Starch has a heterogeneous, semi-crystalline granular structure and the degree of ordered structure can affect its behaviour in foods and bioplastics. A range of methodologies are employed to study starch structure; differential scanning calorimetry, (13)C nuclear magnetic resonance, X-ray diffraction and Fourier transform infrared spectroscopy (FTIR). Despite the appeal of FTIR as a rapid, non-destructive methodology, there is currently no systematically defined quantitative relationship between FTIR spectral features and other starch structural measures. Here, we subject 61 starch samples to structural analysis, and systematically correlate FTIR spectra with other measures of starch structure. A hydration dependent peak position shift in the FTIR spectra of starch is observed, resulting from increased molecular order, but with complex, non-linear behaviour. We demonstrate that FTIR is a tool that can quantitatively probe short range interactions in starch structure. However, the assumptions of linear relationships between starch ordered structure and peak ratios are overly simplistic.

Recent studies of the mechanisms determining the rate and extent of starch digestion by α-amylase are reviewed in the light of current widely-used classifications for (a) the proportions of rapidly-digestible (RDS), slowly-digestible (SDS), and resistant starch (RS) based on in vitro digestibility, and (b) the types of resistant starch (RS 1,2,3,4…) based on physical and/or chemical form. Based on methodological advances and new mechanistic insights, it is proposed that both classification systems should be modified. Kinetic analysis of digestion profiles provides a robust set of parameters that should replace the classification of starch as a combination of RDS, SDS, and RS from a single enzyme digestion experiment. This should involve determination of the minimum number of kinetic processes needed to describe the full digestion profile, together with the proportion of starch involved in each process, and the kinetic properties of each process. The current classification of resistant starch types as RS1,2,3,4 should be replaced by one which recognizes the essential kinetic nature of RS (enzyme digestion rate vs. small intestinal passage rate), and that there are two fundamental origins for resistance based on (i) rate-determining access/binding of enzyme to substrate and (ii) rate-determining conversion of substrate to product once bound.

a-Amylase catalyses the first step in the digestion of starch, a main source of carbohydrate in the human diet. Amylase present in human saliva was one of the first enzymes ever to be recognised but many puzzles remain about the molecular mechanisms involved in amylolysis of starch and even of the physiological role of the salivary amylase itself. Native starch granules represent a formidable challenge for attack from an enzyme in solution. Moreover the frequently reported differences in the susceptibility to amylolysis of starches from various botanical species, plus the changes that occur in starch structure and properties during domestic and commercial food processing means that studies of the enzymology of starch digestion can be challenging. We review the molecular properties of mammalian a-amylase including its genetics, and speculate on the role of salivary amylase in digestion of dietary starch. Also considered are enzyme kinetic approaches that have been used in vitro studies of amylase digestion of starches. Such studies can result in better understanding of reasons for the differences in glycaemic responses of humans following ingestion of different starch containing foods.

No abstract

Studying starch amylolysis kinetics in vitro is valuable for predicting the postprandial glycaemic response to starch intake. Prediction of starch amylolysis behaviour is challenging however, because of the many physico-chemical factors which influence amylolysis. The Logarithm of Slope (LOS) method for analysis of digestibility curves using first-order enzyme kinetics can identify and quantify nutritionally important starch fractions. The early stages of in vitro amylolysis of hydrothermally processed chickpea and durum wheat with variable degrees of structural integrity were studied. The end-point product concentration (C∞) and the pseudo first-order digestibility rate constant k, obtained from LOS analysis, were then used to compute predictive digestibility curves for evaluation of the model performance. LOS analysis enabled rapid identification of nutritionally important starch-fractions. It was clear that purified starches and flours were digested by a single-phase process, but starch amylolysis in macroparticles occurred by a two-phase system that reflected differences in substrate accessibility. The model gave an excellent fit to data obtained from a range of heterogeneous materials. It provides a rigorous means of studying the mechanisms of starch amylolysis in samples of varying complexity, and we strongly recommend its use for the rapid and accurate predictions of amylolysis. Such predictions have implications for prevention and management of type 2 diabetes mellitus and obesity.

Please cite this article as: Zou, W., Sissons, M., Gidley, M.J., Gilbert, R.G., Warren, F.J., Combined techniques for characterising pasta structure reveals how the gluten network slows enzymic digestion rate, Food Chemistry (2015), doi: http://dx.doi.org/10.1016/j.foodchem. 2015.05.032 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. AbstractThe aim of the present study is to characterise the influence of gluten structure on the kinetics of starch hydrolysis in pasta. Spaghetti and powdered pasta were prepared from three different cultivars of durum semolina, and starch was also purified from each cultivar. Digestion kinetic parameters were obtained through logarithm-of-slope analysis, allowing identification of sequential digestion steps. Purified starch and semolina were digested following a single first-order rate constant, while pasta and powdered pasta followed two sequential first-order rate constants. Rate coefficients were altered by pepsin hydrolysis. Confocal microscopy revealed that, following cooking, starch granules were completely swollen for starch, semolina and pasta powder samples. In pasta, they were completely swollen in the external regions, partially swollen in the intermediate region and almost intact in the pasta strand centre. Gluten entrapment accounts for sequential kinetic steps in starch digestion of pasta; the compact microstructure of pasta also reduces digestion rates.

No abstract

No abstract