Non-fermentable Sugars Research Articles

The effect of L-cysteine on starch and protein degradation during barley germination.

In order to investigate the impact of L-cysteine (L-Cys) on starch and protein degradation during barley germination. The amylase activities, degradation of macromolecules during germination were determined in this study. Barley was germinated in petri dish for 0 to 5days with different levels of L-Cys (0mM, 2.5mM, 5mM, 10mM). L-Cys addition increased the total limit dextrinase (LD) activities and decreased the LD inhibitor activities during whole germination stage. The activities of α-amylase, β-amylase and free LD were increased with the addition of 2.5, 5mM L-Cys at germination days 1 to 4. Due to higher amylase in malt with the addition of L-Cys, the non-fermentable sugars were reduced and the glucose, maltotriose were improved. Furthermore, the protein degradation analysis showed that low molecular weight protein increased and middle molecular weight protein decreased obviously in wort from the malt germinated with L-Cys, demonstrating that the L-Cys promote the protein degradation. Lastly, the filtration performance of malt with the addition of L-Cys during malting was better than the control. In conclusion, L-Cys can promote the degradation of storage material (starch, protein) during barley germination, leading to a better green malt quality.

Sustainable Management Strategies for Fruit Processing Byproducts for Biorefineries: A Review

The fruit processing industry generates enormous amounts of byproducts, which are primarily removed through landfill or incineration. However, these processes cause carbon dioxide and methane emissions and release dioxin into the environment. The management of fruit processing byproducts is important for reducing the amount of food waste that is sent to landfills and for developing strategies through the reuse of these products for valorization and economic added value. Fruit processing byproducts are rich sources of bioactive compounds and fermentable and nonfermentable sugars. Therefore, these materials are very attractive feedstocks for developing integrated multifeed biorefineries that coproduce a wide range of natural products and bioenergy. The studies presented here have shown sustainable strategies for managing fruit processing byproducts via a biorefinery approach to achieve full valorization via a circular economy. The full valorization project proposed five main phases, namely, pretreatment, extraction, dark or aerobic fermentation, anaerobic digestion, and post-treatment, as well as two additional pathways to generate additional bioelectricity. When choosing the appropriate directions for the presented concept, a technoeconomic analysis should be carried out, considering the type of biomass and its availability at the site of the biorefinery and throughout the year of production. Applying the proposed concept of biorefineries in closed-loop technology is a promising way to enhance economic efficiency and decrease environmental influence in accordance with sustainable development.

Comparative analysis of malt quality and starch characteristics of three South Korean barley cultivars

In this study, malt was produced in pilot-scale facilities and conditioned using three barley (Hordeum vulgare L.) cultivars in South Korea (Heugho, Hopum, and Kwangmaeg). Quality and starch characteristics were compared. The starch content was considerably reduced in all malts. Coleoptile elongation was higher in Heugho (HHM; 85.7% ± 12.6%) and Hopum (HPM; 83.9% ± 10.7%) than in Kwangmaeg (KMM; 78.1% ± 9.9%) malt. Malt yield ranged from 81.8 to 84.9%, with no significant difference. All samples presented type A crystallinity, and granules showed discoid shapes. After malting, the mono- and di-saccharide contents (not including sucrose) were increased. The fermentable sugar level was the highest in HHM, whereas non-fermentable sugar was the highest in KMM. These results suggest that HPM enables efficient scarification based on the rapid degradation of starch, while Heugho barley and HHM have a high potential for beer and malt production, respectively.

