M. J. Gidley

Publications (2)0 Total impact

• Article: Effects of processing high amylose maize starches under controlled conditions on structural organisation and amylase digestibility

  A. Htoon, A. K. Shrestha, B. M. Flanagan, A. Lopez-Rubio, A. R. Bird, E. P. Gilbert, M. J. Gidley
  [show abstract] [hide abstract]
  ABSTRACT: The amylase digestibility of high-amylose maize starches has been compared before and after thermomechanical processing. Starches were analysed for enzyme-resistant starch yield, apparent amylose content, crystallinity (X-ray diffraction), and molecular order (NMR and FTIR), both before and after treatment with a-amylase. All samples had significant (>10%) enzyme-resistant starch levels irrespective of the type and extent of thermal or enzymic processing. Molecular or crystalline order was not a pre-requisite for enzyme resistance. Near-amorphous forms of high amylose maize starches are likely to undergo recrystallisation during the enzyme-digestion process. The mechanism of enzyme resistance of granular high-amylose starches is found to be qualitatively different to that for processed high-amylose starches. For all samples, measured levels of enzyme resistance are due to the interruption of a slow digestion process, rather than the presence of completely indigestible material.
  Carbohydrate Polymers. 01/2009; 75(2):236-245.
• Article: Influence of storage conditions on the structure, thermal behavior, and formation of enzyme-resistant starch in extruded starches

  H. Chanvrier, S. Uthayakumaran, I. A. M. Appelqvist, M. J. Gidley, E. P. Gilbert, A. Lopez-Rubio
  [show abstract] [hide abstract]
  ABSTRACT: Starch structures from an extrusion process were stored at different temperatures to allow for molecular rearrangement (retrogradation); their thermal characteristics (DSC) and resistance to amylase digestion were measured and compared. The structure of four native and processed starches containing different amylose/amylopectin compositions (3.5, 30.8, 32, and 80% amylose content, respectively) before and after digestion was studied with small-angle X-ray scattering (SAXS) and X-ray diffraction (XRD). Rearrangement of the amylose molecules was observed for each storage condition as measured by the DSC endotherm at around 145 degrees C. The crystalline organization of the starches after processing and storage was qualitatively different to that of the native starches. However, there was no direct correlation between the initial crystallinity and the amount of enzyme-resistant starch (ERS) measured after in vitro digestion, and only in the case of high-amylose starch did the postprocess conditioning used lead to a small increase in the amount of starch remaining after the enzymatic treatment. From the results obtained, it can be concluded that retrograded amylose is not directly correlated with ERS and alternative mechanisms must be responsible for ERS formation.