Modelling of aerobic growth of Saccharomyces cerevisiae in a pH-auxostat

A model for growth and overflow metabolism of Saccharomyces cerevisiae was applied to simulate continuous cultivations in a pH-auxostat. The concentrations of glucose, biomass and ethanol are controlled by the flow ratio r between fresh medium and titrant solution, both of which are pH-regulated. A critical value of r could be derived, below which the culture becomes substrate depleted, resulting in a stop-flow condition with retained biomass but without growth. At r-values slightly above the critical value the pH-auxostat is substrate limited and unstable. Further increase of the r value results in a stable continuous culture growing at w_max. Thus, the pH-auxostat complements the chemostat in the growth range at or close to w_max. Even at w_max conditions, the ethanol concentration can be controlled at a low level.     

鸡腿蘑胞外多糖的形貌结构及分子量动态变化与抗氧化的相关性研究

对鸡腿蘑多糖的结构进行检测,并在此基础上探讨结构与活性的关系,对深度发掘鸡腿蘑多糖的功效具有重要意义.制备发酵时间为72 h、96 h和120 h的鸡腿蘑胞外粗多糖,采用PMP柱前衍生化-HPLC法分析其单糖组成,结果表明发酵72 h、96 h和120 h胞外多糖均由D-甘露糖、L-鼠李糖、D-葡萄糖、D-半乳糖、D-...     

A lipopolysaccharide fromAspergillus flavus conidia

A lipopolysaccharide was isolated by extraction ofAspergillus flavus conidia with 45 % phenol at 68–70 °C. Quantitative analysis revealed 7 % nucleic acids, 5.5 % proteins, 46 % polysaccharides and 49 % lipids, of which 12 % were covalently bound. Glucose, mannose, galactose and fucose were detected as monosaccharide components of the polysaccharide moiety by gas chromatography; palmitic acid, stearic acid, oleic acid, linoleic acid and myristic acid were mainly present in the lipidic fraction. This material differs from the bacterial lipopolysaccharides, both in composition of the polysaccharide moiety and representation of fatty acids in the lipidic fraction.     

Changes in cell wall polysaccharides of germinating barley grains

Decorticated barley grains were germinated at 25° for 6 days, until the endosperm reserves were nearly exhausted. The neutral monosaccharide components of the hydrolysates of the cell walls and gums from the embryo, aleurone layer and starchy endosperm and the endospermic starch were determined at daily intervals. The amount of embryo cell wall polysaccharide increased 40 times and glucose became the major component, followed in abundance by xylose and arabinose. The cell wall and gum polysaccharides of the aleurone layer (plus testa) and the starchy endosperm declined during germination and their compositions altered. The endospermic starch also decreased. In the early stages of germination the apparent composition of the cell walls of the aleurone layer and starchy endosperm depended upon how they had been prepared. After 6 days the cell walls and gums had provided a significant carbohydrate supply to the living tissues, equivalent to 18.5% of the endospermic polysaccharide degraded during growth, starch having provided the remaining 81.5%.     

Studies on xanthan production from Xanthomonas campestris

Xanthan is an heteropolysaccharide produced by Xanthomonascampestris. Xanthan gum fermentation by a local isolate of X. campestris using different carbon sources was studied. The production of polysaccharide was influenced by the carbon source used. The production of the xanthan was 15.654 g/l with synthetic medium. Production of xanthan at various temperatures ranging between 25v°C and 40v°C was studied. The growth and production was maximum between 25-30v°C. Xanthan production was maximum at pH 7.0-7.5.     

灵芝子实体、菌丝体及孢子粉中多糖成分差异比较研究

为探讨灵芝子实体、菌丝体和孢子粉3种材料中多糖成分的差异,分别运用苯酚硫酸法进行多糖含量测定,运用离子色谱分析其酸水解后单糖组成,并运用HPLC分析各多糖图谱及经α-淀粉酶和β-1,3-葡聚糖酶处理后HPLC图谱的变化,结果发现,灵芝菌丝体中多糖含量最高,达到3.81%,孢子粉多糖含量为1.8%,灵芝子实体中多糖含量最低,仅为0.59%;水解后的单糖组成及摩尔比也有差异,子实体的单糖主要为葡萄糖和半乳糖,菌丝体和孢子粉的单糖主要为葡萄糖;HPLC图谱显示3种多糖出峰位置和分子量也不同,酶解效果表明多糖结构也相差较大。各样品多糖对小鼠巨噬细胞RAW264.7释放NO的产量的影响上,菌丝体与子实体多糖都表现出了很好的活性,而孢子粉多糖却呈现出较低活性。实验结果表明灵芝子实体、菌丝体和孢子粉3种材料的多糖成分差异大,在医药保健品使用中应区分使用。     

