Carbon dioxide emission from olive oil pastes during the transformation process: technological spin offs

The emission of carbon dioxide (CO₂) from olive paste during malaxation was investigated in a lab experiment using a hermetically sealed malaxation chamber. A rapid increase in the concentration of CO₂ during malaxation was observed, with an average increase of 32 ml/(l min) for the initial 5 min. Then, the emission progressively decreased to a mean rate of 1.1 ml/(l min). This was probably the result of an initial acceleration in respiration followed by the gradual onset of fermentation processes as ambient oxygen was depleted. After malaxation, small amounts of cellular fermentation products (e.g. ethanol and lactic acid) were detected in the wastewater. In order to examine this phenomenon of the inhibition of oxidation due to evolved CO₂, malaxation experiments were conducted in both a sealed and an open-air mixing apparatus. The differences in chlorophyll concentration of the resulting oils were then measured. Large amounts of chlorophyll, about twice as much, were found in the oil produced under sealed conditions. This increase in the concentration of chlorophyll resulted from the limited oxidation of the sample by atmospheric oxygen due to the protection of the evolved CO₂.     

THE EFFECT OF LOW CO2 PRESSURES ON THE ABSORPTION OF AMINO ACIDS AND PRODUCTION OF FLAVOUR-ACTIVE VOLATILES BY YEAST

Laboratory fermentation of 51 batches of wort under CO₂ pressures of 0·5 and 1·0 atm have shown that whilst the speed of fermentation was affected only slightly, absorption of amino acids, production of several flavour-active compounds and some yeast features were affected. The CO₂ pressure led to reduced absorption of Group B amino acids although Group A compounds were unaffected; fusel oil and ester concentration was reduced whereas that of the vicinal diketones and acetaldehyde was increased. Yeast crop and cell viability fell with increase in pressure and at 1·0 atm the mean cell volume was increased. The results suggest that CO₂ could have significant effects on yeast and beer quality within the range of concentration which can be expected to occur in unpressurized commercial fermentations.     

THE SENSITIVITY OF DIFFERENT BREWING YEAST STRAINS TO CARBON DIOXIDE INHIBITION: FERMENTATION AND PRODUCTION OF FLAVOUR-ACTIVE VOLATILE COMPOUNDS

The sensitivity of brewing yeast strains, with different oxygen demands, to carbon dioxide inhibition was investigated. Laboratory fermentations were performed with, and without, protein-based “yeast foods” to lower dissolved CO₂ during fermentation. Differences were observed in yeast fermentative performance in the presence and absence of “yeast foods” for all yeast strains tested. Fermentation performance was improved with the addition of “yeast foods”. There was improved carbohydrate utilisation and amino acid uptake, while acetaldehyde levels at the end of fermentation were decreased. There was an increase in fusel oil production and acetate ester levels at the end of fermentation. Sulphur dioxide levels at the end of fermentation were unaffected by “yeast food” addition. Different yeast strains displayed differing sensitivity to CO₂ inhibition for all parameters tested. Sensitivity to CO₂ was not found to be related to oxygen demand of the yeast strains.     

On‐Line Estimation and Control of Apparent Extract Concentration in Low‐Malt Beer Fermentation

Apparent extract concentration, which is defined as the apparent total dry matter concentration in the media calculated by measurement of the specific gravity, is a very important variable in the process of beer and low‐malt beer fermentation. In the present study, ethanol formation and the residual apparent extract concentration were estimated using the CO₂ concentration in the exhaust gas. A simple mathematical model involving the CO₂ production rate, temperature and cell activity was constructed and a novel system for on‐line estimation and control of apparent extract concentration was developed. In the control system for the residual apparent extract concentration, cell activity was estimated by monitoring the differences in actual CO₂ production rate. In addition, the future trajectory of the apparent extract concentration was predicted. The degree of fermentation, i.e., the residual apparent extract concentration trajectory, was controlled by raising or lowering the temperature, taking into account the estimated cell activity at that time. The residual apparent extract concentration reached the target value at a given time, using the on‐line estimation of apparent extract concentration and temperature control.     

