Enzymatic modification of high-laurate canola to produce margarine fat

Stearic acid was enzymatically transesterified with high-laurate canola using a nonspecific lipase from Candida antarctica to produce structured lipids (SL) suitable for margarine application. Stearic acid levels ranged from 10 to 40 wt % of high-laurate canola oil. Differential scanning calorimetry was used to evaluate melting characteristics of the transesterified products. A stearic acid level of 30% was found to best match the melting characteristics of fat extracted from commercially available stick margarine. This SL was used to prepare nonrefrigerated and refrigerated margarine samples. Refrigerated margarine was prepared using 60% SL and 40% canola oil, whereas 100% SL was used for the nonrefrigerated margarine. Slip melting point, solid fat content, and hardness index were determined for all samples. Application of a dynamic temperature step using a dynamic stress rheometer showed complete breakdown of the commercial stick margarine and the experimental refrigerated margarine at approximately 30 degrees C and complete breakdown of the nonrefrigerated margarine at approximately 35 degrees C. Addition of canola oil to the SL improved spreadability at refrigeration temperatures and reduced the hardening effect of lauric acid in the SL. The nonrefrigerated margarine was spreadable at room temperature and exhibited no oil exudation or phase separation.     

Changes in molecular weight of transacylated pectin catalyzed by tomato and citrus pectinesterases as determined by gel permeation chromatography

The changes in molecular masses of pectin in 0.5% pectin-pectinesterase (PE) mixtures (2 units/mL) incubated at various temperatures, pH values, and NaCl levels for 30 min were observed by a Toyopearl TSK HW-65 (F) gel permeation chromatography. The molecular mass of pectin was remarkably increased from 103 to 266 kDa when the incubation temperature of pectin-tomato PE was increased from 25 to 45 degrees C. A further increase in molecular mass was observed when a pectin-citrus PE mixture was incubated at 65 degrees C. The values of pH and NaCl levels were also crucial to the transacylation activity of PEs. Reaction at pH 7.5 with tomato PE and citrus PE remarkably expanded the molecular mass of pectin to 410 and 670 kDa, respectively. The NaCl level of 0.3-0.5 and 0.3 M was favorable for the transacylation reaction of tomato PE and citrus PE, respectively. Only high methoxylpectin was the suitable substrate for PE to conduct the transacylation reaction.     

柑橘果实发育中果胶酸钙、草酸钙和果胶动态的研究

以单性结实的龟井蜜柑和自花结实的鄂柑1号橘为试材,对整个果实发育期的子房(幼果)、果皮和果肉的果胶酸钙、草酸钙和果胶含量变化进行了测定。结果表明,1)两品种子房(幼果)果胶酸钙含量呈类似的下降趋势;草酸钙则相反,龟井花后趋下降,而鄂柑1号却明显上升;而且鄂柑1号子房(幼果)果胶酸钙、草酸钙和果胶含量均相对较高。2)在果实增大期内,两品种果皮和果肉的果胶酸钙含量均出现显著上升,对应果皮草酸钙含量虽有波动但居相对较高水平,而果肉草酸钙则趋明显下降。3)两品种果皮和果肉水溶性果胶含量均在增大期内呈显著上升,对应原果胶含量均相对较高,进入增大后期均明显下降。     

Invertebrates increase the sensitivity of non-labile soil carbon to climate change

The fate of global soil carbon stores in response to predicted climate change is a ‘hotly’ debated topic. Considerable uncertainties remain as to the temperature sensitivity of non-labile soil organic matter (SOM) to decomposition. Currently, models assume that organic matter decomposition is solely controlled by the interaction between climatic conditions and soil mineral characteristics. Consequently, little attention has been paid to adaptive responses of soil decomposer organisms to climate change and their impacts on the turnover of long-standing terrestrial carbon reservoirs. Using a radiocarbon approach we found that warming increased soil invertebrate populations (Enchytraeid worms) leading to a greater turnover of older soil carbon pools. The implication of this finding is that until soil physiology and biology are meaningfully represented in ecosystem carbon models, predictions will underestimate soil carbon turnover.     

