THE EFFECT OF OSMOTIC PRESSURE ON THE INTRACELLULAR ACCUMULATION OF ETHANOL IN SACCHAROMYCES CEREVISIAE DURING FERMENTATION IN WORT

An intracellular accumulation of ethanol was observed in Saccharomyces cerevisiae during the early stages of fermentation (3 h) in wort. However, after 12 h fermentation, the intracellular and extracellular ethanol concentrations were similar. Increasing the osmotic pressure in wort by adjusting the carbohydrate concentration, from 10° to 20° plato, was observed to cause an increase in intracellular ethanol concentration and glycerol production. Although intracellular ethanol concentration increased, no adverse effect was observed on cell growth and fermentation rates. Thus, increasing the carbohydrate concentration in wort to at least 20° plato did not affect cell growth and fermentation rates, but did result in the production of more ethanol.     

High-cell-density fermentation for ergosterol production by Saccharomyces cerevisiae

The direct feedback control of glucose using an on-line ethanol concentration monitor for ergosterol production by high-cell-density fermentation was investigated and the fermentation parameters (e.g., pH, dissolved oxygen, ethanol concentration, oxygen uptake rate, carbon dioxide evolution rate and respiratory quotient) were analyzed. Controlling glucose feeding rate in accordance with ethanol concentration and adjusting pH with ammonia during the fermentation process were effective fed-batch methods for ergosterol production. The fermentation parameters well described the variation of the whole fermentation process. Cultivation in a 5 l fermentor was carried out under the following conditions: culture temperature, 30 degrees C; pH, 5.5; agitation speed, 600 rpm; fermentation time, 60 h; controlling ethanol concentration below 1% and keeping respiratory quotient (RQ) at approximately 1.0. Under these conditions, the yeast dry weight reached 120 g/l and the ergosterol yield reached 1500 mg/l.     

Indirect methods for characterization of carbon dioxide levels in fermentation broth

Various factors which influence dissolved carbon dioxide levels were indirectly evaluated in pilot scale and laboratory studies. For pilot scale studies, off-gas carbon dioxide (percentage in exit air) was measured using a mass spectrometer and then its potential impact on dissolved carbon dioxide concentrations qualitatively examined. Greater volumetric air flowrates reduced off-gas carbon dioxide levels more effectively at lower airflow ranges and thus lowered expected dissolved carbon dioxide levels through gas stripping. Lower broth pH values decreased off-gas carbon dioxide levels but increased expected dissolved carbon dioxide levels due to the pH-dependence of the gas/liquid carbon dioxide equilibrium. While back-pressure increases had an insignificant effect on off-gas carbon dioxide levels, they directly affected expected dissolved carbon dioxide levels according to Henry's law. Laboratory studies, conducted using both uninoculated and inoculated fermentation media, quantified the response of the media to pH changes with bicarbonate addition, specifically its buffering capacity. This effect then was related qualitatively to expected dissolved carbon dioxide levels. Higher dissolved carbon dioxide levels, as demonstrated by reduced pH changes with bicarbonate addition, thus would be expected for salt solutions of increased ionic strength and higher protein content media. In addition, pH changes with greater bicarbonate additions declined for fermentation samples taken over the course of a one week cultivation, most likely due to the higher protein content associated with biomass growth. The presence of weak acids/bases initially in the media or formed as metabolic by products, as well as the concentration of buffering ions such as phosphate, also were believed to be important contributing elements to the buffering capacity of the solution.     

THE RESPONSE OF SACCHAROMYCES CEREVISIAE TO FERMENTATION UNDER CARBON DIOXIDE PRESSURE

When laboratory fermenters containing 4 litres of wort were maintained under a variety of conditions at an excess pressure of 2 atm of carbon dioxide throughout fermentation by Saccharomyces cerevisiae (NCYC 1108), the fermentation rate, yeast growth and final concentration of fusel oils all decreased and the final pH increased. This agrees with reported work on the effect of carbon dioxide pressure on fermentation by S. carlsbergensis. The effect of carbon dioxide pressure on the production and removal of vicinal diketones and their precursors by S. carlsbergensis is known to be variable but except at very low temperatures, pressure has either no effect or increases the rate of removal of these compounds in the final stages of fermentation. In the present experiments with a strain of C. cerevisiae, however, carbon dioxide pressure always led to the fresh beer having a higher lever of vicinal diketones and their precursors than the control fermentation, even at temperatures up to 20°C.     