Extracellular polysaccharide synthesis by Nostoc strains as affected by N source and light intensity

A study on the effect of two of the main factors affecting energy flux in N(2)-fixing cyanobacteria, i.e. light intensity and availability of combined nitrogen, on the synthesis of soluble exopolysaccharides was carried out with three strains of the genus Nostoc (PCC 7413, PCC 7936, and PCC 8113) presenting different capsular polysaccharidic morphologies and released polysaccharide productions. Strains acclimated to diazotrophic and non-diazotrophic conditions were cultured at high and low light intensities in aerated batch cultures. High light intensities enhanced total carbohydrate synthesis in all the strains but growth measured as pigment and protein concentration, total and soluble carbohydrate concentrations presented a strain-dependent response to nitrate availability. When adequately acclimated to the presence of nitrate all the capsulated strains tested became non-capsulated, with no extracellular polysaccharide being produced. Carbon availability can be on the basis of the observed correlation between the synthesis of capsular polysaccharides and diazotrophy. The slime-forming strain Nostoc PCC 7413 was the only one releasing polysaccharides into the surrounding medium under both, diazotrophic and non-diazotrophic conditions, with the highest values being obtained in the presence of nitrate. This strain presented the highest total carbohydrate (3.5 gl(-1)), soluble carbohydrate (1.8 gl(-1)) concentrations and viscosity values of all the tested strains. Different mechanisms of nitrogen-control of the synthesis of exocellular polysaccharides are reported for each strain, which results in the requirement of a species-specific optimisation of the cultivation conditions for the development of an efficient technology for the production of cyanobacterial exopolysaccharides.     

Clearance rates in the Arctic bivalves <Emphasis Type="Italic">Hiatella arctica</Emphasis> and <Emphasis Type="Italic">Mya </Emphasis>sp.

Filtration was studied in two Arctic clams, Hiatella arctica and Mya sp., collected in Young Sound, Northeast Greenland. Clearance rates were determined as a function of ambient temperature and algal cell concentration, using the clearance method and feeding with a unicellular flagellate. For both species, clearance rates increased with increasing temperature from <у up to 4-8°C. At higher temperatures, filtration ceased and the clams closed their valves. Clearance rates were also determined in temperate specimens of H. arctica collected on the west coast of Sweden. For these specimens, clearance rates increased with increasing temperature from 0 to 18-20°C. When weight-specific clearance rates were compared between the two populations and between species, there were no differences at 1°C. Clearance rates in Arctic H. arctica were maximal at algal cell concentrations corresponding to 2.5-8 µg chlorophyll a l^-1. Temperature compensation in Arctic bivalves is discussed and it is concluded that adaptations to constant low temperatures consist of a lower minimum temperature, for active filtration. Low clearance rates due to low temperatures did not seem to limit growth, under the prevailing conditions in Young Sound.     

The influence of temperature on light enhanced glycoalkaloid synthesis in potato

The influence of temperature on total glycoalkaloid (TGA) synthesis in tubers exposed to light (250 jumol m“² s”² PAR, Photosynthetically Active Radiation) or dark environments for 96 h was examined in three potato cultivars. Following 96 h light or dark the tubers were stored without light at 5°C or 24°C and TGA concentrations monitored over the subsequent 30 and 90 days. Exposure to light and cultivar were found to be major factors influencing TGA concentrations; temperature had no significant effect. TGA content in illuminated tubers of cvs ‘Pentland Hawk’ and ‘Kerrs Pink’ were significantly higher (P < 0.01) compared with tubers placed in the dark. TGA concentrations in cv. ‘Desiree’ increased significantly only following exposure to light at low temperatures (P < 0.05). Removal of tubers from storage at 5°C and immediate illumination at 24°C altered the ratio of glycoalkaloids in cvs ‘Pentland Hawk’ and ‘Kerrs Pink’. Regardless of cultivar and storage temperature TGA concentrations were higher at the end of the storage period compared with initial TGA concentrations. During storage TGA concentrations fluctuated widely and gradual accumulation of glycoalkaloids with time was rarely demonstrated except in cv. ‘Desiree’. Tubers stored at 24°C accumulated higher TGA concentrations than those stored at 5°C in cv. ‘Kerrs Pink’ but not in cvs ‘Pentland Hawk’ and ‘Desiree’. Tubers of cv. ‘Kerrs Pink’ exposed to light prior to storage accumulated glycoalkaloids more rapidly than unexposed tubers during storage at 24°C and occasionally at 5°C. Light enhanced glycoalkaloids are not degraded over time.     

