Interaction between fenhexamid and yeasts during the alcoholic fermentation of Saccharomyces cerevisiae

The behavior of the fungicide fenhexamid, N-(2,3-dichloro-4-hydroxyphenyl)-1-methyl-cyclohexanecarboxamide, has been studied at concentrations corresponding to the limits fixed for grapes (3 mg kg(-1)), or higher, during the alcoholic fermentation. The presence of the fungicide did not affect the amount of alcohol produced. The amount of fenhexamid in the liquid phase decreased by ca. 15%, but the missing fenhexamid was recovered unchanged from yeasts. This suggests that the fungicide is not degraded during the fermentation process, but adsorbed by yeasts. Two constituents of Saccharomyces cerevisiae cell wall, chitin and glucan, tested as potential adsorbents, exhibited affinity for fenhexamid.     

Pesticides in fermentative processes of wine.

The influence of six fungicides (azoxystrobin, cyprodinil, fludioxonil, mepanipyrim, pyrimethanil, and tetraconazole) on the fermentative activity of two yeasts (Saccharomyces cerevisiae and Kloeckeraapiculata) and two lactic bacteria (Leuconostoc oenos and Lactobacillus plantarum) was studied. The possibility of their being degraded by these yeasts and bacteria was also investigated. The presence of the pesticides did not affect alcoholic fermentation, not even with levels higher than those normally found in grapes in field experiments. On the contrary, their presence stimulated the yeast, especially K. apiculata, to produce more alcohol. The fermentative process did not affect the amount of pesticides either by degradation or by adsorption. During malolactic fermentation by Le. oenos, malic acid decreased slightly less (by approximately 15%) in the presence of all pesticides, except mepanipyrim. A lower effect ( approximately 5%) was found during the fermentative process with La. plantarum. The bacteria studied did not show a degradative effect on pesticides during malolactic fermentation.     

Prolonged fermentation of whole wheat sourdough reduces phytate level and increases soluble magnesium

This work was designed to compare the effects of different leavens (yeast, sourdough, and a mixture of both) on phytic acid (PA) degradation and to assess the repercussions of PA breakdown on phosphorus and magnesium solubility during bread-making. Sourdough fermentation was more efficient than yeast fermentation in reducing the phytate content in whole wheat bread (-62 and -38%, respectively). Furthermore, lactic acid bacteria present in sourdough enhanced acidification, leading to increased magnesium and phosphorus solubility. To intensify phytate breakdown, bran was incubated with microorganisms (yeast or sourdough) before bread-making. Using this new method, the percentage of phytate breakdown was near 90%, whereas 40% of phytate remained in traditional French bread. In conclusion, a prolonged fermentation with sourdough still leads to improved Mg and P solubility by decreasing phytate content and through acidification.     

多菌种分步降解玉米秸秆生产蛋白饲料的工艺

研究了多菌种分步降解玉米秸秆产蛋白饲料的工艺条件,选用黄孢原毛平革菌固体发酵去除部分木质素,接入木霉菌进一步降解木质纤维素,加入酵母发酵产蛋白饲料。木霉菌最佳接种时间为第10 天,经12 d的共发酵,按秸秆与麸皮配比3.0∶1加入麸皮、酵母接种量8%、固液比1∶3.0、硫酸铵用量2.5%,继续共发酵72 h,粗蛋白质量分数可达25.3%。结果表明,多菌种分步降解产蛋白饲料工艺为玉米秸秆生物利用提供了一种新途径。     

Formation of micella containing solubilized sterols during rehydration of active dry yeasts improves their fermenting capacity

