I have situations that the calculated in vitro starch digested ratio exceeded 100% (about 120~130%) using the GOPOD procedure. That's illogical. I am so confused.
Analytical methods do have (sometimes large) margins of error. Have you taken those into account in your calculations and conclusions. Sampling is another, sometimes large, source of variation.
Thanks! C.A. (Kees) Kan. I also agree that the analytical method is the key point, including the enzymes used, enzymatic activity, target hydrolysates corresponding to GOPOD, etc. In vitro starch digestibility protocos using soly α-amylase combined with PAHBAH methods have been widely reported, which could well describe the starch digestion curves. But, how to solve this situation using GOPOD procedure?
https://www.researchgate.net/profile/Peng-Guo-35. I have no personal experience with these procedures, so I am not able to give any further suggestions to solve your problem.
What about your glucose standard? Did it give you a reasonable reading? Then did you use a starch control that the total starch content is known?
Dear Peng,
the reason for that can indeed lay in the nature of the analytical method and your sample. Which kind of samples were you running? And did you run a standard, and did you account for a blank?
However, most of your starch hydrolysis products will not be glucose but maltose, maltotriose and higher DMs due to the action of a-amylase. Therefore other methods, assessing the starch hydrolysis products, such as the spectophotometric DNS assay according to Miller 1959 or HPLC solutions might be more suitable.
Foodengine Team Thanks for your advice. Our samples included native and treated chickpea starch cooked with different conditions. Standard group was also conducted. a-amylase and AMG were purchased from Sigma and Megazyme. We compared the Abs using ultraviolet spectrophotometer and microplate reader, and no difference. Another confusing problem was that the digestion ratio increased incredible too high (about 80%) just at 20min, and then gradually approached to 100%, eventually exceeded at 120min. The digestion data failed to be fitted to a nonlinear curve model. We have tried to reduce the enzyme/substrate ratio to some extent, and the overall digestion rate decreased compared with previous, but still high rate within 20min. I am still confused that DNS assay also showed the same situation.
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