Pasteurization Conditions Research Articles

Kinetics of carrot texture degradation under pasteurization conditions

Texture degradation of carrot dices in different solutions (distilled water, 0.1% and 1.4% CaCl2 solutions) under temperatures ranging from 80 to 110°C was investigated. The effects of preheating (60°C for 20min) before high temperature treatment on carrot texture were studied and kinetic parameters were estimated. Preheating enhanced the texture of the final products, and the improvement in texture became more apparent when CaCl2 was added. High temperature increased the texture degradation rate. The isotonic solution of carrot tissue was evaluated to avoid possible ion leakage of carrot tissue during heating, but no significant differences were found between the texture of carrots immersed in isotonic solution and distilled water after thermal treatments. The texture degradation of preheated carrot dices under the investigated pasteurization conditions follows a 2nd order reaction. Kinetic results obtained were used to recommend processing conditions for carrot products that could control food pathogens and inactivate enzymes.

Effects of UV irradiation in a continuous turbulent flow UV reactor on microbiological and sensory characteristics of cow's milk.

The dairy industry under current pasteurization conditions (15 s at 72°C) and sanitary standards achieves a safe product with excellent quality. In an ever-competitive market there is still a need to improve product quality and extend shelf life of dairy products to increase competitiveness and open up new markets. In an attempt to test the effect of UV irradiation on microbiota of fluid milk, a continuous flow UV system at 254 nm was used to treat 3.5 and 2% fat milk at two UV doses (880 and 1,760 J liter(-1)). Milk was obtained from three processors, and two lots from each processor were assessed. To assess the impact on the most descriptive native microbiota in pasteurized milk after UV illumination, the product was held at two storage temperatures (4 and 7°C) and tested weekly for 5 weeks for aerobic plate counts (psychrotrophic and mesophilic bacteria), laboratory pasteurization counts, aerobic sporeformers, coliform organisms, and titratable acidity. Microbial counts for all tested microorganisms were lower in UV-treated milk when compared with control throughout storage at 4 and 7°C in both 3.5 and 2% fat milk. Sensory analysis indicated that there is a sensory defect associated with UV treatment at the wavelength used.

Acid Diffusion in Solid Foods

Abstract Foods acidified to pH levels below 4.5 can be thermally treated at lower temperatures under pasteurization conditions offering reduced thermal damage to product quality. Considering practical criterion, the main objective of this study was to investigate the proper acidification procedures of solid food particles immersed in liquid solutions. This was performed by testing a variety of factors, including particle type and size, temperature, and type and concentration of acids. Furthermore, the minimum acidification time of food particles was also determined. A standard model for mass transfer (e.g. Fick’s second law) was applied. Mass diffusion coefficients (DAB) were calculated based on experimental data. Average values of DAB were in the range of 10-8 to 10-10 m2/s and in agreement with existing literature data. Minimum acidification times varied depending on the type of acid, food, and treatment temperature, and ranged between 7 to 26 min. Meat particles were slowest to acidify, and acetic acid and tomato juice acidified by citric acid were the strongest acidifying agents.

Optimum Physico-Chemical and Processing Parameters for the Preservation of King Coconut Water

King coconut (Cocos nucifera var. aurantiaca) water is a natural, nutritious and healthy beverage. However, it is underutilized in terms of value addition with extended shelf life. Therefore, an attempt was made to develop the physico-chemical and processing parameters for the value addition of King coconut water with extended shelf life. King coconut water was analyzed for sugar, minerals and vitamin C content based on reviewed methods. Studies were conducted to identify the optimum pH, total soluble solid (TSS), type of acidulant and pasteurization conditions based on sensory properties of the product using semi trained panelists. Processed King coconut water was packed in three different packages and stored at refrigerated (4°C) condition for two months. Changes in pH, TSS and titratable acidity were evaluated in two weeks intervals throughout the storage period. The results showed that optimum pH, TSS, type of acidulant and pasteurization conditions were 4.4, 9, malic acid and 70˚C/15 sec., respectively. The product was microbiologically (less than 50 CFU/ml) safe for consumption even after 8 weeks of storage. These storage studies revealed that the changes in pH, TSS and titratble acidity of King coconut water packed in three packaging materials had no significant difference (p<0.05) during refrigerated storage.