METABOLIC QUOTIENTS OF RESPIRATION-DEFICIENT MUTANTS OF BREWER'S YEAST AND THE APPEARANCE OF A NEGATIVE PASTEUR EFFECT

Four industrial strains of bottom brewer's yeast and a group of their spontaneous respiration deficient (RD) mutants were tested for rates of metabolism of glucose and maltose under aerobic and anaerobic conditions. Q_o2 of all the RD mutants tested (26 isolates) ranged from 1·9 to 6·8 μl/mg yeast dry weight on glucose and was lowered to about one-half on maltose although the original strains had the same Q_o2 values on both sugars. No isolate showed any increase in glucose fermentation in aerobic conditions as compared with the original strains and the decrease of Pasteur effect found in certain isolates was always accompanied by a strong decrease of glycolysis in both aerobic and anaerobic conditions. Two mutants showed a strongly negative Pasteur effect, for their fermentation rates were higher in aerobic conditions than in anaerobic ones. Two other mutants showed a strong negative Pasteur effect only on maltose. The ratio of Q^N_2CO2 on glucose in most mutants was significantly lower than in their parental strains.     

High Gravity Brewing by Continuous Process Using Immobilised Yeast: Effect of Wort Original Gravity on Fermentation Performance

The present work evaluated the influence of all‐malt wort original gravity on fermentative parameters and flavour‐active compound formation during primary fermentation of high gravity brewing by a continuous process using a lager yeast immobilised on a natural carrier obtained from brewer's spent grain (the main brewery by‐product). The all‐malt worts with original gravity (OG) ranging from 13.4 to 18.5°Plato were prepared by diluting a very‐high‐gravity wort (20°Plato) with sterile brewery water. The continuous assay was carried out in a bubble column bioreactor with a total working volume of 5.2 litres, at 15°C, using a constant gas flow rate of 250 mL/min (200 mL/min of CO₂ and 50 mL/min of air) and a dilution rate of 0.04 h^?1 (residence time of 25 h). The results indicated that as the wort OG was increased, the ethanol concentration of the outflowing beer increased. On the other hand, the continuous fermentation of the most concentrated worts (16.6 and 18.5°Plato) resulted in beers with unbalanced flavour profiles due to excessive ethyl acetate formation. The immobilised cell concentration appeared to be nearly independent from increasing wort OG.     

Novel methodology for the in situ assessment of CO2 production rate and its application to anaerobic ripened cheese

CO₂ is produced by many microorganisms present in cheese and it can affect cheese quality both during processing and storage. The knowledge of the extent of CO₂ production by cheese microorganism (CO₂ production rate coefficients) may be used to predict gas exchange in cheese/packaging systems, helping dairy industries in the right choice of the packaging (higher/lower gas permeability) and mastering of cheese ripening. However very few coefficients for CO₂ production rate have been published and the ones assessed in vitro (not inside real food) may not well describe the activity of the microorganisms in situ. We have therefore developed a methodology for the in situ assessment of CO₂ production rate and applied it to cheese with propionic acid fermentation. The proposed methodology is based on infra-red measurement of CO₂ and it allows measuring its accumulation up to 1% with 0.001% resolution, while monitoring the level of oxygen. The method showed a good repeatability, with a low coefficient of variation within samples (6.6%) and between samples (8.4%) compared to 10–30% between samples found in literature. The method was compared with a gas chromatography based method, which is also described.     

Malic Acid as a Source of Carbon Dioxide in Cucumber Juice Fermentations

The degradation of malic acid to lactic acid and CO₂ during fermentation of cucumber juice was investigated. This malolactic reaction was the major source of CO₂ when cucumber juice was fermented by Lactobacillus plantarum. It may also be an important CO₂ source in controlled cucumber fermentations. In addition to CO₂ production, the degradation of malate served to buffer the fermentation and increase sugar utilization. The pH after 7 days’fermentation was 2.8 when 13 mM malic acid was present in the juice and 4.1 with 135 mM malic acid. In the same fermentations, 52% of the sugars were degraded with the low malic acid concentration while complete sugar utilization was observed with the highest malic acid level.     

