Inactivation Of Yeast Research Articles

Inactivation of Dekkera bruxellensis yeasts in wine storage in brand new oak barrels using low electric current technology

Dekkera bruxellensis is one of the species of yeast, which is most damaging to wine quality, and the tools available to control its growth are limited. In previous studies, non-Saccharomyces yeasts and Dekkera bruxellensis have been significantly restricted during wine-making processes using an innovative approach based on low electric current treatment (LEC). In the present study, LEC techniques were assessed for their capacity to inhibit wine spoilage by D. bruxellensis and to prevent formation of undesirable flavours during storage in oak barrels. Although the effect of SO2 treatment on D. bruxellensis viability and ATP content was more immediate, from the 30th day onward no significant variations between LEC and SO2 treatments were observed. At the end of the trial, LEC treatment had had a comparable effect to that of SO2 addition. Acetic acid content was significantly lower after LEC and SO2 treatments than in untreated wines and volatile phenols were also found to be significantly lower in the LEC treated wine. Moreover, the results from the panel test clearly indicate that no significant differences were found between the LEC and the SO2 treated wines. These results clearly indicate that LEC technology could represent a viable tool to limit yeast spoilage caused by D. bruxellensis. The present work represents, to our knowledge, the first attempt to control D. bruxellensis during red wine storage in oak barrels using LEC. The potential industrial applications of LEC technology include the real future possibility of producing a new, marketable range of healthier wines to satisfy the requirements of modern wine consumers.

2P4-11 Effect of ultrasonic frequency on the inactivation of yeast

2P4-11 Effect of ultrasonic frequency on the inactivation of yeast

Influence of a plasma jet on the viability of Candida albicans

Abstract A rapid growth of interest in low temperature plasma in medicine in recent years has given a rise to a number of different applications. We report a low cost kHz driven argon plasma jet with flow rate less than 0.15 L min-1 suitable for treatment of small areas infected with the wide-spread yeast pathogen Candida albicans. The plasma jet has been applied for inactivation of C. albicans seeded on an agar surface as well as yeast suspensions. The effects of different treatment parameters (gas composition, distance and treatment time) have been studied on the efficiency of yeast inactivation. C. albicans viability was evaluated by XTT assay and by measuring diameters of circular transparent zones.

Pulsed Electric Field continuous pasteurization of different types of beers

Thermal pasteurization of bottled beer is used to extend its shelf life. However, the thermal process negatively affects the beer sensory. In this research, beer was processed using Pulsed Electric Fields (PEF), a non-thermal continuous preservation technology that has the potential to be implemented at a commercial scale by the brewing industry. The main goal of this work was to investigate the feasibility of PEF for yeast inactivation and its impact on beer sensory. First, the effect of a PEF process (temperature below 43 °C, 45 kV/cm electrical field intensity, 46 pulses, 70 μs) on Saccharomyces cerevisiae ascospores inactivation in nine different beers comprising ale, lager, dark, low alcohol, and no alcohol, was investigated. Log reductions of 0.2 and 2.2 were registered for 0 and 7% alc/vol beers, respectively, which indicated that the alcohol content is the major beer constituent driving the microbial inactivation. Then, 0, 4, and 7% alc/vol beers containing S. cerevisiae ascospores were submitted to PEF combined with thermal processing up to 53 °C. An increase in the PEF treatment temperature from 43 to 53 °C caused at least an additional 0.7, 2.1 and 1.8 log reductions in the yeast spore population for 0, 4, and 7% alc/vol beers, respectively. Results of another experiment carried out with 4 and 7% alc/vol beers, showed the huge advantage of using PEF compared with thermal processing. Additionally, lightstruck attribute sensory tests revealed six (aroma) and three (flavour) PEF beers did not develop the lightstruck character, being acceptable in terms of sensory. The results of this study can be helpful for designing appropriate PEF conditions to pasteurize beers with different alcohol contents.