Pasteurization of milk: The heat inactivation kinetics of milk-borne dairy pathogens under commercial-type conditions of turbulent flow

This is the first study to report kinetic data on the survival of a range of significant milk-borne pathogens under commercial-type pasteurization conditions. The most heat-resistant strain of each of the milk-borne pathogens Staphylococcus aureus, Yersinia enterocolitica, pathogenic Escherichia coli, Cronobacter sakazakii (formerly known as Enterobacter sakazakii), Listeria monocytogenes, and Salmonella was selected to obtain the worst-case scenario in heat inactivation trials using a pilot-plant-scale pasteurizer. Initially, approximately 30 of each species were screened using a submerged coil unit. Then, UHT milk was inoculated with the most heat-resistant pathogens at ∼107/mL and heat treated in a pilot-plant-scale pasteurizer under commercial-type conditions of turbulent flow for 15s over a temperature range from 56 to 66°C and at 72°C. Survivors were enumerated on nonselective media chosen for the highest efficiency of plating of heat-damaged bacteria of each of the chosen strains. The mean log10 reductions and temperatures of inactivation of the 6 pathogens during a 15-s treatment were Staph. aureus >6.7 at 66.5°C, Y. enterocolitica >6.8 at 62.5°C, pathogenic E. coli >6.8 at 65°C, C. sakazakii >6.7 at 67.5°C, L. monocytogenes >6.9 at 65.5°C, and Salmonella ser. Typhimurium >6.9 at 61.5°C. The kinetic data from these experiments will be used by the New Zealand Ministry of Agriculture and Forestry to populate the quantitative risk assessment model being developed to investigate the risks to New Zealand consumers from pasteurized, compared with nonpasteurized, milk and milk products.

Development of a microchannel based pasteurizer for energy efficient processing of liquids

Abstract This study focuses on the development of an energy efficient small-scale pasteurizer for processing liquids having biological contamination. The device has three sections that perform vital functions in the pasteurization process. The first is a microchannel counterflow heat exchanger for the recovery of thermal energy in the outgoing flow to heat the incoming flow. The second section also uses microchannels along with cartridge heaters to bring the preheated flow to approximately 150 °C. The third section is a residence chamber that ensures the flow remains at approximately 150 °C for at least 2 s satisfying the requirements for Ultra High Temperature (UHT) pasteurization. The integrated compact device has a characteristic channel height of less than 0.2 mm and was composed of chemically etched and diffusion bonded stainless steel shims. The design was improved with CFD modeling with validation from point measurements of the internal fluid temperature. Thermal and biological testing demonstrated successful operation; the heat exchanger effectiveness was shown to be more than 90% and samples collected showed no colony-forming bacteria at the design conditions of UHT pasteurization and 100 mL/min flow.

Antimicrobial Activity of Peptide P34 During Thermal Processing

In the present work, the influence of pH and sodium chloride concentration on thermal stability of antimicrobial peptide P34 was evaluated under different time–temperature conditions by a 22 factorial design experiment. At sterilization conditions (121 °C for 20 min), maximum retention (36%) was obtained at pH between 5.5 and 8.5 and sodium chloride concentration between 0.4 and 0.75 mol/l. For boiling conditions (100 °C for 20 min), antimicrobial activity was about 100% combining pH between 6.0 and 8.0 and salt concentration in the range of 0.65 to 1 mol/l. At low temperature pasteurization conditions (30 min at 65 °C), antimicrobial activity was not affected within the pH range from 5.0 to 8.0. For the three time–temperature conditions tested, the antimicrobial activity was minimal at more acidic or alkaline pH. Sodium chloride concentration of 0.65 mol/l increased thermostability of the peptide P34. Combination of sodium chloride and slight alkaline pH may increase the stability of peptide P34, which is essential to the proper utilization of bacteriocins in food industry.