The critical role of urease in yogurt fermentation with various combinations of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus

The protocooperation between Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus relies on metabolite exchanges that accelerate acidification during yogurt fermentation. Conflicting results have been obtained in terms of the effect of the Strep. thermophilus urease and the NH₃ and CO₂ that it generates on the rate of acidification in yogurt fermentation. It is difficult to perform a systematic study of the effects of urease on protocooperation because it is necessary to distinguish among the direct, indirect, and strain-specific effects resulting from the combination of the strains of both species. To evaluate the direct effects of urease on protocooperation, we generated 3 urease-deficient mutants (ΔureC) of fast- and slow-acidifying Strep. thermophilus strains and observed the effects of NH₃ or CO₂ supplementation on acidification by the ΔureC strains. Further, we examined 5 combinations of 3 urease-deficient ΔureC strains with 2 CO₂-responsive or CO₂-unresponsive strains of L. bulgaricus. Urease deficiency induced a shortage of ammonia nitrogen and CO₂ for the fast- and slow-acidifying Strep. thermophilus and for the CO₂-responsive L. bulgaricus, respectively. Notably, the shortage of ammonia nitrogen had more severe effects than that of CO₂ on yogurt fermentation, even if coculture with L. bulgaricus masked the effect of urease deficiency. Our work established (1) that urease deficiency inhibits the fermentative acceleration of protocooperation regardless of the Strep. thermophilus and L. bulgaricus strain combinations, and (2) that urease is an essential factor for effective yogurt acidification.     

Antioxidant enzyme activities in strawberry fruit exposed to high carbon dioxide atmospheres during cold storage

The effects of storage, in air or a 20% CO₂ in air (16.8% O₂) atmosphere for 12 d at 2 °C, on antioxidant enzymes of strawberry fruit (Fragaria x ananassa Duch. cv. ‘Jewel’) were investigated. The concentrations of acetaldehyde, ethanol and ethyl acetate associated with fermentation were measured, and the activities of peroxidase (POX), catalase (CAT) and superoxide dismutase (SOD) assayed. Ethanol, acetaldehyde and ethyl acetate concentrations increased in CO₂-treated fruit within a day of treatment, but more extensively after four days, while concentrations remained low in air-stored fruit. The total protein content extracted was not affected by CO₂ or storage time. Activities of POX were similar in air- and CO₂-treated fruit, with an increase occurring only in air-treated fruit on day-12. Neither CAT nor SOD activities were affected by CO₂ treatment. In summary, a 20% CO₂ storage treatment induced fermentation but did not significantly affect total antioxidant enzyme activities.     

Viability of commercial cucumber fermentation without nitrogen or air purging

BackgroundBloated cucumber defect, resulting from the accumulation of the biologically produced carbon dioxide (CO₂) in the fruit, reduces yield and economic gains for the pickling industry worldwide. It was the aim of this review to identify commonalities among effective strategies to reduce bloater defect and determine the theoretical viability of commercial cucumber fermentations without bloater defect and/or purging.Scope and approachThis article summarizes the known causes of fermented cucumber bloating defect, including sources of CO₂, and the strategies developed to mitigate the production of the carbonic gas such as controlled fermentation, inoculation of selected starter cultures, cover brine acidification and reformulation and the application of air or nitrogen purging.Key findings and conclusionsIt was understood that microbial activity during fermentation, cucumber tissue respiration, as well as the pressure in the fruits and fermentation tanks, ambient temperature and cover brine composition, impact the levels of dissolved CO₂ in the system. Although the biological conversion of oxygen to CO₂ reduces the cucumbers internal gas pressure, the dissipation of the gas from the tissue is reduced by brining. Once the gas accumulates in the cucumber tissue in concentrations high enough to displace it, the irreversible formation of hollow cavities or bloaters occurs. Residual CO₂ is produced by acid-preserved cucumbers, presumably by tissue respiration, which results in the absence of bloating. Thus, microbial activity seems to contribute most of the CO₂ needed for cucumbers to bloat. It is speculated that colonization of the internal cucumber tissue by indigenous microbes, in particular aerobic gram-negative bacteria, results in the localized production of CO₂ causing bloating defect early in the fermentation. It is concluded that effective manipulation of the microbiota, reduction of dissolved oxygen levels and the use of adequately selected starter cultures may enable cucumber fermentations of acceptable quality without purging.     

