大蒜的营养成分及其保健功能

本文主要论述了大蒜的功能性成分及保健作用,并从化学、保健和药理作用等方面分析了大蒜的利用潜力和发展前景,最后提出了大蒜的食用注意事项。     

Dung pads increase pasture production,soil nutrients and microbial biomass carbon in grazed dairy systems

In grazing systems dung is an important source of nutrients which can increase soil fertility and contribute to nutrient cycling through increased pasture production. Changes in soil chemical and biological properties and pasture production were measured below and around dung pads created in the field. Almost 65% of the total dung P remained after 45 days and about two-thirds of the pad fresh weight had disappeared in that time, indicating that physical degradation is the mechanism of incorporation of dung P. All the pads bar one were completely degraded by 112 days. At this time, soil pH and EC increased under dung pads as did Olsen extractable inorganic phosphorus (Pi) and total phosphorus (Pt), with these changes observed at 0–5 and 5–10 cm depths. Bicarbonate extractable soil organic phosphorus (Po) was not affected by dung and the observed differences in soil Po:Pi ratios were largely influenced by the substantial addition of inorganic P from dung. Dung increased the P buffering capacity of the 0–5 cm soil samples collected at the end of the experiment, potentially contributing to the increased extractable soil P measured under the pads. Dung also changed soil properties in 0–10 cm samples with increases in soil pH, EC, Colwell P and Colwell K recorded even long after the dung had completely disappeared. Microbial biomass carbon increased under dung pads in the 0–10 cm soil samples in the first 45 days after pads were applied. Total herbage production and ryegrass biomass increased significantly under and around the pads by 112 days after dung was applied. The botanical composition changed significantly with increased ryegrass contents observed, but only under the dung pads. This experiment demonstrated that increases in pasture around dung pads in the field are not solely due to animal rejection.     

Effect of chloride salt mixtures on selected attributes and mineral content of fermented cracked Aloreña olives

Sodium chloride is essential in table olive fermentation, storage and packing to guarantee safety and flavor. However, consumers are progressively concerned about sodium intake. In this work, the effect of selected attributes and mineral contents of fermented cracked Aloreña olives as a function of different chloride salt mixtures were studied, using a simplex lattice design with constrains (NaCl + CaCl₂ + KCl = 0.110 kg/l). The best fruit colour was observed at half proportions of KCl and NaCl or CaCl₂; optimum firmness was around the centre of the triangular coordinates but close to the line connecting CaCl₂ and NaCl vertexes; and the best overall quality was obtained in the 0.037 kg/l NaCl and 0.073 kg/l KCl mixture. The concentrations in the fermented olive flesh of the involved elements depended on their initial levels and on the CaCl₂ × NaCl and CaCl₂ × KCl interactions. Results demonstrate that sodium chloride can be replaced in table olives, at least partially, with potassium or calcium chlorides.     

Phytoplankton and benthic algal response to ecosystem engineers and multiple stressors in the nearshore of Lake Huron

Resurgence of nuisance benthic algae in the Great Lakes, despite substantial efforts to reduce phosphorus loading, has stimulated renewed interest in exploring the diverse drivers of near-shore water quality. Interestingly, broad similarity in the underlying causes of shore fouling by benthic algae in Lakes Ontario, Erie, and Michigan appear to contrast with Lake Huron where system productivity and dreissenid abundance are lower. While total phosphorus was the primary predictor of chlorophyll concentrations (70–90% of variation) in the water column, we identified a series of spatial patterns that underpin this relationship (up to 28% of variation) and which integrate catchment processes, tributary influences, shoreline complexity, and distance from shore. Dreissenid mussels were the most important predictors of benthic algae cover and biomass in our models, explaining between 20 and 52% of variation. Spatial patterns explained an additional 21–48% of the variation in benthic algae cover and biomass and highlight the importance of site-specific spatial heterogeneity in benthic algae growth. Our results are consistent with the nearshore shunt hypothesis, wherein higher algal cover and biomass coincided with higher mussel density and biomass, although correlative effects with lake depth and loss of algal and mussel biomass due to physical disturbance must also be considered. These results underscore the difficulty associated with identifying the potential drivers of nearshore water quality as the diverse processes of nutrient loading, changes in catchment land use, and ecosystem change associated with invasion by dreissenids all vary in relative influence over a range of spatial scales.     

