Selectivity for water-unextractable arabinoxylan and inhibition sensitivity govern the strong bread improving potential of an acidophilic GH11 Aureobasidium pullulans xylanase

An acidophilic xylanase of Aureobasidium pullulans (XAPI) was recombinantly produced, characterised and its functionality in bread making compared with that of Bacillus subtilis Xyn A xylanase (XBS), an enzyme frequently used in bread making. Prominent characteristics of XAPI were its high specific activity towards arabinoxylan (AX), its relative preference for hydrolysis of water-unextractable AX (WU-AX), its optimal activity under acidic conditions and its sensitivity towards TAXI (Triticum aestivum xylanase inhibitor) and XIP (xylanase inhibiting protein). Optimally developed dough containing XAPI had a considerably drier feel after mixing and was less sticky after fermentation than dough treated with XBS. Both xylanases improved bread loaf volume by 24% under the conditions of the process. In spite of the higher dosage of XAPI necessary to obtain this result, the similar loaf volume increase coincided with less solubilisation of WU-AX and even lesser degradation of solubilised AX (S-AX) and water-extractable AX (WE-AX) by XAPI than by XBS during the bread making process. This is probably due to different dynamics and extent of xylanase inhibition in the dough matrix for both xylanases. AX solubilisation by the acidophilic XAPI was not boosted by the drop in pH in the dough during fermentation. Results show that significant bread loaf volume increase goes hand in hand with excellent dough properties when a limited solubilisation of WU-AX during mixing is coupled to retention of a high molecular mass of S-AX and WE-AX during the rest of the process.     

Efficient production of cellulolytic and xylanolytic enzymes by the rumen anaerobic fungus, Neocallimastix frontalis, in a repeated batch culture

In a batch culture of Neocallimastix frontalis in a medium (pH 6.8) containing 8 g.l(-1) cellulose, the concentrations of the fermentation products and the cellulolytic and xylanolytic enzymes did not increase in comparison with those of cultures in a medium containing 4 g.l(-1) cellulose. Therefore, kinetic studies were performed to determine the effect that products such as acetate, formate, lactate and ethanol have in inhibiting the growth. The reduction of the specific growth rate by the fermentation products could be expressed by using a noncompetitive inhibition model, and it was found that at low concentrations, acetate was the strongest inhibitor among the inhibitory products studied. In order to reduce the inhibition by the fermentation products, a repeated batch culture was carried out whereby none of the fatty acids exceeded 50 mM. In this repeated batch culture, xylanase, endoglucanase, beta-glucosidase, and avicelase were continuously produced in the medium during cultivation, and 18200, 4550, 3790 and 129 IU g.l(-1) of these enzymes, respectively, were produced up to 20 d of culture.     

Physiology and genetics of xylan degradation by gastrointestinal tract bacteria

Hemicelluloses or xylans are major components (35%) of plant materials. For ruminant animals, about 50% of the dietary xylans are degraded, but only small amounts of xylans are degraded in the lower gut of nonruminant animals and humans. In the rumen, the major xylanolytic species are Butyrivibrio fibrisolvens and Bacteroides ruminicola. In the human colon, Bacteroides ovatus and Bacteroides fragilis subspecies "a" are major xylanolytic bacteria. Xylans are chemically complex, and their degradation requires multiple enzymes. Expression of these enzymes by gut bacteria varies greatly among species. Butyrivibrio fibrisolvens makes extracellular xylanases but Bacteroides species have cell-bound xylanase activity. Biochemical characterization of xylanolytic enzymes from gut bacteria has not been done. A xylosidase gene has been cloned from B. fibrosolvens 113. The data from DNA hybridizations using a xylanase gene cloned from B. fibrisolvens 49 indicate this gene may be present in other B. fibrisolvens strains. A cloned xylanase from Bact. ruminicola was transferred to and highly expressed in Bact. fragilis and Bact. uniformis. Arabinosidase and xylosidase genes from Bact. ovatus have been cloned and both activities appear to be catalyzed by a single, bifunctional, novel enzyme. Continued research in genetic and biochemical areas will provide knowledge and insights for manipulation of digestion at the gut level and improved understanding of colonic fiber digestion.     

