Light-induced oxidation in semihard cheeses. Evaluation of methods used to determine levels of oxidation

Light-induced oxidation in Havarti cheese (38% fat) stored in the dark and exposed to fluorescent light was evaluated by an array of chemical, physical, and spectroscopic methods. Light-induced changes were noticeable already after short exposure times (<12 h). A clear differentiation between samples stored in the dark and samples exposed to 1000 lx fluorescent light was obtained by means of the following methods: color measurements (a values), peroxide value determinations, and evaluations of volatile oxidation products by solid-phase microextraction gas chromatography (SPME-GC). The expected changes in peroxide values in relation to storage time were not evident. Measuring free radicals by electron spin resonance spectrometry could not be done to distinguish between samples, possibly due to the conversion of radicals during sample preparation. However, significant light-exposure effects on secondary oxidation products, detected by SPME-GC, were noted for 1-pentanol, 1-hexanol, nonanal, and benzaldehyde.     

Effect of different membrane separation technologies (Ultrafiltration and microfiltration) on the texture and microstructure of semihard low-fat cheeses

Semihard low-fat cheeses made from ultrafiltered (UF) or microfiltered (MF) milk were compared. The use of MF membranes and milder pasteurization of the milk reduced the retention of whey proteins in the retentate to 35%, compared with approximately 100% retained in the UF process. Microbiological development, physicochemical composition, and cheese ripening were not altered by the concentration processes. The lower retention of whey protein in MF cheeses accounted for their higher hardness, which correlated with higher firmness values in the textural analysis. Microstructure showed a protein matrix with open spaces through the protein network, although micrographs of UF cheeses showed the presence of spongy structures linked to the casein, which did not appear in MF cheeses and which correspond to the denatured whey protein bound to the casein. Firmness was scored better in MF cheeses, although when MF membranes were used, the optimum yields achieved using UF membranes were not attained.     

Comparison of analytical methods for metribuzin.

Determinations of the active ingredient in technical and formulated metribuzin were compared by gas-liquid chromatography (GLC) using various solvents, infrared (IR) spectrophotometry, and high-pressure liquid chromatography (HPLC). Ketones could not be used as a solvent for GLC analysis because of Schiff base formation. The GLC method using ethylene glycol monomethyl ether gave results about 1% higher for technical metribuzin than the other methods. GLC using methylene chloride solvent agreed with IR and HPLC results to within 0.4%. GLC using methylene chloride is the preferred method.     

四种用于雷达遥感图像融合的空间分量提取方法

使用光学多光谱遥感图像对雷达图像进行空间增强,需要从光学多光谱图像中提取其空间分量。提取空间分量的基本方法有两种：主成分分析(PCA)和IHS变换法,PCA法可以对多光谱图像的所有波段进行分析,得到的第一主成分PC-1代表原始多光谱图像的空间信息,而IHS法只能输入多光谱图像的3个波段,经IHS变换得到的I分量代表原图像的空间信息;将用两种方法提取的PC-1和I分量直接与雷达遥感图像融合,发现PCA法的空间增强效果更为显著,而IHS法的色调保持效果更好。将PC-1和I分量分别进行0～255线性拉伸,然后与雷达遥感图像融合,发现二者对雷达图像的空间增强效果都显著增加,而色调保持水平均有所下降,但PCA法的空间增强效果仍然优于IHS法,而IHS法的色调保持水平仍然优于PCA法。该项研究为用户进行雷达图像融合提供了四种可供选择的提取空间分量的方法。     

A comparison of methods used for determination of cation exchange capacity

Abstract

Cation exchange capacity of ten non‐calcareous and non‐saline soils from Queensland, Australia, has been determined by the ammonium acetate method using different procedures, by an ammonium chloride method at pH8.5, and by three methods which attempt to approximate field conditions. Procedural differences in the ammonium acetate method produced variation in results, and methods using approximate field conditions gave much lower values for those soils considered to have variable charge properties.     