Effect of Different Pasteurization Conditions on Yogurt Quality

The effect of different pasteurization time-temperature conditions(A1: 60-70 ℃,30 min;A2: 70-80 ℃,20 min;A3: 80-90 ℃,15 min;A4: 90-95 ℃,10 min;A5: 95-100 ℃,5 min;and A6: 121-130 ℃,10 s) on the quality of freshly processed yogurt and its samples after storage at 4 ℃ was studied based on viscosity,hardness,whey separation,pH and sensory evaluation.The results showed that the thermal sterilization of raw milk at temperatures higher than 80 ℃ for more than 5 min could improve the viscosity and the hardness of yogurt,reduce its whey separation,and stabilize its texture,pH and sensory characteristics during storage.The samples resulting from A3 and A4 treatments displayed higher viscosity and hardness,lower syneresis rate and better mouth feeling and flavor,and their texture and flavor could be maintained better during 4 ℃ storage.

Isolation of Highly Heat-Resistant Listeria monocytogenes Variants by Use of a Kinetic Modeling-Based Sampling Scheme

Stable high-hydrostatic-pressure (HHP)-resistant Listeria monocytogenes LO28 variants were previously isolated and characterized. These HHP variants were also more resistant to heat. In addition, nonlinear heat inactivation kinetics pointed toward the existence of heat-resistant variants, although these could not be isolated so far. In this study, we used kinetic modeling of inactivation curves of two isolated HHP variants and their wild type, and this revealed that the probability of finding resistant variants should depend on the nature of the inactivation treatment and the time of exposure. At specific heat and HHP conditions, resistant LO28 and EGDe variants were indeed isolated. Resistant LO28 variants were even isolated after a heat inactivation at 72°C in milk, and these variants showed high resistance to standard pasteurization conditions. The increased resistance of part of the isolated LO28 and EGDe variants was due to mutations in their ctsR genes. For the variants whose ctsR genes and upstream regions were not altered, the mechanisms leading to increased resistance remain to be elucidated. This research showed the strength of kinetic modeling in unraveling the causes of nonlinear inactivation and facilitating the isolation of heat-resistant L. monocytogenes variants.

Adequacy of current pasteurization standards to inactivate Mycobacterium paratuberculosis in milk and phosphate buffer

Mycobacterium avium subspecies paratuberculosis (MAP) inactivation kinetics was studied to assess whether current legislative pasteurization prescriptions are sufficient to reduce this bacterium to an acceptable level in raw milk. To assess possible protective effects of milk components during pasteurization, raw milk and phosphate-buffered saline (PBS) were compared. Analyzing data from three replicate experiments in milk separately gave D 60°C-values ranging from 114.3 to 244.5 s and z-values ranging from 4.2 to 6.8 °C; in PBS the ranges were 162.4 to 353.3 s and 4.0 to 9.0 °C, respectively. No statistically significant difference was observed between the heat resistance of MAP in milk versus PBS. The currently prescribed minimum HTST pasteurization conditions (71.7 °C, 15 s) were found to be insufficient to kill MAP in milk in 2 out of 6 replicate experiments, while LTLT pasteurization (minimum 62.7 °C, 30 min) was effective, based on extrapolation of the inactivation data obtained.

γ-Glutamyl transferase inactivation in milk and cream: A comparative kinetic study

The degree and rate of inactivation of γ-glutamyl transferase in raw cow's milk containing two levels of fat (skimmed [0%] and whole [3.5%], and cream [45%]) were measured at different time–temperature combinations in order to evaluate the suitability of this enzyme as a marker for the pasteurization of milk and milk products. A detailed comparative kinetic study of γ-glutamyl transferase inactivation was carried in the temperature range of 60 to 85 °C. Kinetic studies showed that the thermal inactivation of enzyme followed first-order kinetics. The influence of temperature on the inactivation rate constant was quantified using the Arrhenius equation and was characterized by activation energy values of 214.8 ± 4.6, 190.2 ± 3.7 and 174.5 ± 3.5 kJ/mol in skimmed milk, whole milk and cream, respectively. The kinetic data regarding inactivation of milk enzymes can be valuable in terms of implementing food safety management systems, including traceability of the heat treatment step as a critical control point for milk and dairy processes. Heat stability profiles of bovine milk γ-GT were examined with the object of being able to monitor heat treatments slightly or even more severely than typical pasteurization conditions by measurements of residual enzyme activity after heating. Assay procedure was limited to simple colorimetric method that would be most likely to form the basis of a quick, simple and inexpensive test. The importance of this work is related to the possibility of establishing potential markers to evaluate the destruction of the target microorganism associated with each heating process, taking into consideration the safety and quality aspects.

