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Impact of adding a second amyloglucosidase digestion to AACCI 32-45.01 (Total Dietary Fiber, Codex Alimentarius Definition) on fiber claims for rice products
W. PARK (1). (1) Texas A&M University, College Station, TX, U.S.A.

The CODEX compliant total dietary fiber assay AOAC 2009.01 differs from traditional dietary fiber assays such as AACC Method 32-05 (AOAC 985.29) and AACC method 32-07 (AOAC 991.43) both by utilization of mammalian α-amylase under more physiological conditions and by inclusion of low molecular weight material with DP >2 that is soluble in 78% ethanol. However the amount of fungal amyloglucosidase (AMG) specified in the original version of AOAC 2009.01 is not always adequate to achieve an actual digestion end-point for the low molecular weight fraction. To resolve this problem, a revised AOAC 2009.01 protocol has been proposed which includes a 2nd AMG digestion of the 78% ethanol soluble fraction. In this report, we specifically examine the impact of the proposed addition of a 2nd AMG digestion to AOAC 2009.01 on dietary fiber claims in different types of rice products. In a group of brown and milled prehydrated shelf stable rice products, for example, we found that inclusion of the proposed 2nd AMG digestion reduced the low molecular weight fraction from 2.4 ± 0.37% of the total dry weight to 0.57 ± 0.24%. This reduced the total dietary fiber value by 27 ± 7.2% for the brown rice samples in this group and by 35 ± 12% for the milled samples. Addition of the 2nd AMG digestion also caused substantial reduction in the amount of the low molecular weight fraction in standard dry rice. Without the 2nd AMG digestion, in some cases the low molecular weight fraction was the predominant fiber fraction in standard dry rice. To avoid substantial inflation of the total dietary fiber values in rice, it is thus important to add the proposed 2nd AMG digestion to AOAC 2009.01 to ensure that an actual digestion endpoint is reached for the low molecular weight fraction.

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