Saccharomyces Cerevisiae Inactivation Research Articles

Sequential Pulsed Light and Ultrasound Treatments for the Inactivation of Saccharomyces cerevisiae and PPO and the Retention of Bioactive Compounds in Sweet Lime Juice.

Designing a pasteurization con dition for sweet lime juice while ensuring microbial safety, enzymatic stability, and high nutritional quality is crucial for satisfying stakeholder demands. The present research investigates the effects of matrix pH, ultrasound treatments, and sequential pulsed light on the microbial population, enzyme activity, and bioactive chemicals in sweet lime juice. The sequential pulsed light (PL: 0.6-0.84 J/cm2) and ultrasound (US: 0.2-0.4 W/cm3) treatments for sweet lime juice were optimized using response surface methodology (RSM). A three-factor full factorial design was used for this purpose. The independent variables encompassed pH (X1), PL effective fluence (X2, J/cm2), and US intensity (X3, W/cm3). The responses assessed included the inactivation of Saccharomyces cerevisiae (Y1, log cfu/mL) and polyphenol oxidase (PPO: Y2 in %) and the retention of vitamin C (Y3, %). The polynomial models were optimized using numerical optimization to attain the maximum desirability value (0.89). The optimized PL + US sample (0.8 J/cm2 + 0.4 W/cm3, respectively) at pH 3.5 resulted in a 5-log cycle reduction in S. cerevisiae count and a 90% inactivation in PPO activity and retained 95% of its vitamin C content. This optimized sample underwent further analysis, including phenolic profiling, assessment of microbial cell morphology, and examination of enzyme conformational changes. After sequential pulsed-light (0.8 J/cm2) and ultrasound (0.4 W/cm3) treatments, yeast cells showed unusual structural changes, indicating additional targets besides membranes. Following PL + US treatment, the PPO composition changed to 2.7 ± 0.1% α-helix, 33.9 ± 0.3% β-sheet, 1.4 ± 0.2% β-turn, and 62 ± 0.7% random coil. Impressively, the optimized PL + US sample maintained a sensory acceptance level similar to that of the untreated sample.

Exploring the role of impedance spectroscopy in assessing 405nm laser-induced inactivation of saccharomyces cerevisiae.

Impedance spectroscopy was employed to assess the electrical properties of yeast following 405nm laser irradiation, exploring the effects of visible, non-ionizing laser-induced inactivation as a more selective and safer alternative for photoinactivation applications compared to the use of DNA targeting, ionizing UV light. Capacitance and impedance spectra were obtained for yeast suspensions irradiated for 10, 20, 30, and 40min using 100 and 200 mW laser powers. Noticeable differences in capacitance spectra were observed at lower frequencies (40Hz to 1kHz), with a significant increase at 40min for both laser powers. β-dispersion was evident in the impedance spectra in the frequency range of 10kHz to 10MHz. The characteristic frequency of dielectric relaxation steadily shifted to higher frequencies with increasing irradiation time, with a drastic change observed at 40min for both laser powers. These changes signify a distinct alteration in the physical state of yeast. A yeast spot assay demonstrated a decrease in cell viability with increasing laser irradiation dose. The results indicate a correlation between changes in electrical properties, cell viability, and the efficacy of 405nm laser-induced inactivation. Impedance spectroscopy is shown to be an efficient, non-destructive, label-free method for monitoring changes in cell viability in photobiological effect studies. The development of impedance spectroscopy-based real-time studies in photoinactivation holds promise for advancing our understanding of light-cell interactions in medical applications.

Inactivation of Saccharomyces cerevisiae by combined high pressure carbon dioxide and high pressure homogenization

A combined treatment of high pressure carbon dioxide (HPCD) and high pressure homogenization (HPH) was investigated to inactivate Saccharomyces cerevisiae in a phosphate buffered solution. The inactivation kinetics, protein leakage, particle size distribution, SEM images, and TEM images of Saccharomyces cerevisiae exposed to HPH alone, HPCD alone, and the combined treatment of HPCD and HPH (HPCD+HPH) were studied. Results showed that HPCD+HPH was superior to HPH alone and HPCD alone in the inactivation of Saccharomyces cerevisiae. The inactivation kinetics of the combined treatment exhibited a fast-slow biphasic curve. The synergic bactericidal ability of HPCD+HPH could be attributed to the enhancing effect of HPH on CO2 germicidal capability. The possibility of the combination of HPH and HPCD for microbial inactivation of Saccharomyces cerevisiae was validated, and the combined treatment has the potential to be a viable approach for microbial inactivation.