Enzymatic modification of saponins from Platycodon grandiflorum with Aspergillus niger

Platycodon grandiflorum A. DC (Campanulaceae) is a traditional medicinal plant. Its root, Platycodi Radix, contains an abundant amount of saponin glycosides, platycodins, of which platycodin D is one of the major components. The chemical structures of platycodins can be modified by various types of chemical processing, but a modification mediated with microorganisms has been not reported yet. In this study, platycodin D was modified to several partially degraded platycodin glycosides after treatment with a crude enzyme extract from Aspergillus niger (A. niger). The modified platycodin D possessed a shorter sugar side-chain, and presented a remarkably reduced V79-4 cell (Chinese hamster lung fibroblasts) cytotoxicity and erythrocyte hemolytic toxicity, whereas the nitrite-scavenging activity was increased in the modified platycodin D. Sensory scores for pungency, bitterness and after-taste were improved as well in the modified platycodin D. Results suggest that A. niger mediated modification yielded a novel partially degraded platycodin glycoside which possesses increased bioactivities and improved sensory values, yet with reduced toxic profiles.     

Enzymatic modification of a model homogalacturonan with the thermally tolerant pectin methylesterase from Citrus: 1. Nanostructural characterization, enzyme mode of action, and effect of pH

Methyl ester distribution in pectin homogalacturonan has a major influence on functionality. Enzymatic engineering of the pectin nanostructure for tailoring functionality can expand the role of pectin as a food-formulating agent and the use of in situ modification in prepared foods. We report on the mode of action of a unique citrus thermally tolerant pectin methylesterase (TT-PME) and the nanostructural modifications that it produces. The enzyme was used to produce a controlled demethylesterification series from a model homogalacturonan. Oligogalacturonides released from the resulting demethylesterified blocks introduced by TT-PME using a limited endopolygalacturonase digestion were separated and quantified by high-pressure anion-exchange chromatography (HPAEC) coupled to an evaporative light-scattering detector (ELSD). The results were consistent with the predictions of a numerical simulation, which assumed a multiple-attack mechanism and a degree of processivity ～10, at both pH 4.5 and 7.5. The average demethylesterified block size (0.6-2.8 nm) and number of average-sized blocks per molecule (0.8-1.9) differed, depending upon pH of the enzyme treatment. The mode of action of this enzyme and consequent nanostructural modifications of pectin differ from a previously characterized citrus salt-independent pectin methylesterase (SI-PME).     

Determination of molecular weight of agars and effect of the molecular weight on the glass transition

A novel procedure to determine the molecular weight (MW) and MW distributions for various agars is described. The MW values of commercial agars, an agarose, an agaropectin, and hydrolyzed agaroses were determined by size exclusion chromatography-low angle laser light scattering, using 4.0 M guanidine hydrochloride as eluent to avoid gelation. The MW for the commercial agars was between 106 400 and 243 500 with polydispersity between 1.283 and 6. 600. The MW of the agarose separated from a commercial agar was lower than that of the agaropectin. To prepare agaroses with different MW values, the obtained agarose was hydrolyzed. The MW of the agarose decreased with hydrolysis time, and the polydispersity, on the contrary, increased. The glass transition temperature (T(g)) of agarose with different MW values and that of agaropectin were measured by differential scanning calorimetry. The T(g) of the agarose was higher than that of the agaropectin with higher MW. The T(g) of agarose increased with MW.     

芬顿反应制备低分子量硫酸软骨素及其降解机制

为了提高硫酸软骨素(chondroitin sulfate,CS)的生物活性和生物利用率,该研究通过芬顿反应制备了不同来源的低分子量硫酸软骨素(low molecular weight chondroitin sulfate,LMCS)并探究了其潜在降解机制。使用鸡来源的硫酸软骨素(chondroitin sulfate from chicken cartilage,CCS)、牛来源的硫酸软骨素(chondroitin sulfate from bovine cartilage,BCS)、鲨鱼来源的硫酸软骨素(chondroitin sulfate from shark cartilage,SCS),通过单因素试验优化CS的降解条件,随后测定了降解产物的化学组成和结构,并且通过密度泛函理论(density functional theory,DFT)和分子动力学模拟(molecular dynamics,MD)试验探究了其潜在的机制。结果表明,CS的降解条件分别为乙酸铜浓度0.5 mmol、pH值7.5和反应温度45℃。降解产物的单糖和双糖组成结果表明,CS中的硫酸软骨素A(CSA)的...     