Effect of extraction temperature on the diffusion coefficient of polysaccharides from Spirulina and the optimal separation method

The extraction temperature had a significant impact on the concentration of polysaccharides derived from solid-liquid extraction of Spirulina. The polysaccharide concentration was significantly higher when the extraction was performed at 90°C than when it was performed at 80, 70, and 50°C. This result is related to the diffusion coefficients of the polysaccharides, which increased from 1.07 × 10^?12 at 50°C to 3.02 × 10^?12 m²/sec at 90°C. Using the Arrhenius equation, the pre-exponential factor (D ₀ ) and the activation energy (E _a ) for Spirulina polysaccharide extraction were calculated as 7.958 × 10^?9 m²/sec and 24.0 kJ/mol, respectively. Among the methods used for the separation of Spirulina polysaccharides, cetyltrimethylammonium bromide (CTAB, method I) and organic solvent (ethanol, in methods II and III) provided similar yields of polysaccharides. However, the separation of polysaccharides using an ultrafiltration (UF) process (method III) and ethanol precipitation was superior to separation via CTAB or vacuum rotary evaporation (method II). The use of a membrane with a molecular weight cut-off (MWCO) of 30 kDa and an area of 0.01 m² at a feed pressure of 103 kPa with a mean permeate flux of 39.3 L/m²/h and a retention rate of 95% was optimal for the UF process. The addition of two volumes (v/v) of ethanol, which gave a total polysaccharide content of approximately 4% dry weight, was found to be most suitable for polysaccharide precipitation. The results of a Sepharose 6B column separation showed that the molecular weights of the polysaccharides in fractions I and II were 212 and 12.6 kDa, respectively.     

Concentration of the proteins of skimmed milk by membraneless,isobaric osmosis

The concentration of skimmed milk proteins by polysaccharides such as gum arabic, arabinogalactan and apple pectin with a high content of methoxyl groups was studied. Investigation of the thermodynamic compatibility of skimmed milk proteins with these polysaccharides at different NaCl concentrations and pH has shown that above a certain polysaccharide concentration termed the ‘threshold of complete incompatibility’ the protein is almost completely excluded from the polysaccharide phase. Phase diagrams obtained for the systems: water-skimmed milk proteins-arabinogalactan, water-skimmed milk proteins-gum arabic and water-skimmed milk proteins-pectin, indicate that highly esterified apple pectin is superior to the other polysaccharides for concentrating skimmed milk proteins.The proposed method of concentration which may be called ‘membraneless isobaric osmosis' has a higher productivity and lower energy consumption than other methods of biopolymer concentration.     

Chlorophyll fluorescence and photosynthetic response to light in 1-year-old needles during spring and early summer in <Emphasis Type="Italic">Pinus leucodermis</Emphasis>

Ten-year-old trees from four Italian populations of Pinus leucodermis (populations A, B, C and D), which were collected from different sites at different altitudes, were grown near Florence, Italy. Needle CO₂ gas exchange and chlorophyll fluorescence response to increasing light intensities were evaluated; gas exchange and chlorophyll fluorescence variation between April and July were also monitored. Populations A, B and C showed a similar photosynthetic response to increasing photosynthetic photon flux density (PPFD) intensities, while at various light intensities population D, which originated from the highest altitude, showed the highest photosynthetic rates. In this population photosynthesis was saturated at PPFDs higher than 900 µmol m^-2s^-1 and a slow decrease of effective photosystem II quantum yield and F'_V/F'_M in response to increasing PPFDs were found. The same trees also showed a faster recovery in photosynthesis from limitations induced by winter temperatures than the other three populations. This work showed that photosynthetic response to light in population D was different from the other populations; trees from this population were probably naturally selected to prevent photoinhibition due to excess light.     

Biomass and associations of benthic marine macroalgae from the inner Potter Cove (King George Island, Antarctica) related to depth and substrate

The biomass of the benthic marine macroalgae from the inner Potter Cove was studied along a depth profile across different substrates during Antarctic summer. Macroalgal associations were identified by means of cluster analysis. Twenty-two species were found in the study site, approximately half of the species present in the area. This paucity may be explained by the strong preponderance of the brown algae Desmarestia anceps and D. menziesii, which are able to exclude other species by competition for light. The mean biomass of all macroalgae was 1,390 g DW/m²ǃ,787 g DW/m². Nine macroalgal associations were identified with different preferences for depth, substrate and the degree of exposure. Overall, there was a tendency for macroalgae to grow on fine substrates with increasing depth. Species richness decreased at 20 m depth, probably due to limiting light conditions. The results are discussed with respect to previous studies in East and West Antarctica.     

