with A. acidoterrestris spores showed that the MICs of these rosemary extracts had relatively low effects on spore numbers in B. acidoterrestris broth, but had a spore number inhibition index >15% in apple juice. A four-fold increase in the rosemary extract concentrations showed the opposite effects: greater reduction in spores in B. acidoterrestris broth (inhibition index, >60%) than in apple juice (inhibition index, <10%). These data indicate that at their MICs, the V20 and V40 rosemary extracts allow outgrowth of spores but reduce vegetative cells, acting together with the low pH or other particular constituents of the apple juice. Rosemary extracts applied at their MICs thus represent an alternative method for the control of A. acidoterrestris in apple juice.     

Laboratory scale Clean-In-Place (CIP) studies on the effectiveness of different caustic and acid wash steps on the removal of dairy biofilms

Seven strains of Bacillus cereus isolated from the environment and from patients with diarrheic symptoms were examined from two angles: their spore surface properties, and their ability to adhere to stainless steel and to resist a cleaning in place (CIP) procedure. Our results revealed significant differences in their morphology (size of exosporium, length and number of appendages), hydrophobic character and surface protein composition. Most of these proteins originated in the vegetative cell and were tightly bound to the external surface of the exosporium such as EA1 or alanine racemase. Spore adhesion properties also varied from strain to strain. The ability to adhere was higher when spores were surrounded by long appendages, while the largest spores displayed the least resistance to cleaning. These observations suggest that food processing line contamination might be due to a given type of strain with specific surface properties (long appendages and small exosporium), which would represent an increased threat under the milder processing conditions required by consumers (minimally heat-treated foods for example) and by legal requirements (to limit effluents caused by hygiene procedures). Elsewhere, no clear relationship of the strain characteristics to the clinical vs. foodborne strains could be established.     

Growth of Clostridium perfringens from spore inocula in cooked cured beef: development of a predictive model

The objective of this study was to develop a model to predict the growth of C. perfringens from spores at temperatures applicable to the cooling of cooked cured meat products. C. perfringens growth from spores was not observed at a temperature of 12 °C for up to 3 weeks. The two parameters: germination, outgrowth, and lag (GOL) time and exponential growth rate, EGR, were determined using a function derived from mechanistic and stochastic considerations and the observed relative growths at specified times. A general model to predict the amount of relative growth for arbitrary temperature was determined by fitting the exponential growth rates to a square root Ratkowsky function, and assuming a constant ratio of GOL and generation times. The predicted relative growth is sensitive to the value of this ratio. A closed form equation was developed that can be used to estimate the relative growth for a general cooling scenario and determine a standard error of the estimate. The equation depends upon microbiological assumptions of the effect of history of the GOL times for gradual changes in temperature. Applying multivariate statistical procedures, a confidence interval was computed on the prediction of the amount of growth for a given temperature. The model predicts, for example, a relative growth of 3.17 with an upper 95% confidence limit of 8.50 when cooling the product from 51 to 11 °C in 8 h, assuming a log linear decline in temperature with time.     

Inactivation of Bacillus subtilis spores in soybean milk by radio-frequency flash heating

An apparatus to pasteurize soybean milk using radio-frequency flash heating (RF-FH) was developed. An electrode surface was covered with a 50-μm thick Teflon film, and 28 MHz RF-FH was applied to soybean milk flowing through the electrode.     

Inactivation strategy for Clostridium perfringens spores adhered to food contact surfaces

The contamination of enterotoxigenic Clostridium perfringens spores on food contact surfaces posses a serious concern to food industry due to their high resistance to various preservation methods typically applied to control foodborne pathogens. In this study, we aimed to develop an strategy to inactivate C. perfringens spores on stainless steel (SS) surfaces by inducing spore germination and killing of germinated spores with commonly used disinfectants. The mixture of l-Asparagine and KCl (AK) induced maximum spore germination for all tested C. perfringens food poisoning (FP) and non-foodborne (NFB) isolates. Incubation temperature had a major impact on C. perfringens spore germination, with 40 °C induced higher germination than room temperature (RT) (20 ± 2 °C). In spore suspension, the implementation of AK-induced germination step prior to treatment with disinfectants significantly (p < 0.05) enhanced the inactivation of spores of FP strain SM101. However, under similar conditions, no significant spore inactivation was observed with NFB strain NB16. Interestingly, while the spores of FP isolates were able to germinate with AK upon their adhesion to SS chips, no significant germination was observed with spores of NFB isolates. Consequently, the incorporation of AK-induced germination step prior to decontamination of SS chips with disinfectants significantly (p < 0.05) inactivated the spores of FP isolates. Collectively, our current results showed that triggering spore germination considerably increased sporicidal activity of the commonly used disinfectants against C. perfringens FP spores attached to SS chips. These findings should help in developing an effective strategy to inactivate C. perfringens spores adhered to food contact surfaces.     