Insights on the effectiveness of pneumatic and ultrasonic atomization in combination with UVC light for processing of fruit juices.

This study evaluated the effectiveness of spraying juices, during shortwave ultraviolet irradiation (UVC) treatments as an alternative to promote more contact area, by means of ultrasonic atomization (UA) and pneumatic atomization (PA). Four juices with dissimilar physical characteristics were processed to assess the effect of suspended solids and turbidity. Antioxidant activity, anthocyanins, ascorbic acid, and inactivation of Saccharomyces cerevisiae inoculated in the juices were evaluated. Five decimal reduction cycles were reached after two passes of orange or grapefruit juice through the UVC + UA arrangement. On the other hand, five decimal reduction cycles were achieved after three passes in the UVC + PA arrangement. Losses of 11% and 14% of ascorbic acid were observed in orange and grapefruit juice, respectively, while anthocyanin content presented losses of 50% and antioxidant activity decreased by 40% for pomegranate and blueberry juice, correspondingly.

Improvement of an annular thin film UV-C reactor by fluid guiding elements

In this paper special elements are inserted into an annular thin film UVC reactor to guide the laminar flow. These “Fluid Guiding Elements” (FGE) divide the flow into three separated laminar currents that are alternatingly directed through a small gap of 0.6 mm facing the UV source by turns. Computational fluid dynamic simulations have been used to visualize the flow dynamics inside the reactor.The residence time distribution and the Bodenstein number show an increase of back mixing in the reactor with the elements. An Iodide/iodate actinometry comparison has shown a better dose distribution throughout the treated volume based on the FGE. The inactivation of E. coli DH5α as an exemplary organism could be improved by more than 4 log levels after 5 passes through the reactor using the FGE independent of the flow rate. The absorbance of a model solution was varied by different dye concentrations and the use of FGE improve the inactivation of Saccharomyces cerevisiae. Industrial relevanceThe stabilization of liquid foods before bottling is a crucial aspect. The consumers often do not accept a chemical additive like sulphites in wine or dimethyl carbonate in juices. A physical alternative is the UV-C Treatment. In contrast to a turbulent flow a laminar flow has a far lower pressure drop. Therefore, a lower amount of energy is needed to pump the liquid. This study shows that with fluid guiding elements a sufficient inactivation can be achieved with laminar flow.

Sonication treatment of pomegranate juice containing Saccharomyces cerevisiae and Byssochlamys fulva: Thermodynamic and predictive modeling after treatment and during shelf life.

The effect of ultrasound treatment (100 W, 30 kHz; 50 and 100% amplitudes) on inactivation of Saccharomyces cerevisiae and Byssochlamys fulva in pomegranate juice and shelf life of the juice during storage at different temperatures (5, 15 and 30 °C) for 30 days was modeled using predictive and thermodynamics models. The Baranyi and square root type models were implemented to determine the growth rate of microorganisms. It was predicted that the minimum growth temperature (Tmin) of B. fulva increased by increasing sonication amplitude, however, the Tmin of S. cerevisiae was not function of sonication amplitude. The predicted shelf life was shown to be in good agreement with the measured sensorial shelf life. Increasing the temperature from 5 to 35 °C, reduced the shelf life from 17.5 to 3.5 days for B. fulva and from 15 to 5 days for S. cerevisiae. Moreover, for B. fulva, the activation energy (Ea) decreased from 43.4 to 27.5 kJ/mol by increasing the amplitude, while no significant change was observed for S. cerevisiae. Besides, thermodynamics properties of the shelf life such as enthalpy (), entropy () and Gibbs free energy ( were proven to be suitable measures to determine the microbial spoilage reaction.

