DETERMINATION OF CRYSTALLINITY OF CARBOHYDRATES BY 13 C CROSS POLARIZATION/MAGIC ANGLE SPINNING NMR WITH APPLICATIONS TO THE NUTRITIVE VALUE OF FORAGES

An NMR technique using solid samples is presented. The relative "crystallinity" of carbohydrates is estimated by the use of a 20 ms delayed contact pulse sequence. There was good agreement between the crystallinity of cellulose determined by the NMR procedure and that estimated by using an acid hydrolysis procedure. The "crystallinity index" (crystallinity relative to that of cellulose powder at 100) of timothy stems increased from seven for samples cut on 30 June to 16 for those cut on 15 July. Mature-weathered timothy stems which were collected in the spring had a "crystallinity index" of 20. The carbohydrate crystallinity index increased from 10 in alfalfa-grass hay to 49 in a sample of fecal fiber from a steer fed this hay indicating that noncrystalline carbohydrate is preferentially digested in the animal. Treatment of fecal fiber with ammonia decreased the crystallinity index. It was concluded that the NMR technique can provide useful information concerning the nature of the carbohydrates in forages. Key words: I3 C CP/MAS NMR, delayed contact pulse sequence, crystallinity, carbohydrates