EFFECTS OF YEAST,FERMENTATION TIME,AND PRESERVATION METHODS ON TARHANA

The physicochemical properties of tarhana soup produced with different dough treatments, fermentation times, and preservation methods were examined. Tarhana doughs were prepared with yogurt (control) or baker's yeast (Saccharomyces cerevisiae) and fermented for 3 days. Samples were taken at 24, 48, and 72 hr. Samples were then preserved via one of four methods: sun dried, dried in the shade, vacumn dried, and frozen. Frozen samples produced lower organic acid levels after 72 hr of fermentation in both control (0.68 g/100 g) and yeast (0.61 g/100 g) applications than samples that were dried (0.94 g/100 g control samples; 0.81 g/100 g samples with yeast). Increasing fermentation time resulted in a significant effect on the formation of organic acid in the tarhana (p < .01). At 72 hr of fermentation, total acidity increased 11%, 17%, and 23% for tarhana samples vacumn-dried, sun-dried, and dried in the shade, respectively. Preservation methods also affected the moisture, ash, crude protein, total acidity, pH, salt, fat, reducing sugar levels, and the sensory assestment of tarhana soup (p < .01). Sensory characteristics were not significantly affected by baker's yeast in any of the preservation methods used (p > .01). However, sensory scores for tarhana prepared from the samples dried in a sheltered area showed a reduction in color desireablilty as the fermentation time increased. The soup prepared from frozen tarhana (72 hr fermentation, with yeast) had the highest scores with respect to color, mouth feel, flavor, and overall acceptability. Vacuum-dried samples' scores in these areas were also high in comparison to the two other drying methods.     

Evaluation of bacterial contamination in a fed-batch alcoholic fermentation process

Alcoholic fermentation by a commercial baker's yeast in a fed-batch process with cell recycling and high-test molasses as substrate was strongly inhibited by Lactobacillus fermentum CCT 1407 after a few recycles. When total acidity (mainly lactic acid) exceeded 4.8 g/l broth it seriously interfered with yeast bud formation and viability and above 6.0 g/l it decreased alcoholic efficiency.     

Superior molasses assimilation, stress tolerance, and trehalose accumulation of baker's yeast isolated from dried sweet potatoes (hoshi-imo)

Yeast strains were isolated from dried sweet potatoes (hoshi-imo), a traditional preserved food in Japan. Dough fermentation ability, freeze tolerance, and growth rates in molasses, which are important characteristics of commercial baker's yeast, were compared between these yeast strains and a commercial yeast derivative that had typical characteristics of commercial strains. Classification tests including pulse-field gel electrophoresis and fermentation/assimilation ability of sugars showed that almost the stains isolated belonged to Saccharomyces cerevisiae. One strain, ONY1, accumulated intracellular trehalose at a higher level than commercial strain T128. Correlated with intracellular trehalose contents, the fermentation ability of high-sugar dough containing ONY1 was higher. ONY1 also showed higher freeze tolerance in both low-sugar and high-sugar doughs. The growth rate of ONY1 was significantly higher under batch and fed-batch cultivation conditions using either molasses or synthetic medium than that of strain T128. These results suggest that ONY1 has potential commercial use as baker's yeast for frozen dough and high-sugar dough.     

Differential importance of trehalose in stress resistance in fermenting and nonfermenting Saccharomyces cerevisiae cells.

The trehalose content in laboratory and industrial baker's yeast is widely believed to be a major determinant of stress resistance. Fresh and dried baker's yeast is cultured to obtain a trehalose content of more than 10% of the dry weight. Initiation of fermentation, e.g., during dough preparation, is associated with a rapid loss of stress resistance and a rapid mobilization of trehalose. Using specific Saccharomyces cerevisiae mutants affected in trehalose metabolism, we confirm the correlation between trehalose content and stress resistance but only in the absence of fermentation. We demonstrate that both phenomena can be dissociated clearly once the cells initiate fermentation. This was accomplished both for cells with moderate trehalose levels grown under laboratory conditions and for cells with trehalose contents higher than 10% obtained under pilot-scale conditions. Retention of a high trehalose level during fermentation also does not prevent the loss of fermentation capacity during preparation of frozen doughs. Although higher trehalose levels are always correlated with higher stress resistance before the addition of fermentable sugar, our results show that the initiation of fermentation causes the disappearance of any other factor(s) required for the maintenance of stress resistance, even in the presence of a high trehalose content.     

