Model System for Aseptic Processing of Paniculate Foods using Peroxidase

Process evaluation for aseptic processing of participate foods was carried out using a model food system with a bioindicator. The model food was alginate spheres in Carboxy-methyl cellulose and the bioindicator was Horseradish peroxidase. Inactivation in the system was studied to determine thermal characteristics in the range 100–130°C using TDT cans. The D-value was 4.1, 2.6, 1.4 and 1.0 min at 100, 110, 120, and 130°C, respectively and the z-value was 48.4°C. Spherical particles containing immobilized peroxidase were made with alginate and dehydrated potato. These were processed in a continuous flow system at 110, 120, or 130°C. Destruction of peroxidase was related to thermal treatment received and was used to verify numerical simulation. Results were compared with those of a simulation for particle heating. Data showed good agreement between experimental and simulated results.     

Comparison of Predictive Models for Bacterial Spore Population Resources to Sterilization Temperatures

Comparisons of characteristics of recent models and the conventional model of bacterial spore populations during thermal sterilization showed the conventional model was inadequate for general representation because it lacks activation of dormant spores. New models accounting for activation differed in other assumptions but obviated heat shock of indicator spores required when using the conventional model in validations of thermal sterilization. Comparisons of rate constants and simulated and experimental responses of models of B. stearother-mophilus spores in constant and dynamic temperatures showed one new model was more general, more accurate and preferred. Arrhenius equations accurately described temperature dependencies of all rate constants of that model.     

Combined effects of heat, nisin and acidification on the inactivation of Clostridium sporogenes spores in carrot-alginate particles: from kinetics to process validation

Combined effects of mild temperatures, acidification and nisin on the thermal resistance of Clostridium sporogenes ATCC 11437 spores were assessed. Inoculated carrot-alginate particles were used as a solid-food model for the validation of the spore inactivation during the flow of a solid-liquid food system through the holding tube of an aseptic processing unit. Inactivation kinetics was studied in a water bath with the spores inoculated into carrot-alginate particles and in Sorensen's phosphate buffer. For temperatures of 70-90 degrees C, D-values in the buffer were 24.9-5.7 min, much lower than those evaluated for the particles (115.1-22.2 min). Statistical analyses showed significant synergistic effects of temperature and pH on spore inactivation for both media. Acidification reduced the heat resistance of the spores by reducing the D-values. Nisin was not significantly effective at the lower concentrations (up to 750 IU/g). The combination of 90 degrees C, pH: 4.5 and 500IU/g nisin resulted in a ten-fold decrease of the D-value for spores inoculated in the particles (from 111.1 to 10.6 min). Microbial validation tests were conducted using a pilot-scale aseptic processing unit with a mixture of carrot cubes (10%) and carrier liquid of 2%-carboxymethylcellulose solution (90%). Spore-inoculated carrot-alginate particles (initial counts of 106 CFU/g, obtained after come-up-time pre-heat) with pH 3.5 and 2000 IU/g nisin were processed at 90 degrees C in the aseptic processing unit. Microbial analysis showed no spore survivors in the particles after passing through the holding tube (5.2-6.0 min of residence time). The proposed combination of these hurdles significantly enhanced the spore inactivation rate (D(90)=1.17 min) as compared to that for thermal treatment only (D(90)=19.6 min).     

Thermal resistance ofAlicyclobacillus acidoterrestrisspores in different buffers and pH

The influence of buffers and pH on the thermal resistance of a novel flat sour-type of spoilage bacterium,Alicyclobacillus acidoterrestris, was investigated. At a low concentration (20 mM), decimal reduction times (D-values) in citrate and phosphate buffers were 13.6 and 12.9 min, respectively, showing little variation. At a high concentration (100 mM), however, theD-value in citrate buffer, 14.4 min, was significantly higher than that in the phosphate buffer, 12.3 min.D-values in McIlvaine buffers did not vary widely within the pH range of 3.0 to 8.0. At 88, 90, 92 and 95°C in McIlvaine buffers,D-values were 24.1–29.1, 14.8–16.8, 5.7–7.1 and 2.2–2.8 min, respectively. The thermal resistance ofA. acidoterrestrisspores was affected very little by varying the pH of the heating menstruum. TheZ-values also did not vary widely as the pH varied among the different buffers, ranging from 6.4 to 7.1°C. It was evident thatA. acidoterrestrisspores showed a special relationship, unknown among other bacterial spores, between their thermal resistance and the pH of the heating menstruum. Therefore,A. acidoterrestrisshould be targeted when the quality of acidic food products is being tested.     

