A mechanistic approach to studies of the possible digestion of retrograded starch by α-amylase revealed using a log of slope (LOS) plot

Highlights

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  Digestion of native and processed starches can be fitted to the LOS plot model.

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  RDS and SDS fractions identified for the digestion of different native starches.

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  C∞ reduced for retrograded starches while k remained constant.

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  Retrograded starch is completely inert to amylase attack.

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  Ordered starch material was investigated by FTIR-ATR.

Abstract

The rate and extent of digestibility of starch were analysed using the logarithm of the slope (LOS) method. Digestibility curves with α-amylase were obtained for starches in their native, gelatinised and 24 h retrograded form. A LOS plot of the digestibility curves was then constructed, which allowed the rate constant ( k) and the concentration of the product at the end of the reaction ( C∞) to be calculated. It also allowed the identification of rapid and slow phases in starch digestion. Upon gelatinisation, both k and C∞ increased with dramatic changes notably in C∞; however after starch samples had been stored for 24 h at room temperature, k was not affected but C∞ decreased. This suggests that retrograded starch is virtually inert to amylase action. Both k and C∞ were strongly related to the increase in degree of order of the α-glucan chains, monitored by FTIR-ATR spectroscopy, in retrograded starch.