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Tondel K.,Norwegian University of Life Sciences | Gjuvsland A.B.,Norwegian University of Life Sciences | Mage I.,NOFIMA Materials | Martens H.,Norwegian University of Life Sciences
Journal of Chemometrics | Year: 2010

Computer simulations are faster and cheaper than physical experiments. Still, if the system has many factors to be manipulated, experimental designs may be needed in order to make computer experiments more cost-effective. Determining the relevant parameter ranges within which to set up a factorial experimental design is a critical and difficult step in the practical use of any formal statistical experimental planning, be it for screening or optimisation purposes. Here we show how a sparse initial range finding design based on a reduced multi-factor multi-level design method-the multi-level binary replacement (MBR) design-can reveal the region of relevant system behaviour. The MBR design is presently optimised by generating a number of different confounding patterns and choosing the one giving the highest score with respect to a space-spanning criterion. The usefulness of this optimised MBR (OMBR) design is demonstrated in an example from systems biology: A multivariate metamodel, emulating a deterministic, nonlinear dynamic model of the mammalian circadian clock, is developed based on data from a designed computer experiment. In order to allow the statistical metamodel to represent all aspects of the biologically relevant model behaviour, the relevant parameter ranges have to be spanned. The use of an initial OMBR design for finding the widest possible parameter ranges resulting in a stable limit cycle for the mammalian circadian clock model is demonstrated. The same OMBR design is subsequently applied within the selected, relevant sub-region of the parameter space to develop a functional metamodel based on PLS regression. © 2010 John Wiley & Sons, Ltd.

Gibalova A.,Bioforsk Ullensvang | Vangdal E.,Bioforsk Ullensvang | Leufven A.,NOFIMA Materials
Acta Horticulturae | Year: 2012

The flavor of apples after storage is important to the consumers. Most often factors like decay, firmness and the contents of soluble solids and acidity are regarded as the limiting factors for storability of apples. The amount of volatile aroma compounds is less studied. Using head space analyses the amounts of 8 compounds known to be important to aroma of apples were studied during storage. Some compounds increased while others decreased during storage. Apples of three cultivars and from trees treated with foliar fertilization with nitrogen and calcium were included. The early ripening cultivar 'Discovery' had more aroma compounds in November and less in February. In the late ripening cultivar 'Elstar' the content of aroma compounds was low in November. However, the amounts were more than doubled in February. The foliar fertilization with nitrogen tended to reduce the amount of aroma compounds while the highest content was found in apples from trees treated with calcium. However, these tendencies were not statistically significant. In 'Discovery' the content of aroma compounds may be a limiting factor to the storability of this cultivar.

Rubingh C.M.,TNO | Martens H.,NOFIMA Materials | Van der Voet H.,Wageningen University | Smilde A.K.,University of Amsterdam
Chemometrics and Intelligent Laboratory Systems | Year: 2013

Each data-driven action in data modelling consumes degrees of freedom, whether it concerns estimation of parameters, estimation of meta-parameters or selecting variables. By using a double cross validation approach for degrees of freedom calculation the costs for meta-parameter estimation and variable selection can be determined explicitly. The only assumptions are independent and identically distributed errors, which make the approach applicable to many predictive modelling techniques. © 2013.

Ottestad S.,NOFIMA Materials | Ottestad S.,Norwegian University of Life Sciences | Sorheim O.,NOFIMA Materials | Heia K.,Nofima Marin | And 2 more authors.
Journal of Agricultural and Food Chemistry | Year: 2011

It has previously been observed that the color of mackerel muscle is dependent on the status of heme as myoglobin and hemoglobin and hence the storage atmosphere. This study gives strong indications of this being the case also in salmon. Three different storage conditions were used to promote the oxidized, reduced, and carbon monoxide (CO) bound forms of heme in salmon and mackerel fillets. Color determination (instrumental color analysis, imaging, and sensory evaluation) and spectroscopic measurements were performed to study how spectral changes corresponded to color variations. Storage in CO significantly increased the redness in mackerel. This was also seen in salmon to such a degree that it was visible over normal levels of salmon carotenoids. Air storage increased the yellowness and reduced the redness in mackerel, but this effect was partly concealed in salmon by the astaxanthin absorption. The spectral differences due to storage condition could be ascribed to the spectral features characterizing heme of different oxidation states and bound to different ligands. The status of heme should therefore always be considered when experiments related to salmon color are performed. The findings could help in the understanding, control, and prediction of color loss in salmon during processing, storage, and transport. © 2011 American Chemical Society.

Ottestad S.,NOFIMA Materials | Ottestad S.,Norwegian University of Life Sciences | Isaksson T.,Norwegian University of Life Sciences | Wold J.P.,NOFIMA Materials
Aquaculture | Year: 2012

The purpose of this work was to investigate how natural changes in optical properties in salmon muscle during storage affected the color of salmon and the prediction of astaxanthin based on spectroscopic measurements. Atlantic salmon (Salmo salar) were stored for 6. days at 2-4°C and measured once per day by an interactance probe at 449-744. nm. RGB (Red, Green, Blue) images were taken and were used to calculate average L*a*b* values and redness index (a*/b*). The interactance data revealed a systematic time dependent variation in the absorption at 450 and 600. nm. The redness index increased and the L* value decreased during storage. Partial least squares regression was used to calibrate the interactance spectra from day one against values of astaxanthin determined by high performance liquid chromatography. The calibration model was then used to predict astaxanthin concentrations in the same samples based on spectroscopic measurements performed during the following days. The optical changes were large enough to affect the prediction errors of astaxanthin significantly. A storage time of six days before measurement more than doubled the prediction errors compared to applying the models on data collected after two days. These results demonstrate the importance of keeping full control of the storage time and conditions, when making and applying spectroscopy based models for astaxanthin quantification. © 2011 Elsevier B.V.

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