喷钙对红地球葡萄果实钙、果胶含量和品质的影响

为明确适用于红地球葡萄的补钙钙源、 时期和部位,设计了在葡萄果实发育的不同时期（幼果膨大期和采收前2周）对不同部位（叶片和果实）分别喷施硝酸钙和糖醇钙的田间试验,分析了喷钙后果实钙、 果胶含量和果实品质的变化。结果表明, 外源喷钙显著提高了红地球葡萄叶柄和果实各部位的钙含量。从喷钙时期上看,幼果膨大期喷钙对果实各部位钙含量的提高明显大于采收前2周喷钙;从钙源种类上看,硝酸钙适合叶片喷施,糖醇钙适合果穗喷施;从喷钙部位看,叶片喷糖醇钙对提高果实采收期的叶柄钙含量效果最为明显,喷钙后,在果实各部位中,果皮钙含量增加最多,为对照的6.6~20.3倍。在幼果膨大期和采收前2周两个时期,果穗喷钙对果皮钙含量的影响均明显大于叶片喷钙,叶片喷钙则更有利于果籽中钙含量的提高。幼果膨大期果穗喷糖醇钙处理采收后的果肉钙含量最高,达到3.98 mg/g,DW,是对照的2.84倍。果肉钙含量与果肉原果胶含量、 总果胶含量以及果粒硬度均呈极显著正相关,说明通过喷钙来提高果肉钙含量有助于提高果实的贮运品质。     

Enrichment of higher molecular weight fractions in inulin

Inulin (general formulas GFn and Fm, with G = anhydroglucose and F = anhydrofructose) naturally occurs as a homologous series of oligo- and polysaccharides with different chain lengths. For reasons of growing interest in the food and pet food industries, the short chain inulins have to be separated from their long chain analogues because their properties (digestibility, prebiotic activity and health promoting potential, caloric value, sweetening power, water binding capacity, etc.) differ substantially. To study these properties in relation to the number average degree of polymerization (DPn), ultrafiltration, specific crystallization from aqueous solution, and precipitation from solvent/water mixtures were used to enrich native chicory and dahlia inulin in the higher molecular weight fractions. Depending on the membrane module used, the DPn of chicory inulin (DPn = 8.1) and dahlia inulin (DPn = 29) could be increased by ultrafiltration to a maximum value of, respectively, 22 and 43. With crystallization from aqueous solutions (25 degrees C), similar results were obtained but at a much higher yield. Finally, long chain inulin could be precipitated from aqueous solutions in the presence of high concentrations of methanol, ethanol, and acetone. Acetone demonstrated to be the best solvent system to increase the DPn, followed by ethanol and methanol. However, for safety reasons and food purposes, ethanol was evaluated to be the best choice. With ethanol, the DPn could be raised to 25 for chicory inulin and up to 40 for dahlia inulin.     

小分子有机物质螯合钙肥的应用效果

采用盆栽试验,将两种小分子有机物(氨基酸、糖醇)为主剂的螯合钙肥与单质硝酸钙和市场钙肥产品糖醇钙(糖醇螯合钙)比较,研究叶面喷施和根施两种施肥方式对小白菜生长、品质和养分吸收的影响。结果表明：与硝酸钙和糖醇钙相比,无论是喷施还是根施,两种小分子有机物质螯合钙肥都能在不同程度上提高小白菜的钙吸收量,提高其生物量,改善品质;喷施和根施小分子有机物螯合钙肥Ⅰ与分别施用硝酸钙相比,小白菜生物量分别提高了33.63％和31.55％;喷施和根施小分子有机物质螯合钙肥Ⅱ与施用硝酸钙相比,小白菜的生物量分别提高了18.95％和49.95％。与硝酸钙相比,两种小分子有机物质螯合钙肥喷施可使植株钙累积量分别平均提高5.31％和6.84％;根施则使植株钙累积量分别提高13.51％和45.31％。另外,喷施、根施两种小分子有机物质螯合钙肥与施用硝酸钙与糖醇钙相比,均不同程度地提高了小白菜的Vc和可溶性蛋白含量,降低了硝态氮含量。因此,以氨基酸和糖醇为主剂的螯合钙肥无论采用喷施还是根施,都能对小白菜起到良好的增产提质效果。     

