Rapid determination of alginate monomer composition using spectroscopy and chemometrics
Special Symposium - Innovations in Food Technology (LMC Congress)
Modern Analysis: Chemical & Multivariate Analysis (Food-6a)
Keywords: Alginate, spectroscopy, chemometrics
Tina Salomonsen1,2, Henrik Max Jensen1, Flemming Hofmann Larsen2 & Søren Balling Engelsen2
1Danisco A/S, Advanced Analysis, HPLC & NMR Laboratory, Edwin Rahrs Vej 38, 8220 Brabrand, Denmark
2University of Copenhagen, Faculty of Life Sciences, Department of Food Science, Quality & Technology, Rolighedsvej 30, 1958 Frederiksberg C, Denmark
Alginates are used as stabilisers, gelling and viscosity agents in the food and pharmaceutical industry. Alginates are linear polymers extracted from brown seaweed (Phaeophyceae) consisting of a mixture of mannuronic acid (M) and guluronic acid (G) units. The functionality of alginate in different applications is closely related to the M/G ratio and to the distribution of M and G along the chain. The M/G ratio and the M and G distribution of alginates in solution, can be determined by 1H NMR (Grasdalen et al. 1979 & 1983). However, at the concentrations convenient for NMR analysis, alginate solutions are too viscous to give well-resolved spectra. To reduce the viscosity, it is necessary to hydrolyse the alginate chain prior to NMR analysis. This hydrolysis is a relatively time-consuming and labour intensive and will shatter the M and G distribution of the original alginate polysaccharide. It will thus be preferable to have an alternative method (e.g. a rapid spectroscopic technique). FT-IR, NIR and Raman spectroscopy have been tested as alternative rapid methods for prediction of the M/G ratio. Using the multivariate regression method partial-least-squares (PLS) regression, the M/G ratio of alginate can be predicted from the FT-IR spectra with a prediction error comparable to the error from the NMR reference method. As a result, the measurement time is reduced considerably. Another issue of concern is the destructive nature of the hydrolysis procedure. It cannot be excluded that a source of error is introduced in the form of degraded, terminal carbohydrates during the hydrolysis. For this reason the potential of using non-destructive solid-state NMR techniques to determine the composition of alginate powders has been investigated.
References
Grasdalen, H., Larsen, B. & Smidsrød, O. (1979). NMR study of the composition and sequence of uronate residues in alginates. Carbohydrate Research, 68, 23-31.
Grasdalen, H. (1983). High-field 1H spectroscopy of alginate: sequential structure and linkage conformations. Carbohydrate Research, 118, 255-260.
Presented Thursday 20, 11:30 to 11:45, in session Modern Analysis: Chemical & Multivariate Analysis (Food-6a) Continued.
