I am trying to use an in vitro assay to measure the rapidly digestible starch, slowly digestible starch and resistant starch content of whole wheat and white flour bread. We have done this assay successfully on many other products but I am getting some odd results with the bread. We are getting about 2% rapidly digestible starch and 30% resistant starch with estimated glycemic index of 80-100. The resistant starch seems too high. We have tried using fresh bread, freeze dried bread, and boiled freeze dried bread. The results have been comming out the same no matter how we treat the samples. All of our enzmes are fresh. Does anyone have an idea what may be going wrong?
There are problems in using this methodology for characterising starch, especially when the starch is part of a complex heterogeneous food matrix and may or may not have been subjected to physical disruption and/or hydrothermal processing. Characterising starch and starch-rich foods into different categories, namely “slowly” and “rapidly”, or as we prefer, “readily” digestibility types (SDS and RDS, respectively), when no check has been made whether the digestion follows first-order digestion kinetics leads to false ideas about starch digestibility. Clearly, if the digestion process is first order, all of the starch is of the same intrinsic activity. However, if experiments reveal that digestion follow more complex kinetics, this may provide hints as to the availability of certain starch fractions to alpha-amylase action. The following references are recommended, since these explain the problems and pitfalls inherent in RDS and SDS classification. Indeed, these references highlight an alternative approach to analysis of starch digestibility curves, especially for complex food systems such as your bread samples.
Butterworth, P.J., Warren, F.J., Grassby, T., Patel, H. and Ellis, P.R. (2012) Analysis of starch amylolysis using plots for first-order kinetics. Carbohydrate Polymers 87, 2189-2197.
Butterworth, P.J., Warren, F.J. and Ellis, P.R. (2011) Human α-amylase and starch digestion: An interesting marriage. Starch/Stärke 63, 395–405.
Peter Ellis and Peter Butterworth
Peter,
Thank you for your informative answer. I will have a look at those papers.
I need to know the best practical routine method to do meat species identification using pcr techenic , and send trainer to take course in the department related .
Fahiim, I think Campden BRI and Leatherhead Food Research in the UK, offer training courses, their websites are:
http://www.campdenbri.co.uk/
http://www.leatherheadfood.com/
By the way, you will probably get more answers by posting your own question rather than as an answer to an unrelated one.
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