The sediment-stabilizing effect of benthic diatoms was investigated in a laboratory setting. Axenic cultures of the benthic diatoms Nitzschia cf. brevissima and Cylindrotheca closterium were inoculated in Petri dishes containing sand and incubated under axenic conditions. By ensuring aseptic routines throughout the experiments, interference from other organisms occurring with diatoms in natural photothrophic biofilms was avoided. This allowed the examination of the role of benthic diatoms in sediment stabilization. Increases in the critical erosion shear stress of the sediment were observed in the presence of both diatom taxa relative to sterile sediment. However, N. cf. brevissima was more effective than C. closterium. Values of critical shear stress in the experimental system were in the same range as those observed in natural biofilms, which indicates that diatoms are important agents for biogenic stabilization. Extracellular carbohydrate contents in the microcosms were similar for both diatom species. However, in the presence of N cf. brevissima, extracellular carbohydrate correlated significantly to critical shear stress, explaining up to 80% of the variation, whereas this was not the case for C. closterium. Therefore, it was concluded that the quantity of extracellular polymeric substances (EPS) alone did not explain the biogenic stabilization. Observed adsorption of EPS to sediment particles depended on the relative amount of uronic acids in the exopolymers. Using fluorescently labeled lectins, confocal laser scanning microscopy showed that EPS secretion by N. cf. brevissima resulted in ordered three-dimensional matrix structures. It is suggested that the structuring of EPS plays an prominent role in the process of biostabilization, and that diatoms such as N. cf. brevissima are actively involved in producing the structure of EPS, whereas others such as C. closterium do not do so to the same extent.

The beneficial role of dietary fibre in human nutrition has lead to a growing demand for incorporation of novel fibres, particularly barley β-glucans, into foods. Barley β-glucans are regarded as dietary fibre ingredients that are partially soluble in water. The aim of the present work was to investigate the possibility of using barley β-glucan in milk systems in relation to the coagulation properties of milk containing β-glucan, and to the rheology, texture and microstructure of fresh curds. The rate of coagulation and optimum coagulum cutting time were evaluated using rheological measurements. Results show that coagulation/gelation time of the milk can be reduced significantly with the incorporation of β-glucan; curd yield increased and the viscoelastic properties of the curd were altered with β-glucan additions. The relationships between curd rheological behaviour and its microstructure are discussed in relation to use of novel hydrocolloids in dairy processing. The results suggest that barley β-glucan has the potential to be used as a fat replacer in low-fat dairy systems.

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[1] The drag coefficient (C D ) is a fundamental parameter in the determination of shear stress or the drag force between a fixed object and fluid moving over it. In natural settings, conventional methods of defining it are largely impractical and so either smooth-bed C D or constant values are used irrespective of bed roughness or flow strength. This paper deals with the determination of C D over naturally roughened beds. The work was carried out in two annular flumes of known, constant water mass. In an otherwise balanced system, flow deceleration is a manifestation of the total drag force exerted at the rigid boundaries (Newton's second law). The inversion of this relationship is used to yield the bed drag coefficients. The advantages of this method include its accurate use over rough and irregular beds, as shown by experiments over patchy and homogeneous gravel beds and over a wide range of Reynolds numbers. The value of C D was found to converge to the constant value of 3 Â 10 À3 determined by Sternberg [1968] at intermediate velocities, and a reduction in the drag coefficient occurred at high velocities. Results showed that patch spacing did not influence the shear stress value in the case of one-grainthick gravel patches. A modification of the equipment for field use may give advantages where traditional methods fail due to difficulties in obtaining accurate velocity profile measurements.

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