Changes in activities of cell wall degrading enzymes during fermentation of cassava (Manihot esculenta Crantz) with citrobacter freundii

The cell wall degrading enzymes polygalacturonase (EC 3.2.1.15),pectinase (EC 3.1.1.11), cellulose (EC 3.2.1.4) and xylanase (EC 3.2.1.8), as well as α-amylase (EC 3.2.1.1) and phosphorylase (EC 2.4.1.1), were monitored during fermentation of cassava (Manihot esculenta Crantz) with Citrobacter freundii. All the enzymes were detected in cassava at the start. During fermentation, initial decreases in polygalacturonase, cellulase and xylanase were followed by increases which peaked as the tissue softened. There were significant (P<0.05) increases in pectinase, xylanase, cellulase, polygalacturonase and phosphorylase in inoculated cassava and the fermentation medium relative to controls (uninoculated cassava and medium) during the softening period. The control cassava did not ferment, indicating that the textural changes in inoculated cassava were due to enzymes secreted by C freundii. Studies on the effect of enzyme inhibition on fermentation showed that the pectic enzymes and cellulase were of primary importance and that inhibition of α-amylase and phosphorylase had no effect on the process.     

Screening methods for the proteolytic breakdown of gluten by lactic acid bacteria and enzyme preparations

 Gluten is the major protein in wheat and it is largely responsible for the rheological characteristics of bread dough. The sourdough process is a traditional dough fermentation process with lactic acid bacteria. The proteolytic activity of lactic acid bacteria derived from starter cultures used in sourdough or meat fermentation was tested on gluten as a substrate. The activities of commercial enzyme preparations, which were derived from bacterial or fungal sources, were also evaluated. Proteolytic breakdown of gluten protein in an agar medium by either bacterial culture or enzymes was evident by a clear zone around wells after staining with Coomassie blue. The increase in TCA-soluble material due to gluten breakdown was measured spectrophotometrically. A third test evaluated the release of free amino acids due to exoproteolytic activity. The agar based test showed positive results for the commercial enzyme preparations and one Micrococcus strain. All sourdough strains were positive in the enzyme test whereas some starters from the meat fermentation process were not able to break down gluten under test conditions. Variations in the release of free amino acid indicated differences in the enzyme systems of the lactic acid bacteria tested. Received: 25 February 1999     

Changes of bacterial numbers and carbohydrate fermenting groups during in vitro rumen incubations with feedstuff materials

Short in vitro incubations of mixed ruminal bacteria with feedstuff materials were conducted. In each series of experiments, the rumen bacterial population was divided into equal portions. One portion was washed anaerobically by centrifugation in a mineral buffer prior to initiation of incubation, whereas the other portion was not washed. Changes of carbohydrate group composition of the populations, of bacterial cell composition, and of incubation fluid characteristics were monitored over 24 h. Washing the bacterial inoculum did not affect adversely the ensuing feed fermentation and resulted in lower background carbohydrates and fermentation acids. Unwashed bacterial incubations had a greater tendency to produce more lactate. When the feedstuff substrate contained more soluble nutrients, the microbial population exhibited batch culture type growth, and bacteria fermenting soluble carbohydrate predominated. When alfalfa hay was the sole substrate, a more balanced fermentation resulted with respect to both carbohydrate group composition and fermentation acid production. Implications of these findings in relation to use of in vitro methods to estimate digestibility of feedstuff are addressed.     

In vitro effects of the thiopeptide A10255 on ruminal fermentation and microbial populations.

Experiments used unadapted mixed cultures of ruminal microorganisms in batch or continuous culture fermentation to investigate the effect of a thiopeptide, A10255, on ruminal fermentation and microbial populations. After 24 h of fermentation in batch culture, addition of A10255 (.5 to 20 ppm of the culture fluid) to 0, 45, 60, and 75% concentrate diets had no effect on total VFA but increased molar proportion of propionate and decreased butyrate. The molar proportion of acetate was decreased by treatment only in the 0 and 75% concentrate diets. The increase in molar proportion of propionate by 20 ppm of A10255 was less than the increase caused by a similar concentration of monensin. The same concentration of A10255 (20 ppm) decreased ADF digestion less than 20 ppm of monensin. In continuous culture, A10255 (33 mg/kg of dietary DM) did not affect total VFA concentration, culture pH, OM digestion, or ADF digestion. Ruminal bacterial populations of total anaerobes and lactate-producing, lactate-utilizing, cellulolytic and amylolytic bacteria were unaffected by treatment. However, molar proportions of acetate, butyrate, and isovalerate were decreased, and propionate was increased, by addition of A10255.     

