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Preparation and characterisation of retrograded resistant starch

Published online by Cambridge University Press:  15 April 2015

H. Patel
Affiliation:
School of Medicine, King's College London, SE1 9NH
G. Williams
Affiliation:
School of Pharmacy, 29–39 Brunswick Square, University of London, WC1N 1AX
S. Gaisford
Affiliation:
School of Pharmacy, 29–39 Brunswick Square, University of London, WC1N 1AX
D. McCarthy
Affiliation:
School of Pharmacy, 29–39 Brunswick Square, University of London, WC1N 1AX
F. J Warren
Affiliation:
Centre for Nutrition and Food Sciences, Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, Australia
P. J Butterworth
Affiliation:
School of Medicine, King's College London, SE1 9NH
P. R. Ellis
Affiliation:
School of Medicine, King's College London, SE1 9NH
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Abstract

Type
Abstract
Copyright
Copyright © The Authors 2015 

Starch digestion is of great importance to human health with a large fraction being digested in the small intestine. However, starch material that escapes digestion by amylolytic enzymes in the upper gastrointestinal tract is termed ‘resistant starch’ (RS). RS has been subdivided into four groups; physically inaccessible starch (RS1), native (uncooked) starch (RS2), retrograded (cooked and cooled) starch (RS3), and chemically modified starch (RS4). The amount of RS can vary considerably depending upon the botanical source and the food processing conditions applied. Many groups have reported that starches of high amylose content that have undergone temperature-cycled retrogradation contain increased amounts of retrograded starch (RS3)Reference Zhang, Hu and Xu1. The purpose of this project is to harvest, characterise and perform enzyme inhibition studies on isolated RS from high amylose maize starch (HA).

In our study, retrogradation of HA at cycles of 4/37°C for 1 week significantly increased the RS content to 95%. This allows accurate enzyme inhibition studies to be performed. X-ray diffraction (XRD), scanning electron microscopy (SEM) and nuclear magnetic resonance (13C NMR) was then used to determine the structure of RS. Surprisingly, upon XRD and NMR analysis, our results suggested that the isolated RS possessed low crystallinity. SEM images showed a web – like pattern connecting the starch material together. This resulted in associated ‘lumps’ of starch material rather than a continuous polymer network which is commonly seen in gelatinised starches. Thus the majority of the starch material is believed to be amorphous; however this amorphous material is clearly of a different form compared with the SEM images of amorphous gelatinised starchesReference Slaughter, Ellis and Jackson2. Upon digestion with pancreatic α-amylase, no starch products were detected indicating RS is totally inert to digestion (n = 4). In addition to this, inhibition studies suggest RS acts as a non-competitive inhibitor of pancreatic α-amylase.

To conclude, ready to eat chilled foods which have undergone retrogradation may have reduced starch digestibility. Therefore, the physiological effects of RS on human metabolism may have beneficial relevance in the management of health and disease (e.g. obesity and type II diabetes).

References

1.Zhang, L, Hu, X, Xu, X et al. (2011) Carbohydr. Polym 84, 970974.Google Scholar
2.Slaughter, SL, Ellis, PR, Jackson, EC et al. (2002) Biochim Biophys Acta 1571, 5563.Google Scholar