圆红冬孢酵母发酵菊芋块茎产油脂的研究

研究了圆红冬孢酵母Y4发酵菊芋块茎,菊芋品种及其处理方法对发酵产油的影响。结果表明,菊芋浸提汁、酸水解液或菊芋浆均可直接被圆红冬孢酵母Y4利用,发酵积累油脂,但白皮菊芋比紫皮菊芋更有利于油脂发酵。发酵菊芋浸提汁或酸水解液时,无需添加外源营养物,干菌体油脂含量可达到40%（w/w）;发酵菊芋浆时,白皮菊芋转化率达到12.1 g油/100 g去皮干菊芋。菊芋油脂发酵产品主要以16碳和18碳系脂肪酸为主,与常规植物油的脂肪酸组成相似,可作为制备生物柴油的新型替代原料。     

Leavening ability of baker's yeast exposed to hyperosmotic media

To develop a simple and rapid method for enhancing the leavening ability of baker's yeast, we examined the fermentation ability of baker's yeast exposed to hyperosmotic media. When baker's yeast cells were incubated at 25 degrees C for 1 h in a hyperosmotic medium containing 0.5% yeast extract, 0.5% peptone and 20% sucrose, the cells showed a higher fermentation ability in the subsequent fermentation test than those untreated. The increased ratios were from 40 to 60% depending on the strains used. Glucose and fructose showed a similar effect to that of sucrose, but sorbitol was less effective. A high correlation between the intracellular glycerol content and fermentation ability after the osmotic treatment suggested that glycerol accumulated during the hyperosmotic treatment was used in the subsequent fermentation as a substrate, lessened the lag time, and consequently enhanced the fermentation ability. Various baker's yeasts also showed a high leavening ability in dough after the hyperosmotic treatment.     

Fermentation and microencapsulation of the nematophagous fungus <Emphasis Type="Italic">Hirsutella rhossiliensis</Emphasis> in a novel type of hollow beads

In this work, fermentation and formulation aspects of the nematophagous fungus Hirsutella rhossiliensis BBA were investigated. When incubated in 2% (w/w) glucose and 0.5% (w/w) yeast extract medium in a 1-L Erlenmeyer flask without baffles, heavy pellet formation was observed. Only 40% of the mycelium had a size less than 500 μm. When a flask with three baffles was used, the portion of mycelium <500 μm rose to 95%. In the next step, the influence of aeration rate and stirrer speed on production of finely dispersed mycelium in a stirred tank reactor was investigated. The best fermentation results were obtained at 0.4 vvm and 400 rpm stirrer speed with 90% mycelium <500 μm and 5 g/L biomass. Then, mycelium was microencapsulated in hollow beads based on sulfoethylcellulose (SEC). Experiments on the capsule nutrient reservoir showed that 15% (w/w) corn gluten and 0.5% (w/w) yeast extract could be replaced with 3% (w/w) autoclaved baker's yeast which was never used as capsule additive before. Radial growth of mycelium out of dried hollow beads containing 1% (w/w) biomass and 3% (w/w) baker's yeast was faster than for alginate beads containing equivalent amounts of biomass and yeast indicating a higher bio-control potential.     

Isolation and characterization of acetic acid-tolerant galactose-fermenting strains of Saccharomyces cerevisiae from a spent sulfite liquor fermentation plant.

From a continuous spent sulfite liquor fermentation plant, two species of yeast were isolated, Saccharomyces cerevisiae and Pichia membranaefaciens. One of the isolates of S. cerevisiae, no. 3, was heavily flocculating and produced a higher ethanol yield from spent sulfite liquor than did commercial baker's yeast. The greatest difference between isolate 3 and baker's yeast was that of galactose fermentation, even when galactose utilization was induced, i.e., when they were grown in the presence of galactose, prior to fermentation. Without acetic acid present, both baker's yeast and isolate 3 fermented glucose and galactose sequentially. Galactose fermentation with baker's yeast was strongly inhibited by acetic acid at pH values below 6. Isolate 3 fermented galactose, glucose, and mannose without catabolite repression in the presence of acetic acid, even at pH 4.5. The xylose reductase (EC 1.1.1.21) and xylitol dehydrogenase (EC 1.1.1.9) activities were determined in some of the isolates as well as in two strains of S. cerevisiae (ATCC 24860 and baker's yeast) and Pichia stipitis CBS 6054. The S. cerevisiae strains manifested xylose reductase activity that was 2 orders of magnitude less than the corresponding P. stipitis value of 890 nmol/min/mg of protein. The xylose dehydrogenase activity was 1 order of magnitude less than the corresponding activity of P. stipitis (330 nmol/min/mg of protein).     