Physiological energetics of the protobranch bivalve <Emphasis Type="Italic">Yoldia hyperborea</Emphasis> in a cold ocean environment

Yoldia hyperborea is a deposit-feeding circumpolar protobranch that also inhabits muddy sediments of the cold water boreal system of Conception Bay, Newfoundland, Canada. Little is known about this species, despite its wide distribution and frequent high density in the benthos. The present work deals with oxygen consumption and ammonia excretion under cold ambient conditions. Y. hyperborea showed low basal metabolism [0.051 ml O₂ h^у·(g dry weight)^у, T=у°C] and low ammonia excretion rates [4.212 µg·NH₄-N·h^у·(g dry weight)^у, T=у°C]. Low metabolic activity could prove a useful strategy during periods of low food availability. In addition, Y. hyperborea was able to regulate its O₂ consumption rate at very low pO₂ levels, which may be advantageous for a species that may experience periods of hypoxia.     

Optimization of aqueous-assisted extraction of polysaccharides from pumpkin (Cucurbita moschata Duch) and their biological activities

The pumpkin pulp contains a greater composition of edible polysaccharides and has reported with excellent biological applications. This research pertains to optimize the extraction of polysaccharides from the fleshy portion of the pumpkin using aqueous assisted extraction (AAE). The result showed that the optimal extraction condition of pumpkin polysaccharide was as follows: extraction temperature at 55 °C, pH 4.5, and enzyme concentration of 4000 µ/g for 80 min. Under the optimal extraction condition, the yield of pumpkin polysaccharide via AAE (15.4) was significantly higher. The biological activities of extracted polysaccharide including α-amylase inhibition (57.41% at 1000 µg/mL) and anti-inflammatory (50.41% at 25 µg/mL) activity increased significantly. Additionally, the antioxidant activities of extracted pumpkin polysaccharides including IC₅₀ values of DPPH and ABTS were 59.87% and 58.74%, respectively. The pumpkin polysaccharide has maximum inhibitory effects against bacterial strains especially for Escherichia coli than that of fungal strains. It is suggested that the aqueous assisted extraction of is a cost-effective promising method to decrease the processing time as well as enhancing extracted polysaccharide yield – times.     

Non-Cellulosic Polysaccharides from Cotton Fibre Are Differently Impacted by Textile Processing

Cotton fibre is mainly composed of cellulose, although non-cellulosic polysaccharides play key roles during fibre development and are still present in the harvested fibre. This study aimed at determining the fate of non-cellulosic polysaccharides during cotton textile processing. We analyzed non-cellulosic cotton fibre polysaccharides during different steps of cotton textile processing using GC-MS, HPLC and comprehensive microarray polymer profiling to obtain monosaccharide and polysaccharide amounts and linkage compositions. Additionally, in situ detection was used to obtain information on polysaccharide localization and accessibility. We show that pectic and hemicellulosic polysaccharide levels decrease during cotton textile processing and that some processing steps have more impact than others. Pectins and arabinose-containing polysaccharides are strongly impacted by the chemical treatments, with most being removed during bleaching and scouring. However, some forms of pectin are more resistant than others. Xylan and xyloglucan are affected in later processing steps and to a lesser extent, whereas callose showed a strong resistance to the chemical processing steps. This study shows that non-cellulosic polysaccharides are differently impacted by the treatments used in cotton textile processing with some hemicelluloses and callose being resistant to these harsh treatments.     

Feeding rates of the woodlouse Armadillidium vulgare on herb litters produced at two levels of atmospheric CO2

The consumption and assimilation rates of the woodlouse Armadillidium vulgare were measured on leaf litters from five herb species grown and naturally senesced at 350 and 700 µl l^-1 CO₂. Each type of litter was tested separately after 12, 30 and 45 days of decomposition at 18°C. The effects of elevated CO₂ differed depending on the plant species. In Medicago minima (Fabaceae), the CO₂ treatment had no significant effect on consumption and assimilation. In Tyrimnus leucographus (Asteraceae), the CO₂ treatment had no significant effect on consumption, but the elevated CO₂ litter was assimilated at a lower rate than the ambient CO₂ litter after 30 days of decomposition. In the three other species, Galactites tomentosa (Asteraceae), Trifolium angustifolium (Fabaceae) and Lolium rigidum (Poaceae), the elevated CO₂ litter was consumed and/or assimilated at a higher rate than the ambient CO₂ litter. Examination of the nitrogen contents in these three species of litter did not support the hypothesis of compensatory feeding, i.e. an increase in woodlouse consumption to compensate for low nitrogen content of the food. Rather, the results suggest that in herbs that were unpalatable at the start of the experiment (Galactites, Trifolium and Lolium), more of the the litter produced at 700 µl l^-1 CO₂ was consumed than of that produced at 350 µl l^-1 because inhibitory factors were eliminated faster during decomposition.     

