RI-ERP-FINALACTION-Recommendations

H ALL : J OURNAL OF AOAC I NTERNATIONAL V OL . 92, N O . 1, 2009 49

and average values for standard curves, starch detection limits were 0.2% for AB and 0.3% for ExtAOAC analysis of sample dry matter based on a 100 mg sample of 90% dry matter that required no dilution of the final volume for each assay.

ExtAOAC provided an economical use of laboratory resources that would be worthwhile to consider if revising method AB.

Recommendations

Selectivity

All methods gave very low starch values for sucrose, indicating that run conditions and enzyme preparations used did not appreciably hydrolyze this common feed component, which has been shown to interfere with starch analysis (Table 1; 8). Use of separate free glucose determinations allowed correction for free glucose and background absorbance associated with each sample. The final detection method is specific for glucose, which limits interference from other carbohydrates. Without use of an aqueous ethanol pre-extraction, maltooligosaccharides present in the samples would be determined as starch, but the error should be consistent across methods and should be small with the sample types used in this study. Unless samples are known to contain no maltooligosaccharides, or the explicit intent is to measure starch + maltooligosaccharides, a pre-extraction with an aqueous ethanol solution should be performed to remove these oligosaccharides to exclude them from starch analysis (3, 10). The standard deviations of replicates for starch + maltooligosaccharide analysis of the food and feed substrates and for purified substrates were low and did not differ among assays (Tables 1 and 2; P > 0.36). These values are comparable to or less than the repeatability standard deviation values (1.6–2.2) previously reported for method ExtAOAC when food or feed samples were analyzed (17). Both methods AB and ExtAOAC had the advantage that they allowed all additions to samples to be made in tubes, and they did not require a transfer of sample until the final dilution and measurement of glucose. With method AB, care did not need to be taken to ensure that samples were tapped to the bottom of the tube, as with method ExtAOAC, because the entire interior of the tube was rinsed with solution during mixing on a Vortex mixer. Measurement of the density of sample solutions in method ABmay not be necessary, because of the consistency of the value over time (0.999 g/mL, standard deviation = 0.002, n = 120, from 16 analysis runs over 16 months). Dilution by weight used in method AB offered an accurate way to handle the sample solutions that present pipetting difficulties, as well as a check on the accuracy of dilution that is not possible with volumetric methods. Use of the same temperature for the amyloglucosidase and glucose analysis incubations in method Repeatability Ease of Use

On the basis of achievement of greater values and recovery for starch + maltooligosaccharide analysis, very good repeatability among replicates, ease of handling of samples, and avoidance of known defects that can reduce the accuracy of other starch assays, the modification of the acetate buffer assay developed by Bach Knudsen (14) appears to be a viable candidate for full single-laboratory validation and collaborative study to establish an official method for determination of starch in animal feeds. (1) Huntington, G.B. (1997) J. Anim. Sci. 75 , 852–867 (2) Official Methods of Analysis (2005) 18th Ed., AOAC INTERNATIONAL, Gaithersburg, MD, Method 920.40 (3) ISO 15914E (2004) Animal Feeding Stuffs–Enzymatic Determination of Total Starch Content , 1st Ed., International Organization for Standardization, Geneva, Switzerland (4) Bernal-Santos, G., Perfield II, J.W., Barbano, D.M., Bauman, D.E., & Overton, T.R. (2003) J. Dairy Sci. 86 , 3218–3228 (5) Pham, T.H., Mauvais, G., Vergoignan, C., De Coninck, J., Cachon, R., & Feron, G. (2008) Biotechnol. Lett. 30 , 287–294 (6) Approved Methods of the American Association of Cereal Chemists (2000) 10th Ed., AACC International, St. Paul, MN, Method 776-11 (7) Hodge, J.E., & Osman, E.M. (1976) in Principles of Food Science, Part 1, Food Chemistry , O.R. Fennema (Ed.), Marcel Dekker, Inc., New York, NY, p. 58 (8) Hall, M.B., Jennings, J.P., Lewis, B.A., & Robertson, J.B. (2000) J. Sci. Food Agric. 81 , 17–21 (9) Gaillard, B.D.E. (1958) J. Sci. Food Agric. 9 , 170–177 (10) Official Methods of Analysis (2005) 18th Ed., AOAC INTERNATIONAL, Gaithersburg, MD, Method 996.11 (11) Dias, F.F., & Panchal, D.C. (1987) Starch/Stärke 39 , 64–66 (12) Antrim, R.L., Solheim, B.A., Solheim, L., Auterinen, A.-L., Cunefare, J., & Karppelin, S. (1990) Starch/Stärke 43 , 355–360 (13) Holm, J., Björck, I., Drews, A., & Asp, N.-G. (1986) Starch/Stärke 38 , 224–226 (14) Bach Knudsen, K.E. (1997) Anim. Feed Sci. Technol. 67 , 319–338 (15) Application Note 322 (2000) YSI Inc., Yellow Springs, OH (16) AOAC Guidelines for Single Laboratory Validation of Chemical Methods for Dietary Supplements and Botanicals (2002) AOAC INTERNATIONAL, Gaithersburg, MD (17) McCleary, B.V., Gibson, T.S., & Mugford, D.C. (1997) J. AOAC Int. 80 , 571–579 References

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