Isolation and characterization of acetic acid-tolerant galactose-fermenting strains of Saccharomyces cerevisiae from a spent sulfite liquor fermentation plant.

From a continuous spent sulfite liquor fermentation plant, two species of yeast were isolated, Saccharomyces cerevisiae and Pichia membranaefaciens. One of the isolates of S. cerevisiae, no. 3, was heavily flocculating and produced a higher ethanol yield from spent sulfite liquor than did commercial baker's yeast. The greatest difference between isolate 3 and baker's yeast was that of galactose fermentation, even when galactose utilization was induced, i.e., when they were grown in the presence of galactose, prior to fermentation. Without acetic acid present, both baker's yeast and isolate 3 fermented glucose and galactose sequentially. Galactose fermentation with baker's yeast was strongly inhibited by acetic acid at pH values below 6. Isolate 3 fermented galactose, glucose, and mannose without catabolite repression in the presence of acetic acid, even at pH 4.5. The xylose reductase (EC 1.1.1.21) and xylitol dehydrogenase (EC 1.1.1.9) activities were determined in some of the isolates as well as in two strains of S. cerevisiae (ATCC 24860 and baker's yeast) and Pichia stipitis CBS 6054. The S. cerevisiae strains manifested xylose reductase activity that was 2 orders of magnitude less than the corresponding P. stipitis value of 890 nmol/min/mg of protein. The xylose dehydrogenase activity was 1 order of magnitude less than the corresponding activity of P. stipitis (330 nmol/min/mg of protein).     

Fluorescence sensing of fermentation parameters using fiber optics

A method has been developed for measuring fermentation parameters such as dissolved oxygen, pH, and cell density that differs from traditional techniques that require electrodes and off-line samples. Fluorescent indicators, each sensitive to a single variable, are dissolved directly into a fermentation broth. A fiber-optic probe fluorimeter measures the fluorescence intensities that can then be correlated with parameter values. In addition, an integrated scatter scanning technique can be used to monitor cell density in situ. Results have been obtained using simulated baker's yeast broth and during actual baker's yeast fermentations.     

The use of lactic acid-producing,malic acid-producing,or malic acid-degrading yeast strains for acidity adjustment in the wine industry

In an era of economic globalization, the competition among wine businesses is likely to get tougher. Biotechnological innovation permeates the entire world and intensifies the severity of the competition of the wine industry. Moreover, modern consumers preferred individualized, tailored, and healthy and top quality wine products. Consequently, these two facts induce large gaps between wine production and wine consumption. Market-orientated yeast strains are presently being selected or developed for enhancing the core competitiveness of wine enterprises. Reasonable biological acidity is critical to warrant a high-quality wine. Many wild-type acidity adjustment yeast strains have been selected all over the world. Moreover, mutation breeding, metabolic engineering, genetic engineering, and protoplast fusion methods are used to construct new acidity adjustment yeast strains to meet the demands of the market. In this paper, strategies and concepts for strain selection or improvement methods were discussed, and many examples based upon selected studies involving acidity adjustment yeast strains were reviewed. Furthermore, the development of acidity adjustment yeast strains with minimized resource inputs, improved fermentation, and enological capabilities for an environmentally friendly production of healthy, top quality wine is presented.     

Influence of the mycotoxins aflatoxin B1, rubratoxin B,patulin and diacetoxyscirpenol on the fermentation activity of baker's yeast

The fermentation activity of baker's yeast (measured by the amount of produced CO₂) is inhibited by 100µg/ml and 10µg/ml aflatoxin B₁, and by 100µg/ml and 10µg/ml diacetoxyscirpenol. Lower concentrations of these mycotoxins as well as of rubratoxin B enhance the fermentation. Only 0.001µg/ml aflatoxin B₁, 0.00001µg/ml diacetoxyscirpenol and 0.01µg/ml rubratoxin B are without effect or slightly inhibitory. Patulin in all concentrations tested does not influence the CO₂ production significantly. Cytochemical studies show that the enzyme alcohol dehydrogenase is inhibited by 100µg/ml and enhanced by 1µg/ml and 0.1µg/ml aflatoxin B₁. It is suggested that the influence of at least aflatoxin B₁ on the fermentation activity of the yeast cells is due to an interaction with alcohol dehydrogenase. It is possible that the activity of other enzymes of yeast is also influenced by mycotoxins.     