Effectiveness of pulsed light treatments assisted by mild heat on Saccharomyces cerevisiae inactivation in verjuice and evaluation of its quality during storage

The effects of pulsed light (PL) processing parameters such as depth of juice layer (1, 3, 5 mm), distance from the lamp (5, 10 cm) and number of pulses (0–50 pulses) on the inactivation of Saccharomyces cerevisiae in verjuice, a clarified beverage obtained from freshly-squeezed unripe grapes, were investigated. A reduction of 0.96 ± 0.27 log CFU/mL was achieved by applying a dose of 34 J/cm2 (1-mm layer depth, 5-cm distance, 50 pulses). PL was combined with mild heating (MH) at 43, 45 and 47 °C to increase its inactivation efficacy. Pasteurization was achieved by applying 17 J/cm2 at 45 °C (PLMH45–3) and 6.12 J/cm2 at 47 °C (PLMH47–3) to a 3-mm juice layer with S. cerevisiae reductions of 5.10 ± 0.24 and 5.06 ± 0.08 log CFU/mL, respectively. Quality properties of PLMH47–3-pasteurized verjuice were monitored during 6 weeks of storage at refrigerated (5 °C) and room temperature (25 °C), The results were compared to those of untreated and thermally pasteurized (72 °C/18 s) samples. Untreated juice spoiled within 2 weeks at 25 °C. No growth was detected in other conditions for 6 weeks. Among quality characteristics, only optical properties changed slightly during storage. It was concluded that mild MH-assisted pulsed light treatments have potential for verjuice pasteurization compared to conventional thermal pasteurization due to the better preservation of its fresh-like characteristics.

Synergistic Inactivation Mechanism of Combined Plasma-Activated Water and Mild Heat against Saccharomyces cerevisiae

This study aimed to elucidate the mechanism of synergistic inactivation of Saccharomyces cerevisiae by the combined use of plasma-activated water (PAW) and mild heat (40 to 50°C). A reduction of 4.40 log CFU/mL in S. cerevisiae was observed after the synergistic combination of PAW and mild heat at 50°C for 6 min, whereas the individual treatments of PAW at 25°C and mild heat at 50°C for 6 min resulted in a reduction of 0.27 and 1.92 log CFU/mL, respectively. The simultaneous application of PAW and mild heat caused significant increases in membrane permeability, resulting in the leakage of intracellular components (such as nucleic acids and proteins) and increased uptake of propidium iodide. The combined treatment of PAW and mild heat also resulted in significant increases in the intracellular levels of reactive oxygen species and disruption of mitochondrial membrane potential in S. cerevisiae cells. In summary, this study illustrates the potential of PAW treatment combined with mild heat to rapidly inactivate microorganisms in food products.

Heat-Assisted Pulsed Electric Field Treatment for the Inactivation of Saccharomyces cerevisiae: Effects of the Presence of Citral.

Pulsed electric field (PEF) treatment is a non-thermal technology that has shown good potential for microbial inactivation. However, in many cases, it cannot be sufficient to avoid microbial proliferation, and the combination with other stabilizing technologies is needed. In the framework of the hurdle concept, several researches have been focused on the use of PEF in combination with heat and/or antimicrobials to increase its efficacy. This study investigated the inactivation effect of PEF on a strain of Saccharomyces cerevisiae (isolated from spoiled beverages) in a model system (growth medium). The efficacy of PEF treatment was evaluated in relation to different variables, such as electric field strength (25 and 50 kV/cm), treatment time (from 1 to 5 s), initial inoculum level (4 or 6 log cfu/ml), preheating at 50°C, medium pH (4 or 6), and addition of citral at sublethal concentration (i.e., half of minimum inhibiting concentration). The data from plate counting, modeled with the Weibull equation, showed that one of the main factors affecting yeast inactivation was the preheating of the suspension at 50°C. Indeed, higher cell load reductions were obtained with heat-assisted PEF, especially in the presence of citral. The effect of initial cell load was negligible, while pH affected yeast inactivation only without preheating, with higher death kinetics at pH 6. Flow cytometry (FCM) analysis confirmed higher mortality under these conditions. However, the occurrence of injured cells, especially in samples treated at pH 4, was observed. The ability of these cells to recover from the damages induced by treatments was affected by both citral and preheating. The synergic effects of PEF, preheating, and citral were likely due to the increase of membrane permeability (especially at pH 6), as the primary target of electroporation, which favored the solubilization of citral in the cell membrane, enhancing the efficacy of the whole process. The multi-analytical approach (traditional plate counting and FCM) allowed defining parameters to increase PEF efficacy against S. cerevisiae. Moreover, FCM, able to discriminate different physiological states of the yeast population, was helpful to better clarify the action mechanism and the potential recovery of cells after treatment.