Clostridium botulinum Neurotoxin Type B Is Heat-Stable in Milk and Not Inactivated by Pasteurization

Foodborne botulism is caused by the ingestion of foods containing botulinum neurotoxins (BoNTs). To study the heat stability of Clostridium botulinum neurotoxins, we needed to measure and compare the activity of botulinum neurotoxins, serotypes A and B, under various pasteurization conditions. Currently, the only accepted assay to detect active C. botulinum neurotoxin is an in vivo mouse bioassay, which raises ethical concerns with regard to the use of experimental animals. In this study, noninvasive methods were used to simultaneously detect and distinguish between active BoNT serotypes A and B in one reaction and sample. We developed an enzymatic activity assay employing internally quenched fluorogenic peptides corresponding to SNAP-25, for BoNT-A, and VAMP2, for BoNT-B, as an alternative method to the mouse bioassay. Because each peptide is labeled with different fluorophores, we were able to distinguish between these two toxins. We used this method to analyze the heat stability of BoNT-A and BoNT-B. This study reports that conventional milk pasteurization (63 °C, 30 min) inactivated BoNT serotype A; however, serotype B is heat-stable in milk and not inactivated by pasteurization. Using this activity assay, we also showed that the commonly used food processes such as acidity and pasteurization, which are known to inhibit C. botulinum growth and toxin production, are more effective in inactivating BoNT serotype A than serotype B when conventional pasteurization (63 °C, 30 min) is used.

Kinetic study of high pressure microbial and enzyme inactivation and selection of pasteurisation conditions for Valencia Orange Juice

SummaryKeeping quality of fresh orange juice is highly dependent on pectinolytic enzyme activity and the growth of spoilage microorganisms. The inactivation kinetics of indigenous pectin methylesterase (PME) and of the two more pressure resistant species of spoilage lactic acid bacteria (LAB) Lactobacillus plantarum and L. brevis in freshly squeezed Valencia orange juice under high hydrostatic pressure (100–500 MPa) combined with moderate temperature (20–40 °C) was investigated. PME inactivation followed first order kinetics with a residual PME activity (15%) at all pressure–temperature combinations used. The values of activation energy and activation volume were estimated at each pressure and at each temperature, respectively. Values of 90 kJ/mol and −30 mL/mol at reference pressure of 300 MPa and reference temperature of 35 °C were estimated respectively. The corresponding zT and zP values of LAB inactivation were also estimated at all conditions tested. Values of 19.5 °C and 95 MPa at reference pressure of 300 MPa and reference temperature of 30 °C were estimated respectively for L. plantarum, while the corresponding values for L. brevis were 40 °C and 82 MPa, respectively, at the same reference conditions. Pressure and temperature were found to act synergistically both for PME and LAB inactivation. The PME and LAB inactivation rate constants were expressed as functions of the temperature and pressure process conditions. These functions allow the determination of the pressure/temperature conditions that achieve the target enzyme and microbial inactivation at a selected processing time. The process conditions of 350 MPa at 35 °C for 2 min are proposed as effective for Valencia orange juice cold pasteurisation.

Thermal Stability of Tagatose in Solution

Tagatose, a monosaccharide similar to fructose, has been shown to behave as a prebiotic. To deliver this prebiotic benefit, tagatose must not degrade during the processing of foods and beverages. The objective of this study was to evaluate the thermal stability of tagatose in solutions. Tagatose solutions were prepared in 0.02 and 0.1 M phosphate and citrate buffers at pHs 3 and 7, which were then held at 60, 70, and 80 degrees C. Pseudo-1st-order rate constants for tagatose degradation were determined. In citrate and phosphate buffers at pH 3, minimal tagatose was lost and slight browning was observed. At pH 7, tagatose degradation rates were enhanced. Degradation was faster in phosphate buffer than citrate buffer. Higher buffer concentrations also increased the degradation rate constants. Enhanced browning accompanied tagatose degradation in all buffer solutions at pH 7. Using the activation energies for tagatose degradation, less than 0.5% and 0.02% tagatose would be lost under basic vat and HTST pasteurization conditions, respectively. Although tagatose does breakdown at elevated temperatures, the amount of tagatose lost during typical thermal processing conditions would be virtually negligible. Practical Application: Tagatose degradation occurs minimally during pasteurization, which may allow for its incorporation into beverages as a prebiotic.