Na2SiO3浓度对碳化法制备纳米白炭黑粉体性能影响研究*

二氧化碳碳化法制备纳米白炭黑, Na2SiO3浓度是非常重要的影响因素,本文通过对的纳米白炭黑粉体结构、形态、表面活性等性能研究,寻找该因素对纳米白炭黑性能的影响规律。通过从20g/l到80g/l调整Na2SiO3浓度,得到二氧化硅粉体的一次颗粒粒径和平均孔隙介于5-25nm和4.345-98.55nm,粉体的粒径、孔径和孔体积都随Na2SiO3浓度的增加变大;而比表面积与Na2SiO3浓度呈反比趋势,从376.744 m2/g降到250.7m2/g。通过对粉体进行的TG热重分析观察并结合红外光谱（IR）对白炭黑的表面有机结构的观察分析,发现粉体表面羟基密度与Na2SiO3的浓度也呈递减关系,而且加热失重率和主要的失重温度区间也有所不同也显示了粉体表面不同羟基群的密度也有差异。     

Modeling the inactivation of Neosartorya fischeri ascospores in apple juice by high pressure,power ultrasound and thermal processing

Neosartorya fischeri is a mould that spoils acid foods and can produce mycotoxins. In this work, the efficacy of high pressure processing (HPP, 600 MPa) and power ultrasound (24 kHz, 0.33 W/mL) in combination with 75 °C for the inactivation of four week old N. fischeri ascospores in apple juice was investigated and compared with 75 °C thermal processing alone. The HPP-75 °C process was the most effective technique for inactivating N. fischeri spores, resulting in 3.3 log reductions after 10 min vs. no inactivation for thermosonication (TS) and thermal processing. Unexpectedly, activation shoulders were observed during the TS process. Then, the effect of different temperatures on the ascospore inactivation in apple juice by HPP-thermal, TS and thermal processing was investigated, and the log survivors vs. time were modeled. Faster inactivation was achieved at higher temperatures for all the technologies tested, indicating the significant role of temperature for the spore inactivation, alone or combined with other processes. The Weibull model described the spore inactivation better by 600 MPa HPP-thermal (50, 60, 75 °C) and thermal (85, 90 °C), whereas Lorentzian was more appropriate for the TS treatment (65, 70, 75 °C). In conclusion, HPP is the best food preservation technology due to higher spore inactivation in apple juice at the same temperature.     

Impact of dissociation equilibrium shift on bacterial spore inactivation by heat and pressure

The shift of the dissociation equilibrium under pressure and temperature plays a decisive role in the inactivation of bacterial spores. To obtain the dissociation equilibrium shift in water and buffer systems, the thermodynamic dissociation constants in a wide range of pressure and temperature were modelled. Heat and pressure inactivation of Geobacillus stearothermophilus spores at different initial pH-values in ACES and phosphate buffer confirmed the modelled data. Thermal inactivation in both buffers at 114, 122 and 127 °C resulted in higher logarithmic reductions with ACES. Contrary, after pressure treatment at 500, 600 and 900 MPa with 80 °C phosphate buffer showed higher inactivation. These results indicated the different dissociation equilibrium shifts in buffer systems by heat and pressure.     

UV disinfection of indigenous aerobic spores: implications for UV reactor validation in unfiltered waters

Conventional validation testing of UV reactors use cultured microorganisms spiked into test water flowing through a reactor. These tests are limited by the microbe titer it is possible to grow, thus limiting the size of the reactor it is possible to validate. The goal of this study was to examine the UV inactivation of indigenous aerobic spores naturally occurring in raw/unfiltered water supplies and to assess their use as an alternative indicator for validation testing of UV reactor performance, specifically for unfiltered water supplies planning large UV reactors. These spores were found in all raw waters tested in concentrations ranging between 20 and 12,000 CFU/100 mL and were very resistant to UV irradiation compared to a range of different microbes in the literature (i.e. adenovirus, MS-2 coliphage, and Cryptosporidium parvum). The inactivation of indigenous natural aerobic spores followed first-order kinetics with an inactivation coefficient ranging between 0.013 and 0.022 cm2/mJ with a high correlation coefficient. It was determined that naturally occurring aerobic spores, well characterized with respect to UV 253.7 nm inactivation, can be a useful tool when validating plant performance, and might also be used as a regular monitor of UV fluence and performance in a water treatment plant.