Determination of the nitrogen compound balance between the atmosphere and a Norway spruce forest ecosystem

Wet, throughfall and stemflow deposition measurements of nitrogen compounds (NH₄ ⁺- and NO₃ ^–-ions) were carried out in a Norway spruce forest in Hungary, together with direct dry deposition and emission estimates (NH₃, NO, NO₂, HNO₃, N₂O gases, NH₄ ⁺ and NO₃ ^– particles). The total deposition of nitrogen compounds from the atmosphere to the forest ecosystem, estimated as the sum of the wet deposition and the measured dry flux, was 1.9 g N m^–2 yr^–1 for the examined period (1996–1998). The net deposition (difference of the deposition and the emission) was 1.8 g N m^–2 yr^–1. About 61% of the deposition is due to dry deposition processes. Ammonia gas dominates in the dry deposition (48%). Soil emission of nitric oxide (NO) and nitrous oxide (N₂O) constitutes only 5% of the total (wet and dry) deposition. From the comparison of directly measured dry deposition figures and the dry deposition calculated as the difference of the throughfall plus stemflow and wet deposition, it is probable that around 60% of the dry deposited nitrogen compounds (36% of the total, dry and wet deposition) are taken up by stomata, mostly in gaseous form. The remaining part (64%) of the deposited nitrogen compounds is leached to the ground where it is partly taken up by the root system, takes part in the soil mineralisation processes, or leaves the ecosystem by ground or surface water run-off.     

Identification of nutrients limiting cassava yield maintenance on a sedimentary soil in southern Benin,West Africa

Market opportunities will drive intensification of cassava production and fertilizer will play a role in this. A trial was initiated on 15 farmers fields (replications) in one village territory in Benin on a relatively fertile sedimentary soil site to identify nutrients limiting cassava yield using nutrient omission plots over three cropping years. There was no response to fertilizer in the first year when fresh root yields in the unamended control averaged 19.1 t ha^–1. In the second year, the control yield was 16 t ha^–1 and there were significant reductions from withholding P (3.5 t ha^–1) and K (2 t ha^–1) from a complete fertilizer regime. Nutrient balance after 1 and 2 years (cumulative) showed substantial P and K deficits in unamended plots. In the third year, the control yield was 12.9 t ha^–1 and effects of withholding K (5.3 t ha^–1), P (5.0 t ha^–1) and N (3.0 t ha^–1) were statistically significant. Soil K was a significant source of variation in yield in the third year. In the third year of annual nutrient additions soil P and K in the top 0.3 m were increased by 37 and 40%, respectively. Based on the cumulative nutrient balance calculation, the annual application needed to compensate nutrient depletion was 13 kg N, 10 kg P, and 60 kg K ha^–1. Partial budget analysis based on these amounts of fertilizer suggested that investment was clearly justified in the third year of continuous cropping at current low cassava prices.     