Influence of calcium carbonate on mean weight diameter of soil

Lime influences on soil structure and water stability of aggregates are vague and inconsistent. An understanding of the mechanism involved is needed for better management of soil structure. Calcium carbonate was added to soil samples from the BC horizon of two Mollisols to bring the calcium carbonate content to 0, 2, 4, 8, 16 and 32% on a dry weight basis. Increasing calcium carbonate content from 0 to 4% decreased the specific absorption rate of water but increased the mean weight diamter (MWD) of aggregates. Further increase in calcium carbonate content increased specific absorption rate and decreased MWD. Addition of calcium carbonate influenced porosity and pore size distribution of both subsoil samples. The rate of water absorption, and consequently the rate and extent of air-pressure build-up within aggregates, varied according to the variation in soil porosity and pore sizes. Variation in pressure build-up characteristics within aggregates influenced the disruption of aggregates in water to change the MWD. At any specific absorption rate, evacuation of air from aggregates prior to their immersion in water caused the MWD to be about 10 fold greater than their values when the aggregates were wetted in the presence of air.     

Metal binding with root exudates of low molecular weight

Root exudates were collected from maize plants ( Zea mays L .), grown under sterile and hydroponic conditions. Exudates of low molecular weight were isolated by filtration and dialysis (MW 1000) of the nutrient solution and analysed. Metal binding properties of the exudates were investigated at 25°C in 0.1 m NaCIO₄ ionic medium, using a potentiometric method. The total acidity of the exudates and the successive stability constants of complexes formed with Cu²⁺, Pb²⁺ and Zn²⁺ were determined.
Sugars and organic acids were the major components of the exudates. Measured total acidity was resolved into strong (5.85meq g⁻¹C), weak (2.10meq g⁻¹C) and very weak (2.20 meq g⁻¹ C) acidities. Mono-complexes were formed with Cu, Pb and Zn and bis-complexes with Cu. At pH 5, stability constants followed the order Cu>Pb>Zn.     

Molecular affinity and permeability of different molecular weight chitosan membranes

Membranes were prepared from chitosan with different molecular weights by a casting method. The molecular affinity and permeability of the membranes for sodium chloride, glucose, tyrosine, and bovine serum protein were measured at 4 degrees C and pH 7. The molecular permeability of the chitosan membranes was inversely related to molecular weight. All prepared membranes showed a molecular affinity to bovine serum protein. The higher the molecular weight of chitosan membrane, the higher the affinity and the lower permeability of the membrane to bovine serum protein.     

低分子量有机酸对红壤磷酸单酯酶活性的影响

采用室内模拟试验研究了低分子量有机酸(柠檬酸、草酸、苹果酸、酒石酸)对红壤磷酸单酯酶活性的影响。结果表明,低浓度有机酸(<1μmol g-1)对磷酸单酯酶活性有促进作用,且促进作用大小依次为柠檬酸≈草酸>苹果酸>酒石酸;而高浓度有机酸(>5μmol g-1)则为抑制作用,且抑制作用大小依次为柠檬酸>草酸>苹果酸>酒石酸。当体系pH趋向酶促反应最佳pH时,磷酸单酯酶活性增强;反之,当体系pH远离酶促反应最佳pH时,磷酸单酯酶活性减弱。有机酸根一方面通过羧基的辅助作用提高磷酸单酯酶活性;另一方面通过释放土壤A l3+、Fe3+等金属离子,对土壤磷酸单酯酶活性有一定的抑制作用。     

莲藕的酶促褐变及其贮藏中褐变的控制

为有效控制莲藕褐变,试验研究了温度、pH值、底物浓度以及抑制剂对莲藕多酚氧化酶（PPO）的影响。结果表明：莲藕PPO最适pH值为7.5,最适温度为35℃,以邻苯二酚为底物,米氏常数Km为0.0273 mol/L。亚硫酸钠、抗坏血酸（VC）对莲藕PPO活性具有较好抑制作用,乙酸、柠檬酸、植酸、木瓜蛋白酶、半胱氨酸也对莲藕PPO活性具有一定抑制作用。0.2%VC+2%乙酸+0.03%亚硫酸钠抑制剂处理对莲藕褐变的抑制效果最佳。可以通过浸泡亚硫酸钠和抗坏血酸（VC）、调节pH值、低温贮藏等方法来抑制莲藕PPO活性,控制莲藕褐变。     