农田排涝模数计算方法的比较

正确计算排涝模数,对于确定排涝工程的适宜规模具有重要现实意义。该文以湖北省四湖流域螺山排区为例,根据排区下垫面条件进行产流计算,分别采用经验公式法和平均排除法计算不同排涝标准下的排涝模数,分析2种计算方法中排涝天数、排涝模数及排涝重现期之间的关系。结果表明:经验公式法对应于平均排除法的排涝天数为3.5d。当经验公式法求得的排涝模数小于平均排除法求得的排涝模数时(本区对应排涝天数小于3.5d),选用平均排除法计算排涝模数偏于安全;而当经验公式法求得的排涝模数大于平均排除法求得的排涝模数时(本区对应排涝天数大于3.5d),则选用经验公式法计算排涝模数偏于安全。此外,在排涝模数确定的条件下(即工程的排水能力一定),采用不同的排水公式校核排水标准时存在差异。一日暴雨时,采用平均排除法(采用三日排除)10年一遇和20年一遇的设计标准分别相当于经验公式法15年一遇和33年一遇的设计标准;而在三日暴雨下,平均排除法(采用五日排除)10年一遇和20年一遇的设计标准则分别相当于经验公式法4年一遇和7年一遇的设计标准。研究成果对合理选择排涝模数计算方法具有一定参考价值。     

Comparison of soil sampling devices used for sampling submerged soils

Abstract

Environmental sampling designed for soil chemical analyses requires precise procedural collection methods. Furthermore, soils which are submerged, represent an enigmatic sampling situation as the sample is withdrawn through the overlaying liquid layer. Contamination may arise from the liquid as well as solid material above the collected sample. A procedural problem is that close‐faced, lined samplers do not provide enough axial friction to maintain the sample within the sampler. Since the choice of proper sampling equipment is critical in site assessments, we compared two types of soil probes in this study. Both samples were nickel (Ni)‐chromium (Cr) plated having 2‐cm diameter bores. One was an open‐faced slotted sampler while the other was a closed‐faced sampler with a PETG copolyester liner. The open‐faced slotted sampler had no significantly different Ni or Cr content than did the PETG‐lined probe and maintained the soil within the sampling tube.     

Comparison of two immunochemical methods with thin-layer chromatographic methods for determination of aflatoxins

Three different methods were compared for the determination of total flatoxins in corn and peanuts naturally contaminated with aflatoxins and in corn, peanuts, cottonseed, peanut butter, and poultry feed spiked with aflatoxins B1, B2, and G1. The 3 methods were an enzyme-linked immunosorbent assay (ELISA) screening test; a monoclonal antibody-affinity column-solid-phase separation method; and the AOAC official thin-layer chromatography (TLC) methods for all except poultry feed, for which Shannon's TLC method for mixed feed was used. The ELISA test is designed to provide only positive results for total aflatoxins at greater than or equal to 20 ng/g or negative results at less than 20 ng/g. The affinity column separation is coupled with either bromination solution fluorometry to estimate total aflatoxins or liquid chromatography (LC) to quantitate individual aflatoxins. Fluorodensitometry was used to determine aflatoxins in commodities analyzed by the TLC methods. The LC and TLC results were in good agreement for all the analyses. The results for the affinity column using bromination solution fluorometry were similar except those for cottonseed, which were about 60% higher. The ELISA screening method correctly identified naturally contaminated corn and peanut positive samples. No false positives were found for controls. The correct response for spiked corn, raw peanuts, peanut butter, and cottonseed at greater than or equal to 20 ng aflatoxins/g was about 90%. The correct response for spiked poultry feed at greater than or equal to 20 ng aflatoxins/g was about 50%.     

Potential methods for estimating nitrogen fertilizer value of organic residues

New organic fertilizers based on waste products are continually being introduced in agriculture. Their nitrogen (N) fertilizer value of their total N and mineral N content varies widely, creating a demand for standardized laboratory methods. This study evaluated some potential methods for estimating the N fertilizer value of different kinds of organic fertilizers. The methods were evaluated against the N fertilizer value obtained from a ryegrass pot experiment. Fifteen fertilizers were tested, including different kinds of manure, powders from meat, bone, blood and feathers, rapeseed cake, lucerne pellets, sewage sludge, biogas residue, vinasse and mussel compost. Mineral fertilizer equivalents (MFE) were calculated as the fraction of total N (MFE) or organic N (MFE_org) out of total N that has the same availability to plants as inorganic N. Mineral N content (% of total N added with organic residue) after 4 weeks of incubation of soil was correlated to MFE (r² = 0.78), but was on average 17% lower. Warm water‐extractable N, amino acid N and crude fibre analysis all proved to be unsatisfactory as methods for estimating MFE or MFE_org. However, the carbon/nitrogen ratio accurately reflected short‐term plant‐available N through a negative linear relationship (r² = 0.83) and would thus be a very useful method for estimating MFE, with MFE decreasing by 5% per unit increase in C/N ratio. The results also indicated that the analysis of near infrared reflectance (NIR) spectra can be an even quicker and cheaper method to estimate MFE of organic residues, but this issue requires further research.     