Ethanol production from carob pods by Saccharomyces cerevisiae

The production of ethanol from carob pods extract by Saccharomyces cerevisiae in static and shake flask fermentation was investigated. Shake flask fermentation proved to be a better fermentation system for the production of ethanol than static fermentation. The external addition of nutrients into the carob pods extract did not improve the production of ethanol. The maximum concentration of ethanol (75 g/l) was obtained at an inoculum amount of 0.3%, a pH of 4.5, 30°C and an initial sugar concentration of 200 g/1. Under the same fermentation conditions both sterilized and non‐sterilized carob pods extract gave the same final ethanol concentration.     

基于统计分析的发酵溶解氧与二氧化碳关系的研究

由理论分析及经验得到溶解氧与尾气二氧化碳模型,通过布拉酵母菌发酵得到实测溶解氧及尾气二氧化碳检测数据,依据经验模型计算出近似溶解氧值。应用统计分析软件SPSS得到实测溶解氧与二氧化碳及计算溶解氧的Pearson相关系数分别为-0.632和0.862,说明溶解氧与尾气二氧化碳之间存在负相关关系,而经验模型计算的溶解氧值与实际溶解氧之间具有较强的相关性。进一步采用曲线拟合对计算溶解氧值进行修正,使其更接近实际溶解氧。     

Polyethylene Film Packaging of Citrus Fruit: Containment of Decaying Fruit

Decaying grapefruit (Citrus paradisi Macf.) stored under nonventilated conditions caused a substantial reduction in the oxygen and an increase in the carbon dioxide concentrations in the atmosphere. A comparable increase in the internal carbon dioxide concentration of sound fruit in the same container was also observed. Low oxygen caused an increase in the ethanol concentration in the juice of the sound fruit and the development of an undesirable stale flavor. Containment of the decaying fruit in polyethylene film limited the oxygen depletion. Thus, flavor quality of sound fruit from the containers with PE film-sealed decaying fruit was comparable to that of sound fruit stored in the absence of decaying fruit.     

Variations of internal pH in typical Italian sourdough yeasts during co-fermentation with lactobacilli

The effects of organic acids (lactic and acetic) and extracellular pH (pHex) on the intracellular pH (pHi) of Saccharomyces cerevisiae and Candida milleri during co-fermentation with lactobacilli were investigated by using Fluorescence-Ratio-Imaging-Microscopy (FRIM). Yeasts were grown in a system that partially mimics sourdough composition, using individual fermentation and combinations with lactic acid bacteria. Fermentations were carried out at 25 °C for 22 h at an initial pH of 5.3. The two yeast species grew equally well during the co-fermentations with lactobacilli. Our results reveal large differences in pHi values between the two yeast species, primarily in relation with pHex changes, while the concentration of organic acids did not seem to affect the pHi. Moreover, the pHi of S. cerevisiae seemed to be affected by maltose consumption. The pH gradient (difference between internal and external pH) of S. cerevisiae remained rather constant, ranging from 2.0 to 2.5. C. milleri instead exhibited a higher pHi, that remained constant throughout the experiments and was unaffected by pHex and/or sugar consumption. Thus, the pH gradient of C. milleri varied much more than that of S. cerevisiae, ranging from 2.3 to 3.8. Our results suggest that the two yeast species have different pHi regulation mechanisms.     

Design and characterisation of jet cold atmospheric pressure plasma and its effect on Escherichia coli,colour, pH,and bioactive compounds of sour cherry juice

A new system for cold atmospheric pressure plasma (CAPP) generation was designed and characterised. The effects of voltage (10, 15, 20 kV), frequency (10, 15, 20 kHz), gas flow rate (3, 5, 7 L min⁻¹) and percentage of oxygen (0%, 0.5%, 1%) on the plasma jet length (PJL) were investigated. Then, different volumes (5, 10, 15 mL) of sour cherry juice were treated by CAPP to compare their physicochemical properties (colour and pH), Escherichia coli count, and bioactive compounds with samples treated by the conventional process. According to the results, PJL was increased by increasing the voltage and frequency and then remained constant. Also, PJL increases and then decreases by increasing the gas flow rate. Furthermore, CAPP treatment reduced E. coli count but did not alter the colour and pH of samples. Moreover, increasing the voltage, plasma treatment duration, and oxygen percentage enhanced the inactivation of E. coli. The best sterilisation effect was 6-log cycle decrease in E. coli count which was achieved at a voltage of 19.6 kV, an oxygen concentration of 1%, and a gas flow rate of 4.5 L min⁻¹. Besides, the total phenol content of juice was 277 GAE/100 g and was changed to 279 and 359 after plasma treatment and conventional process, respectively.     