Shifts in bacterial community structure associated with inputs of low molecular weight carbon compounds to soil

Low molecular weight carbon (C) substrates are major drivers of bacterial activity and diversity in the soil environment. However, it is not well understood how specific low molecular weight C compounds, which are frequently found in root exudates and litter leachates, influence bacterial community structure or if there are specific groups of soil bacteria that preferentially respond to these C inputs. To address these knowledge gaps, we added three simple C substrates representative of common root exudate compounds (glucose, glycine, and citric acid) to microcosms containing three distinct soils from a grassland, hardwood forest, and coniferous forest. CO₂ production was assessed over a 24 h incubation period and, at the end of the incubation, DNA was extracted from the samples for assessment of bacterial community structure via bar-coded pyrosequencing of the 16S rRNA gene. All three C substrates significantly increased CO₂ production in all soils; however, there was no relationship between the magnitude of the increase in CO₂ production and the shift in bacterial community composition. All three substrates had significant effects on overall community structure with the changes primarily driven by relative increases in β-Proteobacteria, γ-Proteobacteria, and Actinobacteria. Citric acid additions had a particularly strong influence on bacterial communities, producing a 2-5-fold increase in the relative abundance of the β-Proteobacteria subphylum. These results suggest that although community-level responses to substrate additions vary depending on the substrate and soil in question, there are specific bacterial taxa that preferentially respond to the substrate additions across soil types.     

Soil respiration rate and its sensitivity to temperature in pasture systems of dry-tropics

Abstract

Tree clearing is a topical issue the world over. In Queensland, the high rates of clearing in the past were mainly to increase pasture production. The present research evaluates the impact of clearing on some soil biological properties, i.e. total soil respiration, root respiration, microbial respiration, and microbial biomass (C and N), and the response of soil respiration to change in temperature.

In-field and laboratory (polyhouse) experiments were undertaken. For in-field studies, paired cleared and uncleared pasture plots were selected to represent three major tree communities of the region, i.e. Eucalyptus populnea, E. melanophloia, and Acacia harpophylla. The cleared sites were chosen to represent three different time-since-clearing durations (5, 11–13, and 33 years; n=18 for cleared and uncleared plots) to determine the temporal impact of clearing on soil biological properties. Experiments were conducted in the polyhouse to study in detail the response of soil respiration to changes in soil temperature and soil moisture, and to complement in-field studies for estimating root respiration.

The average rate of CO₂ emission was 964 g CO₂/m²/yr, with no significant difference (P<0.05) among cleared and uncleared sites. Microbial respiration and microbial biomass were greater at uncleared compared with those at cleared sites. The Q ₁₀-value of 1.42 (measured for different seasons in a year) for in-field measurements suggested a small response of soil respiration to soil temperature, possibly due to the limited availability of soil moisture and/or organic matter. However, results from the polyhouse experiment suggested greater sensitivity of root respiration to temperature change than for total soil respiration. Since root biomass (herbaceous roots) was greater at the cleared than at uncleared sites, and root respiration increased with an increase in temperature, we speculate that with rising ambient temperature and consequently soil temperature, total soil respiration in cleared pastures will increase at a faster rate than that in uncleared pastures.     

Determination of the absolute molecular weight averages and molecular weight distributions of alginates used as ice cream stabilizers by using multiangle laser light scattering measurements

High-performance size exclusion chromatography with multiangle laser light scattering detection (HPSEC-MALLS) was used for characterizing complete molecular weight distributions for a range of commercial alginates used as ice cream stabilizers. For the samples investigated, molecular weight averages were found to vary between 115 000 and 321 700 g/mol and polydispersity indexes varied from 1. 53 to 3.25. These samples displayed a high content of low molecular weights. Thus, the weight percentage of material below 100 000 g/mol ranged between 6.9 and 54.4%.