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Session 1
Analysis of Aquaculture feed using near infrared spectroscopy
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Pérez Robres, Y. (1); Antolín Giraldo, G. (2)
1 CARTIF Foundation, Boecillo (Valladolid). Spain
2 Chemical Engineering and Environmental Technology Department. Valladolid University. Valladolid. Spain.
Aquatic organisms like fishes and crustaceans have high protein requirements and consequently, feeds rich in this nutrient are used for their feeding. Fish meal is typically regarded as the main protein source in diets for carnivorous fish due to its high level of protein.
The control of the protein concentration in aquaculture feed is needed because each aquatic specie has different nutrition necessities. The most used method to determine the protein content in feed is the kjeldahl. In this method, nitrogen is converted into ammoniacal nitrogen wich is determined by back titration; this value is multiplied by a conversion factor that takes into account the nitrogen content of a known or average amino acid composition. Although this method has high accuracy and reproducibility, it is slow and cumbersome and so unsuitable for rapid screening. With this purpose other alternative methods, like Near Infrared (NIR) spectroscopy, are been studied. The aim of this work was to develop a NIR method to quantify protein in aquaculture feed. Different systems of measure were used and a comparison between them based on the time of analysis and on the errors of validation was made.
Materials and methods 130 samples of feed with considerably variability in their composition and physical aspect were used. Among them, 70 samples were used for calibration and the other ones for external validation.
The reference method used to determine the concentration of protein was the kjeldahl. The range observed was 41,20-48,22 % expressed in dry weight.
The spectroscopic analysis were performed with a FT-NIR spectrometer (Bruker Optics) in a range of 12500 to 4000 cm-1 with a resolution of 8 cm-1. Samples were analyzed intact and milled by reflectance difusse in a rotating cup. Intact samples were also analyzed with a fiber-optic probe in order to diminish the time of analysis.
The chemometric analysis of data was made using the Bruker-OPUS software. Calibration models were developed with spectra absorbance units applaying PCR analysis. Cross-validation was used to test the models. The optimum factor number for calibration was selected based on R2. The model with the best predictive ability was selected by computing the RMSEE (Root Mean Square Error of Estimation ) and the RMSECV (Root Mean Square Error of Cross Validation).
An external calibration was made also; for that, a set of samples different from the calibration ones was utilized and the RMSEP (Root Mean Square Error of Prediction) was calculated.
Results
Table 1. Statistical descriptors
The statistical descriptors obtained with the different modes of measure in calibration and in validation are shown in table 1.
Discussion The results show that all the methods discussed are suitable for the determination of protein in aquaculture feed. The method developed with milled samples was the most accurate, however this is the most time-consuming because the preparation of the sample is required. The analysis realized employing the fiber-optic probe in direct contact with the sample are the most rapid.
In conclusion, one or other method will be used in function of the accuracy required.
Keywords: NIR spectroscopy, protein, aquaculture feed
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