The search for a healthy sugar substitute in aid to lower the incidence of Early Childhood Caries: a comparison of sucrose, xylitol, erythritol and stevia

A pursuit to find a healthy alternative to sucrose with less cariogenic potential, which can potentially lower the incidence of Early Childhood Caries (ECC), by means of comparison. Primary tooth enamel blocks (n=32) were randomly divided into four groups and exposed to 5% concentrations of the respective test groups (sucrose, xylitol, erythritol and stevia). All samples were inoculated with S. mutans standard strain (ATCC 25175) at room temperature. Analysis of Colony Forming Units (CFUs), acidity measurements (pH) and Scanning Electron Microscopy (SEM) observations were done after 6, 12, 18 and 24 h and compared. After 6 h, the marginal mean CFU count indicated equal S. mutans growth in all groups. Stevia showed lower CFU counts compared to other groups at 12, 18 and 24 h. The pH levels for all non-fermentable sugar substitutes (NSS) initially decreased but never below the critical pH=5.5 and stabilized from 12 to 18 h. The pH levels of sucrose dropped and remained below pH=5.5 at all time intervals. The SEM analysis of S. mutans supported the CFU results indicating growth in the presence of sucrose and reduction in the presence of the NSS.Compared to sucrose, xylitol, erythritol and stevia have less cariogenic potential with reduced growth of S. mutans and subsequent acidity levels. Stevia had the least cariogenic potential of all the NSS tested, followed by erythritol and then xylitol.

The impact of grain sorghum on the carbohydrate composition of wort for non-alcoholic beer

The production of non-alcoholic beer requires brewing wort with a low degree of digestion. That is possible with the use of non-traditional raw materials in production. The research object presented below is grain sorghum varieties Kazakhstan-16 and Kazakhstan-20. Nowadays, the production of non-alcoholic beer with technological methods is not studied enough. Therefore, plants with small capacities cannot produce it. This study justifies the use of grain sorghum to produce low-digestion wort. In addition, we justify that Kazakhstan-16 had the best indicators for producing non-alcoholic beer. The following ratio of malt for wort preparation to sorghum 60:40 and hydro module 1:6 are proposed. The prepared wort had an extractivity of 6.62 % and digestible carbohydrates of 25.89 % of the total. The ratio of digestible sugars to non-fermentable substances in the wort was 1:1.79, so 79 % constituted mainly non-fermentable sugars. Mathematical experiment planning has been used to study the effect of malt and sorghum filling ratio and hydro module on the brewing wort's extractive matter yield. Based on the results of this study, the brewing wort has a low digestion rate. However, the carbohydrate composition of the wort is due to the presence of mono- and disaccharides. This wort will produce a beer with an ethanol content of up to 0.5 % of alcohol and the organoleptic characteristics set. High extractivity in the raw materials and their high gelling temperature account for these results. These factors made it possible to select a jumping mashing regime, which resulted in deep hydrolysis of the sugars into dextrins. This study will allow using non-traditional grain raw materials and producing non-alcoholic beer in breweries of any capacity. These methods are cost-effective and do not require expensive equipment

Manipulation of an α-glucosidase in the industrial glucoamylase-producing Aspergillus niger strain O1 to decrease non-fermentable sugars production and increase glucoamylase activity.

Dextrose equivalent of glucose from starch hydrolysis is a critical index for starch-hydrolysis industry. Improving glucose yield and decreasing the non]-fermentable sugars which caused by transglycosylation activity of the enzymes during the starch saccharification is an important direction. In this study, we identified two key α-glucosidases responsible for producing non-fermentable sugars in an industrial glucoamylase-producing strain Aspergillus niger O1. The results showed the transglycosylation product panose was decreased by more than 88.0% in agdA/agdB double knock-out strains than strain O1. Additionally, the B-P1 domain of agdB was found accountable as starch hydrolysis activity only, and B-P1 overexpression in ΔAΔB-21 significantly increased glucoamylase activity whereas keeping the glucoamylase cocktail low transglycosylation activity. The total amounts of the transglycosylation products isomaltose and panose were significantly decreased in final strain B-P1-3 by 40.7% and 44.5%, respectively. The application of engineered strains will decrease the cost and add the value of product for starch biorefinery.