During their rehydration in aqueous media, active dry yeasts (ADY) may be supplemented with inactive yeasts, yeast derivatives, or other optional complementary nutrients to improve their fermentation capacity. We found that yeast sterols solubilized in situ during ADY rehydration were particularly efficient for stimulating the fermenting capacity of ADY. Spontaneous solubilization of sterols during rehydration occurred by the formation of micelles by membrane phospholipids and specific cell wall polysaccharides and sterols, both compounds being provided by inactive dry yeasts (IDY). These micelles contained a specific distribution of the initial sterols from the inactive yeasts. Above a concentration of 100 mg L(-1) in the rehydration medium, these micelles acted as emulsifiers. Their critical micellar concentration (cmc) was found to be about 4 g L(-1). During rehydration, purified micelles, at a concentration near the cmc, were able to interact quickly with yeast cell membranes by modifying the yeast plasma membrane order [monitored by steady-state fluorescence anisotropy of 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene-p-toluenesulfonate (TMA-DPH) probe] and by increasing the sterol contents of ADY. Such an enrichment of ADY by very low concentrations of solubilized sterols was very efficient for the completion of fermentations. This is useful when musts are limited in available phytosterols or when micro-oxygenation is not desirable during fermentation.     

Apple polyphenols and products formed in the gut differently inhibit survival of human cell lines derived from colon adenoma (LT97) and carcinoma (HT29)

Colorectal tumor risks could be reduced by polyphenol-rich diets that inhibit cell growth. Here, apple polyphenols were studied for effects on the survival of colon adenoma (LT97) and carcinoma-derived (HT29) cell lines. Three apple extracts (AEs) from harvest years 2002-2004 were isolated (AE02, AE03, and AE04) and fermented in vitro with human fecal flora. Extracts and fermentation products were analyzed for polyphenols with HPLC. The cells were treated with AEs (0-850 microg/mL) or fermented AEs (F-AEs, 0-9%), and survival was measured by DNA staining. All AEs contained high amounts of polyphenols (311-534 mg/g) and reduced cell survival (in LT97 > HT29). AE03 was most potent, possibly because it contained more quercetin compounds. Fermentation of AEs resulted in an increase of short chain fatty acids, and polyphenols were degraded. The F-AEs were approximately 3-fold less bioactive than the corresponding AEs, pointing to a loss of chemoprotective properties through fermentation.     

固定化酵母粒子强化及其对甜高粱茎秆汁液乙醇发酵的影响

采用正交试验设计开展了三亚乙基四胺(TTA)和戊二醛(GLU)的浓度和处理时间对海藻酸钙固定化酵母粒子的化学强度影响的试验研究，并以甜高粱茎秆汁液为原料，在5 L的反应器中进行乙醇发酵试验，考察强化后的固定化酵母粒子对乙醇发酵的影响。结果表明，最优的固定酵母粒子强化处理的方案为：TTA浓度为0.5%，处理时间为120 min；GLU浓度为0.5%，处理时间为8 min。连续8批次的甜高粱茎秆汁液乙醇发酵试验结果表明，最优组合强化后固定化酵母粒子用于乙醇发酵时，平均乙醇得率和变异系数(CV%)分别为84.78%和8.08%，而未强化的固定化酵母籽子为84.32%和9.68%，可见，最优组合强化后的固定化酵母粒子的发酵性能略优于未强化的固定化酵母籽子。该文为固定化酵母发酵甜高粱茎秆汁液制取生物乙醇技术的研究提供了参考。     

Solid-substrate fermentation of corn fiber by Phanerochaete chrysosporium and subsequent fermentation of hydrolysate into ethanol

The goal of this study was to develop a fungal process for ethanol production from corn fiber. Laboratory-scale solid-substrate fermentation was performed using the white-rot fungus Phanerochaete chrysosporium in 1 L polypropylene bottles as reactors via incubation at 37 degrees C for up to 3 days. Extracellular enzymes produced in situ by P. chrysosporium degraded lignin and enhanced saccharification of polysaccharides in corn fiber. The percentage biomass weight loss and Klason lignin reduction were 34 and 41%, respectively. Anaerobic incubation at 37 degrees C following 2 day incubation reduced the fungal sugar consumption and enhanced the in situ cellulolytic enzyme activities. Two days of aerobic solid-substrate fermentation of corn fiber with P. chrysosporium, followed by anaerobic static submerged-culture fermentation resulted in 1.7 g of ethanol/100 g of corn fiber in 6 days, whereas yeast ( Saccharomyces cerevisiae) cocultured with P. chrysosporium demonstrated enhanced ethanol production of 3 g of ethanol/100 g of corn fiber. Specific enzyme activity assays suggested starch and hemi/cellulose contribution of fermentable sugar.     

