Values for fructan in grass determined by a colorimetric method (McCleary) were consistently lower than those obtained by HPLC. This discrepancy was at least partially due to incomplete hydrolysis of grass fructan by the McCleary fructanase.
Introduction
Insulin resistance (IR) is associated with elevated intakes of WSC. WSC comprise simple sugars and fructans (oligo-or polyfructosyl sucrose). To enable appropriate ration formulation for IR horses, it is important that WSC components can be quantified accurately. Two methods are mainly used to analyse fructans, an enzymatic/colorimetric method and an HPLC technique. The former relies on quantification of monomers released after fructan hydrolysis by fructanase. Some values for grass fructan using this method seem low. Therefore, the fructan values obtained by both techniques were compared.
Materials and Methods
Samples of Phleum pratense, Dactylis glomerata and Lolium perenne were analysed for fructan by both the colorimetric and HPLC methods. Selected samples were then analysed by HPLC both before and after fructanase treatment.
Results
Values obtained by the McCleary method ranged from 10 to 94 percent of those obtained by HPLC. Post-fructanase treatment analysis revealed incomplete (28-50%) hydrolysis of grass fructan.
Discussion
Fructans in these grass samples were differentially sensitive to the fructanase employed in the McCleary method.
Clinical Relevance
If using fructan values for grass forage obtained by the colorimetric method for IR equid ration formulation, the efficacy of the fructanase against the forage should first be determined
Conclusion
The colorimetric method may yield artificially low values for grass fructan.
1Equine and Livestock Nutrition Services, Tregaron, Ceredigion, Wales, UK
2WALTHAM Centre for Pet Nutrition, Waltham-on-the-Wolds, Leicestershire, England, UK
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