The measurement of carbon dioxide transmission of edible films by a static method

A static method is proposed for the measurement of CO₂ transmission of edible films. It is based on the absorption of CO₂ transmitted through the film on an absorbent ascarite II. Water is evolved during absorption of CO₂ by ascarite II and that is absorbed by a desiccant, anhydrous CaCl₂. Total CO₂ transmission is determined from the increase in weight of the absorbents. The transmission parameters, CO₂ transmission rate (CO₂TR), CO₂ permeance and CO₂ permeability (CO₂P), are also calculated. The edible film used was composed of methyl cellulose and polyethylene glycol. An attempt was made to determine the optimum amounts of ascarite II and CaCl₂ to be used. Finally, the effect of CO₂ pressure on the transmission parameters was also examined. CO₂TR was found to increase with increasing pressure while CO₂ permeance and CO₂P values were found to decrease with increasing pressure. © 1999 Society of Chemical Industry     

The influence of carbon dioxide on gas exchange of mungbean sprouts at aerobic and anaerobic conditions

Gas-exchange models are often used to predict gas conditions inside modified atmosphere (MA) packages of fresh plant products. Current models describing CO₂ production of harvested plant products do not account for an inhibition of a high partial pressure of CO₂ on fermentation rates, whereas such as inhibition on plant metabolism is often found. An existing gas-exchange model was modified to include this inhibition. Gas-exchange data of mungbean sprouts were collected under various partial pressures of O₂ and CO₂ and used to validate the model. With the modification applied, CO₂ production rates were better described. Although CO₂ production at low O₂ was reduced by high partial pressures of CO₂, no influence was found on ethanol and acetaldehyde levels. The data found also indicate large differences between gas-exchange rates of different batches of mungbean sprouts. It is suggested that microbial metabolism attributes substantially to total CO₂ production rates found and that it might explain these differences. © 1998 SCI.     

EFFECT OF PRESERVATION WITH SACCOGLOTTIS GABONENSIS ON THE BIOCHEMISTRY AND SENSORY ATTRIBUTES OF FERMENTING PALM WINE

Fresh palm‐wine, from Raphia hookeri was treated with different amounts of Saccoglottis gabonensis. The alcohol content, refractive index, assimilation of sugars and assimilation of nitrates were mcnitored (for 4 days) in treated samples and untreated controls (containing no S. gabonensisj. Fermentation rates were monitored by determining CO₂ production as well as pH and tit ratable acidity changes within the same period. Sensory attributes of fresh and treated palm wine were compared. Sensory evaluation studies were carried out on (1) The fresh palm wine, (2) Palm‐wine stored for 4 days at ambient temperature (27C‐29C) and (3) Palm‐wine stored for 30 days at ambient temperature. Treatment with S. gabonensis led to increased alcohol content and CO₂ production with lower sugar content (sucrose, glucose and maltose) and pH, than in control samples. There were no significant variations in the refractive indices of treated and untreated samples. CO₂ production decreased with each successive fermentation day in both treated and untreated samples. Panelists preferred the sensory properties of fresh palm‐wine to that of palm‐wine treated with S. gabonensis. However, by the second day the sensory characteristics of treated palm‐wine was preferred. Until the 4th day, the color and taste of treated palm‐wine ‐was acceptable while the untreated samples became unacceptable. By the 30th day both treated and untreated palm‐wine samples became unacceptable.     