Regulation of carbon metabolism in chemostat cultures of Saccharomyces cerevisiae grown on mixtures of glucose and ethanol

Growth efficiency and regulation of key enzyme activities were studied in carbon- and energy-limited chemostat cultures of Saccharomyces cerevisiae grown on mixtures of glucose and ethanol at a fixed dilution rate. Biomass yields on substrate carbon and oxygen could be adequately described as the net result of growth on the single substrates. Activities of isocitrate lyase and malate synthase were not detected in cell-free extracts of glucose-limited cultures. However, both enzymes were present when the ethanol fraction in the reservoir medium exceeded the theoretical minimum above which the glyoxylate cycle is required for anabolic reactions. Fructose-1,6-bisphosphatase activity was only detectable at high ethanol fractions in the feed, when activity of this enzyme was required for synthesis of hexose phosphates. Phospho-enol-pyruvate-carboxykinase activity was not detectable in extracts from glucose-grown cultures and increased with the ethanol fraction in the feed. It is concluded that, during carbon-limited growth of S. cerevisiae on mixtures of glucose and ethanol, biosynthetic intermediates with three or more carbon atoms are preferentially synthesized from glucose. Synthesis of the key enzymes of gluconeogenesis and the glyoxylate cycle is adapted to the cells′ requirement for these intermediates. The gluconeogenic enzymes and their physiological antagonists (pyruvate kinase, pyruvate carboxylase and phosphofructokinase) were expressed simultaneously at high ethanol fractions in the feed. If futile cycling is prevented under these conditions, this is not primarily achieved by tight control of enzyme synthesis.     

气调库中二氧化碳和氧气浓度的自动控制系统

在气调库中,二氧化碳和氧气浓度的控制是十分重要的,不同的果蔬对各种气体的浓度有不同的要求,二氧化碳和氧气浓度过高或过低都将直接影响储藏质量。手动控制难以及时准确地调整二氧化碳和氧气浓度。因此,自动控制二氧化碳和氧气浓度有着重要的意义。经长期研究与试验,我们开发出二氧化碳和氧气浓度的自动控制系统。     

Effect of Oxygen, Carbon Dioxide, and Nitrogen on Maple Syrup Stored in Plastic Jugs

Six maple syrups were stored in the dark for 6 months in pigmented and unpigmented high-density polyethylene jugs at room temperature (72°F) in three gas environments-nitrogen, oxygen, and carbon dioxide. The syrup was analyzed for changes in flavor, color, and pH. A taste panel, tasting syrup from pigmented jugs only, detected flavor change in both the oxygen and carbon dioxide environments. There were statistically significant interactions for changes in both color and pH between gas and syrup treatments. The greatest darkening of color and decrease in pH were associated with the carbon dioxide. Jug pigmentation had no detectable effect on the syrup.     

Ethanol production from carob pod extract by immobilized saccharomyces cerevisiae cells on the mineral kissiris

The production of ethanol from carob pod extract by immobilized S. cerevisiae cells on the mineral kissiris was investigated. The optimum conditions for carob pod extract fermentations were pH 3.5 ‐ 6.5, temperature 30°C and initial sugar concentration of 250g/l. A maximum ethanol concentration (64.5g/l), ethanol yield (28.3%) and sugar utilization (94%) was achieved at an initial sugar concentration of 250, 200 and 250g/l, respectively. In repeated batch fermentations, the immobilized S. cerevisiae cells on kissiris retained their ability to produce ethanol for 30 days.     