Constant temperature mashing at 72 °C for the production of beers with a reduced alcohol content in micro brewing systems

In this paper, we present a constant temperature mashing procedure where grist made of Pilsner malt is mashed-in directly in the temperature regime of alpha-amylase activity, thus omitting all conventional steps, followed by constant temperature mashing at 72 °C. The aim was to investigate an alternative mashing procedure for the production of alcohol-reduced beers. The mashing proceeds with a rapid buildup of sugars and is completed after 120 min at the latest, giving an iodine normal and clear wort. However, the distribution of the different sugars in the worts is strongly altered, in comparison to a more classical mashing procedure. The free amino nitrogen (FAN) concentration is sufficient for vivid fermentation with the bottom fermenting yeast Saccharomyces pastorianus TUM 34/70. The lag phase and initial fermentation performance of this yeast strain are comparable for conventionally and isothermally (72 °C) mashed wort. Under the given conditions the fermentation of the isothermally (72 °C) made wort is finished after 6 days whereas a conventional wort needs 4–5 days more to be completed. The alcohol concentration is remarkably reduced by isothermal mashing leading to roughly 3.4 vol.-% with an original gravity of 11°P whereas with a conventional mashing procedure 4.4 vol.-% are obtained for the same original gravity. In both cases the concentrations of the fermentation by-products are comparable. A preliminary comparison of taste and foam stability did not show striking differences. Constant temperature mashing at 72 °C is a simple way to reduce the alcohol content of beer enriching it at the same time with non-fermentable sugars.

A Cultivar-Based Screening of Hops for Dextrin Degrading Enzymatic Potential

Enzymes in hops have recently been demonstrated to hydrolyze beer dextrins, produce fermentable sugars in finished beer, and pose significant safety and quality challenges for brewers. In an effort to mitigate beer refermentation following dry-hopping in the presence of yeast and the effect of “hop creep,” brewers look to adjust recipes, selection of ingredients, and dry-hopping conditions. With phytochemical/secondary metabolite based flavor differences known to exist across hop cultivars, it was posited that there may also exist unique enzymatic activities based upon cultivar and that brewers may use these differences to guide their hopping practices. The enzymatic power of 30 hop cultivars was screened using specific enzyme assay kits (α-amylase, β-amylase, amyloglucosidase) on hops as well as quantifying via liquid chromatography the nonfermentable dextrin degradation and sugar production in beer dry-hopped with different hops. Differences across all cultivars were found and cluster analysis revealed groupings that were not based on pedigree, genetic makeup, or specific enzyme activities. The influence of growing and harvest practices, processing conditions, and presumably age post processing on hop enzymatic power warrants more investigation. These findings indicate that the choice of hop cultivar may influence the degree of refermentation in finished beer as a result of dry-hopping.

Analysis of the oligosaccharide composition in wort samples by capillary electrophoresis with laser induced fluorescence detection

Determination of the oligosaccharide composition in different wort samples is important to monitor their change during the brewing process with different yeast types. In our work, the concentration of fermentable and non-fermentable sugars were monitored by capillary electrophoresis to observe the effect of two different types of yeasts, Saccharomyces pastorianus and Saccharomycodes ludwigii. The former first ferments the monosaccharides, then the higher sugar oligomers, such as maltose and maltotriose, to ethanol, while the latter fully ferments the monosaccharides, but ferments only very low percentages of the oligosaccharides. Therefore, breweries use Saccharomycodes ludwigii to produce beers with low alcohol content. The CE-LIF traces of the wort samples represented unique oligosaccharide signatures.

Cisplatin cytotoxicity is dependent on mitochondrial respiration in Saccharomyces cerevisiae.

Objective(s):To understand the role of mitochondrial respiration in cisplatin sensitivity, we have employed wild-type and mitochondrial DNA depleted Rho0 yeast cells.Materials and Methods:Wild type and Rho0 yeast cultured in fermentable and non-fermentable sugar containing media, were studied for their sensitivity against cisplatin by monitoring growth curves, oxygen consumption, pH changes in cytosol/mitochondrial compartments, reactive oxygen species production and respiratory control ratio.Results:Wild-type yeast grown on glycerol exhibited heightened sensitivity to cisplatin than yeast grown on glucose. Cisplatin (100 μM), although significantly reduced the growth of wild- type cells, only slightly altered the growth rate of Rho0 cells. Cisplatin treatment decreased both pHcyt and pHmit to a similar extent without affecting the pH difference. Cisplatin dose-dependently increased the oxidative stress in wild-type, but not in respiration-deficient Rho0 strain. Cisplatin decreased the respiratory control ratio.Conclusion:These results suggest that cisplatin toxicity is influenced by the respiratory capacity of the cells and the intracellular oxidative burden. Although cisplatin per se slightly decreased the respiration of yeast cells grown in glucose, it did not disturb the mitochondrial chemiosmotic gradient.