The Case of Botulinum Toxin in Milk: Experimental Data

Botulinum neurotoxin (BoNT) is the most toxic substance known to man and the causative agent of botulism. Due to its high toxicity and the availability of the producing organism Clostridium botulinum, BoNT is regarded as a potential biological warfare agent. Because of the mild pasteurization process, as well as rapid product distribution and consumption, the milk supply chain has long been considered a potential target of a bioterrorist attack. Since, to our knowledge, no empirical data on the inactivation of BoNT in milk during pasteurization are available at this time, we investigated the activities of BoNT type A (BoNT/A) and BoNT/B, as well as their respective complexes, during a laboratory-scale pasteurization process. When we monitored milk alkaline phosphatase activity, which is an industry-accepted parameter of successfully completed pasteurization, our method proved comparable to the industrial process. After heating raw milk spiked with a set amount of BoNT/A or BoNT/B or one of their respective complexes, the structural integrity of the toxin was determined by enzyme-linked immunosorbent assay (ELISA) and its functional activity by mouse bioassay. We demonstrated that standard pasteurization at 72 degrees C for 15 s inactivates at least 99.99% of BoNT/A and BoNT/B and at least 99.5% of their respective complexes. Our results suggest that if BoNTs or their complexes were deliberately released into the milk supply chain, standard pasteurization conditions would reduce their activity much more dramatically than originally anticipated and thus lower the threat level of the widely discussed "BoNT in milk" scenario.

Occurrence of Campylobacter in commercially broken liquid egg in Japan.

Samples of unpasteurized liquid egg (whole egg, egg yolk, and egg white) and pasteurized liquid whole egg were collected from egg-breaking facilities in Japan and were tested for the presence of Campylobacter. Isolates recovered were tested for freeze-thaw response, sensitivity to antimicrobials, and heat resistance. Campylobacter was isolated from 27.9% of unpasteurized liquid whole egg samples and 36.0% of unpasteurized liquid egg yolk samples. No Campylobacter was isolated from unpasteurized liquid egg white or pasteurized liquid whole egg samples. The contamination levels of Campylobacter ranged from <3 to 240/100 ml. Freeze-thaw response was tested by freezing and thawing liquid whole egg and egg yolk to examine whether those conditions influenced the survival rate. It was shown that freezing and thawing reduced Campylobacter counts. Sensitivity to all antimicrobials used in this study was observed in 47.6% of the isolates. The most predominant antibiotic resistance profile was similar to that of isolates from chicken. D(55 degrees C)-values of 0.16 to 0.38 min and 0.47 to 0.84 min were determined for Campylobacter isolates in liquid whole egg and egg yolk, respectively. These values were lower than those reported for Salmonella. The very weak heat tolerance of Campylobacter indicated that it could be eliminated at the current legal pasteurization condition. There is no safety concern for commercially broken pasteurized liquid egg pertaining to Campylobacter contamination.

