Nutrient standards

The urgent need for nutrient standards was demonstrated during the recently completed World Ocean Circulation Experiment (WOCE) and Joint Global Ocean Flux Study (JGOFS) measurements which were made by different laboratories. The internal consistency of the nutrient data was evaluated by comparing measurements made in deep water (depth over 3500 m) at nearby stations on different cruises. If one assumes that nutrient concentrations in deep water at the same location should not... 

The techniques used to determine mineral requirements are the same as those used to determine energy and protein requirements. A theoretical framework is provided by using the factorial approach, whereas practical estimates of requirements can be obtained using nutrient balance or growth trials. Since the mineral contents of foods are usually expressed as the total or gross amounts present, requirements are stated in the same terms. Nutrient standards must therefore take into accoimt the differences in mineral availabUity that occiu between different species and age classes of animal (see Chapter 10). 

Tanner, J.T., Angyal, G., Smith, J.S., Weaver, C., Bueno, M., Wolf, W.R., and Ihnat, M., 1988. Survey of selected materials for use as an organic nutrient standard. Frezenius Zeitschrift fur Analytische Chemie. 322 701-703. 

Prepare a series of five dilutions of a basic matrix (LNSW, ASW or NaO) from lowest to highest expected sample salinities. Spike aliquots of the zero matrix with individual or mixed nutrient standard solutions to give five concentrations of each series from 0 to a high standard concentration (just above the expected maximum sample concentration). 

Analyse the samples and calibrate against the high-nutrient standard solution with medium salinity. Plot the deviations of the resulting concentrations from the nominal (spike) concentrations versus the spike concentrations (Fig. 10-3a). The plot should display a series of five straight lines (one regression line per salinity). If the basic matrix contains traces of nutrients, these concentrations or the respective dilutions must be added to the determined and the nominal concentrations. The medium (standard) salinity line is p u allel to the abscissa in concentration deviation zero and the higher and lower salinity lines are sjrmme-trically below and above. The plot indicates the linearity of the determination and shows whether the correction for a salt effect can improve the analytical accuracy. 

Normal blood plasma or semm levels of the mineral nutrients and the usual form ia circulating blood are given ia Table 2. Modes of absorption and excretion are summarized ia Table 3. Standard treatises on mineral nutrients (r4—r6, rlO—r21) and standard sources of nutrient composition (22,23) are available ia the Hterature. 

Feeding standards, which have been instituted nationally, indicate the amount of the essential amino acids (together with other nutrients) for the rational breeding of domestic animals. The feeding standards of the National Research Council (NRC) of the United States and Agricultural Research Council (ARC) of the United Kingdom are well known (the former indicates the minimal amount and the latter shows the recommended amount). 

Another standard test, which is much simpler and more convenient, is the membrane filter technique. A suitable volume of sample is filtered through a sterile, 0.45-p.m membrane filter. The filter is placed in a petri dish containing a specific growth medium (M-Endo nutrient broth, M-Endo medium) and incubated for 24 h at 35°C. If after this time the colonies show the characteristic green sheen, this is taken as positive evidence for the presence of the coliform group (see Water, sewage). 

Phenol Coefficient Test. The first important attempt at standardizing testing methods was known as the phenol coefficient test (96). It has been modified several times, and is an official AO AC screening test recognized by EPA and PDA. The phenol coefficient test compares the activity of disinfectants to that of phenol, under specific conditions, to give a number that measures the activity of the chemical tested with respect to that of phenol, ie, the phenol coefficient. The AO AC method employs visual examination of bacterial growth in a nutrient medium. The Kelsey-Sykes test (1969) is a modified method popular in British circles. 

In each cycle, the library of mutated genes is first inserted in a standard bacterial host such as Escherichia coli or Bacillus subtilis. Subsequently, bacterial colonies are plated out on agar plates and harvested individually by a colony picker. Each colony is placed in a separate well of a microtiter plate containing nutrient broth, so that the bacteria grow and produce the protein of interest. Because each colony originates... 

A shortage of any of some two dozen chemical elements that are essential for the growth of organisms can reduce ecosystem productivity, but phosphorus and nitrogen are often the most limiting nutrients, which is why these two elements are standard components of commercial fertilizers. Phosphorus is often limiting because it moves through soil pores and aquatic... 

Biological indicators (Bis) for use in thermal, chemical or radiation sterilization processes consist of standardized bacterial spore preparations which are usually in the form either of suspensions in water or culture medium or of spores dried on paper, aluminium or plastic carriers. As with chentical indicators, they are usually placed in dummy packs located at strategic sites in the sterilizer. Alternatively, for gaseous sterihzation these may also be placed within a tubular hehx (Line-Pickerill) device. After the sterilization process, the aqueous suspensions or spores on carriers are aseptically transferred to an appropriate nutrient medium which is then incubated and periodically examined for signs of growth. Spores of Bacillus stearothermophilus in sealed ampoules of cultrrre medium are used for steam sterilization morritoring, and these may be incubated directly at 55°C this eliminates the need for an aseptic transfer. 

Stoepplbr M and Zeisler R, eds. (1993) Biological environmental specimen banking. A collection of papers presented at the ist International Symposium on Biological Environmental Specimen Banking. Vienna, Austria, 22-25 September 1991. Sci Total Environ, Vols. 139 and 140. Tanner JT (1984) The FDA-IFC infant formula methods study and standards for organic nutrients. In Wolf WR, ed. Biological Reference Materials, pp 197-205. John Wiley Sons. 

Sharpless KE, Gill LM, Margolis SA, Wise SA, Elkins E (1999) Preparation of standard reference material 2383 (baby food composite) and use of an interlaboratory comparison exercise for value assignment of its nutrient concentrations. J AOAC Inti 82 276-287. 

USDA 1993) Nutrient Data Base for Standard Reference, Release. No. 10. Agricultural Research Service, Beltsville Human Nutrition Research Center, Nutrient Data Laboratory, BdtsviQe MD, USA. 

Currently, nutrient analytical methods development often utilizes the method of standard additions as an intrinsic aspect of the development process. Essentially, the analyte to be measured exists in the matrix to which an identical known pure standard is added. The spiked and non-spiked matrix is extracted and analysed for the nutrient of interest. By spiking at increasing levels the researcher can establish, to some degree of certainty, the recovery and linearity of the standard additions. One can also evaluate data to determine reproducibility, precision, and accuracy. Unfortunately, the method of standard additions does not allow the evaluation of the method at nutrient concentrations less than 100 % of the endogenous level. 

In practice, the Peclet number can always be ignored in the diffusion-convection equation. It can also be ignored in the root boundary condition unless C > X/Pc or A, < Pe. Inspection of the table of standard parameter values (Table 2) shows that this is never the case for realistic soil and root conditions. Inspection of Table 2 also reveals that the term relating to nutrient efflux, e, can also be ignored because e < Pe [Pg.343]

Table 2 Standard Parameter Values for the Uptake of Mineral Nutrients by Maize ...

Regular soil analysis is also important for checking the levels of the important nutrients - phosphorus, potassium, calcium and magnesium. Care should be taken to confirm the method of analysis, because the Scottish system and that carried out by organic laboratories and by Agricultural Development and Advisory Service (ADAS) laboratories have different standards. For instance, on the Scottish system, very low for potassium (the lowest level) is less than 40, whereas the... 

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