Yes, we believe that it is possible to accurately measure the galactomannan content based on the known galactose/mannose ratio. In studies we performed many years ago, we found that there was little difference in the ratio of galactomannans extracted from a wide range of carob seed varieties or of guar seed varieties; please refer to the papers cited below:
McCleary, B. V. (1981). Galactomannan quantitation in guar varieties and seed fractions. Lebensm. – Wiss. Technol., 14, 188-191.
McCleary, B. V., Dea, I. C. M., Clark, A. H. and Rees, D. A. (1985). The fine structures of guar and carob galactomannans. Carbohydrate Research, 139, 237-260.