Engineering of Corynebacterium glutamicum for xylitol production from lignocellulosic pentose sugars

Xylitol is a non-fermentable sugar alcohol used as sweetener. Corynebacterium glutamicum ATCC13032 was metabolically engineered for xylitol production from the lignocellulosic pentose sugars xylose and arabinose. Direct conversion of xylose to xylitol was achieved through the heterologous expression of NAD(P)H-dependent xylose reductase (xr) gene from Rhodotorula mucilaginosa. Xylitol synthesis from arabinose was attained through polycistronic expression of l-arabinose isomerase (araA), d-psicose 3 epimerase (dpe) and l-xylulose reductase (lxr) genes from Escherichia coli, Agrobacterium tumefaciens and Mycobacterium smegmatis, respectively. Expression of xr and the synthetic araA-dpe-lxr operon under the control of IPTG-inducible Ptac promoter enabled production of xylitol from both xylose and arabinose in the mineral (CGXII) medium with glucose as carbon source. Additional expression of a pentose transporter (araTF) gene enhanced xylitol production by about four-fold compared to the parent strain. The constructed strain Cg-ax3 produced 6.7±0.4g/L of xylitol in batch fermentations and 31±0.5g/L of xylitol in fed-batch fermentations with a specific productivity of 0.28±0.05g/g cdw/h. The strain Cg-ax3 was also validated for xylitol production from pentose rich, acid pre-treated liquor of sorghum stover (SAPL) and the results were comparable in both SAPL (27±0.3g/L) and mineral medium (31±0.5g/L).

Bioethanol production from carbohydrate-enriched residual biomass obtained after lipid extraction of Chlorella sp. KR-1

The residual biomass of Chlorella sp. KR-1 obtained after lipid extraction was used for saccharification and bioethanol production. The carbohydrate was saccharified using simple enzymatic and chemical methods using Pectinex at pH 5.5 and 45°C and 0.3N HCl at 121°C for 15min with 76.9% and 98.2% yield, respectively, without any pretreatment. The residual biomass contained 49.7% carbohydrate consisting of 82.4% fermentable sugar and 17.6% non-fermentable sugar, which is valuable for bioethanol fermentation. Approximately 98.2% of the total carbohydrate was converted into monosaccharide (fermentable+non-fermentable sugar) using dilute acid saccharification. The fermentable sugar was subsequently fermented to bioethanol through separate hydrolysis and fermentation with a fermentation yield of 79.3%. Overall, 0.4g ethanol/g fermentable sugar and 0.16g ethanol/g residual biomass were produced.

Presence of Low Concentrations of Acetic Acid Improves Fermentations using Saccharomyces cerevisiae

Fermentation of sugars released from lignocellulosic biomass (LCMs) is potentially a sustainable option for the production of bioethanol. LCMs release fermentable hexose sugars and the currently non-fermentable pentose sugars; ethanol yield from lignocellulosic residues is dependent on the efficient conversion of available sugars to ethanol. One of the challenges facing the commercial application for the conversion of lignocellulosic material to ethanol is the presence of inhibitors released by the breakdown of plant cell walls. Presence of acetic acid is an inevitable side-effect for the release of fermentable sugars from the deconstruction of plant cell walls, increasing temperatures used for the pre-treatment process releases acetic acid from the lignin component of the plant cell wall. Using phenotypic microarray analysis revealed that low concentrations (20 mM) acetic acid augmented metabolic output in yeast for an initial period, however, assays at higher concentrations (>50 mM) reduced metabolic output. Fermentations in the presence of acetic acid where characterized by an improved fermentation efficiency in assays containing 20 mM acetic acid compared with control conditions, however, efficiency was reduced in assays using 50 mM acetic acid. Yeast cells in the presence of 20 mM acetic acid produced less glycerol, and produced more ATP when compared with control conditions or in the presence of 50 mM acetic acid.

