Development and single-laboratory validation of a method for the determination of total fructans in infant formula

A number of methods have previously been developed for the determination of fructans in food products, resulting in the frequently used AOAC Official Methods 997.08 and 999.03. Method 997.08 has a lower LOQ, but the accuracy may suffer if significant quantities of sucrose are present. Method 999.03 is less affected by sucrose, but the LOQ is not as low as that of the other method. In this work we have combined these two methods, using the sample preparation steps of AOAC Method 999.03 to remove sucrose and other free sugars, and the detection procedure of AOAC Method 997.08 to achieve a low LOQ. The resulting new method achieved an LOQ of 0.13 g/100 g with powdered products (using 1 g sample weight) and recoveries in the range of 83-103% in the presence of sucrose at 12 g/100 g. Expanded measurement uncertainties were calculated and ranged from +/-17.4% at oligofructose and fructooligosaccharide (FOS) concentrations of around 0.2 g/100 g to -/+21.0% at FOS concentrations of 0.6 g/100 g.