A time temperature integrator for particulated foods: thermal process evaluation

 A time temperature integrator (TTI) was developed by immobilizing Bacillus stearothermophilus spores in a cylindrical particle consisting of an alginate-starch-mushroom purée. The particle showed homogeneous spore distribution, and when heated over a temperature range of 121 – 130° C negligible spore leakage was observed after the thermal process. The experimental data on spore survivor levels obtained for each temperature-time combination were compared with theoretical predictions using a mathematical model. The results showed a good correlation between the experimental and theoretical data. All these results provide evidence that this artificial particle could be a very reliable TTI for monitoring the thermal impact on micro-organisms during validating sterilization processes in continuous aseptic systems. Received: 25 February 1997     

BIOLOGICAL VALIDATION OF TOMATO PULP CONTINUOUS HEAT PROCESS

This research validated the commercial process applied to tomato pulp (pH 4.3 and 8 Brix) packed in Tetra Brik packages. Spores of Bacillus coagulans and Neosartorya fischeri were selected as targets. The heat resistance of both microorganisms, tested independently, was compared. The redesigned thermal processes were carried out in a aseptic processing and tested by indirect inoculation and retrieval with spores immobilized in alginate/tomato balls. The results showed that processes for 30 s at 115C or greater did not allow the survival of heat‐resistant molds. For bacterial spores, processes for 30 s at 109C or greater showed no survivors. Although, 30 s at 115C will control both types of spoilage spores, concern for possible C. botulinum growth attributed to metabiosis in product with varying initial populations of molds and residual oxygen content dictated, a process recommendation of 60 s at 126C for safety reasons.     

Immobilized Peroxidase: A Potential Bioindicator for Evaluation of Thermal Processes

The heat-stable fraction of covalently immobilized peroxidase on/in porous glass beads in an environment of dodecane was studied as a bioindicator for evaluation of thermal processes under conditions of pasteurization. The verified bioindicator had a z value of 10.1°C and a Dref (at 70°C) of 22 min. At processing temperatures of 70°C and 80°C, the lethalities (F)_bio as read from the bioindicator agreed very well with the target Ft^10.0 values calculated from the time temperature data according to the general method.     

Radiation-heat synergism for inactivation of Alicyclobacillus acidoterrestris spores in citrus juice

The objective of this study was to investigate the influence of electron-beam and gamma-ray irradiation and temperature (85 to 95 degrees C) on Alicyclobacillus acidoterrestris GD3B strain (NCIMB 13137) spores by calculating and comparing the decimal reduction dose or time (D-values). The survival rate of A. acidoterrestris spores decreased exponentially with irradiation doses of an electron beam or gamma ray. D-values determined for electron-beam and gamma-ray irradiated spores on filter paper ranged from 1.02 to 1.10 kGy. On the other hand, the thermal sterilization effect showed a single exponential decrease within 1.5-log decreases in cell numbers (D85 degrees C = 70.5 min, D90 degrees C = 16.1 min, and D95 degrees C = 5.19 min and z-value [change in temperature required to change the D-value] was 8.83 degrees C), and prolonged heating produced an increase of 10 to 13 times that of the thermal resistance. However, within all time ranges studied (5 to 360 min), a linear decrease in the D-value was observed with an increase in the temperature. A combination of two different methods, irradiation before heating, was appropriate for reducing the duration of the heat treatment required to achieve the inactivation of conidia. Moreover, a necessary radiation dosage for complete inactivation of A. acidoterrestris spores that contaminated dextrin was examined. Dextrin is often used in the juice industry as an augmentor, and it is known to be sometimes contaminated by these spores. The D-values of the spores in dextrin for electron-beam and gamma-ray irradiations were 1.72 and 1.79 kGy, respectively. The doses required for elimination of the spores could be lowered by using irradiation in combination with heat sterilization. When dextrin powder contaminated with 10(4) CFU/g of A. acidoterrestris was preirradiated at 1.0 kGy of electron beam, the citrus juice containing dextrin at a concentration of 10% (wt/vol) was completely sterilized by heating for 20 min at 95 degrees C.     