Multi-pulsed high hydrostatic pressure inactivation of microorganisms: A review

Multi-pulsed high hydrostatic pressure (mpHHP) treatment, which has been applied for two decades, is broadly more effective than the classical or single-pulsed HHP (spHHP) for inactivation of viruses, yeasts, bacterial cells, and fungal and bacterial spores. The effectiveness of the mpHHP treatment could be increased with a smart choice of pressure, initial and target temperature, pulse number, pulse holding time, and compression and decompression rates. The effectiveness of the mpHHP treatment is well documented and at the moment it seems that it is not feasible to apply the mpHHP treatment commercially for the food industry. However, with the availability of new technologies it may be possible to speed up the HHP processing by decreasing compression and decompression rates and to produce repeated pulses of high pressure. The mpHHP treatment could be very beneficial to the food industry and could replace the pressure-assisted thermal sterilization (PATS) with lower pressure and temperature values. Most of the studies have shown that the mpHHP treatment could be used to inactivate the microrganisms in foods at lower pressure values than the spHHP treatment for the same amount of holding time but for a longer processing time (including the compression and decompression periods of the pulses). The mpHHP treatment has a potential to sterilize the food products with the help of developing technology if the optimization between pressure, temperature, number of pulses, pulse holding time and compression and decompression rates could be possible. • This contribution compiles the studies about the mpHHP inactivation of microorganisms. • The mpHHP treatment inactivates the viruses, yeasts, bacteria and spores effectively. • Pulse number, pulse holding time, and compression and decompression rates are important factors during the mpHHP treatment.

Synergistic impact of sonication and high hydrostatic pressure on microbial and enzymatic inactivation of apple juice

The combination of innovative, non-thermal technologies for the production of safe and quality fruit juices is a recent trend in food processing. The purpose of this study was to evaluate the effects of combined treatment of ultrasound (US) and high hydrostatic pressure (HHP) on enzymes (polyphenolase, peroxidase and pectinmethylesterase), microorganisms (total plate counts, yeasts and molds) and phenolic compounds (total phenols, flavonoids and flavonols) of apple juice. Moreover, its effects on ascorbic acid, antioxidant capacity and DPPH free radical scavenging activity, color values, pH, soluble solids and titratable acidity were investigated. Fresh apple juice was treated with US (25 kHz and 70% amplitude) at 20 °C for 60 min with subsequent HHP treatment at 250, 350 and 450 MPa for 10 min at room temperature. The results revealed that the combined US-HHP450 treatment caused highest inactivation of enzymes with complete inactivation of total plate counts, yeasts and molds. It also significantly improved the phenolic compounds, ascorbic acid, antioxidant capacity, DPPH free radical scavenging activity and color values. The present results suggest that the combination of US and HHP can act as a potential hurdle to produce safe and high quality apple juice with reduced enzymes and microbial activity and improved nutrition.

Inactivation of bacteria and yeast using high-frequency ultrasound treatment

High-frequency (850 kHz) ultrasound was used to inactivate bacteria and yeast at different growth phases under controlled temperature conditions. Three species of bacteria, Enterobacter aerogenes, Bacillus subtilis and Staphylococcus epidermidis as well as a yeast, Aureobasidium pullulans were considered. The study shows that high-frequency ultrasound is highly efficient in inactivating the bacteria in both their exponential and stationary growth phases, and inactivation rates of more than 99% were achieved. TEM observation suggests that the mechanism of bacteria inactivation is mainly due to acoustic cavitation generated free radicals and H2O2. The rod-shaped bacterium B. subtilis was also found to be sensitive to the mechanical effects of acoustic cavitation. The study showed that the inactivation process continued even after ultrasonic processing cessed due to the presence of H2O2, generated during acoustic cavitation. Compared to bacteria, the yeast A. pullulans was found to be more resistant to high-frequency ultrasound treatment.

Thermal inactivation of polyphenoloxidase and peroxidase in Jubileu clingstone peach and yeast isolated from its spoiled puree