Comparison of several spatial prediction methods for soil pH

A survey of topsoil pH has been designed specifically to compare the performance of several two-dimensional spatial prediction methods. These methods have been classified as global or local, and interpolating or non-interpolating, and smooth or non-smooth predictors. The techniques tested were global means and medians, moving averages, inverse squared distance interpolation, Akima's interpolation, natural neighbour interpolation, quadratic trend surface, Laplacian smoothing splines and ordinary kriging. All methods showed some deficiencies; for example, prediction sums-of-squares were higher than expected for all methods. Interpolating methods either were very poor predictors, or suffered from theoretical drawbacks, or both. Of the non-interpolating methods, Laplacian smoothing splines and kriging generally performed best. Estimates of variance derived from models which assume independent errors were greater than estimates of variance derived from neighbouring pairs of data sites, suggesting that short range correlations definitely exist, and should be taken into account in any predictive modelling.     

小鼠ES细胞神经分化的方法比较研究

采用类胚体法(EB)的EB分化4-／4 程序和单层分化法研究不同的实验方法对胚胎干细胞神经分化的影响。用4-／4 分化程序进行胚胎干细胞的神经分化时，饲养层细胞的存在对类胚体的形成无影响，在神经分化的13d，仍可观察到46C细胞的Sox1-GFP绿色荧光，此时的免疫染色结果显示，分化细胞中除了有Nestin阳性的神经干细胞及胶质纤维酸性蛋白(GFAP)阳性的神经胶质细胞外，以β-tubulin Ⅱ阳性神经元细胞最为多见，这些神经元呈现出多种形态；用单层分化法进行胚胎干细胞(ES)细胞的神经分化至13d时，分化形成的神经细胞种类与类胚体法相同，但神经元的细长纤维形成了复杂的网状结构，提示两种分化方法获得的神经元处于不同发育阶段。研究结果表明，两种分化方法均能为ES细胞提供从神经分化的起始到继续分化所需的环境，EB分化法适合于大量地获取分化的细胞，而单层分化法可直观地研究分化过程的细胞变化。     

玉米生育期空间插值方法比较

采用合适的空间插值方法可以估计全国主产区玉米生育期的空间分布情况,从而指导不同地区的种植生产。该文通过比较反距离加权法、径向基函数法、克里格法等插值方法的异同,以调查县夏播玉米5个阶段的生育期为数据源,对黄淮海夏播玉米区生育期的数据进行空间插值处理,并使用交叉验证对表面精度进行分析。结果表明：播种期、出苗期和成熟期的最适合插值方法为径向基函数法,其均方根预测误差分别为5.077、5.320、5.243 d,拔节期和抽雄期的最佳插值方法为反距离加权法,其均方根预测误差分别为7.826、6.403 d;播种期和出苗期由西南至东北逐渐延后,其余阶段生育期以东南至西北为中轴线向两侧逐渐延后。     

Comparison of some methods for determination of sulfate in soils

Abstract

Sulfate (SO₄ ^2‐) is present in soils as salts of various metals, and the different metals associated with sulfate may influence adsorption of SO₄ ^2‐by soils. The analytical method used for determination of SO₄ ^2‐could be affected by the type of metal associated with the SO₄ ^2‐. Four analytical methods based on different principles were evaluated for determination of SO₄ ^2‐in different metal salts and in soil extracts obtained with three extractants {0.1M lithium chloride (LiCl), 0.15% calcium chloride (CaCl₂), and 500 mg P/L as calcium phosphate [Ca(H₂PO₄)2]}. The analytical methods were: (i) a methylene blue (MB) colorimetric method after the reduction of SO₄ ^2‐to hyrogen sulfide (H₂S), (ii) an ion Chromatographie (IC) method, (iii) a turbidimetric (TD) method, and (iv) an indirect barium (Ba) atomic absorption spectrophotometric (SP) method. The recovery of SO₄ ^2‐associated with various mono‐, di‐, and tri‐valent metals was quantitative by the MB method. But, trivalent metals, such as aluminum (Al), indium (In), lanthanum (La), and scandium (IC), decreased the recovery of SO₄ ^2‐by the other three methods. The MB and IC methods gave similar values for SO₄ ^2‐in soils by using the three extractants. The TD and SP methods gave variable results and, in general, underestimated the amounts of SO₄ ^2‐in soils. Among the four methods, the MB and IC methods were the most accurate and precise.     