固定化酵母粒子强化及其对甜高梁茎秆汁液乙醇发酵的影响

采用正交试验设计开展了三亚乙基四胺(TTA)和戊二醛(GLU)的浓度和处理时间对海藻酸钙固定化酵母粒子的化学强度影响的试验研究,并以甜高粱茎秆汁液为原料,在5 L的反应器中进行乙醇发酵试验,考察强化后的固定化酵母粒子对乙醇发酵的影响.结果表明,最优的固定酵母粒子强化处理的方案为TTA浓度为0.5%,处理时间为120 min;GLU浓度为0.5%,处理时间为8 min.连续8批次的甜高粱茎秆汁液乙醇发酵试验结果表明,最优组合强化后固定化酵母粒子用于乙醇发酵时,平均乙醇得率和变异系数(CV%)分别为84.78%和8.08%,而未强化的固定化酵母籽子为84.32%和9.68%,可见,最优组合强化后的固定化酵母粒子的发酵性能略优于未强化的固定化酵母籽子.该文为固定化酵母发酵甜高粱茎秆汁液制取生物乙醇技术的研究提供了参考.     

瓦克青霉F10-2对川楝树皮残渣纤维素酶解研究

以川楝树皮残渣为原料进行纤维素酶解研究,测定了不同培养时间培养基质中主要胞外酶活性的变化,并对发酵前后残渣结构进行扫描电镜观察和红外光谱分析。结果表明:瓦克青霉F10-2具有木质纤维素降解能力,酶解液中纤维素酶、半纤维素酶、木质素过氧化物酶和锰过氧化物酶活性在发酵的8～16d内分别达到最大值6.42U·g-1、7.62U·g-1、6.55U·g-1和3.33U·g-1。利用扫描电镜对降解后底物表面结构进行观察,可看到残渣表面变得疏松、柔软,且具有部分微孔。底物残渣傅立叶红外光谱分析表明,该菌株对残渣中各组分均有一定降解。固态发酵培养试验表明,培养24d后残渣中纤维素、半纤维素和木质素的降解率分别达到42.70%、33.96%和24.62%。     

Whey liquid waste of the dairy industry as raw material for potable alcohol production by kefir granules

Kefir granular biomass was used in the fermentation of sweet whey and proved to be more effective compared to single-cell biomass of kefir yeast. The operational stability of the biocatalyst was assessed by carrying out 20 repeated batch fermentations. Levels of ethanol productivity reached 2.57 g L(-1) h(-1)), whereas the yield was 0.45 g/g. The fermentation time was only 8 h. Mixtures of sweet whey with molasses were fermented at initial densities ranging from 4.2 to 10.2 degrees Be and resulted in ethanol yield factors between 0.36 and 0.48 g of ethanol/g of utilized sugar. Lower degrees Be values led to an increase of percentages of ethyl acetate on total volatiles determined and a reduction of amyl alcohols. The addition of 1% black raisin extract to whey appears to promote whey fermentation, whereas the same was not observed in the case of white sultana extract addition. It was finally established that it is preferable to ferment mixtures of whey-molasses by adding molasses in whey after the completion of whey fermentation.     

Improved bread-baking process using Saccharomyces cerevisiae displayed with engineered cyclodextrin glucanotransferase

A bread-baking process was developed using a potential novel enzyme, cyclodextrin glucanotransferase[3-18] (CGTase[3-18]), that had previously been engineered to have enhanced hydrolyzing activity with little cyclodextrin (CD) formation activity toward starch. CGTase[3-18] was primarily manipulated to be displayed on the cell surface of Saccharomyces cerevisiae. S. cerevisiae carrying pdeltaCGT integrated into the chromosome exhibited starch-hydrolyzing activity at the same optimal pH and temperature as the free enzyme. Volumes of the bread loaves and rice cakes prepared using S. cerevisiae/pdeltaCGT increased by 20% and 45%, respectively, with no detectable CD. Retrogradation rates of the bread and rice cakes decreased significantly during storage. In comparison to the wild type, S. cerevisiae/pdeltaCGT showed improved viability during four freeze-thaw cycles. The results indicated that CGTase[3-18] displayed on the surface of yeast hydrolyzed starch to glucose and maltose that can be used more efficiently for yeast fermentation. Therefore, display of an antistaling enzyme on the cell surface of yeast has potential for enhancing the baking process.     