The thermal inactivation of yeast isolated from spoiled Jubileu peach puree and that of polyphenoloxidase (PPO) and peroxidase (POD) in cv. Jubileu, which is widely cultivated in southern Rio Grande do Sul state, Brazil, were studied. PPO and POD were extracted using the protein powder method and submitted to partial purification by precipitation followed by dialysis. The enzymatic activity was determined measuring the increase in absorbance at 420 nm for PPO and 470 nm for POD. The yeast used in this investigation was isolated from spoiled Jubileu peach puree at 22 °Brix, with total initial microbial count of 22 × 10² UFCmL- 1. Stock cultures were maintained on potato dextrose agar (PDA) slants at 4 °C and pH 5 for later use for microbial growth. In all cases, kinetic analysis of the results suggests that the thermal inactivation was well described by a first-order kinetic model, and the temperature dependence was significantly represented by the Arrhenius law. Both enzymes were affected by heat denaturation, and PPO was more thermostable. PPO was also more thermosTable than the yeast isolated from peach puree. The D60-values were 1.53 and 1.87 min for PPO and yeast isolated from spoiled Jubileu peach puree, respectively.

Effects of thermal treatments on the stability of trans-resveratrol and yeast inactivation in trans-resveratrol-amplified grape juice

For the production of trans-resveratrol-amplified grape juice, both trans-resveratrol quantity and microbial quality are important for the functionality and shelf life of the juice. Therefore, the thermal stability of trans-resveratrol and thermal inactivation of Saccharomyces cerevisiae within the grape juice was investigated at 60?C, 80?C and 100?C. Inactivation of S. cerevisiae was fitted to first-order kinetics, and the inactivation rate (k1) and decimal reduction time (D-value) at each treatment temperature were estimated. The control grape juice had an inactivation rate of 0.0014 (s-1) and a D-value of 11.90 min at 60?C, whereas the trans-resveratrol-amplified grape juice had an inactivation rate of 0.0016 (s-1) and a Dvalue of 10.42 min at the same temperature. Similar inactivation kinetics of the control and trans-resveratrol-amplified grape juice were observed at 80?C and 100?C, which indicates that increased trans-resveratrol content does not affect the thermal inactivation of inoculated S. cerevisiae.

High-pressure homogenization: a non-thermal process applied for inactivation of spoilage microorganisms in beer

The inactivation of spoilage microorganisms in beer using high-pressure homogenization (HPH) was studied with the aim of evaluating the possibility of changing the conventional pasteurization process using this particular process. The homogenization pressure required for the inactivation of lactic acid bacteria, acetic bacteria and yeasts was investigated. For the most resistant microorganisms, the pressure inactivation kinetics and the effects of multiple process passes, initial temperature of the beer and the CO2 concentration were studied. The results indicated that Lactobacillus delbrueckii was the most resistant microorganism tested, requiring 250 MPa to reach a six decimal reduction. Additionally, results showed that L. delbrueckii inactivation followed a second-order kinetic process. A multi-pass process and the use of a high initial beer temperature increased inactivation by HPH with L. delbrueckii, allowing the use of 150 MPa to achieve a five log cycle of inactivation. In contrast, a high CO2 concentration reduced the efficacy of the HPH process. The results that were obtained are useful for high-pressure homogenization applications in breweries and help to elucidate the effect of this new technology in a beverage that is both alcoholic and carbonated. Copyright © 2013 The Institute of Brewing & Distilling

Inactivation of microorganisms naturally present in raw bovine milk by high‐pressure carbon dioxide

SummaryThis study assessed the inactivation of microorganisms naturally present in raw bovine milk by high‐pressure carbon dioxide (HPCD) at 10–30 MPa and 20–50 °C for 20–70 min. The log reduction of microorganisms increased as raw bovine milk was exposed to higher pressures and temperatures and longer treatment times. The maximum reduction of aerobic bacteria (AB) was 4.96‐log at 25 MPa and 50 °C for 70 min. At lower temperatures and treatment times, a complete inactivation of yeasts and moulds (Y&M) and coliform bacteria (CB) was obtained at 25 MPa. Changes in microorganisms naturally present in raw bovine milk during storage were also assessed. There were 1.83‐log survival of AB, 0.65‐log survival of Y&M and a complete inactivation of CB in raw bovine milk when subjected to HPCD at 25 MPa and 40 °C for 50 min. Moreover, the AB, Y&M and the CB in raw bovine milk exhibited insignificant alterations during storage at 4 °C for 15 days, indicating a potential capability of HPCD to extend the shelf life of milk.