Incidence and Heat Resistance of Clostridium botulinum Type E Spores in Menhaden Surimi

Raw menhaden surimi (Brevoortia tyrannus) was examined to determine the incidence of Clostridium botulinum spores. Seven of 565 test portions (1.2%) were positive for type E spores. The thermal death time (TDT) tube method was used to determine the heat resistance of C. botulinum type E spores inoculated into the remaining 558 negative portions. Calculated mean D-values in mm were 8.66 at 73.9°C, 3.49 at 76.7°C, 2.15 at 79.4°C, and 1.22 at 82.2°C. The z-value of the phantom TDT curve was 9.78C^o. Our data indicate previously reported minimal time/temperature thermal processes used to set surimi gel provide an adequate margin of safety with regard to C. botulinum type E.     

Measurement of optical absorbance of Clostridium sporogenes PA 3679 spores as a method for determining their thermal inactivation

 The loss of optical density of Clostridium sporogenes PA 3679 spores after heating at temperatures of 121, 126, 130 and 135°C was studied, together with the relationship between this parameter and the recovery capacity of the heated spores. The results show that the spores suffered a greater loss of optical density when they were subjected to more severe heating. A linear relationship was observed between the loss of viability and the optical absorbance of the spores. A certain parallel was detected between the heat resistance parameters of the spores D_T (decimal reduction time) and z (thermal inactivation coefficient), and the kinetic parameters D_T ^A and z^A, which describe the reduction in absorbance. Received: 14 April 1997     

Apparent thermal resistance of Bacillus stearothermophilus spores recovered under anaerobic conditions

 The effect of recovering Bacillus stearothermophilus spores under anaerobic conditions on their apparent thermal resistance was studied. Spores were suspended in bidistilled water as a reference medium, heated at 115, 117, 119, 121, 123 and 125°C and recovered under aerobic and anaerobic conditions. D values (decimal reduction time) obtained following recovery under anaerobic conditions were lower than those obtained under aerobic conditions. Reductions of between 31 and 48% were found for all the temperatures studied. When spores were suspended in mushroom extract and recovered under anaerobic conditions the apparent heat resistance was much lower than that obtained under aerobic conditions (D _121°C was 4.3 min and 1.7 min, under aerobic and anaerobic conditions, respectively). Heating the spores in mushroom extract and recovering the spores under anaerobic conditions produced an additive effect, decreasing the apparent heat resistance of the B. stearothermophilus spores. Received: 1 July 1997     

Measurement of optical absorbance of Clostridium sporogenes PA 3679 spores as a method for determining their thermal inactivation

 The loss of optical density of Clostridium sporogenes PA 3679 spores after heating at temperatures of 121, 126, 130 and 135°C was studied, together with the relationship between this parameter and the recovery capacity of the heated spores. The results show that the spores suffered a greater loss of optical density when they were subjected to more severe heating. A linear relationship was observed between the loss of viability and the optical absorbance of the spores. A certain parallel was detected between the heat resistance parameters of the spores D_T (decimal reduction time) and z (thermal inactivation coefficient), and the kinetic parameters D_T ^A and z^A, which describe the reduction in absorbance. Received: 14 April 1997     

Effect of Nisin on the Outgrowth of Clostridium botulinum Spores

Nisin, an antibiotic produced by certain strains of Streptococcus lactis, is effective in preventing the outgrowth of Clostridium botulinum spores. Type A C. botulinum spores were the most resistant to the inhibitory action of nisin requiring 1000-2000 I.U. of nisin/ml for a 50% inhibition of outgrowth on TPYG agar plates. Type E spores were more sensitive requiring only 50-100 I.U./ml for 50% inhibition of outgrowth on TPYG agar plates. Type B spores displayed an intermediate level of sensitivity requiring 500-1000 I.U. of nisin/ml for 50% inhibition of outgrowth on TPYG agar plates. Similar levels of nisin were necessary to prevent spore outgrowth in TPYG broth and BHI broth over a 7-day incubation period. With prolonged incubation periods of up to 65 days in TPYG broth, spore outgrowth was observed sporadically at higher nisin levels with the type A and B spores which may indicate some decomposition of nisin with storage. Nisin levels of 5000 I.U./ml for the type A spores and 2000 I.U./ml for the type B spores and the Minnesota E spores were insufficient to prevent spore outgrowth by C. botulinurn in cooked meat medium. For the Beluga E spores, a nisin level of 2000 I.U./ml was necessary to prevent spore outgrowth in cooked meat medium. The need for higher levels of nisin in cooked medium to prevent spore outgrowth may be due to the binding of the nisin by meat particles.     