Behavior of Fermentable Sugars in the Traditional Production Process of Cassava Bioethanol

The aim of study is to evaluate the ferment ability of cassava must in the ethanol production process from cassava in Congo. Three traditional methods of ethyl fermentation were tested: spontaneous fermentation, fermentation with yeast inoculation and fermentation led with yeasting and sugaring. Consumption of fermentable sugars was further in the case of directed fermentation with yeast inoculation (3° Brix residual extract from 48 h) compared to spontaneous fermentation without yeast inoculation (3.8° Brixresidual extract from 120 heures). Total sugars have been consumed only partially (66.7% of limit attenuation), while reducing sugars have been almost completely (about 91%). The addition of yeast in the cassava wort have led to a lower assessment of dextrins (2.7% glucose equivalent) compared to spontaneous fermentation (3.6%). It have also assured a better overall ethanol productivity (PTE = 0.83 g ethanol/L.h) than sugaring proceeding (PTE = 0.61 g/L.h) and without yeast additional (PTE = 0.32 g/L.h). Among the fermentable sugars developed in the cassava mash there are reducing sugars, such as glucose and maltose. Non-fermentable sugars represent a significant slice of stock of soluble carbohydrate (on average 3.24% dextrose equivalent) of the must in the three cases of fermentation tested.

Metabolic pathway of 3,6-anhydro-L-galactose in agar-degrading microorganisms

Recently, agarose-containing macroalgae have gained attention as possible renewable sources for bioethanol-production because of their high polysaccharide content. Complete hydrolysis of agarose produces two monomers, D-galactose (D-Gal) and 3,6-anhydro-L-galactose (L-AnG). However, at present, bioethanol yield from agarophyte macroalgae is low due to the inability of bioethanolproducing microorganisms to convert non-fermentable sugars, such as L-AnG, to bioethanol. Therefore, to increase the bioethanol productivity of agarophytes, it is necessary to determine how agar-degrading microorganisms metabolize L-AnG, and accordingly, construct recombinant microorganisms that can utilize both D-Gal and L-AnG. Previously, we isolated a novel microorganism belonging to a new genus, Postechiella marina M091, which hydrolyzes and metabolizes agar as the carbon and energy source. Here, we report a comparative genomic analysis of P. marina M091, Pseudoalteromonas atlantica T6c, and Streptomyces coelicolor A3(2), of the classes Flavobacteria, Gammaproteobacteria, and Actinobacteria, respectively. In this bioinformatic analysis of these agarolytic bacteria, we found candidate common genes that were believed to be involved in L-AnG metabolism. We then experimentally confirmed the enzymatic function of each gene product in the L-AnG cluster. The formation of two key intermediates, 2-keto-3-deoxy-L-galactonate and 2-keto-3-deoxy-D-gluconate, was also verified using enzymes that utilize these molecules as substrates. Combining bioinformatic analysis and experimental data, we showed that L-AnG is metabolized to pyruvate and D-glyceraldehyde-3-phosphate via six enzymecatalyzed reactions in the following reaction sequence: 3,6-anhydro-L-galactose → 3,6-anhydro-L-galactonate → 2-keto-3-deoxy-L-galactonate → 2,5-diketo-3-deoxy-L-galactonate → 2-keto-3-deoxy-D-gluconate → 2-keto-3-deoxy-6-phospho-D-gluconate → pyruvate + D-glyceraldehyde-3- phosphate. To our knowledge, this is the first report on the metabolic pathway of L-AnG degradation.