Non-thermal Technologies as Alternative Methods for Saccharomyces cerevisiae Inactivation in Liquid Media: a Review

The ongoing demand for high-quality processed foods which would preserve their natural and fresh-like characteristics has awakened a growing interest in non-thermal technologies. Thanks to their ability to inactivate microorganisms under mild conditions, these technologies avoid drawbacks usually attributed to the use of thermal treatments, such as nutrient loss, off-flavors, and changes in the food’s physical and chemical properties. Saccharomyces cerevisiae (S. cerevisiae) mainly causes spoilage in liquid foods with high sugar content and low pH values. Thus, it is one of the most undesirable microorganisms in the food industry since its presence may lead to important economic losses. This review offers an exhaustive compilation and critical revision of research conducted in the field of S. cerevisiae inactivation in liquid media, emphasizing the use of non-thermal technologies, such as high pressure processing, high-power ultrasound, supercritical carbon dioxide, pulsed electric fields, and others. Likewise, using these technologies in combination (the hurdle approach) may enhance their individual effect and significantly reduce the treatment time needed to obtain a given level of S. cerevisiae inactivation. In general, non-thermal technologies are proving to be able to successfully inactivate S. cerevisiae in liquid media. However, the need for further investigation and complete industrial implementation is made evident throughout this review.

Effect of ultrasound treatment conditions on Saccharomyces cerevisiae by response surface methodology

ObjectivesThis study aimed to investigate the effect of different ultrasound treatment conditions on the inactivation of Saccharomyces cerevisiae with the application of response surface methodology (RSM). MethodsUltrasound treatment were applied on different concentrations of S. cerevisiae cells with different pH, temperature, ultrasound power, irradiating time, and pulse duty ratio. Cell viability was determined by plate counting method. Response surface methodology was used to analyze the correlation among various factors. ResultsLimited with low ultrasound power, lower pH value slightly improved the ultrasound treatment efficiency. Also, higher nonlethal temperature and ultrasound power, longer irradiation time, and lower pulse duty ratio facilitated the inactivation of S. cerevisiae. Cell concentration had no effect on ultrasound efficiency. ConclusionsUltrasound power played the most important role in the ultrasound irradiation process according to RSM analyses. Information derived from this study may aid in the control of the sublethal injury of S. cerevisiae during ultrasound treatment in food industry.

Antioxidant activity of high-pressure processed tangerine juice

The objective of the study was to combine shortwave ultraviolet irradiation (UVC-Light) with ultrasonic atomization (UA) to generate microdroplets by atomizing the juices to enhance contact with UVC-Light and to evaluate its effect on the inactivation of Saccharomyces cerevisiae as well as on selected physicochemical parameters of tangerine and grapefruit juices. UVC lamps and an ultrasonic atomizer were used individually and in combination. The effect of lamps' orientation (horizontal or vertical) and the number of lamps (1 or 2) were assessed. No significant (p > 0.05) changes on pH, °Bx, and color of studied juices were observed, since the contact time of the microdroplets with the UVC-Light was short. After processing 250 mL of juice, microbial population was reduced by 0.84 log cycles when using a single UVC lamp combined with UA while a 2.8 log cycles reduction was observed after three passes. Tested configurations with two lamps did not achieve effective inactivation of S. cerevisiae, possibly because the generated microdroplets were not in close contact with UVC-light as was the case with one lamp.The ultrasonic atomization for the UVC-treatment of juices was assessed for the first time in this work. The ultrasonic atomization of juices may be suitable for the inactivation of yeasts when combined with UVC-Light as long as atomization takes place near the irradiation site. These combined technologies have the potential to generate foods minimally processed.