Use of Laser‐Etched Pouches to Control the Volume Expansion of Kimchi Packages During Distribution: Impact of Packaging and Storage on Quality Characteristics

Use of laser‐etched pouches was investigated to develop kimchi packages with gas control functions. According to the degree of laser processing, the headspace pressure, atmospheric composition, and water vapor transmission rate of the kimchi packages were measured to investigate the potential use of laser‐etched packages for kimchi. In addition, the pH, titratable acidity, organic acid, and microbial population of the packaged kimchi were examined to study the effect of packaging and storage conditions on its quality characteristics. The concentration of carbon dioxide in the pouches with a high gas transmission rate was less than that in other pouches (P < 0.05), indicating that low a carbon dioxide concentration resulted in less volume expansion. During the storage period (P < 0.05), the gas pressure in some pouches started to increase after the 15th d at 10 °C. Few differences were observed between the quality characteristics of kimchi (for example, pH, titratable acidity, organic acid, and microbial count). In addition, this study indicated that the higher the storage temperature, the more rapid the fermentation. Consequently, laser‐etched pouches demonstrate the potential for controlling the gas, which in turn maintains the quality of kimchi. The use of laser‐etched films could exert marked effects on alleviating the volume expansion or pressure build‐up in kimchi packages.     

Whey Protein Coatings for Fresh Fruits and Relative Humidity Effects

ABSTRACT: Whey protein isolate (WPI) films have proven to be excellent gas barriers in previous studies, making them potential coatings for fresh produce. WPI‐coated apples and controls were stored at 20 °;C under RH's ranging from 54 to 92%. Results showed performance of WPI coatings depended on the environment RH. The internal oxygen was lowered, and carbon dioxide increased with decreasing RH conditions. RH did not affect control fruits. At low RH (about 70 to 80% RH), anaerobic respiration was induced in coated fruits due to low oxygen levels (about 0.025 atm). Controlling thickness and film permeability will allow attainment of the appropriate oxygen and carbon dioxide levels for coated fruit.     

Modeling of Active Modified Atmosphere Packaging of Endives Exposed to Several Postharvest Temperatures

Endives were sealed in low‐density polyethylene flexible pouches containing or not containing individual oxygen or carbon dioxide scavenger sachet and stored at 5 °C and 20 °C. A mathematical model has been applied to predict gas changes for these passive and active modified atmosphere packaging (MAP). The model took into account the respiration rate of endives, the transmission rate of gases through the film, the absorption kinetics of gas scavengers, and the temperature influence of all these parameters. Whatever the temperature, the model was successfully validated with root mean square error values still lower than 1 kPa and thus represented a real tool to improve the design of MAP for fresh fruits and vegetables. Oxygen scavengers reduced by half the transient period duration (50 h compared with 100 h without scavengers) and did not modify the gas equilibrium composition, suggesting a beneficial influence on keeping the quality of the product. The carbon dioxide scavengers’ influence was limited and needs further study with carbon dioxide‐sensitive products.     

Formulations and processing of yogurt affect the microbial quality of carbonated yogurt

Carbonation, flavor, culture type, pH, and storage time were varied to investigate the effects of these variables and their interactions on the growth of both typical and nontypical yogurt cultures and some contaminating bacteria. Two types of yogurt cultures (YC-470 and YC-180) were used as the source of typical yogurt bacteria, Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus. In addition, Lactobacillus acidophilus (LA-K) and Bifidobacterium longum ATCC 15707 were added as nontypical yogurt cultures to make sweetened low fat (1%) Swiss-style plain, strawberry, and lemon yogurts. Samples were incubated at 43 degrees C until pH values of 5.0 or 4.2 were reached. Strawberry yogurts at low (4.2) and high (5.0) pHs were divided into three portions, which were separately inoculated with contaminating bacteria, Bacillus licheniformis ATCC 14580, Escherichia coli ATCC 11775, and Listeria monocytogenes Scott A. After incorporation of carbon dioxide (1.10 to 1.27 volume of CO2 gas dissolved in water), the yogurt was stored at 4 degrees C for a 90-d period. Carbon dioxide did not affect the growth of typical or nontypical yogurt bacteria. Also, CO2 did not inhibit the growth of undesirable microorganisms. In general, low levels of CO2 did not affect the bacterial population in yogurt. The microflora of yogurt were influenced by culture type, pH, flavor type, and storage time or their interactions.     

