doi:10.1094/CFW-58-5-0923 | VIEW ARTICLE

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Dietary Fiber Content of Cross-linked Phosphorylated Resistant Starch (RS4) Determined by the Prosky and McCleary Methods. Part II. Comparison of Assay Data1,2

C. C.Maningat,⁴P. A.Seib,^3,5 and S. D.Bassi<sup>4

1</sup>Statement related to conflict of interest: C. C. Maningat is vice president and S. D. Bassi is the former chief science officer of MGP Ingredients, Inc., the manufacturer of cross-linked phosphorylated resistant wheat starch (RS4). P. A. Seib is a consultant for the company.²Contribution No. 13-373-J from the Kansas Agricultural Experiment Station.³Corresponding author. Department of Grain Science and Industry, Shellenberger Hall, Kansas State University, Manhattan, KS 66506. E-mail: paseib@k-state.edu; Tel: +1.785.532.4088; Fax: +1.785.532.7010.⁴MGP Ingredients, Inc., Atchison, KS, U.S.A.⁵Kansas State University, Manhattan, KS, U.S.A. Cereal Foods World 58(5):252-263.

Cross-linking normal starch with a low level of phosphate groups (≈1/30 anhydroglucose units) is a general method used to dramatically increase the resistant starch (RS) content of a starch. Currently, total dietary fiber is recognized by Codex Alimentarius to be the sum of nondigestible polysaccharides, resistant oligosaccharides, and RS. Determining total dietary fiber in a food containing a substantial level of RS is difficult. RS is chemically equivalent to digestible starch, including the majority (≈97%) of the sparsely cross-linked phosphorylated (CLP) RS4-type starches. Resistance to digestion arises principally from variations in microstructure that limit the diffusion of alpha-amylase to starch molecules. For CLP (≈0.4% P) wheat starch, the McCleary method for measurement of total dietary fiber (AACCI Approved Methods 32-45.01 and 32-50.01 or AOAC Methods 2009.01 and 2011.25) gives a total dietary fiber content of ≈25% compared with ≈85% given by the Prosky method (AACCI Approved Methods 32-05.01 and 32-07.01 or AOAC Methods 985.29 and 991.43). We speculate that the difference results from the stronger starch-hydrolysis conditions of the McCleary method. Decreasing the digestion time in the McCleary method from 16 to 5 hr results in 95% digestion of wheat starch (negative control) and 30% digestion of the CLP wheat starch, which translates to ≈70% total dietary fiber. The classic Englyst in vitro assay, which has been validated by in vivo data for RS1-, RS2-, and RS3-type starches, also gives ≈70% RS for the CLP wheat starch.