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Selected physical properties of 13 coconut coir dusts from Asia, America, and Africa were compared to physical properties of sphagnum peat. All properties studied differed significantly between and within sources, and from the peat. Coir dusts from India, Sri Lanka, and Thailand were composed mainly of pithy tissue, whereas most of those from Costa Rica, Ivory Coast, and Mexico contained abundant fiber which was reflected by a higher coarseness index (percentage by weight of particles larger than 1 mm in diameter). Coir dust was evaluated as a lightweight material, and its total porosity was above 94% (by volume). It also exhibited a high air content (from 24% to 89% by volume) but a low easily available and total water-holding capacity which ranged from <1% to 36% by volume and from 137 to 786 mL·L–1, respectively. Physical properties of coir dust were strongly dependent on particle size distribution. Both easily available and total water-holding capacity declined proportionally with increasing coarseness index, while air content was positively correlated. Relative hydraulic conductivity in the range of 0 to 10 kPa suction dropped as particle size increased. Coir dusts with a particle size distribution similar to peat showed comparatively higher aeration and lower capacity to hold total and easily available water. An air–water balance similar to that in peat became apparent in coir dust at a comparatively lower coarseness index (29% vs. 63% by weight in peat). Stepwise multiple regression analysis showed that particles with diameters in the range of 0.125 to 1 mm had a remarkable and highly significant impact on the physical properties studied, while particles <0.125 mm and >1 mm had only a slight or nonsignificant effect.

The use of carbon nanoparticles is shown for the detection and identification of different Shiga toxin-producing Escherichia coli virulence factors (vt1, vt2, eae and ehxA) and a 16S control (specific for E. coli) based on the use of lateral flow strips (nucleic acid lateral flow immunoassay, NALFIA). Prior to the detection with NALFIA, a rapid amplification method with tagged primers was applied. In the evaluation of the optimised NALFIA strips, no cross-reactivity was found for any of the antibodies used. The limit of detection was higher than for quantitative PCR (q-PCR), in most cases between 104 and 105 colony forming units/mL or 0.1–0.9 ng/μL DNA. NALFIA strips were applied to 48 isolates from cattle faeces, and results were compared to those achieved by q-PCR. E. coli virulence factors identified by NALFIA were in very good agreement with those observed in q-PCR, showing in most cases sensitivity and specificity values of 1.0 and an almost perfect agreement between both methods (kappa coefficient larger than 0.9). The results demonstrate that the screening method developed is reliable, cost-effective and user-friendly, and that the procedure is fast as the total time required is <1 h, which includes amplification.FigureResults achieved with multi-analyte NALFIA for E. coli virulence factors. First strip: blank; second to sixth strip: each of the STEC factors; seventh strip: all factorsElectronic supplementary materialThe online version of this article (doi:10.1007/s00216-010-4334-z) contains supplementary material, which is available to authorized users.

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The microstructure of the mesocarp pithy tissue and short-length fibres of 2 differently processed coconut coir dusts from Mexico and Sri Lanka was studied using scanning electron microscopy and compared with that of a Sphagnum moss peat. Selected physical properties of these materials were also determined for their use in potting media. The 2 coir dusts did not significantly differ in the microstructural parameters studied, whereas they differed remarkably in their particle size and therefore in their physical properties. Pithy tissue was the major constituent of coir dust. Coarse pithy tissue particles (larger than 1 mm) were highly porous, with an internal porosity of 41.0% by volume. These particles exhibited round-shaped external pores which ranged in diameter from 30 to 80 μm, with an average of 44.3 μm, and which accounted for a relative surface porosity of about 40.9%. By contrast, the cells of Sphagnum peat moss leaves showed oval-shaped pores of 20.1 × 11.5 μm, which accounted for a relative surface porosity of only 12.0%. The internal porosity of peat moss leaves was 51.1% by volume. The retting process (soaking in water) applied to the coconut husks in Sri Lanka partially degraded the pithy tissue and coir fibres. Coir dust from Mexico showed lower water-holding capacity and higher aeration than peat, whereas air–water relationships in coir dust from Sri Lanka were similar to those in peat. Although differences observed in microstructure and porosity characteristics could explain the differential physical properties of the three materials studied, the major reason was the different size distribution of their constituent particles.