Response of Spores to High‐Pressure Processing

ABSTRACT: This review focuses on the responses of microbial spores to food processes that incorporate high hydrostatic pressures. While the majority of information deals with spores of Bacillus species, spores of Clostridium and Alicyclobacillus species are also discussed, and a section of the review surveys the responses of fungal spores to high‐pressure processing. The mechanisms of the germination of bacterial spores are outlined in detail with regard to spore physiology and structure, along with molecular aspects of germinants and the interaction with spore receptors. Use of treatments combining pressure and temperature for a range of different food products is reviewed, including examples of hurdle technology employing high hydrostatic pressure. Pressure‐assisted thermal sterilization is also discussed.     

Thermal inactivation of <Emphasis Type="Italic">Alicyclobacillus acidoterrestris</Emphasis> spores under conditions simulating industrial heating processes of tangerine vesicles and its use in time temperature integrators

The aim of the present study was to characterize the thermal inactivation of Alicyclobacillus acidoterrestris spores under isothermal and non-isothermal conditions simulating industrial heating processes applied to tangerine vesicles. A microbiological time temperature integrator (TTI) suitable for estimating the severity of thermal processes applied to acid foods was also developed. The heat resistance of A. acidoterrestris was characterized by D _105 °C = 0.63 min and z = 10.8 °C in tangerine juice, showing linear survival curves, without shoulders and tails. Under non-isothermal conditions, the use of isothermal data allowed for an accurate prediction of the inactivation. The spores were included in alginate TTIs and they were used to estimate the severity of thermal treatments applied both in a thermoresistometer Mastia and in a food pilot plant scale system, which allows fast heating of the product to 93 °C and then a short holding time (2 min). In the thermoresistometer, tangerine juice was used as heating medium. In the food pilot plant scale system, thermal treatments were applied in batch to unpackaged tangerine vesicles. In both equipments, the TTIs accurately predicted the lethality of the thermal treatments applied. The percent coefficients of variation for survivor counting in TTIs showed that distribution of heat is homogeneous both in the thermoresistometer and in the reactor, being lower than 10% in all cases. The logistic and normal distributions were found to be the best for fitting the different survivor datasets.     

Relative value of surrogate indicators for detecting pathogens in lakes and reservoirs

This study investigated the relative behavior of pathogens, fecal indicator organisms, and particles of varying size during transport through a reservoir following a storm event inflow in Myponga Reservoir, South Australia. During the inflow, samples were collected from the river and at various locations within the reservoir to determine the fate and transport of microroganisms as they progressed through the water body. Microbiological analysis included the indicator organisms Escherichia coli, enterococci, Clostridium perfringens, aerobic spores, and somatic coliphages, the protozoan pathogens Cryptosporidium spp. and Giardia spp., and the potential physical surrogates of pathogen contamination including particle size and turbidity. Of the microbial indicator groups, C. perfringens spores were the most highly correlated with Cryptosporidium spp. concentrations (Spearman Rho = 0.58), closely followed by enterococci (Spearman Rho = 0.57). Cryptosporidium spp. oocysts were predominantly associated with small sized particles (range of 14.3-27.7 microm). All of the microbial indicator groups tested were associated with larger sized particle ranges (> 63.3 microm) except C. perfringens spores which were associated with particles in the size range of 45.5-63.3 microm. Although indicators may rank correlate with Cryptosporidium spp., the variation in settling rates of different microorganisms has significant implications for the use of surrogates to estimate pathogen attenuation within reservoirs. For example, concentrations of Cryptosporidium spp. oocysts were reduced by a factor of 3 on reaching the dam wall, whereas enterococci were reduced by a factor of 10.     

Mathematical Evaluation of Process Schedules for Aseptic Processing of Low-Acid Foods Containing Discrete Particulates

A quantitative methodology was developed for evaluating thermal process schedules for low-acid foods containing particulates of any shape. The methodology uses finite element analysis to determine temperature distributions within particulate foods subjected to timevarying boundary conditions. Simulations were conducted to study the effects of particle size, residence time distributions within heat exchanger and holding tube, and convective heat transfer coefficients. Results indicate that all these factors have significant effects on the thermal process schedule required to achieve commercial sterility. For large particles, simulations indicate that little credit can be given for lethality within the heating section.     