Multi-enzyme production by pure and mixed cultures of Saccharomyces and non-Saccharomyces yeasts during wine fermentation

Saccharomyces and non-Saccharomyces yeasts release enzymes that are able to transform neutral compounds of grape berries into active aromatic compounds, a process that enhances the sensory attributes of wines. So far, there exists only little information about enzymatic activity in mixed cultures of Saccharomyces and non-Saccharomyces during grape must fermentations. The aim of the present work was to determine the ability of yeasts to produce extracellular enzymes of enological relevance (β-glucosidases, pectinases, proteases, amylases or xylanases) in pure and mixed Saccharomyces/non-Saccharomyces cultures during fermentation. Pure and mixed cultures of Saccharomyces cerevisiae BSc562, Hanseniaspora vinae BHv438 and Torulaspora delbrueckii BTd259 were assayed: 1% S. cerevisiae/99% H. vinae, 10% S. cerevisiae/90% H. vinae, 1% S. cerevisiae/99% T. delbrueckii and 10% S. cerevisiae/90% T. delbrueckii. Microvinifications were carried out with fresh must without pressing from Vitis vinifera L. c.v. Pedro Jiménez, an autochthonous variety from Argentina. Non-Saccharomyces species survived during 15-18days (BTd259) or until the end of the fermentation (BHv438) and influenced enzymatic profiles of mixed cultures. The results suggest that high concentrations of sugars did not affect enzymatic activity. β-Glucosidase and pectinase activities seemed to be adversely affected by an increase in ethanol: activity diminished with increasing fermentation time. Throughout the fermentation, Saccharomyces and non-Saccharomyces isolates assayed produced a broad range of enzymes of enological interest that catalyze hydrolysis of polymers present in grape juice. Vinifications carried out by a pure or mixed culture of BTd259 (99% of T. delbrueckii) showed the highest production of all enzymes assayed except for β-glucosidase. In mixed cultures, S. cerevisiae outgrew H. vinae, and T. delbrueckii was only detected until halfway the fermentation process. Nevertheless, their secreted enzymes could be detected throughout the fermentation process. Our results may contribute to a better understanding of the microbial interactions and the influence of some enzymes on vinification environments.     

In vitro evaluation of cashew nut shell liquid as a methane-inhibiting and propionate-enhancing agent for ruminants

Cashew nut shell liquid (CNSL) containing antibacterial phenolic compounds was evaluated for its potency as a feed additive for ruminants. In experiment 1, ruminal responses to CNSL supplementation were assessed using a batch culture system. Rumen fluid from cattle was diluted with artificial saliva and incubated for 18 h in a batch culture with a mixed diet containing a 30:70 hay:concentrate diet to which raw or heated CNSL was added at a final concentration of 500 μg/mL. In experiment 2, a Rusitec, using rumen fluid from the same cattle, was operated over a period of 7 d during which only raw CNSL was tested at concentrations of 0, 50, 100, or 200 μg/mL, and variations in fermentation and bacterial population were assessed. In experiment 3, a pure culture study was conducted using selected bacteria to determine their susceptibility to CNSL. In experiment 1, methane production was inhibited by raw CNSL (56.9% inhibition) but not by heated CNSL. Total volatile fatty acid concentration was not affected, whereas increased concentrations of propionate and decreased concentrations of acetate and butyrate were observed using either raw or heated CNSL. These changes were more obvious when raw CNSL was tested. In experiment 2, raw CNSL inhibited methanogenesis and increased propionate production in a dose-dependent manner, showing maximum methane inhibition (70.1%) and propionate enhancement (44.4%) at 200 μg/mL supplementation. Raw CNSL increased total volatile fatty acid concentration and dry matter digestibility. Raw CNSL also appeared to induce a dramatic shift in the population of rumen microbiota, based on decreased protozoa numbers and changes in quantitative PCR assay values for representative bacterial species. In experiment 3, using pure cultures, raw CNSL prevented the growth of hydrogen-, formate-, and butyrate-producing rumen bacteria, but not the growth of bacteria involved in propionate production. Based on these data, raw CNSL, rich in the antibacterial phenolic compound anacardic acid, is a potential candidate feed additive with selective activity against rumen microbes, leading to fermentation that results in decreased methane and enhanced propionate production.     