Effects of Hexametaphosphate on Soybean Pectic Polysaccharide Extraction

The effects of sodium hexametaphosphate concentration, incubation temperature, and pH on the extraction of polysaccharide from soybean okara (soybean curd waste) were examined. The results suggest that the soybean polysaccharides were almost completely extracted with 50 times their volume of a 2% hexametaphosphate solution at 100°C for 2h, avoiding protein contamination. The viscosity, molecular weight, and sugar composition of the polysaccharides were compared with those of the commercially available samples. No differences were observed in the molecular weight or neutral sugar composition. However, it was found that the galacturonate distribution in the molecules of the two polysaccharides was different. The viscosity of the polysaccharide solution was changed by adding small amount of salt.     

Short-term variability in the flux of rapidly sinking particles in the Antarctic marginal ice zone

A sediment trap deployment was made at a station (64°42'S, 139°59'E) at five depths (537, 796, 1,259, 1,722, 2,727 m) in the marginal ice zone (MIZ) of the Antarctic Ocean during a summer productive period from 26 December 1994 to 20 January 1995. This aim of the study was to reveal a possible occurrence of a sporadic bloom in surface layers and to evaluate the role of fast-sinking particles in transportation processes of bloom-derived material down to mesopelagic and bathypelagic layers. During the observation, a marked flux increase (70.5 mg C m^-2 day^-1, 7.7 mg N m^-2 day^-1) was observed at the depth of 537 m on 7-9 January. The increased flux at 537 m decreased with depth and time. The same mass of sinking particles forming the flux maximum at each depth sank down from the shallowest trap (537 m) to the deepest trap (2,727 m) within 4-11 days, indicating that these particles were transported downward to the bottom with the sinking rate of >200 m day^-1. Collected particles were composed of two major particle fractions; one was dominated by fecal pellets of macrozooplankton (mainly Euphausia superba) with relatively fast sinking rates (FSP; fast-sinking particles) and the other by minute diatoms of Fragilariopsis curta with slow sinking rates (SSP; slowly sinking particles). According to the comparison of time depth changes of these two fractions, the SSP had unexpectedly faster sinking rates comparable with the FSP during the periods of maximum fluxes, probably indicating the SSP were transformed from the FSP during sinking. The present result strongly suggests that a local bloom of F. curta and intensified zooplankton grazing activities occurred in surface layers in a few days in the MIZ, and then the egested fecal pellets were rapidly transported downward with fragmentation processes into small-sized minute particles in mesopelagic and bathypelagic layers.     

Optimization of the Extraction Process and Antioxidant Activity of Polysaccharide Extracted from Centipeda minima

The purpose of this study is to optimize the extraction process and study antioxidant activity of Polysaccharide extracted from Centipeda minima. The Box-Behnken design-response surface methodology was adopted to optimize the extraction process of polysaccharides from Centipeda minima. We purified the crude polysaccharides from Centipeda minima, as well as determined the purity, monosaccharide composition, and molecular weight of the purified fraction. Fourier transform infrared spectrometer (FT-IR) and scanning electron microscopy (SEM) were used to analyze the structural features of the polysaccharides. Further, we investigated the antioxidant activities of different fractions of polysaccharides. Consequently, the results showed that the optimum extraction conditions for polysaccharides were: a liquid-solid ratio of 26 mL/g, extraction temperature of 85.5 °C, and extraction time of 2.4 h. Moreover, the yield of polysaccharides measured under these conditions was close to the predicted value. After purification, we obtained four components of Centipeda minima polysaccharides (CMP). The purity, monosaccharide composition, molecular weight, and structural characteristics of CMP were different, but with similar infrared absorption spectra. CMP exhibited a typical infrared absorption characteristic of a polysaccharide. Besides, CMP displayed good antioxidant activity, with potential to scavenge DPPH radical, hydroxyl radical, and superoxide radical. Therefore, this study provides a reference for future research on the structure and biological activity of CMP, and lays a theoretical foundation for food processing and medicinal development of CMP.