Changes in major components of tea fungus metabolites during prolonged fermentation

Changes in major components and microbes in tea fungus broth (or kombucha; teakwass) prepared from nine different sources during a prolonged fermentation of up to 60 days were investigated. Cell concentrations of both yeasts and acetic acid bacteria in broth were generally higher than those in the cellulosic pellicles. The residual sucrose concentration decreased linearly with time, although the rate fell after the first month. Metabolic fates of glucose and fructose produced as a result of the hydrolysis of sucrose were different. Glucose was not produced in parallel with fructose (0.085 g 100 ml(-1) d(-1)) but was produced with a lower initial rate (0.041 g 100 ml(-1) d(-1)). Both titratable acidity and gluconic acid increased steadily with time for all samples, although gluconic acid was not generated for 6 days until the fermentation had begun. Acetic acid increased slowly to a maximum value of 1.1 g 100 ml(-1) after 30 days; thereafter, it decreased gradually. Gluconic acid contributed to the titratable acidity and thus, the taste of tea fungus broth, during the final stage of fermentation. It is concluded that the desired quality or composition of kombucha can be obtained through the proper control of fermentation time.     

Use of Saccharomyces cerevisiae cells immobilized on orange peel as biocatalyst for alcoholic fermentation

A biocatalyst was prepared by immobilizing a commercial Saccharomyces cerevisiae strain (baker's yeast) on orange peel pieces for use in alcoholic fermentation and for fermented food applications. Cell immobilization was shown by electron microscopy and by the efficiency of the immobilized biocatalyst for alcoholic fermentation of various carbohydrate substrates (glucose, molasses, raisin extracts) and at various temperatures (30-15 degrees C). Fermentation times in all cases were low (5-15 h) and ethanol productivities were high (av. 150.6 g/ld) showing good operational stability of the biocatalyst and suitability for commercial applications. Reasonable amounts of volatile by-products were produced at all the temperatures studied, revealing potential application of the proposed biocatalyst in fermented food applications, to improve productivities and quality.     

Efficient production of 2-deoxyribose 5-phosphate from glucose and acetaldehyde by coupling of the alcoholic fermentation system of Baker's yeast and deoxyriboaldolase-expressing Escherichia coli

2-Deoxyribose 5-phosphate production through coupling of the alcoholic fermentation system of baker's yeast and deoxyriboaldolase-expressing Escherichia coli was investigated. In this process, baker's yeast generates fructose 1,6-diphosphate from glucose and inorganic phosphate, and then the E. coli convert the fructose 1,6-diphosphate into 2-deoxyribose 5-phosphate via D-glyceraldehyde 3-phosphate. Under the optimized conditions with toluene-treated yeast cells, 356 mM (121 g/l) fructose 1,6-diphosphate was produced from 1,111 mM glucose and 750 mM potassium phosphate buffer (pH 6.4) with a catalytic amount of AMP, and the reaction supernatant containing the fructose 1,6-diphosphate was used directly as substrate for 2-deoxyribose 5-phosphate production with the E. coli cells. With 178 mM enzymatically prepared fructose 1,6-diphosphate and 400 mM acetaldehyde as substrates, 246 mM (52.6 g/l) 2-deoxyribose 5-phosphate was produced. The molar yield of 2-deoxyribose 5-phosphate as to glucose through the total two step reaction was 22.1%. The 2-deoxyribose 5-phosphate produced was converted to 2-deoxyribose with a molar yield of 85% through endogenous or exogenous phosphatase activity.     

Mechanism of Fermentation Conversion from Polyalcohol Fermentation to Ethanol Fermentation by Pichia miso

A possible mechanism of fermentation conversion is described from polyalcohol fermentation to ethanol fermentation by Pichia miso. Little alcohol dehydrogenase activity was found in polyalcohol-producing cells, whereas higher enzyme activity was induced by ethanol-producing cells. The fermentation conversion may be caused by the different levels of alcohol dehydrogenase activity between polyalcohol- and ethanol-producing cells. It was also shown that yeast growth was inhibited and that yeast cells were lysed by ethanol (at 6g/100ml) that accumulated in 24 hr.     