Enhancement of UVC-light treatment of tangerine and grapefruit juices through ultrasonic atomization

Abstract The objective of the study was to combine shortwave ultraviolet irradiation (UVC-Light) with ultrasonic atomization (UA) to generate microdroplets by atomizing the juices to enhance contact with UVC-Light and to evaluate its effect on the inactivation of Saccharomyces cerevisiae as well as on selected physicochemical parameters of tangerine and grapefruit juices. UVC lamps and an ultrasonic atomizer were used individually and in combination. The effect of lamps' orientation (horizontal or vertical) and the number of lamps (1 or 2) were assessed. No significant (p > 0.05) changes on pH, °Bx, and color of studied juices were observed, since the contact time of the microdroplets with the UVC-Light was short. After processing 250 mL of juice, microbial population was reduced by 0.84 log cycles when using a single UVC lamp combined with UA while a 2.8 log cycles reduction was observed after three passes. Tested configurations with two lamps did not achieve effective inactivation of S. cerevisiae , possibly because the generated microdroplets were not in close contact with UVC-light as was the case with one lamp. Industrial relevance The ultrasonic atomization for the UVC-treatment of juices was assessed for the first time in this work. The ultrasonic atomization of juices may be suitable for the inactivation of yeasts when combined with UVC-Light as long as atomization takes place near the irradiation site. These combined technologies have the potential to generate foods minimally processed.

Combined use of thermo-ultrasound and cinnamon leaf essential oil to inactivate Saccharomyces cerevisiae in natural orange and pomegranate juices

The inactivation of Saccharomyces cerevisiae in natural orange and pomegranate juices untreated (control) and treated with mild temperature (50 °C), cinnamon leaf essential oil, thermo-ultrasound (24 KHz; 33.31 W mL−1; 30 min; 50 °C), alone or in combination, and its survival under refrigerated conditions (5 °C, 28 days) were studied. Additionally, the maximum concentration of cinnamon leaf essential oil accepted by consumers in both juices was determined by sensory analysis. A significant reduction in the yeast population was obtained compared to controls. The most effective treatment to inactive yeast cells was the combination of ultrasound and cinnamon leaf essential oil during 30 min at 50 °C, which, from an initial population of 5.13 log cfu ml−1, achieved significant 2.81 ± 0.19 and 2.52 ± 0.26 log-reductions in natural pomegranate and orange juices respectively. During refrigerated storage (5 °C, 28 days), the S. cerevisiae population in orange and pomegranate juices, treated with ultrasound and cinnamon leaf essential oil at 50 °C for 30 min, decreased by 1.55 ± 0.19 and 0.68 ± 0.16 log respectively, while the controls kept the yeast population without significant changes.

Assistance of human serum albumin to photo-sensitized inactivation of Saccharomyces cerevisiae with axially pyridinio-bonded P-porphyrins