Fermentation Reduces Free Asparagine in Dough and Acrylamide Content in Bread

Free asparagine is an important precursor for acrylamide in cereal products. The content of free asparagine was determined in 11 milling fractions from wheat and rye. Whole grain wheat flour contained 0.5 g/kg and whole grain rye flour 1.1 g/kg. The lowest content was found in sifted wheat flour (0.2 g/kg). Wheat germ had the highest content (4.9 g/kg). Fermentation (baker's yeast or baker's yeast and sourdough) of doughs made with the different milling fractions was performed to investigate whether the content of free asparagine was reduced by this process. In general, most of the asparagine was utilized after 2 hr of fermentation with yeast. Sourdough fermentation, on the other hand, did not reduce the content of free asparagineas efficiently but had a strong negative impact on asparagine utilization by yeast. This indicates that this type of fermentation may result in breads with higher acrylamide content than in breads fermented with yeast only. The effect of fermentation time on acrylamide formation inyeast‐leavened bread was studied in a model system. Doughs (sifted wheat flour with whole grain wheat flour or rye bran) were fermented for a short (15+15 min) or a long time (180+180 min). Compared with short fermentation time, longer fermentation reduced acrylamide content in bread made with whole grain wheat 87%. For breads made with rye bran, the corresponding reduction was 77%. Hence, extensive fermentation with yeast may be one possible way to reduce acrylamide content in bread.     

Effects of Bran Fermentation on Quality and Microstructure of High‐Fiber Wheat Bread

We compared the effects of spontaneous fermentation of the bran fraction and fermentation with added yeast or added yeast and lactic acid bacteria (Lactobacillus brevis) on the quality of wheat bread supplemented with bran. Prefermentation of wheat bran with yeast or with yeast and lactic acid bacteria improved the loaf volume, crumb structure, and shelf life of bread supplemented with bran. The bread also had added flavor and good and homogenous crumb structure. Elasticity of the crumb was excellent. Spontaneous fermentation of the bran fraction did not have the same positive effects on bread quality. The microstructure of the breads was characterized by light microscopy. The positive effect of fermentation of bran on bread quality was evident when comparing the well‐developed protein network structure of the breads baked with fermented bran with the control bread. Prefermentation of the bran with yeast and lactic acid bacteria had the greatest effect on the structure of starch. The starch granules were more swollen and gelatinized in the breads made with prefermented bran. The pretreatments of the bran fraction had no detectable effect on the microstructure of the cell wall particles in the test breads.     

混菌发酵黑青稞甜醅工艺优化及品质特性研究

为改善单一菌株发酵制备青稞甜醅的风味与口感,提高其质量品质,本试验采用米根霉和酵母菌为发酵菌株,以氨基酸态氮含量及感官评分为指标,确定混菌发酵黑青稞甜醅的最佳工艺条件,并比较单一菌株发酵黑青稞制品与混菌发酵黑青稞制品中酚类物质含量、抗氧化活性及风味物质组成的差异。结果表明,混菌发酵黑青稞制品最佳发酵条件为:发酵温度33℃,发酵时间48 h,菌种比例(酵母菌J7∶米根霉)1∶1.20,接种量6.81%,在此条件下混菌发酵黑青稞制品的氨基酸态氮含量为9.32 mg·100 g^-1,感官评分为95.48分。与单一菌株发酵黑青稞制品相比,混菌发酵黑青稞的黄酮含量(32.22 mg·100 g^-1)、 多酚含量(230.68 mg·100 g^-1)及DPPH自由基清除能力(95.03 μmol·L^-1)显著提高。气相色谱-质谱(GC-MS)分析结果表明,酵母菌单独发酵的黑青稞中共检出33种挥发性风味物质,米根霉单独发酵的黑青稞中共检出41种挥发性风味物质,混菌发酵的黑青稞中共检出46种挥发性风味物质,其中酯类和醇类是3种发酵方式黑青稞制品的主要风味组分。混菌发酵黑青稞的醇类、酯类和酸类种类及含量均显著高于其余两种发酵方式,其相对含量分别达到59.09%、29.44%和6.46%,风味更丰富。综上分析,混菌发酵使黑青稞制品在功能及风味方面具有一定的优势。本研究结果为混菌发酵黑青稞制品的开发和应用奠定了基础。     