Sourdough Bread Made from Wheat and Nontoxic Flours and Started with Selected Lactobacilli Is Tolerated in Celiac Sprue Patients

This work was aimed at producing a sourdough bread that is tolerated by celiac sprue (CS) patients. Selected sourdough lactobacilli had specialized peptidases capable of hydrolyzing Pro-rich peptides, including the 33-mer peptide, the most potent inducer of gut-derived human T-cell lines in CS patients. This epitope, the most important in CS, was hydrolyzed completely after treatment with cells and their cytoplasmic extracts (CE). A sourdough made from a mixture of wheat (30%) and nontoxic oat, millet, and buckwheat flours was started with lactobacilli. After 24 h of fermentation, wheat gliadins and low-molecular-mass, alcohol-soluble polypeptides were hydrolyzed almost totally. Proteins were extracted from sourdough and used to produce a peptic-tryptic digest for in vitro agglutination tests on K 562(S) subclone cells of human origin. The minimal agglutinating activity was ca. 250 times higher than that of doughs chemically acidified or started with baker's yeast. Two types of bread, containing ca. 2 g of gluten, were produced with baker's yeast or lactobacilli and CE and used for an in vivo double-blind acute challenge of CS patients. Thirteen of the 17 patients showed a marked alteration of intestinal permeability after ingestion of baker's yeast bread. When fed the sourdough bread, the same 13 patients had values for excreted rhamnose and lactulose that did not differ significantly from the baseline values. The other 4 of the 17 CS patients did not respond to gluten after ingesting the baker's yeast or sourdough bread. These results showed that a bread biotechnology that uses selected lactobacilli, nontoxic flours, and a long fermentation time is a novel tool for decreasing the level of gluten intolerance in humans.     

Sourdough bread made from wheat and nontoxic flours and started with selected lactobacilli is tolerated in celiac sprue patients

This work was aimed at producing a sourdough bread that is tolerated by celiac sprue (CS) patients. Selected sourdough lactobacilli had specialized peptidases capable of hydrolyzing Pro-rich peptides, including the 33-mer peptide, the most potent inducer of gut-derived human T-cell lines in CS patients. This epitope, the most important in CS, was hydrolyzed completely after treatment with cells and their cytoplasmic extracts (CE). A sourdough made from a mixture of wheat (30%) and nontoxic oat, millet, and buckwheat flours was started with lactobacilli. After 24 h of fermentation, wheat gliadins and low-molecular-mass, alcohol-soluble polypeptides were hydrolyzed almost totally. Proteins were extracted from sourdough and used to produce a peptic-tryptic digest for in vitro agglutination tests on K 562(S) subclone cells of human origin. The minimal agglutinating activity was ca. 250 times higher than that of doughs chemically acidified or started with baker's yeast. Two types of bread, containing ca. 2 g of gluten, were produced with baker's yeast or lactobacilli and CE and used for an in vivo double-blind acute challenge of CS patients. Thirteen of the 17 patients showed a marked alteration of intestinal permeability after ingestion of baker's yeast bread. When fed the sourdough bread, the same 13 patients had values for excreted rhamnose and lactulose that did not differ significantly from the baseline values. The other 4 of the 17 CS patients did not respond to gluten after ingesting the baker's yeast or sourdough bread. These results showed that a bread biotechnology that uses selected lactobacilli, nontoxic flours, and a long fermentation time is a novel tool for decreasing the level of gluten intolerance in humans.     

Effect of time of storage and method of drying on the digestibility in vitro of alkali-treated barley straw

Samples of barley straw, chopped to 5 cm nominal particle length, were treated with 7.5 g NaOH in 120 ml solution per 100 g dry matter (DM) and either dried immediately after treatment or stored at ?15°C for 24 days prior to drying. The samples were either dried at 100°C in a forced-draught oven, or were freeze-dried. For the samples dried immediately after treatment, incubation in vitro commenced 40 h after treatment. Digestibility in vitro was higher for oven-dried than for freeze-dried samples, particularly when the samples were incubated 40 h after treatment with alkali. Digestibility was also higher for samples which were stored prior to being dried than for those dried directly after treatment with alkali. This suggests that the reaction of alkali with straw continued during the storage of undried material at ?15°C.