As singlet-oxygen (1O2) sensitizer, water-soluble P-porphyrins (1) were prepared by the modification of axial ligands of tetraphenylporphyrinatophosphorus by N-alkyl-pyridinium group to give bis[3-(1-alkyl-4-pyridinio)propoxo]tetraphenylporphyrinatophosphorus(V) (alkyl=hexyl (1a) and butyl (1b)) and bis[5-(3-alkyl-1-pyridinio)-3-oxapentyloxo] tetraphenylporphyrinatophosphorus(V) (alkyl=hexyl (1c), butyl (1d), and ethyl (1e)). The quantum yields (ΦΔ) for the formation of 1O2 were extremely high (e.g. ΦΔ=0.88 (1a) and 0.87 (1c)). The 1 could bind human serum albumin (HSA) with high binding constants to produce a complex of HSA with 1 (1/HSA). Here, inactivation of Saccharomyces cerevisiae (yeast) was examined using the complex of HSA (400nM) with 1 (20–50nM) under visible-light irradiation. The bactericidal activity of 1 was evaluated by half-life (T1/2 in min) which was time required to be reduced to one-half initial concentration of yeasts. Under irradiation in the presence of HSA, minimum concentrations ([P]) of 1 were adjusted as T1/2 became the values among 0–120min. The [P] values were determined to be 20nM for 1a, 30nM for 1b, and 50nM for 1c–1e. The 1/HSA sterilized yeast with 12–36min of T1/2 when the concentration of 1 was set to [P]. In the photo-activation in the absence of HSA at the concentration of [P] of 1, however, the T1/2 values of 1a, 1b, 1d, and 1e were >120min and T1/2 of 1c was 44min. Thus, the complexation of 1 with HSA apparently enhanced the bactericidal activity of 1. This is the first finding on the assistance of HSA to the photo-inactivation of yeast cell by porphyrins.

Ultrasound-assisted supercritical CO2 treatment in continuous regime: Application in Saccharomyces cerevisiae inactivation

Laboratory continuous regime equipment was designed and built for supercritical CO2 microbial inactivation assisted by high power ultrasound (SC-CO2-HPU). Apple juice, previously inoculated with 1–10 × 107 CFU/ml of Saccharomyces cerevisiae, was treated in the equipment at different juice residence times (3.06–9.2 min), temperatures (31–41 °C) and pressures (100–300 bars). Inactivation ratios were fitted to a hybrid (boolean-real) model in order to study the effect of the process variables. The maximum inactivation achieved by the system was 7.8 log-cycles. The hybrid model demonstrated that HPU has a significant effect on inactivation after shorter residence times. A multi-objective optimization performed with the hybrid model showed that 6.8 log cycles of inactivation could be obtained after a minimum residence time (3.1 min) with HPU application, whereas under the same conditions but without HPU, the inactivation would be 4.3 log-cycles. Therefore, the ultrasound assisted continuous system has shown a great potential for microbial inactivation using SC-CO2 under mild process conditions.

In situ Raman quantification of the dissolution kinetics of carbon dioxide in liquid solutions during a dense phase and ultrasound treatment for the inactivation of Saccharomyces cerevisiae

In this work, a Raman based optical approach is presented that enables remote, real time and in situ quantification of the amount of carbon dioxide (CO2) dissolved in distilled water and coconut water during a dense phase carbon dioxide (DPCD) and a combined dense phase carbon dioxide and ultrasound (DPCD+US) pasteurization.CO2 dissolution kinetics were measured in an optically accessible high pressure cell at different temperatures (25, 35, 40°C) and pressures (8 and 12MPa). Two different mixing devices (mechanical and magnetic) during DPCD treatment, and different ultrasound powers (10, 20, 30W) during the DPCD+US treatment were applied. The dissolution data were then related with the inactivation ratio of Saccharomyces cerevisiae inoculated into the solutions. The results demonstrated that an increase of pressure or time during DPCD treatment enhances the amount of CO2 dissolved into the liquid, leading to a higher inactivation degree; the same trend was observed when the temperature was increased, although in this latter case, the amount of dissolved CO2 decreased. The increase of pressure during a combined DPCD+US treatment led to a higher amount of dissolved CO2, which positively influenced the microbial inactivation while no effect was obtained increasing the ultrasound power. Concerning the effect of the mixing devices, the mechanical stirrer was the one that enhanced the pasteurization efficiency as it influenced CO2 dissolution kinetics and, consequently, the microbial inactivation ratio. The composition of the liquid solutions also influenced the amount of dissolved CO2 but no correlations were found with S. cerevisiae inactivation.

Effective inactivation of Saccharomyces cerevisiae in minimally processed Makgeolli using low-pressure homogenization-based pasteurization.