Losses of volatile compounds during fermentation

The ability of fermentative CO₂ to blow off the volatile compounds that are synthesized during fermentation has been studied. Model solutions simulating a fermenting must were purged at different CO₂ flow rates and temperatures, and the amount of volatile compounds blown off by the stream of CO₂ was recorded by high-resolution gas chromatography. Data showed that under normal fermenting conditions, fatty acid ethyl esters and some fusel alcohol acetates are blown off the solution at a high rate. The maximum loss rate was observed for ethyl decanoate. The purging speed is doubled when temperature increases from 17 °C to 27 °C. Losses can be interpreted by a linear model and are a function of the compound and the flow rate of CO₂. These models allow us to reconstruct the volatile synthesis vs time functions through graphic calculus and to estimate the proportion of volatile material retained, hydrolysed and purged. Synthesis takes place during the tumultuous period of fermentation together with CO₂ production that blows off the volatile material. Hydrolysis takes place in the last stages of fermentation. In a 10-1 open fermenter, up to 80% of volatile material can be blown off while an average of 10% is retained. Residual esterase activity accounts for about 20% of the total amount of ester synthesized.     

Effect of Temperature on the Solubility of CO2 in Bread Dough

Dough expansion during fermentation is caused by CO₂ production by yeast, and its transfer from liquid state in the dough liquor to gaseous phase in the gas cells. The liquid-gas equilibrium is controlled by the solubility of CO₂ in the dough and by the Henry coefficient. The solubility of CO₂ in bread dough was measured for different temperatures with a specific device based on the evolution of the pressure during fermentation at constant volume. The measurements range from 15 to 40°C. Data obtained was extrapolated to 0 and 50°C. Values were found between 1.6 × 10^?5 and 5 × 10^?6 g CO₂ kPa^?1 g^?1 LPD, at 0 and 50°C, respectively (LPD: Liquid Phase of Dough).     

Technical note: Interchangeability and comparison of methane measurements in dairy cows with 2 noninvasive infrared systems

This study aimed to compare measurements of methane (CH₄) and carbon dioxide (CO₂) concentrations in the breath of dairy cows kept in commercial conditions using the Fourier-transform infrared spectroscopy (FTIR) and nondispersive infrared spectroscopy (NDIR) methods. The measurement systems were installed in an automated milking system. Measurements were carried out for 5 d using both systems during milkings. The measurements were averaged per milking, giving 467 observations of CH₄ and CO₂ concentrations of 44 Holstein Friesian cows. The Pearson correlation between observations from the 2 systems was 0.86 for CH₄, 0.84 for CO₂, and 0.88 for their ratio. The repeatability of FTIR (0.53 for CH₄, 0.57 for CO₂, and 0.28 for their ratio) was somewhat higher than that of NDIR (0.57 for CH₄, 0.47 for CO₂, and 0.25 for their ratio). The coefficient of individual agreement was 0.98 for CH₄, 0.89 for CO₂, and 0.89 for their ratio; the concordance correlation coefficient was 0.48 for both gases and 0.24 for their ratio. We showed that FTIR and NDIR give similar results in commercial farm conditions. They can therefore be used interchangeably to generate a larger data set, which could then be further used for genetic evaluation.     

Effect of chemical pretreatments on the fermentation and ultimate digestibility of bagasse by Phanerochaete chrysosporium