Proof of concept for a novel functional screening system for plant sucrose effluxers

Membrane transporters play pivotal roles in facilitating sucrose transport in plants and their activities have been shown to impact plant growth rates and crop yield. In contrast to the well-defined mechanism of sucrose influx across plasma membranes, less is known about sucrose efflux mechanisms and the membrane proteins supporting this function. A major impediment blocking progress in this key area of plant science is the absence of a functional screening system for genes encoding sucrose effluxers. Here we report a novel yeast system for screening sucrose effluxers based on sucrose release from yeast cells genetically modified to synthesize, but not to metabolize, sucrose. Inhibiting sucrose metabolism was achieved using yeast strains, SEY 6210 and YSL4-6, carrying mutations in genes encoding invertase and maltase, respectively. Genes encoding essential components of sucrose biosynthesis, sucrose phosphate synthase (SPS) and sucrose phosphate phosphatase (SPP), were used to transform the two yeast hosts to make strains SuPy (from SEY6210) and Ysu (from YSL4-6). Cultures of SuPy15 cells were found to be capable of synthesizing sucrose when supplied with various compounds as the sole carbon source, including non-fermentable sugars and non-sugar substrates. A proof of concept of the screening system was demonstrated by transforming SuPy15 with sucrose transporter genes known to encode plasma membrane proteins that mediate sucrose efflux. The robustness of the yeast SuPy15 system as a novel platform to screen putative plant sucrose effluxers is discussed.

Production of a high‐protein meal and fermentable sugars from defatted soybean meal, a co‐product of the soybean oil industry

SummaryThe goal of this research was to produce a high‐protein meal by treating defatted soybean meal, a by‐product of soybean oil production, with dilute acid. Treatments were a mild hydrolysis at 80 °C with sulphuric acid at concentrations ranging from 0.5% to 2.0% (w/v) and times varying from 1 to 16 h that were arranged according to a central composite rotatable experimental design. The end products were an enhanced‐protein meal and a carbohydrate concentrate of fermentable and nonfermentable sugars. The highest protein content rise, from 48% to 58%, was for treatments with concentrations of acid ranging between 1.2% and 1.7% and times between 1.0 and 2.6 h. The maximum yield of fermentable sugar was 21.0% d.b. at 2.0% H2SO4 and treatments of at least 6 h. The conditions that provide a highest protein and sugar contents were the treatments with concentrations of sulphuric acid ranging from 0.9 to 1.9% H2SO4 for 1–4 h.