豆酱不同发酵阶段细菌群落多样性及动态变化分析

以东北传统自然发酵豆酱为研究对象,采用聚合酶链式反应-变性梯度凝胶电泳(polymerase chain reactiondenaturing gradient gel electrophoresis,PCR-DGGE)技术结合高通量测序方法分析豆酱发酵过程中细菌的多样性及动态变化。结果显示,细菌的可操作分类单元数值在发酵过程中上下波动,并在后发酵第21天时达到最大值,此时细菌数目最多;整理分析PCR-DGGE图谱鉴定结果以及细菌在属水平上的分布得出,明串珠菌属、肠球菌属、四联球菌属和乳杆菌属为豆酱样品不同发酵阶段的优势细菌菌属,其中四联球菌属波动性较大,易受内外环境的影响;屎肠球菌、明串珠菌属、绿色魏斯菌随着发酵时间的延长在减少,说明这些细菌主要参与豆酱发酵初期产酶分解物质过程,并在整个发酵过程中起到调整发酵内环境等作用。     

Functional properties of curry paste in relation to digestibility and fermentation by gut microbiota

The prebiotic properties of sour curry paste in the upper gut and the gut microbiota were investigated in vivo during digestion. The effect of the addition of garcinia as souring agent in curry paste was studied. Curry paste without garcinia (P1) and curry paste with garcinia (P2) increased the number of beneficial bacteria in the gut microbiota, especially bifidobacteria and lactobacilli, and significantly (p < 0.05) decreased the number of harmful bacteria (Clostridia). Fecal fermentation with P1 resulted in a prebiotic index (PI) of 1.19, whereas fermentation with P2 resulted in a PI of 2.75. The fermented metabolites produced were lactic acid; vitamins; and short-chain fatty acids (SCFAs) such as acetic acid, propionic acid, and butyric acid. P1 produced metabolites including lactic acid, SCFAs, and B vitamins in higher amounts than P2. After a 24 h fermentation period with colonic microbiota, P1 produced vitamins B1 (18.38 ± 0.10 µg/ml) and B2 (45.28 ± 2.02 µg/ml) but not folic acid, whereas P2 produced only vitamin B1 (5.99 ± 0.48 µg/ml).     

The presence of Enterococcus, coliforms and E. coli in a commercial yeast manufacturing process

This study evaluated a typical commercial yeast manufacturing process for bacterial contamination. Product line samples of a commercial yeast manufacturing process and the corresponding seed yeast manufacturing process were obtained upstream from the final compressed and dry yeast products. All samples were analysed before (non-PI) and after preliminary incubation (PI) at 37 degrees C for 24 h. The PI procedure was incorporated for amplification of bacterial counts below the lower detection limit. Enterococcus, coliform and Escherichia coli counts were quantified by standard pour-plate techniques using selective media. Presence at all stages and progressive increases in counts of Enterococcus, coliforms and E. coli during processing in the commercial manufacturing operation suggested that the primary source of contamination of both compressed and dry yeast with these bacteria was the seed yeast manufacturing process and that contamination was amplified throughout the commercial yeast manufacturing process. This was confirmed by surveys of the seed yeast manufacturing process which indicated that contamination of the seed yeast with Enterococcus, coliforms and E. coli occurred during scale up of seed yeast biomass destined as inoculum for the commercial fermentation.     

Influence of amylases and xylanase on chemical, sensory, amylograph properties and microstructure of chapati

Effect of enzymes on the quality of chapati - the flat unleavened bread made from different wheat varieties was studied. Doughs treated with fungal α-amylase, bacterial α-amylase, xylanase and combination of bacterial α-amylase and xylanase were examined for chapati making quality. The shear force of chapatis treated with bacterial α-amylase, xylanase, fungal α-amylase and combination of bacterial α-amylase and xylanase were in the range of 2.5-2.8 N, 2.3-2.5 N, 3.5-3.7 N and 2.2-2.5 N, respectively, and they were found to be lower and significantly different than that of their corresponding controls (4.7-6.5 N). Soluble starch and soluble amylose content of the chapatis prepared from dough treated with amylases were significantly different than that of control. Chapatis prepared from dough treated with bacterial α-amylase had shown higher amount of soluble amylose (around 0.5 g/100 g) compared to other treatments (0.2-0.25 g/100 g). In chapatis prepared from dough treated with bacterial α-amylase, and combination of bacterial α-amylase and xylanase, the amylograph paste viscosities were 38-66 BU, and were very much lower and significantly different from that of control (232-390 BU) may be due to the residual enzyme activities. The microstructures of chapatis prepared from dough treated with enzymes were uniform with distorted starch granules surrounded with protein matrix, while in control, the starch granules were spherical with protein matrix overlapping on one another to form aggregation. Chapatis prepared from dough treated with enzymes had softer texture, better pliability and higher overall quality scores compared to control.     

