X-ray microtomography: a new tool in assessing the properties of aquatic feed
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X-ray microtomography: a new tool in assessing the properties of aquatic feed

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Sustainability of aquafeeds implies the use of ingredients originating from different sources and alternative locations. As a result of this, there is an increasing trend to replace fishery-derived ...

Sustainability of aquafeeds implies the use of ingredients originating from different sources and alternative locations. As a result of this, there is an increasing trend to replace fishery-derived ingredients with a variety of plant sources, especially legumes, cereals and oilseeds. If we look further into the future it is likely that other sources, for example bacterial, yeast and algae, will also become viable. Besides the nutritional quality of feed, it is necessary to acquire knowledge about the functionality of these sources in the production process, before they can be fully used in a commercial context. In other words, how these ingredients behave in terms of their processing, their interaction with other ingredients and the end physical quality of the feed.

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X-ray microtomography: a new tool in assessing the properties of aquatic feed X-ray microtomography: a new tool in assessing the properties of aquatic feed Document Transcript

  • I N C O R P O R AT I N G f i s h far m ing t e c h no l og y January | February 2014 X-ray microtomography: a new tool in assessing the properties of aquatic feed International Aquafeed is published six times a year by Perendale Publishers Ltd of the United Kingdom. All data is published in good faith, based on information received, and while every care is taken to prevent inaccuracies, the publishers accept no liability for any errors or omissions or for the consequences of action taken on the basis of information published. ©Copyright 2014 Perendale Publishers Ltd. All rights reserved. No part of this publication may be reproduced in any form or by any means without prior permission of the copyright owner. Printed by Perendale Publishers Ltd. ISSN: 1464-0058 The International magazine for the aquaculture feed industry
  • FEATURE X-ray microtomography: a new tool in assessing the properties of aquatic feed by Vukasin Draganovic, feed production researcher, Skretting Aquaculture Research Centre, Norway S ustainability of aquafeeds implies the use of ingredients originating from different sources and alternative locations. As a result of this, there is an increasing trend to replace fishery-derived ingredients with a variety of plant sources, especially legumes, cereals and oilseeds. If we look further into the future it is likely that other sources, for example bacterial, yeast and algae, will also become viable. Besides the nutritional quality of feed, it is necessary to acquire knowledge about the functionality of these sources in the production process, before they can be fully used in a commercial context. In other words, how these ingredients behave in terms of their processing, their interaction with other ingredients and the end physical quality of the feed. The substitution of one ingredient for another is not simple, as it can alter physical properties of pellets including their durability and the absorption of oil. These mechanical properties of feed pellets can be clearly understood if we can effectively describe their structure. The problem lies in finding a suitable technique that can help in characterising the internal structure of the pellet. The downsides of traditional imaging techniques like light or electron microscopy are that these techniques are two-dimensional, and that they just give information about the fracture plane of a product. In addition, a sample needs to be prepared. This usually involves cutting, which can in turn alter the product structure. Another option is pycnometry, where the pressure is applied for the penetration of gas into the porous fish feed pellets. This can however cause cracks in the cell walls and it seems therefore to be a less suitable technique. Figure 1: Micro-CT principle (Source: Bruker micro CT) ‘As is’ analysis X-ray microtomography is an invasive imaging technique, meaning that no sample preparation is needed and the structure is analysed ‘as is’. So, no coating or vacuum treatment is needed to prepare the sample. Microtomography, like tomography, uses X-rays to create cross-sections of a threedimensional object (see Figure 1). The term ‘micro’ is used to indicate that the pixel sizes of the cross-sections are in the micrometer range. The principle is very similar to that of a medical CT scanner. The only difference to a clinical one is that in the case of the micro CT scanner, the X-ray source and detector remain