When sugarcane bagasse was pretreated at room temperature with various chemicals singly or in combination, (0.25 m NaOH; 0.5 m H₂SO₄; 2.6 M NH₃;0.14 M Ca(OH)₂+0.12 M Na₂CO₃;4.2 m EDA; and 0.5 M H₂SO₄ or 0.25 M NaOH followed by 4.2 M EDA), increases in in-vitro digestibility range from 28.9 to 48.6% depending on the particular chemicals. With most pretreatments, the hemicellulose content decreased and the cellulose content increased slightly, while lignin levels decreased only with NaOH + EDA pretreatments. Further fermentation of the chemically pretreated bagasse with Phanerochaete chrysosporium gave increased digestibilities, the highest final digestibility (59%) being achieved by pre-treatment with 0.25 M NaOH. Pretreatment with NaOH or Ca(OH)₂+Na₂CO₃ and fermentation gave greatly increased levels of hemi-cellulose and cellulose and substantial decreases in lignin levels. Chemical pretreatments of bagasse together with autoclaving considerably enhanced in-vitro digestibility (up to 75%) and lignin degradation (1.4%). Pretreatment with NaOH, Ca(OH)₂+Na₂CO₃, and EDA plus autoclaving gave large increases in total hemicelluloses and cellulose and marked decreases in lignin. Further fermentation with P. chrysosporium gave only slight increases in digestibility.     

Responses of Lotus corniculatus to environmental change. 2. Effect of elevated CO2, temperature and drought on tissue digestion in relation to condensed tannin and carbohydrate accumulation

Clonal plants of three genotypes of Lotus corniculatus (cv Leo) were grown in eight controlled environments under combinations of two temperature regimes, two CO₂ concentrations and two watering regimes. Condensed tannins (proanthocyanidins), in-vitro digestibility, initial rates of gas evolution (as an indicator of the initial rates of fermentation of the substrate), volatile fatty acid evolution, and non-structural carbohydrate (NSC) levels were determined in leaves, stems and roots at full flowering. Under control conditions (average midsummer conditions in the United Kingdom) the total condensed tannin content of leaves varied six-fold between genotypes but condensed tannin contents in stems and roots were similar. Condensed tannin levels were significantly increased in leaves and stems of all three genotypes by doubling the CO₂ concentration while raising the temperature towards the optimum for growth significantly reduced condensed tannin levels. Drought stress significantly reduced condensed tannin levels in leaves and, particularly, in roots. Nutritive value was inversely related to condensed tannin levels in leaves and a negative relationship was observed between condensed tannin concentrations of more than 25–30 g kg⁻¹ dry matter and the initial rates of gas evolution when subjected to in-vitro fermentation with rumen micro-organisms. In leaves, digestibility was significantly increased by drought and by increasing temperature but reduced by high CO₂. In stems, digestibility was significantly increased by drought, but not significantly affected by increasing temperature, or by high CO₂ alone. In roots, digestibility was significantly increased by drought, and decreased by increasing temperature or CO₂. Increasing the growth temperature towards optimum growth reduced the content of NSC in all tissues with the greatest changes occurring in root tissue. Doubling the CO₂ concentration increased NSC levels in leaves and stems with starch content more than doubled under high CO₂ while, in roots, increased levels were only observed in combination with drought stress. There was a linear correlation between condensed tannin concentration and total NSC that was positive for leaves, neutral for stems and negative for roots. The relationship between carbohydrate levels and rates of gas production was negative for leaves and positive for stem and roots. © 1999 Society of Chemical Industry     

Influence of temperature on continuous high gravity brewing with yeasts immobilized on spent grains

Flavor compounds’ formation and fermentative parameters of continuous high gravity brewing with yeasts immobilized on spent grains were evaluated at three different temperatures (7, 10 and 15 °C). The assays were performed in a bubble column reactor at constant dilution rate (0.05 h⁻¹) and total gas flow rate (240 ml/min of CO₂ and 10 ml/min of air), with high-gravity all-malt wort (15°Plato). The results revealed that as the fermentation temperature was increased from 7 to 15 °C, the apparent and real degrees of fermentation, rate of extract consumption, ethanol volumetric productivity and consumption of free amino nitrogen (FAN) increased. In addition, beer produced at 15 °C presented a higher alcohols to esters ratio (2.2–2.4:1) similar to the optimum values described in the literature. It was thus concluded that primary high-gravity (15°Plato) all-malt wort fermentation by continuous process with yeasts immobilized on spent grains, can be carried out with a good performance at 15 °C.