鹰嘴豆α-低聚半乳糖的肠道益生功能

以鹰嘴豆为材料,通过提取与活性炭-硅藻土柱层析分离纯化,制备鹰嘴豆粗提物和不同纯化程度的鹰嘴豆α-低聚半乳糖(α-GOS)样品。采用体外厌氧粪样混合培养与荧光原位杂交技术,评价鹰嘴豆α-GOS的益生功能。结果表明：鹰嘴豆α-GOS对肠道有益菌(双歧杆菌、乳酸菌)有较好的增殖作用,而对有害菌(拟杆菌、梭状菌)的生长有一定的抑制作用;鹰嘴豆α-GOS只是改变了肠道内菌体的组成,而对总体菌群的数量基本没有影响;α-GOS含量高于90%的鹰嘴豆α-GOS样品的益生指数(PI)最高(2.00),α-GOS含量为70%～80%、80%～90%的鹰嘴豆α-GOS样品及鹰嘴豆粗提物的PI值依次为1.39、1.73和0.89,而对照组(不加任何碳源的处理)为负值 (－0.29)。总之,鹰嘴豆α-GOS具有很好的肠道益生功能。     

Molecular Characterization and Identification of Bioactive Peptides Producing Lactobacillus sps. Based on 16S rRNA Gene Sequencing

In the present study, 3 bacterial cultures were isolated from faecal samples of human infant. The biochemical traits showed similarity with Lactobacillus sps and 16S rRNA sequence analyses, confirmed as Lactobacillus plantarum, Lactobacillus casei, and Lactobacillus rhamnosus. The cultures were screened for their proteolytic activity and good ability to release peptides from milk proteins was found. Hence, these bacteria were used as a proteolytic starter culture for the fermentation of skim milk and whey for the liberation of small peptides. Bioactive nature of the peptides released from whey and skim milk was tested, and results demonstrated that peptides obtained after fermentation of whey and skim milk by Lactobacillus strains showed antimicrobial activity against all the pathogens causing food borne infections in humans. These peptides also indicated antioxidant as well as ACE (angiotensin-converting enzymes) inhibitory activity.     

辐照处理对魔芋葡甘聚糖肠道益生作用的影响

为探究辐照改性技术对魔芋葡甘聚糖（konjac glucomannan,KGM）肠道益生性的影响,以60Co为辐射 源制备0、10、20、30 kGy辐照剂量的KGM样品,采用健康志愿者粪便体外厌氧发酵,比较不同辐照剂量KGM 体外发酵液pH值、短链脂肪酸含量、有益菌及有害菌数目、双歧杆菌数量/大肠杆菌数量（B/E值）、益生元指数 （prebiotic index,PI）的差异。结果表明：相对于葡萄糖阳性对照,不同辐照剂量KGM均能有效降低发酵液pH 值,维持酸性环境,促进短链脂肪酸生成,同时改善发酵液微生物构成,提高B/E值及PI。在0～30 kGy辐照范围 内,随辐照剂量增大,KGM发酵液短链脂肪酸生成量增加,PI升高,0、10、20、30 kGy KGM的PI分别为0.48、 0.61、0.76、0.78。综上,KGM具有良好的肠道益生元作用,γ-辐照改性有助于进一步提高KGM的肠道益生性,综 合考虑辐照效率及KGM肠道PI,推荐20 kGy作为制备KGM低聚糖的适宜辐射剂量。     

气相色谱-质谱法分析乳酸菌发酵苹果汁香气成分

以乳酸菌单一菌种和多菌组合分别发酵苹果汁,采用紫外-可见分光光度计测定发酵过程中苹果汁光密度(optical density,OD)的变化,采用顶空固相微萃取和气相色谱-质谱联用技术检测9组发酵苹果汁的香气成分,结合不同香气物质的阈值与香气值分析特征香气成分,并对各组苹果汁进行感官评价。结果表明:在发酵过程中苹果汁的OD值呈对数上升趋势。各组苹果汁中共鉴定出48种香气成分,主要包含醇类、酯类、醛类、酮类和酚类,其中酯类是各发酵组中种类最多且含量最大的香气类别,其次是醇类。9组苹果汁的主要香气成分和香气值较大并有突出贡献的特征香气成分均为丁酸乙酯、2-甲基丁酸乙酯、2-甲基丁基乙酸酯和乙酸己酯等。多菌发酵和单菌发酵苹果汁的香气成分含量及香气值差异显著(P0.05),说明多菌发酵中醇类、酯类和其他类香气物质的总含量明显高于单菌发酵,且赋予苹果汁更强烈的果香、青香和花香。多菌发酵组的总体感官评分高于单菌发酵组,当副干酪乳杆菌20241、动物双歧杆菌6165、嗜热链球菌6063、嗜酸乳杆菌6005活菌数比为1∶1∶1∶1时,感官评分最优。研究结果为今后乳酸菌在发酵果蔬汁方面的研究和应用提供理论依据。     