Killer strains of Saccharomyces: application for apple wine production

The aim of this study was to evaluate possible application of killer strains Saccharomyces paradoxus CBS 3702 (K1), S. cerevisiae CBS 6505 (K2) and S. capensis CBS 7903 (K3) for apple wine production. Apple musts were obtained from Jonagold apples. The optimal pH value of killer toxins activity, the temperature of their formation and the spectrum of activity against selected wine spoilage fungal strains were analysed. The influence of yeast strains on the chemical composition, volatile profile and sensory properties of apple wines was determined using high‐performance liquid chromatography and gas chromatography methods. The pH values of 4.2 (K1, K3) and 4.6 (K2), and a temperature of 28 °C, were optimal for the action of toxins. The analysed killer strains inhibited growth of seven of the 11 tested wine spoilage fungal strains. The samples obtained using the S. cerevisiae killer strain were characterized by the highest fermentation rate, highest ethanol concentration and a balanced level of volatiles, but their taste was described as bitter. S. capensis gained the highest scores in the sensory evaluation. It could be used for semi‐sweet or semi‐dry cider production, because of the lower amounts of ethanol formation but higher synthesis of glycerol, volatile esters and higher alcohols. Copyright © 2016 The Institute of Brewing & Distilling     

Physiological requirements for growth and competitiveness of Dekkera bruxellensis under oxygen-limited or anaerobic conditions

The effect of glucose and oxygen limitation on the growth and fermentation performances of Dekkera bruxellensis was investigated in order to understand which factors favour its propagation in ethanol or wine plants. Although D. bruxellensis has been described as a facultative anaerobe, no growth was observed in mineral medium under complete anaerobiosis while growth was retarded under severe oxygen limitation. In a continuous culture with no gas inflow, glucose was not completely consumed, most probably due to oxygen limitation. When an air/nitrogen mixture (O₂‐content ca. 5%) was sparged to the culture, growth became glucose‐limited. In co‐cultivations with Saccharomyces cerevisiae, ethanol yields/g consumed sugar were not affected by the co‐cultures as compared to the pure cultures. However, different population responses were observed in both systems. In oxygen‐limited cultivation, glucose was depleted within 24 h after challenging with S. cerevisiae and both yeast populations were maintained at a stable level. In contrast, the S. cerevisiae population constantly decreased to about 1% of its initial cell number in the sparged glucose‐limited fermentation, whereas the D. bruxellensis population remained constant. To identify the requirements of D. bruxellensis for anaerobic growth, the yeast was cultivated in several nitrogen sources and with the addition of amino acids. Yeast extract and most of the supplied amino acids supported anaerobic growth, which points towards a higher nutrient demand for D. bruxellensis compared to S. cerevisiae in anaerobic conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

Enzymatic Production of Ethanol from Cassava Starch Using Two Strains of Saccharomyces cerevisiae

Cassava starch from TMS 30572 and Idileru were hydrolyzed with α-amylase and amylo-glucosidase before fermentation using two strains of Saccharomyces cerevisiae from palm wine and bakers’ yeast. The per cent yield of sugars and total dissolved solids were 66 % and 26% respectively while pH was 7. Spectrophotometric measurement of the cell growth revealed steady but insignificant (p ≤ 0.05) increase in cell concentrations up to 48 h fermentation time with a gradual decline by 72 h. Saccharomyces cerevisiae strain from palm wine grew best on TMS 30572 hydrolysate at 20% sugar concentration (optical density 0.663; fermentation time 48 h) while on Idileru hydrolysate it grew best at 25% (optical density 0.698; fermentation time 60 h). The pH values obtained from the fermenting hydrolysates for both yeast strains declined gradually as the fermentation progressed with the lowest pH values (3.01 for S. cerevisiae from palm wine; 3.06 for S. cerevisiae from bakers’ yeast) obtained for TMS 30572 cassava variety at 25% sugar concentration. Changes in pH were significant (p ≤ 0.05). The Saccharomyces cerevisiae strain from palm-wine had a higher conversion of available sugar into ethanol. The yield of ethanol was found to vary but the highest ethanol concentration obtained was 5.3% at 10% initial sugar concentration, which gave a sugar conversion efficiency of 37.3%. The results obtained suggest that Saccharomyces cerevisiae strains from sources other than those used conventionally can serve as good substitutes for bio-conversion processes in the industrial production of ethanol.