고농도 CO2노출에 의한 Aspergillus nidulans의 유성생식 촉진효과

진균의 분화과정은 다양한 환경요인에 의하여 영향을 받는다. 모델 사상성 진균인 Aspergillus nidulans의 경우 빛이 존재하거나 높은 염 농도, 비 발효성 당에 의하여 무성분화가 촉진되며 반대로 빛이 없거나 발효성 당이 풍부할 때, 그리고 저산소 조건일 경우 유성분화를 촉진하게 된다. 또한 veA나 nsdD와 같은 유성생식 양성조절유전자들도 유성분화를 유도하는 것으로 알려져 있다. 본 연구에서는 A. nidulans에서 <TEX>$CO_2$</TEX>의 농도와 분화패턴의 관계를 알아보고자 하였다. 정상적인 조건에서 <TEX>$veA^+$</TEX> 야생형 균주는 유성생식과 무성생식이 균형을 이룬 상태의 분화를 진행하게 된다. 그러나 5% 정도의 높은 <TEX>$CO_2$</TEX> 조건에서 배양하였을 경우 무성분화는 일어나지 않고 유성생식으로만 분화과정이 일어나게 된다. 뿐만 아니라 이러한 분화 양상은 veA와 nsdD에 의존적으로 일어나게 된다. 고농도의 <TEX>$CO_2$</TEX> 조건이라 할지라도 <TEX>$veA^-$</TEX> 혹은 <TEX>$nsdD^-$</TEX> 돌연변이 균주에서는 유성분화는 일어나지 않고 무성분화만이 일어나는 것을 관찰할 수 있었는데, 이는 <TEX>$CO_2$</TEX> 농도가 높아져도 유성생식에 있어서 이들 유전자의 기능이 필요하다는 것을 시사한다. 또한 5% <TEX>$CO_2$</TEX> 조건은 인간 병원성 진균에게 있어서 사람의 신체 내에 살아남기 위하여 적응하여야 하는 대기 조건으로, 이러한 A. nidulans의 <TEX>$CO_2$</TEX> 농도에 따른 분화양상의 변화는 A. fumigatus와 같은 인간 병원균의 생리, 분화적 변화에 대한 비교분석에 사용될 수 있다. Fungal development is largely affected by many environmental factors. In a model filamentous fungus Aspergillus nidulans, asexual development is promoted by exposure of light, presence of salt and non-fermentable sugars. In other hand, sexual development is largely induced by absence of light, fermentable sugars and hypoxic condition. Also, some important genes including veA and nsdD play positive roles in activating sexual development. Here, we reported that the effect of high concentration of <TEX>$CO_2$</TEX> on developmental decision in A. nidulans. When wild-type <TEX>$veA^+$</TEX> strain was cultured in normal condition, sexual and asexual development occurred in balanced manner. However, high concentration of <TEX>$CO_2$</TEX> (~5%) strongly activated sexual development and inhibited asexual development. Furthermore, this <TEX>$CO_2$</TEX> effect was controlled by the veA or nsdD gene. High <TEX>$CO_2$</TEX> culture of <TEX>$veA^-$</TEX> or <TEX>$nsdD^-$</TEX> mutant didn't activate sexual development, suggesting that the activation of sexual development induced by high <TEX>$CO_2$</TEX> cannot overcome the genetic requirement of sexual development such as veA or nsdD. Since 5% <TEX>$CO_2$</TEX> is an important condition for human pathogenic fungi for surviving and adapting in human body, this developmental pattern of A. nidulans affected by <TEX>$CO_2$</TEX> concentration may provide interesting clues for comparative study with human fungal pathogens including Aspergillus fumigatus.

Production of fermentable sugars from oil palm empty fruit bunch using crude cellulase cocktails with Trichoderma asperellum UPM1 and Aspergillus fumigatus UPM2 for bioethanol production

Utilization of oil palm empty fruit bunch (OPEFB) for bioethanol production with crude cellulase cocktails from locally isolated fungi was studied. Enzymatic saccharification of alkaline pretreated OPEFB was done using different cellulase enzyme preparations. Crude cellulase cocktails from Trichoderma asperellum UPM1 and Aspergillus fumigatus UPM2 produced 8.37 g/L reducing sugars with 0.17 g/g yield. Production of bioethanol from OPEFB hydrolysate using Baker’s yeast produced approximately 0.59 g/L ethanol, corresponding to 13.8% of the theoretical yield. High reducing sugars concentration in the final fermentation samples resulted from accumulation of non-fermentable sugars such as xylose and cellobiose that were not consumed by the yeast. The results obtained support the possible utilization of OPEFB biomass for bioethanol production in the future.

The regulatory effect of fermentable sugar levels on the production of leukotoxin by Actinobacillus actinomycetemcomitans.

The relationship between sugar availability and RTX (repeats in toxin) cytotoxin (leukotoxin) production in the periodontopathic bacterium, Actinobacillus actinomycetemcomitans, was investigated using a chemostat. A actinomycetemcomitans 301-b produced significant amounts of leukotoxin in anaerobic fructose-limited chemostat cultures at a dilution rate of 0.15 h-1 and at pH 7.0. When the growth limitation was relieved by pulsing the cultures with 50 or 150 mM fructose (final concentrations), leukotoxin production immediately stopped and the amount of cellular leukotoxin decreased until the culture was returned to fructose-limited conditions. Leukotoxin synthesis was also repressed in the chemostat cultures by pulsing with glucose but not with the non-fermentable sugar analog, alpha-methyl-D-glucoside. Leukotoxin production was also repressed by fructose in chemostat cultures of ATCC 33384, which is generally recognized as a non-leukotoxin-producing or minimally leukotoxic strain.