AOAC RI ERP E-Book - DS DF

pancreatic α -amylase (PAA) plus amyloglucosidase (AMG) was reduced from 16 h to 4 h, inline with the likely time of residence of food in the small intestine. To ensure complete hydrolysis of non-resistant starch, PAA levels were increased 2-fold and AMG was increased 12-fold and under these conditions, resistant starch (RS) values obtained for a set of RS containing samples, were in line with RS values obtained for these samples from ileostomy studies. Resistant maltodextrins formed from non- resistant starch under incubation conditions of AOAC Method 2009.01 were no longer produced. HMWDF values obtained for samples which do not contain RS were essentially the same as those obtained with AOAC Method 985.29 and 991.43. The HMWDF values for many samples containing RS, were very similar to those obtained with AOAC Method 2009.01. Samples containing RS 2 (native, high amylose maize starch) and RS 4 (phosphate cross-liked native starches) however, gave much higher dietary fiber values. The current method, employing TSKgel ® G2500PW XL columns for chromatography, gave higher dietary fiber values for fructo-oligosaccharides than were obtained in previous methods using the Waters Sugar-Pak ® column. With the Sugar-Pak ® column, inulinotriose co-elutes with disaccharides and thus is not included in the dietary fiber value. Glycerol is used in place of D-sorbitol as the internal standard, inline with AOAC Method 2001.03, because D-sorbitol co-elutes with D- glucose on TSKgel ® G2500PW XL columns. An improved method for sample preparation for HPLC involves removal of the bulk of the anions and cations (salt) in the sample by mixing the sample with cation and anion exchange resins in a polypropylene tube. This step removes ~ 95% of the cations and anions, allowing more efficient use of the expensive, in-line, desalting pre-columns. With the shorter PAA/AMG incubation time, it is possible to eliminate the use of sodium azide in the incubation buffer solutions. The method described here measures HMWDF gravimetrically and SDFS by HPLC and the values are combined to give TDF. The method was evaluated through an ICC/AACC International collaborative study. A total of 13 laboratories participated, with all laboratories returning valid assay data for most of the 16 test portions (8 blind duplicates) consisting of samples with a range of content of traditional dietary fibers, resistant starch and non-digestible oligosaccharides. In total, just 4 sets of data from the 104 sets submitted were statistically excluded as outliers. The dietary fiber content of the 8 test pairs ranged from 6.79 to 60.6%. Within laboratory variability (s r ) ranged from 0.29 to 0.74 and the AOAC Research Institute ERP Use Only

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