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

Patel, Hamung, Day, Richard, Butterworth, Peter J., Ellis, Peter R.
Carbohydrate polymers 2014 v.113 pp. 182-188
Fourier transform infrared spectroscopy, alpha-amylase, ambient temperature, digestibility, gelatinization, starch
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 24h 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 24h 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.