The K-FRUC method measures all native fructans. If the sample contains hydrolysed fructan such as riftilose, the terminal reducing sugar will be reduced to a sugar alcohol in the pre-treatment step. This sugar will then not be measured. Typically, for a product as Riftilose, the underestimation of fructan due to this reaction is ~ 20%.

If the fructan is a native (non-reducing) fructan, it will be measured quantitatively independent of the molecular size.