Volatile Compounds in Crumb of Whole‐Meal Wheat Bread Fermented with Different Yeast Levels and Fermentation Temperatures

The influence of fermentation temperatures (8, 16, and 32°C) and yeast levels (2, 4, and 6%) on the formation of volatile compounds in the crumb of whole‐meal wheat bread was investigated. Volatile compounds were extracted by dynamic headspace extraction and analyzed by gas chromatography–mass spectrometry. Results were evaluated with multivariate data analysis and ANOVA. Bread fermented at a high temperature (32°C) had higher peak areas of the Maillard reaction products 2‐furancarboxaldehyde, 2‐acetylfuran, 2‐methylpyrazine, and phenylacetaldehyde compared with bread fermented at lower fermentation temperatures. Bread fermented at low temperatures (8 and 16°C) was characterized by having higher peak areas of the fermentation products 3‐methylbutanal, 2‐methylbutanal, ethyl acetate, ethyl hexanoate, ethyl propanoate, and 3‐methylbutanol. Fermentation of bread with 6% yeast resulted in a higher peak area of the important fermentation product 2‐phenylethanol. It also reduced the peak areas of important lipid oxidation products. The peak area of 2,3‐butanedione was also relatively higher in bread fermented with 6% yeast compared with lower yeast levels; however, an interaction was seen between the high yeast level and all three fermentation temperatures. In contrast, fermentation with a low yeast level (2%) resulted in bread with relatively higher peak areas of 2‐ and 3‐methylbutanal, as well as (E)‐2‐nonenal and (E,E)‐2,4‐decadienal, which are important lipid oxidation compounds in bread.     

Low-temperature alcoholic fermentation by delignified cellulosic material supported cells of kefir yeast.

A novel system for low-temperature alcoholic fermentation of glucose is described. This system consists of kefir yeast immobilized on delignified cellulosic materials. Batch fermentations were carried out at various pH values, and the effect of temperature on kinetic parameters, in the range of 5-30 degrees C, was examined. At pH 4.7 the shortest fermentation time was obtained. The formation of volatiles indicates that the concentration of amyl alcohols (total content of 2-methylbutanol-1 and 3-methylbutanol-1) is reduced as the temperature becomes lower. Propanol-1 and isobutyl alcohol formation drops significantly below 15 degrees C. The percentage of ethyl acetate increases as the temperature is diminished. At 5 degrees C the content of total volatiles in the product was only 38% of the volatiles formed during fermentation at 30 degrees C.     

Immobilization of yeast cells with polymeric carrier cross-linked using radiation technique

Various compositions of 2-hydroxyethacrylate (HEA) and methoxy polyethylene glycol methacrylate (M23G) monomers were irradiated by gamma-rays at low temperature (-78 degrees C) to synthesize polymer carriers for effectively immobilizing yeast cells. The yeast cells were immobilized by cell adhesion onto/in these polymers. The ethanol productivity of immobilized yeast cells with the polymer carriers was higher than that of free cells, increasing by 1-3 times. However, the ethanol productivity of immobilized yeast with the polymer carrier resulting from 7%/7% (HEA/M23G) monomer was low, comparatively. The effect of adding cross-linking reagent (4G) to the low concentration of HEA/M23G monomers on the activity of yeast cells immobilized with the cross-linked carriers by radiation polymerization was investigated. The ethanol productivity of immobilized cells with the carriers, which were cross-linked by adding 3-6% 4G to the low concentration of HEA/M23G monomer, was increased by 20-30%, because the pore size, network structure, and mechanical strength of the polymer carriers was well adjusted and cell leakage from the polymer carriers decreased. The relationship between the ethanol productivity of immobilized yeast cells and the interior structure of polymer carriers is discussed and indicated that the interior structure of polymer carriers is crucial for effective immobilization of yeast cells.     

