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 mea suring alginate content would be beneficial in a variety of applications. T his study reports on the use of near infra-red (NIR) analysis to monitor th e 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 degradatio n experiments and the total alginate content varied from 2.2 to 40.8% Na-al ginate (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 so me dependence on material type, probably reflecting differences in polyphen ol content. In the end, a PLS1 model with 9 components was selected. The ca lculated model was validated both with internal data and with an external t est set. Internal full cross validation explained 96.6% of the variance in alginate content. The external validation showed that the PLS1 model was ab le to predict the alginate concentration with a root mean square prediction accuracy of 2.1%.