Direct determination of alginate content in brown algae by near infra-red (NIR) spectroscopy

The methods used to quantify total alginate in brown algal tissue are time-consuming and may also be misleading, so faster and simpler methods for measuring alginate content would be beneficial in a variety of applications. This study reports on the use of near infra-red (NIR) analysis to monitor the alginate content of Laminaria hyperborea stipe during biodegradation. NIR reflectance spectra were recorded for 78 different freeze-dried samples of its stipe. The samples were collected during several biological degradation experiments and the total alginate content varied from 2.2 to 40.8% Na-alginate (w/w), determined by established methods based on ion exchange. Data analysis was performed using multivariate calibration methods in order to relate the spectral data to the alginate content. PLS2 analysis revealed some dependence on material type, probably reflecting differences in polyphenol content. In the end, a PLS1 model with 9 components was selected. The calculated model was validated both with internal data and with an external test set. Internal full cross validation explained 96.6% of the variance in alginate content. The external validation showed that the PLS1 model was able to predict the alginate concentration with a root mean square prediction accuracy of 2.1%. This revised version was published online in June 2006 with corrections to the Cover Date.