Comparison of biotransformation of inorganic selenium by Lactobacillus and Saccharomyces in lactic fermentation process of yogurt and kefir

The aim of the present study was to characterize, quantify, and compare the different selenium species that are produced when lactic fermentation with two different types of microorganisms, bacteria (Lactobacillus) and yeast (Saccharomyces), take place to produce yogurt and kefir, respectively, and to study the transformation process of these species as a function of time. These two dairy products were chosen for the study because they are highly consumed in different cultures. Moreover, the microorganisms present in the fermentation processes are different. While the bacteria Lactobacillus is the one responsible for yogurt fermentation, a partnership between bacteria and the yeast Saccharomyces causes kefir fermentation. A comparative study has been carried out by fermenting Se(IV) enriched milk in the presence of both types of microorganisms, where the concentration range studied was from 0.5 to 20 microg g (-1). Enzymatic extraction enabled selenium speciation profiles, obtained by anionic exchange and ion-pairing reversed phase high performance liquid chromatography (IP-RP-HPLC) with inductively coupled plasma mass spectrometry (ICP-MS) detection. Scanning electron microscopy (SEM) applied to the enriched samples showed segregated Se (0), at added concentrations higher than 5 microg g (-1). The main Se species formed depended on the type of microorganism involved in the fermentation process, SeCys 2 and MeSeCys being the main species generated in yogurt and SeMet in kefir. The results obtained are different for both kinds of samples. Lactic fermentation for yogurt produced an increment in selenocystine (SeCys 2) and Se-methylselenocysteine (MeSeCys), while fermentation to produce kefir also incremented the selenomethionine (SeMet) concentration. The Se species are stable for at least 10 and 15 days for kefir and yogurt, respectively. After this period, selenocystine concentration decreased, and the concentration of Se-methylselenocysteine was found to significantly increase.     

Antifreeze Activity of γ‐Polyglutamic Acid and Its Impact on Freezing Resistance of Yeast and Frozen Sweet Dough

This study investigated the antifreeze activity (AF) of γ‐polyglutamic acid (γ‐PGA), freezing resistance of yeast cells and sweet dough, and the mechanism influenced by γ‐PGA. Properties studied included AF of γ‐PGA, water‐holding capacity of flour, survival ratio and oxidation resistance capability of yeast cells, ice melting enthalpy (ΔH), and fermentation and breadmaking properties of sweet dough. The AF of γ‐PGA was 8.03 g of unfrozen water/g of sample, indicating good AF. γ‐PGA was tested on yeast cells and sweet dough stored frozen for 0, 1, 2, 4, and 8 weeks at four levels (0, 0.5, 1, and 3%). Survival ratio of yeast cells with γ‐PGA was significantly higher than the corresponding control. A possible mechanism might be related to the modulation of oxidation resistance capability of yeast cells by γ‐PGA. A decrease in glutathione release from frozen yeast cells and an increase in water‐holding capacity of wheat dough were observed with the addition of γ‐PGA. In the presence of γ‐PGA, ΔH, ice melting temperature, and proofing time of frozen sweet dough decreased significantly, and fermentation parameters improved, compared with the corresponding control sample. Specific volume of bread made from frozen sweet dough with 0.5, 1, and 3% γ‐PGA increased by 6.3, 8.9, and 3.3%, respectively, after 8 weeks of frozen storage. γ‐PGA enhanced the freezing resistance of yeast cells and sweet dough effectively, and the effect on specific volume of bread was not linear, with 1% showing better results.