Baffled membrane bioreactor (BMBR) for efficient nutrient removal from municipal wastewater

Submerged membrane bioreactors (MBRs) are now widely used for various types of wastewater treatment. One drawback of submerged MBRs is the difficulty in removing nitrogen because intensive aeration is usually carried out in the tank and the MBRs must therefore be operated under aerobic conditions. In this study, the feasibility of treating municipal wastewater by a baffled membrane bioreactor (BMBR), particularly in terms of nitrogen removal, was examined. Simultaneous nitrification/denitrification in a single and small reaction tank was possible by inserting baffles into a normal submerged MBR as long as wastewater was fed in the appropriate way. To examine the applicability of the BMBR, pilot-scale experiments were carried out using real municipal wastewater. Although neither external carbon addition nor mixed liquor circulation was carried out in the operation of the BMBR, average removal rates of total organic carbon (TOC), total phosphorus (T-P) and total nitrogen (T-N) reached 85%, 97% and 77%, respectively, with the hydraulic retention time (HRT) of 4.7h. Permeability of the membrane could be maintained at a high level throughout the operation. It was found that denitrification was the limiting step in removal of nitrogen in the BMBR in this study. Various types of monitoring carried out in the BMBR also demonstrated the possibility of further improvements in its performance.     

Spurious Correlation in the USEPA Rating Curve Method for Estimating Pollutant Loads

Water quality models are important tools used for developing total maximum daily loads (TMDLs), which are used to implement water quality standards. The writers have developed a tool which spatially interpolates output from the Chesapeake Bay Program Watershed Model (WSM) and requires little time, data, or training. In contrast, the WSM requires extensive time, data, and training to run. This study examines if the writers’ tool provides accurate estimates of pollutant loads as compared to observed pollutant loads calculated using two different rating curve methods. The accuracy of the tool was assessed based on Nash–Sutcliffe coefficients. This study found that the tool provided moderate estimates of total nitrogen, poor estimates of total phosphorus, and that the rating curve method used to calculate observed loads affected the conclusion of the accuracy of the writers’ tool for predicting total sediment. A key finding of this study is that the widely used load-derived method for calculating observed loads exhibits spurious correlation. The writers discuss the imperative need to use sound statistical methods when estimating pollutant loads and TMDLs, and suggest an alternative approach for developing rating curves which is not subject to the problem of spurious correlation.     

Hydrogen production by Escherichia coli growing in different nutrient media with glycerol: Effects of formate,pH, production kinetics and hydrogenases involved

The Escherichia coli BW25113 or MC4100 wild type parental strains growth and H₂ production kinetics was studied in batch cultures of minimal salt medium (MSM) and peptone medium (PM) at pH of 5.5–7.5 upon glycerol (10 g L^?1) fermentation and formate (0.68 g L^?1) supplementation. The role of formate alone or with glycerol on growth and H₂ production via hydrogenases (Hyd) was investigated in double hyaB hybC (lacking large subunits of Hyd 1 and 2), triple hyaB hybC hycE (lacking large subunits of Hyds 1-3) and sole selC (lacking formate dehydrogenase H) mutants during 24 h bacterial growth. H₂ production was delayed and observed after 24 h bacterial wild type strains growth on MSM. Moreover, it reached the maximal values after 72 h growth at the pH 6.5 and pH 7.5. Biomass formation of the mutants used was inhibited ～3.5 fold compared with wild type, and H₂ production was absent in hyaB hybC hycE and selC mutants upon glycerol utilization on MSM at pHs of 5.5–7.5. Formate inhibited bacterial growth on MSM with glycerol, but enhanced and recovered H₂ production by hybC mutant at pH 7.5. H₂ evolution was delayed at pH 7.5 in PM, but observed and stimulated at pH 6.5 upon glycerol and formate utilization in hyaB hybC mutant. H₂ production was absent in hyaB hybC hycE and selC mutants upon glycerol, formate alone or with glycerol fermentation at pH 6.5 and pH 7.5; formate supplementation had no effect. The results point out E. coli ability to grow and utilize glycerol in MSM with comparably high H₂ yield: as well as they suggest the key role of Hyd-3 at both pH 6.5 and pH 7.5 and the role of Hyd-2 and Hyd-4 at pH 7.5 in H₂ production by E. coli during glycerol fermentation with formate supplementation. The results obtained are novel and might be useful in H₂ production biotechnology development using different nutrient media and glycerol and formate as feedstock.