Dynamic high pressure–induced gelation in milk protein model systems

The structure-functional properties of milk proteins are relevant in food formulation. Recently, there has been growing interest in dynamic high-pressure homogenization effects on the rheological-structural properties of food macromolecules and proteins. The aim of this work was to evaluate the effects of different homogenization pressures on rheological properties of milk protein model systems. For this purpose, sodium caseinate (SC) and whey protein concentrate (WPC) were dispersed at different concentrations (1, 2, and 4%), pasteurized, and then homogenized at 0, 18MPa (conventional pressure, CP), 100MPa (high pressure, HP), and 150MPa (HP+). Differences in viscosity were observed between WPC and casein dispersions according to concentration, heat treatment, and homogenization pressure. Mechanical spectra described the characteristic behavior of solutions except for the WPC 4% pasteurized sample, in which a network formed but was broken after homogenization. Dispersions with different ratios of WPC and SC were also made. In these systems, pasteurization alone did not determine network formation, whereas homogenization alone promoted cold gelation. A total concentration of at least 4% was required for homogenization-induced gelation in pasteurized and unpasteurized samples. Gels with higher elastic modulus (G′) were obtained in more concentrated samples, and a bell-shaped behavior with the maximum value at HP was observed. The HP treatment produced stronger gels than the CP treatment. Similar G′ values were obtained when different concentrations, pasteurization conditions, and homogenization pressures were combined. Therefore, by setting appropriate process conditions, systems or gels with tailored characteristics may be obtained from dispersions of milk proteins.

Physicochemical and Functional Characterization of Cocosin, the Coconut 11S Globulin

The physicochemical and functional characteristics of the major coconut storage protein, 11S globulin or cocosin, were investigated.Cocosin was purified by a combination of salt extraction, selective precipitation, and gel filtration chromatography. The solubility of cocosin at different pH was higher at µ=0.5 than at µ=0.08. The 24 and 21 kDa basic polypeptides of cocosin were more resistant to chymotrypsin digestion than the 35 and 32 kDa acidic polypeptides. Cocosin emulsions were most stable at 0 M NaCl, followed by emulsions in 0.1 M and 0.4 M NaCl. The available SH groups were found to be 21.6 mole SH/mole cocosin. Cocosin was observed to be stable under various pasteurization conditions from 63°C, 30 min to 100°C, 10 sec. However, heating at 100°C for 10 min and longer degraded cocosin up to 60%. The thermal denaturation midpoint temperature, Tm, of the trimeric cocosin was 77.6°C while that of the hexameric form was 100.5°C.

Simulation of heat transfer for solid–liquid food mixtures in cans and model validation under pasteurization conditions

During processing of canned mixtures of solid–liquid foods, conduction and convection occur simultaneously. The literature lacks in a complete simulation study where a large number of solids are dispersed in the liquid phase, e.g. canned peas. Therefore, the objectives of this study were to determine temperature changes inside a can containing solid–liquid food mixtures. For this purpose, dispersed stationary solids (canned peas in water) in a 2D (axi-symmetrical) configuration were applied. Ansys V11 (Ansys Inc., Canonsburg, PA) was used to solve continuity, energy and momentum equations. For experiments, canned pea samples were prepared in 500 g cans, and heating process was conducted in a retort under pasteurization conditions at ≈98 °C. Temperature changes were measured using needle type thermocouples, and simulation results were validated against experimental data. This study is expected to be a significant contribution to the literature for further optimization studies and to form basis of an industrial project to improve canning process of solid–liquid mixtures.

Controlling the Bleeding of Carmine Colorant in Crabstick

Carmine used to color surimi seafood often seeps or bleeds from red-colored meat to white meat when vacuum-packed products go through high-temperature long-time pasteurization. Various physical and chemical treatments were examined to investigate means to inhibit or minimize carmine bleeding in surimi seafood products. Degree of bleeding was analyzed using L* (lightness) and a* (redness) as affected by carmine concentrations, pH, pasteurization conditions, and added calcium compounds. Bleeding was significantly affected by carmine concentrations. Optimum carmine concentration in color paste was 0.1%. Bleeding increased when pasteurization time and/or temperature increased. Color bleeding was also affected by moisture content of surimi paste. Carmine bleeding was minimized as pH of color solution decreased. The degree of bleeding was controlled as calcium compounds were added in color solution in a descending order of calcium chloride, calcium acetate, and calcium hydroxide. Minimal inhibition was obtained when color solutions contained calcium citrate, tricalcium phosphate, and calcium lactate. Practical Application: This manuscript addresses one of the long time problems in the surimi crabstick industry. Various means to control carmine bleeding or color transfer under high temperature for long time pasteurization were demonstrated. However, further study must continue to stop bleeding completely.