Effects of high‐pressure processing on fungi spores: Factors affecting spore germination and inactivation and impact on ultrastructure

Food contamination with heat‐resistant fungi (HRF), and their spores, is a major issue among fruit processors, being frequently found in fruit juices and concentrates, among other products, leading to considerable economic losses and food safety issues. Several strategies were developed to minimize the contamination with HRF, with improvements from harvesting to the final product, including sanitizers and new processing techniques. Considering consumers’ demands for minimally processed, fresh‐like food products, nonthermal food‐processing technologies, such as high‐pressure processing (HPP), among others, are emerging as alternatives to the conventional thermal processing techniques. As no heat is applied to foods, vitamins, proteins, aromas, and taste are better kept when compared to thermal processes. Nevertheless, HPP is only able to destroy pathogenic and spoilage vegetative microorganisms to levels of pertinence for food safety, while bacterial spores remain. Regarding HRF spores (both ascospores and conidiospores), these seem to be more pressure‐sensible than bacterial spores, despite a few cases, such as the ascospores of Byssochlamys spp., Neosartorya spp., and Talaromyces spp. that are resistant to high pressures and high temperatures, requiring the combination of both variables to be inactivated. This review aims to cover the literature available concerning the effects of HPP at room‐like temperatures, and its combination with high temperatures, and high‐pressure cycling, to inactivate fungi spores, including the main factors affecting spores’ resistance to high‐pressure, such as pH, water activity, nutritional composition of the food matrix and ascospore age, as well as the changes in the spore ultrastructure, and the parameters to consider regarding their inactivation by HPP.     

Effect of input data variability on estimations of the equivalent constant temperature time for microbial inactivation by HTST and retort thermal processing

Abstract: Consumer demand for food safety and quality improvements, combined with new regulations, requires determining the processor's confidence level that processes lowering safety risks while retaining quality will meet consumer expectations and regulatory requirements. Monte Carlo calculation procedures incorporate input data variability to obtain the statistical distribution of the output of prediction models. This advantage was used to analyze the survival risk of Mycobacterium avium subspecies paratuberculosis (M. paratuberculosis) and Clostridium botulinum spores in high‐temperature short‐time (HTST) milk and canned mushrooms, respectively. The results showed an estimated 68.4% probability that the 15 sec HTST process would not achieve at least 5 decimal reductions in M. paratuberculosis counts. Although estimates of the raw milk load of this pathogen are not available to estimate the probability of finding it in pasteurized milk, the wide range of the estimated decimal reductions, reflecting the variability of the experimental data available, should be a concern to dairy processors. Knowledge of the C. botulinum initial load and decimal thermal time variability was used to estimate an 8.5 min thermal process time at 110 °C for canned mushrooms reducing the risk to 10^?9 spores/container with a 95% confidence. This value was substantially higher than the one estimated using average values (6.0 min) with an unacceptable 68.6% probability of missing the desired processing objective. Finally, the benefit of reducing the variability in initial load and decimal thermal time was confirmed, achieving a 26.3% reduction in processing time when standard deviation values were lowered by 90%. Practical Application: In spite of novel technologies, commercialized or under development, thermal processing continues to be the most reliable and cost‐effective alternative to deliver safe foods. However, the severity of the process should be assessed to avoid under‐ and over‐processing and determine opportunities for improvement. This should include a systematic approach to consider variability in the parameters for the models used by food process engineers when designing a thermal process. The Monte Carlo procedure here presented is a tool to facilitate this task for the determination of process time at a constant lethal temperature.     

Optimization and evaluation of heat-shock condition for spore enumeration being used in thermal-process verification: Differential responses of spores and vegetative cells of Clostridium sporogenes to heat shock

To evaluate a heat-shock condition for the enumeration of Clostridium sporogenes spores, a surrogate for C. botulinum spores, we examined the heat tolerance of C. sporogenes spores and vegetative cells exposed to a heat shock at 90°C. From the D values of the spores determined in the temperature range of 113–121°C, z value (±SD) and D_90°C value were estimated to be 10.16±0.90°C and 1,071.52 min, respectively, and the inactivation rates were predicted to be only approximately 2% at 90°C for up to 10 min. Meanwhile, the viable count of spores was significantly higher when activated under a heat-shock condition of 90°C for over 9 min than those activated for shorter time periods. The heat tolerance of vegetative cells was extremely low, showing a D_90°C value (±SD) of 0.21±0.01 min. Finally, 3 different heat-shock conditions were compared: 70°C for 30 min, 80°C for 20 min, and 90°C for 10 min, and the experimental comparative data showed no significant differences in viable spore counts. Consequently, these results support that the heat-shock treatment at 90°C for 10 min is suitable to activate spores and to inactivate vegetative cells of C. sporogenes.