Fermentation of feruloyl and non-feruloyl xylooligosaccharides by mixed fecal cultures of human and cow: a comparative study in vitro

For the first time, a comparative study was undertaken with respect to the fermentation of (a) monosaccharides (glucose, galactose, arabinose, and xylose); (b) disaccharide (lactulose); (c) Jerusalem artichoke; (d) xylooligosaccharides (XO); and (e) feruloyl xylooligosaccharides (FXO) by mixed fecal cultures of human and cow. Among monosaccharides, arabinose and xylose exhibited prebiotic properties, and among these arabinose was found to be a better substrate than xylose. Glucose and galactose did not have any impact with respect to either increase or decrease in different bacterial populations present in both human and cow feces and liberated very small amounts of SCFA indicating them to be the least prebiotic among all the substrates tried. Both lactulose and Jerusalem artichoke increased the lactobacilli and bifidobacteria in pooled fecal cultures of human and cow. Bovine fecal bacteria utilized XO and FXO more effectively than human fecal bacteria as indicated by relatively high levels of the cell wall–degrading enzyme activities. Growth of different bacterial populations was monitored by the fluorescent in situ hybridization method at 12 and 24 h. XO increased the growth of lactobacilli and bifidobacteria and decreased the growth of Bacteriodes and clostridia, whereas FXO increased the growth of lactobacilli in cow fecal cultures. In human fecal cultures, FXO promoted the growth of bifidobacteria, but to a lesser extent compared with cow fecal bacteria. Quantitative variations were observed with respect to the profile of short-chain fatty acids liberated in the fecal culture filtrates of human and cow grown on XO and FXO.     

Interaction between Lactococcus lactis and Lactococcus raffinolactis during growth in milk: development of a new starter culture

Many milk fermentations use mixed cultures of lactic acid bacteria. To select a new mixed starter culture, 100 acid-producing bacterial strains were isolated from raw cow milk. Of these, 13 strains identified as belonging to the genera Lactococcus, Lactobacillus, Leuconostoc, or Weissella (based on phenotypic and genotypic tests) were assessed for a symbiotic effect between pairs of isolated strains during growth in milk. Among the strains tested, a mixed culture of Lactococcus lactis ssp. lactis strain 54 and Lactococcus raffinolactis strain 37 stimulated greater acid production during fermentation than occurred with pure fermentation. This stimulatory effect was not observed in milk supplemented with yeast extract or glucose or in constituted medium. Addition of a cell-free filtrate from milk fermented by strain 54 increased acid production by strain 37; however, the converse effect was not observed. The increased acid production by this mixed culture was, therefore, due to stimulation of strain 37 by metabolic products of strain 54, suggesting that the interaction between strains 54 and 37 is commensal. Analysis with a taste-sensing system indicated that fermented milk containing the mixed culture was more acidic, had more anionic bitterness, had greater aftertastes of anionic bitterness and astringency, and was less salty and umami than milk containing the individual cultures. This study identifies a new commensal relationship between 2 lactococcal strains that are commonly used for making dairy products.     

固定化酵母用于白酒丢糟降解液乙醇发酵的研究

为了提高白酒生产中废弃物的资源化利用效率,探讨了利用固定化酵母实现丢糟降解液连续发酵生产乙醇的工艺。采用固定化的LR3.1300酵母菌株(Saccharomyces sp)进行丢糟降解液的批次和连续乙醇发酵试验。批次发酵试验结果显示,固定化酵母在白酒糟降解液与葡萄糖混合液中发酵的底物利用和产酒效率都较高。在固定化酵母连续发酵中,当固定化酵母液为60 mL,降解糖液进料速度为15 mL/h时,还原糖利用率为83.7%,流出液酒精度达到了3.97%vol,乙醇发酵的效率与前期的游离酵母发酵相比提高了43%。