Optimization of cellular uptake of zinc(II) 2,9,16,23-tetrakis[4-(N-methylpyridyloxy)]phthalocyanine for maximal photoinactivation of Candida albicans

Cellular uptake and photodynamic action of zinc(II) 2,9,16,23-tetrakis[4-(N-methylpyridyloxy)]phthalocyanine (ZnPPc4+) was examined in Candida albicans. In vitro investigations showed that ZnPPc4+ was rapidly bound to C. albicans cells. The binding of phthalocyanine to cells was dependent on ZnPPc4+ concentrations (1–10 μM) and cells densities (106–108 cells mL−1). A high amount of ZnPPc4+ retained in the cells after two washing steps, indicating a strong interaction between the photosensitizer and C. albicans. The uptake was temperature dependent, although the difference between 37 °C and 4 °C was about 10 %. Also, the amount of ZnPPc4+ bound to C. albicans was affected when the cells were incubated for a longer time with azide and 2,4-dinitrophenol (DNP) prior to treatment with ZnPPc4+. Cell survival after irradiation was dependent on the irradiation period, ZnPPc4+ concentration and cells density. Photoinactivation of C. albicans cells was elevated even after two washing steps. The strong dependence of uptake on cell density reveals the strength and avidity of the binding of ZnPPc4+ to C. albicans cells. The accumulation behaviour of ZnPPc4+ suggests that mainly an affinity-mediated binding mechanism can be involved. Therefore, ZnPPc4+ is an interesting phthalocyanine for photodynamic inactivation (PDI) of yeasts in liquid suspensions.

Modeling of yeast inactivation of PEF-treated Chinese rice wine: Effects of electric field intensity, treatment time and initial temperature

The application of pulsed electric field (PEF) technology as an alternative method of spoilage microbiological control for Chinese rice wine was investigated. PEF was applied at the initial temperature of 25–35°C, the electric field strength of 12–21kV/cm, with respective treatment time of 30–180μs to evaluate the efficiency of this technology on the inactivation of spoilage yeast Saccharomyces cerevisiae commonly associated with rice wine. The results from atomic force microscope imaging of yeast cells indicated that PEF treatment induced the destruction of cell membrane structures, which supported by the decrease of yeast number, the blurring of images, and the flattened yeast border. The highest inactivation values, corresponding to approximately 5.5-log cycles, were obtained at 21kV/cm and 180μs with the initial treatment temperatures of 30 and 35°C, respectively. Based on calculations by both log-linear and Weibull models, the decimal reduction times (5-D values) over the range of treatment conditions were 336.53–1804.1μs and 150.17–1127.6μs, respectively. Then the 5-D values were fitted as a function of electric field strength and initial treatment temperature, with R2 of 0.986 and 0.963 for log-linear and Weibull model, respectively. The model validation results showed that the 5-D values calculated from Weibull model (Af=1.169 and Bf=0.996) provided more accuracy than those from log-linear model (Af=1.773 and Bf=1.773), suggesting that the Weibull model was more suitable for calculating the survival ratio of PEF-treated spoilage microorganisms in Chinese rice wine. Finally, the effects of PEF treatment on physicochemical properties (including °Brix, pH, conductivity and color) of rice wine exactly after treatment and during storage at room temperature (22°C) were also investigated. The results indicated that PEF was able to inactivate (to some degree) the yeast in rice wine with minor variations in the physicochemical parameters and affect the quality indices of rice wine positively.

Photodynamic Inactivation of Yeast and Bacteria by Extracts of Alternanthera brasiliana

This study was undertaken to evaluate the effect of Alternathera brasiliana (Amaranthaceae) extracts as photosensitizing agents in photodynamic antimicrobial therapies (PACT) against Staphylococcus aureus, Staphylococcus epidermidis and Candida dubliniensis. The crude hexane and ethanol extracts were obtained from A. brasiliana whole plant and showed absortion from 650 to 700 nm. Also, singlet molecular oxygen (1O2) production (type II photosensitization reaction) was examined, and the results show that 1,3-diphenylisobenzofuran photodegradation was greatly enhanced in the presence of the A. brasiliana extracts. One plate in each assay was irradiated while the other was not irradiated, the number of colony-forming units per milliliter (CFU/mL) was obtained, and data analyzed by the Tukey test. The chemical composition of the extracts was determined by chromatographic and spectrometric techniques; steroids, triterpenes, and flavonoids were identified. Laser irradiation alone at 685 nm using diode laser, output power of 35 mW, and energy of 28 J/cm2, or non-irradiated crude extracts in sub-inhibitory concentration did not reduce the number of CFU/mL significantly, whereas irradiated hexane and ethanol extracts, in sub-inhibitory concentrations, inhibited the growth of these microorganisms. The photoactivation of hexane and ethanol extracts of A. brasiliana, in sub-inhibitory concentrations, using red laser radiation at 685 nm had an antimicrobial effect.

