AOAC RI ERP E-Book - DS DF

incubation. Thus, sodium azide is not added to the incubation buffer. Maltodextrin chromatographic standard solution and the glucose/glycerol reference solutions are prepared in 0.02 % sodium azide allowing these solutions to be stored and used over several years. In this method, SDFS is analysed using TSKgel ® G2500PW XL columns with in-line removal of anions and cations (10). The in-line desalting cartridges obtained from Bio- Rad have a limited capacity (25-30 samples). To reduce this cost factor (the cartridges are expensive), the SDFS fraction is deionized with anion and cation exchange resins in a polypropylene tube prior to HPLC. Deionisation removes 90-95% of ions and extends the life of the deionization cartridges by 15 to 20-fold. In the current method, SDFS is analysed on TSKgel ® G2500PW XL columns with a glycerol internal standard (6). For samples containing glycerol, diethylene glycol is a suitable alternative standard. In AOAC Method 2009.01, a Waters Sugar-Pak ® column is employed for measurement of SDFS. However, this column does not separate inulinotriose from disaccharides, resulting in a significant underestimation of the DF content of fructo-oligosaccharide mixtures. Based on the HPLC chromatographic traces supplied by collaborating laboratories along with their results, it was evident that in some laboratories the HPLC systems were not being run optimally. There was a significant upward slant of the baseline of the chromatogram during a run, indicating that column was partially blocked and operating pressure was likely above the recommended level. Backwashing of the column over 24-48 h prior to its continued use will re-optimise the column performance. Collaborator Comments No negative comments were received concerning the method, but one collaborator did notice an allergic reaction to the PAA/AMG powder mixture. Therefore the protocol now includes an option where a non-allergic analyst can suspend the enzyme powder mixture in ammonium sulphate solution to produce a stabilized liquid form that reduces the risk to a susceptible analyst. One collaborator did not have access to the deionising pre-columns, so they deionised the samples according to the formats in AOAC Research Institute ERP Use Only

Method updated 2008--08-10 This copy printed 22 August 2017

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