土壤速效磷含量空问插值方法比较研究

采用土壤空间变异及其插值方法,对上海五四农场现代化农业园区水稻田60m×60m间隔采样,得到280个土壤有机质含量、速效磷、速效钾、全N、全P等采样数据,用逆距离加权、球面多项式、局部多项式、辐射基础函数、简单克立格、通用克立格、平常克立格(指数模型、球形模型、高斯模型、静态模型)等插值方法,对该区土壤速效磷含量的140采样点进行插值,得到各种插值的速效磷连续空间分布,将插值所得拟合值与同期测得的另140个采样点数据进行比较,则局部多项式插值、球面多项式和3种克立格插值方法效果较好,其中局部多项式插值方法效果最佳,平常克立格的静态模型、高斯模型和球形模型插值效果较佳。     

水稻硅吸收动力学参数固定方法的研究

本文采用常规耗竭法和改进耗竭法研究了水稻苗期硅的吸收动力学参数,着重对测定方法、数据处理方式及参数的量纲表示等进行了初步探讨。结果表明,不同的试验方法、数据处理方式及不同的量纲表示得到的水稻苗期硅吸收动力学参数值的大小不同。为使试验结果真实可靠,应该用不同的数据处理方式对数据进行处理并用相关系数的大小对数据作出评价。在本试验中,根据相关系数的大小得出,改进耗竭法优于常规耗竭法;不同的数据处理方式中,作图法得到的数据准确性最高;Vmax用mg/(g.h),DW作量纲时得到的硅吸收动力参数值较为合理。     

Comparison of collection methods for determination of forage nutritive status

Abstract

Forage samples were collected from pastures amended with one of five biosolids (municipal sludges) and fertilizer treatments (year one) or eleven treatments in year two. Forage samples were collected six times during each year, once every 28 d, beginning in mid‐June. Two methods of forage collection were compared, the cage method and the transect method. The transect method involved collecting samples at different areas of a pasture to more closely mimic what the animals appeared to consume. In year one, forage samples obtained using the cage method were collected from permanent cages (approximately 2 m diameter) randomly placed, but then fixed in position in each pasture. In year two, the cages were randomly moved to new spots following each sampling and mowing. During year one, copper (Cu), zinc (Zn), and iron (Fe) concentrations differed (P<0.05) by collection method several times, with microelement concentrations from cage samples routinely being higher than from transect samples. Differences were observed at fewer sampling times during year two for Cu and Fe, but Zn concentrations differed at each sampling time. The macroelements followed a similar pattern, with more differences due to collection method observed during year one than year two. The in vitro organic matter digestibility (IVOMD) and crude protein (CP) results suggest an effect of increasing maturity for the transect samples contributing to the differences observed in collection methods in year one. When forage collection methods differed in forage mineral concentrations, cage samples gave routinely higher units but this difference was reduced when cages were moved to new locations following sampling.     

Comparison of several methods for determining free iron in soils

In the previous paper (1), for determining free iron in paddy soils the writers proposed a new method in which free iron was removed by reduction with sodium hydrosulfite in disodium ethylendiamine tetraacetate solution. As described in that paper, many methods have been proposed up to the present time. In this paper the writers are to compare their method with some of those methods, especially with both methods using sodium hydrosulfite and dilute hydrochloric acid and using hydrogen sulfide and dilute hydrochloric acid. The latter method has generally been employed for free iron determination of paddy soils in Japan.     

Comparison of two chemical methods for extracting residual N fertilizer

Summary Considerable effort has been spent in developing chemical indices to predict N mineralization. However, in spite of numerous studies, the relationship between the index value and plant N uptake has not been as apparent as hoped, and therefore, additional work is required to evaluate the ability of promising new indices to predict the extraction of mineralizable N from soil. The objective of the present study was to evaluate the use of phosphate borate and hot KCl to extract immobilized ¹⁵N-labeled fertilizer, applied 1 and 2 years previously. Soil samples (0–15 cm) were collected on 12 June 1989 from field soil fertilized in either 1987 or 1988 with ¹⁵N-labeled urea. In the laboratory, net N mineralization over 51 days and the amount of N extracted by the phosphate borate and hot KCl methods were determined. In the field, the amount of residual fertilizer and soil plus fixed N in soybeans (Glycine max) at the V5 growth stage were determined on 12 June 1989. The extractability ratio (ER^*) and the mineralizable extractability ratio (MER) were higher for mineralizable N and phosphate borate N for fertilizer applied in 1988 than 1987, while ER^* and MER values for the hot KCl were similar for both application dates. These results suggest that compositional changes occurred which influenced the extractability and mineralization of residual fertilizer applied 1 and 2 years previously, and that the phosphate borate was able to predict these changes while the hot KCl method was not.