회분식 고전압 Exponential Decay Pulse 전기장 처리에 의한 막걸리의 비열 살균

Makgeolli, a traditional Korean turbid rice wine, was treated with pulsed electric fields (PEF) for the purpose of a development of a new cold pasteurization processes. Inactivation of yeast in the makgeolli increased with increase in intensity of the electric field strength and treatment time. The initial yeast count of the makgeolli was 2×108 cfu/ ml. A reduction of 2D was obtained at 30 kV/cm and 256 exponential decay pulses at room temperature. The combination of PEF and conventional thermal treatment inactivated the yeast more effectively. Reductions of up to 8D were observed when the makgeolli was treated with PEF of 20 kV/cm and 256 pulses at 50°C. The inactivation of the yeast in makgeolli increased with an increase in alcohol content. When the alcohol content of the makgeolli increased to 12%, PEF treatment with 30 kV/cm and 256 pulses resulted in a 4.8D reduction of yeast. No changes in pH, acidity, or the growth of yeast were observed in the PEF treated makgeolli during storage at 4°C for 4 weeks.

회분식 고강도 광원 처리에 의한 막걸리 효모의 살균

Intense pulsed light (IPL) treatment is one of the emerging non-thermal techniques being investigated as an alternative to conventional thermal treatment because it has been proven to be effective for microbial inactivation in air, water, and foods. The aim of this study was to evaluate the possibility of using IPL treatment for the effective inactivation of isolated yeast in makgeolli. The key parameters of intense pulsed light are light intensity (input voltage), treatment time, frequency of pulse, and depth of sample. The results show that there is a significant reduction of population along with an increase of light intensity and IPL treatment duration. The highest level of inactivation achieved in this study was approximately a 7 log CFU/mL reduction. In addition, the inactivation rates of yeast cells decrease with increasing initial cell population and depth of samples. But pulse frequency did not affect the inactivation of yeast. Temperature was not changed during IPL treatment.

An Optimization Study on the Ultrasonic Treatments for Saccharomyces cerevisiae Inactivation in Red Grape Juice with Maintaining Critical Quality Attributes

AbstractThis study was conducted to decrease Saccharomyces cerevisiae cell count and to maximize levels of quality characteristics in red grape juice during ultrasound process using response surface methodology (RSM). The effects of three process parameters (considered as independent variables), namely temperature (25–50C), time (20–40 min) and frequency (0–135 Hz), on the yeast inactivation, total anthocyanin content (TAC), total color difference (TCD), antioxidant activity (AA), polymeric color content (PCC), pH, total titratable acidity (TTA) and total soluble solids (TSS) (considered as dependent variables) were studied based on RSM. The optimum operating conditions for the maximum yeast inactivation and the optimal juice quality characteristics were found to be frequency of 135.0 kHz, temperature of 30.9C and time of 40.0 min. In these conditions, the yeast inactivation, TAC, PCC, AA, TCD, pH, TTA and TSS were 1 cfu/mL, 808.0 mg/g, 67.85%, 0.94 mmol/L, 1.64, 3.47, 977.4 mg citric acid/100 mL and 20.04, respectively.Practical ApplicationsIn recent years, emerging nonthermal methods, such as ultrasound (US), for inactivating microorganisms have been developed in food industries to manufacture natural products. Red grape juice, due to the presence of anthocyanins and flavonoids, has many health‐promoting effects. As the nutritive and organoleptic characteristics of grapes decrease during storage and ripening periods because of their high susceptibility to pathogenic infection and physiological deterioration, the use of US method as a potential technology can inactive foodborne spoilage or pathogenic microorganisms and produce juices with organoleptic and nutritional qualities. Moreover, the optimization of US conditions enabled us to shorten the process duration and to reduce the production costs while maintaining the quality at a relatively high level.