In order to address the limitations associated with the inefficient pasteurization platform used to make Makgeolli, such as the presence of turbid colloidal dispersions in suspension, commercially available Makgeolli was minimally processed using a low-pressure homogenization-based pasteurization (LHBP) process. This continuous process demonstrates that promptly reducing the exposure time to excessive heat using either large molecules or insoluble particles can dramatically improve internal quality and decrease irreversible damage. Specifically, optimal homogenization increased concomitantly with physical parameters such as colloidal stability (65.0% of maximum and below 25-μm particles) following two repetitions at 25.0 MPa. However, biochemical parameters such as microbial population, acidity, and the presence of fermentable sugars rarely affected Makgeolli quality. Remarkably, there was a 4.5-log reduction in the number of Saccharomyces cerevisiae target cells at 53.5°C for 70 sec in optimally homogenized Makgeolli. This value was higher than the 37.7% measured from traditionally pasteurized Makgeolli. In contrast to the analytical similarity among homogenized Makgeollis, our objective quality evaluation demonstrated significant differences between pasteurized (or unpasteurized) Makgeolli and LHBP-treated Makgeolli.Low-pressure homogenization-based pasteurization, Makgeolli, minimal processing-preservation, Saccharomyces cerevisiae, suspension stability.Electronic supplementary materialThe online version of this article (doi:10.1186/s40064-015-0936-4) contains supplementary material, which is available to authorized users.

Heat transfer analysis of pasteurization of bottled beer in a tunnel pasteurizer using computational fluid dynamics

Abstract Beer is one of the most widely consumed alcoholic beverages in the world. Pasteurization is an important unit operation in beer processing that inactivates the spoilage microorganisms present in beer thereby extending its shelf life. It is difficult to determine the temperature profile and slowest heating zone (i.e. minimum heating region) inside the bottle during industrial scale tunnel pasteurization. Computational fluid dynamics (CFD) modeling can be used as a tool to determine the temperature distribution pattern inside the bottled beer. This study is unique in terms of using the actual thermophysical properties of beer unlike in earlier published works. Further, CFD simulation prediction of the temperature profile in the bottled beer was validated with experimental measurements. The study was extended to investigate the effects of different zones' temperatures on inactivation of Saccharomyces cerevisiae , the most common beer spoilage organism. A tunnel pasteurizer with seven zones was selected to study the temperature profile inside the bottled beer and found to be in good agreement with the published temperature profiles in different zones. In addition, the effectiveness of pasteurization was investigated in terms of pasteurization unit (PU) and the resultant PU value (15 to 30 PU) was adequate for achieving the maximum sterility of beer. Industrial relevance In recent years, a rapid development in the application of CFD in food processing operations has been witnessed. The main need for CFD analysis of pasteurization is to determine the uniform and effective heat distribution inside the bottled beer and to examine the position of slowest heating zone (SHZ). Relatively few works have been published related to applications of CFD during beer pasteurization. However, all the studies were performed with water as a model fluid. So far no work has been published on the CFD simulation during the pasteurization process in bottled beer by using the thermophysical properties of beer. Hence, the present study was aimed at investigating the temperature distribution inside the beer bottle during the pasteurization process and in each zone of the industrial tunnel pasteurizer. This model can be used for the brewery industry to ensure that the required pasteurization temperature has been reached inside the beer bottle when conveyed through a tunnel pasteurizer. This is very essential to render a safe product with extended shelf life to the consumers.

Inactivation of Saccharomyces cerevisiae by equipment pressurizing at ambient temperature after generating CO2 microbubbles at lower temperature and pressure

To improve the inactivation efficiency of low pressure CO2 microbubbles (MB-CO2), we developed the MB-CO2 equipment from batch system to two-stage MB-CO2 system which was additionally pressurized at ambient temperature after MB-CO2 was mixed with a solution at lower temperature and pressure. Therefore, the effect of the two-stage MB-CO2 treatment for inactivating Saccharomyces cerevisiae was investigated. The two-stage MB-CO2 efficiency for the inactivation of S. cerevisiae dramatically increased by lowering the temperature and by increasing the pressure in the mixing vessel. Furthermore, its effectiveness significantly enhanced by increasing the temperature in the heating coil, although not by the pressure. As a result, using the two-stage MB-CO2 equipment was suggested as a new effective technique to inactivate S. cerevisiae.