in a fixed position (see Figure 2). This technique allows Skretting techni- Figure 2: Difference between clinical and micro CT instrument (Source: University of Leicester) 34 | InternatIonal AquAFeed | January-February 2014 cians to see cross-sections of the inner pellet, without the usual need to physically cut the sample with a razor blade. Once the pellet is scanned, software can generate three-dimensional images of the sample’s morphology and internal microstructure with resolution down to the sub-micron level. Subsequently, various microstructural features of the porous pellet including the average size of the cells, pore size distribution, cell wall thickness and its open and closed porosity can be quantified. Applications Skretting Aquaculture Research Centre has applied this imaging technique to both dry kernels and pellets coated with oil. Differences in density between the solid matrix, oil and air (void cells) can be easily detected by X-rays. The measurements were limited to an appropriate volume of interest, that is, a cylinder located in the centre of each pellet (see Figure 3). From the right-hand image it can be seen that some cells are still not yet filled with oil, although both products have the same density, were coated with the same amount of oil and have the same visual appearance. These results indicate that the infusion of oil into the product could be studied further with this technique. For example, the effect of different protein sources could be visualised in future research. Using X-ray microtomography to visualise the microstructure of fish feed can also assist
  • FEATURE Figure 3: Three-dimensional models of two coated products obtained by XMT. The objects presented are the volume of interest, not the whole pellet. The blue areas represent oil, white areas are void cells, and the continuous solid matrix is represented as green or red (dense material) in the further optimisation of the physical quality of the pellet. Applications include the reduction of undesired fat migration out of the product, increasing pellet durability or controlling the sinking-floating behavior of aquafeed. Feed pellets must meet a series of physical specifications. They must be sufficiently durable to withstand the stresses exerted during transport and handling, and by pneumatic feeding devices. In addition to this, the pellets must be consistent in appearance, size and density, the last of which must be controlled precisely during the extrusion process to give the required oil absorption and sinking speed characteristics. Pellets that stay afloat will not be eaten, and pellets that sink too fast may escape being eaten by the fish altogether. The X-ray technology can, in addition play an important role in developing new feeds with the inclusion of novel raw materials that meet all required quality criteria. From the x-ray scans, we can see how one ingredient affects the structure of the pellet. A more compact structure from increased cell wall thickness inside the pellet will in turn result in a more durable product. The size of the pores also plays an important role when it comes to oil absorption. Using this technology, we have defined an optimal range of pore size distribution and interconnectedness between the pores, which will ensure good oil infusion and reduced fat leakage during product storage. At Skretting we are always screening different ingredients and looking at how they affect these parameters. Knowing this, we can select the right ingredients. Extruder OEE for the Production of Fish Feed AMANDUS KAHL GmbH & Co. KG, Dieselstrasse 5-9, D-21465 Reinbek / Hamburg, Phone: +49 40 727 71 0, Fax: +49 40 727 71 100, info@amandus-kahl-group.de January-February 2014 | InternatIonal AquAFeed | 35 www.akahl.de View slide
  • LINKS This digital re-print is part of the January | February 2014 edition of International Aquafeed magazine. Content from the magazine is available to view free-of-charge, both as a full online magazine on our website, and as an archive of individual features on the docstoc website. Please click here to view our other publications on www.docstoc.com. I N C O R P O R AT I N G f I s h fA R m I N G T e C h N O l O G y Successful moisture control in aquatic feeds Current challenges and opportunities in amino acid nutrition of salmonids • See the full issue • Visit the International Aquafeed website • Contact the International Aquafeed Team • Subscribe to International Aquafeed Whisky by-products: – a sustainable protein source for aquaculture Closing the food waste loop: – a new angle for insect-based feeds Vo l u m e 1 7 I s s u e 1 2 0 1 4 - JA N uA RY | F e B R uA RY To purchase a paper copy of the magazine, or to subscribe to the paper edition please contact our Circulation and Subscriptions Manager on the link above. INFORMATION FOR ADVERTISERS - CLICK HERE www.aquafeed.co.uk View slide