Occurrence and low pressure ultraviolet inactivation of yeasts in real water sources

Low pressure ultraviolet photolysis proved to be an efficient treatment to achieve inactivation of different yeast species (Candida sp., Cryptococcus carnescens, Metschnikowia viticola/Candida kofuensis, Rhodosporidium babjevae, Rhodotorula minuta, and Rhodotorula mucilaginosa) isolated from water sources with very different compositions. The sensitivity degree of various yeast isolates to UV treatment varied among different genera. Species isolated from surface water gained additional photoprotective resistance as a defence mechanism to be able to survive under constant sunlight conditions compared to the groundwater isolates. Yeasts were found to be more resistant to UV treatment than E. coli, Cryptosporidium, and Giardia.

Assessment of fungal viability after long-wave ultraviolet light irradiation combined with riboflavin administration

Corneal collagen cross-linking (CXL), a technique that combines riboflavin administration with long-wave ultraviolet light irradiation, was primarily developed to increase the biomechanical strength of collagen fibrils of the cornea to avoid the progression of keratoconus. Recently, this method has been proposed to treat selected cases of infectious keratitis. To test the protocol used for progressive keratoconus in infectious keratitis, Candida albicans, and Fusarium solani, strains were exposed to irradiation using a wavelength of 365 nm at a power density of 3 mW/cm(2) for 30 min in the presence of riboflavin photosensitizer. All experiments were performed in triplicate. Qualitative and quantitative measurements of fungal viability used plate cultures and an automated trypan blue dye exclusion method respectively. Fungal cell diameter was also assessed in all groups. Statistical analyses were performed using the triplicate values of each experimental condition. Experimental findings of photodynamic therapy applied to the cell inactivation of both yeasts and filamentous fungi were compared with control groups. Qualitative results were corroborated with quantitative findings which showed no statistical significance between challenged samples (experimental groups) and the control group (p-value = 1). In comparison with a control group of live cells, statistical significance was observed when riboflavin solution alone had an effect on the morphologic size of filamentous fungi, while ultraviolet light irradiation alone showed a slight decrease in the cell structure of C. albicans. The impact of long-wave ultraviolet combined with riboflavin photosensitizer showed no antifungal effect on C. albicans and F. solani. The significant decrease in cell morphology of both filamentous fungi and yeasts submitted to photosensitizing riboflavin and exposure to ultraviolet light, respectively, may be promising in the development and standardization of alternatives for fungal cell inactivation, because of their minimal cytotoxic effects on the corneal surface. The methodological improvement in the preparation and application of individual chemical compounds, such as riboflavin, or physical systems, such as a long-wave light source, as antifungal agents may also assist in establishing promising therapeutic procedures for keratomycosis.

Hsp70 targets Hsp100 chaperones to substrates for protein disaggregation and prion fragmentation

Hsp100 and Hsp70 chaperones in bacteria, yeast, and plants cooperate to reactivate aggregated proteins. Disaggregation relies on Hsp70 function and on ATP-dependent threading of aggregated polypeptides through the pore of the Hsp100 AAA(+) hexamer. In yeast, both chaperones also promote propagation of prions by fibril fragmentation, but their functional interplay is controversial. Here, we demonstrate that Hsp70 chaperones were essential for species-specific targeting of their Hsp100 partner chaperones ClpB and Hsp104, respectively, to heat-induced protein aggregates in vivo. Hsp70 inactivation in yeast also abrogated Hsp104 targeting to almost all prions tested and reduced fibril mobility, which indicates that fibril fragmentation by Hsp104 requires Hsp70. The Sup35 prion was unique in allowing Hsp70-independent association of Hsp104 via its N-terminal domain, which, however, was nonproductive. Hsp104 overproduction even outcompeted Hsp70 for Sup35 prion binding, which explains why this condition prevented Sup35 fragmentation and caused prion curing. Our findings indicate a conserved mechanism of Hsp70-Hsp100 cooperation at the surface of protein aggregates and prion fibrils.