Starch Granule Hydration—A MAS NMR Investigation

Insights into the gelatinization of potato starch by in situ1H NMR

The gelatinization of potato starch and the effect of NaCl on starch gelatinization were monitored successfully in situ by ¹H NMR spectroscopy. Variable temperature (VT) ¹H NMR measurement, from 316 K to 340 K, was conducted on a suspension of potato starch and deuterium water as well as a mixture of potato starch, NaCl and deuterium water. The hydration level of starch was determined with the increase of temperature. In the presence of NaCl, the initial gelatinization temperature of potato starch was decreased from 331 to 328 K. Meanwhile, in situ¹H NMR spectroscopy as a function of time was also carried out to monitor the gelatinization with a time resolution of 90 s per spectrum. Furthermore, the effect of using different processing methods during gelatinization, including varying the temperature or time duration, was investigated in detail. It was confirmed that protons from different groups of starch showed different accessibility for water during hydration of starch granules. In comparison with temperature, gelatinization time as the major factor for reaching complete gelatinization was confirmed. We expect that this research, as a continuing effort to apply NMR spectroscopy for characterizing starch, will pave a new way in the structural elucidation of starch.

The gelatinization of potato starch and the effect of NaCl on starch gelatinization were monitored successfully in situ by ¹H NMR spectroscopy.

Structural heterogeneities in starch hydrogels

Hydrogels have a complex, heterogeneous structure and organisation, making them promising candidates for advanced structural and cosmetics applications. Starch is an attractive material for producing hydrogels due to its low cost and biocompatibility, but the structural dynamics of polymer chains within starch hydrogels are not well understood, limiting their development and utilisation. We employed a range of NMR methodologies (CPSP/MAS, HR-MAS, HPDEC and WPT-CP) to probe the molecular mobility and water dynamics within starch hydrogels featuring a wide range of physical properties. The insights from these methods were related to bulk rheological, thermal (DSC) and crystalline (PXRD) properties. We have reported for the first time the presence of highly dynamic starch chains, behaving as solvated moieties existing in the liquid component of hydrogel systems. We have correlated the chains' degree of structural mobility with macroscopic properties of the bulk systems, providing new insights into the structure-function relationships governing hydrogel assemblies.

Hydration and swelling of amorphous cross-linked starch microspheres

Hydration of cross-linked starch microspheres, commercially available as a medical device, was investigated using a multi-method approach. We found that the uptake of water is accompanied by substantial swelling and changes of the polymer structure. Sorption calorimetry provided information about thermodynamics of water sorption, revealed presence of isothermal glass transition and absence of hydration-induced crystallization, observed in non-cross linked starch material. The changes in the surface and bulk properties of microspheres at different water-starch concentrations were investigated using synchrotron radiation X-ray scattering and analyzed using concept of fractals. The obtained information, combined with the results of differential scanning calorimetry, was used to construct a phase diagram of the studied material. Finally, hydration induced evolution of polymer structure revealed by the X-ray scattering was linked to the changes observed during swelling with optical microscopy.

Effect of enzymatic treatment of different starch sources on the in vitro rate and extent of starch digestion

Gelatinized wheat, potato and waxy maize starches were treated enzymatically in order to increase the degree of branching of the amylopectin fraction and thereby change the starch degradation profile towards a higher proportion of slowly digestible starch (SDS). The materials were characterized by single-pulse (1)H HR-MAS NMR spectroscopy and in vitro digestion profile according to the Englyst procedure. Using various concentrations and incubation times with branching enzyme (EC 2.4.1.18) without or with additional treatment with the hydrolytic enzymes; β-amylase (EC 3.2.1.2), α-glucosidase (EC 3.2.1.20), or amyloglucosidase (EC 3.2.1.3) the proportion of α-(1-6) linkages was increased by up to a factor of 4.1, 5 and 5.8 in waxy maize, wheat and potato starches, respectively. The proportion of SDS was significantly increased when using hydrolytic enzymes after treatment with branching enzyme but it was only for waxy maize that the proportion of α-(1-6) bonds and the in vitro digestion profile was significantly correlated.

The interaction between tea polyphenols and rice starch during gelatinization

The interaction between tea polyphenols (TPLs) and rice starch (RS) during gelatinization has been studied. In the RVA analysis, TPLs-fortified RS exhibited no clearly defined peak viscosity and hot paste viscosity. After excluding other factors, irregular viscosity changes were attributed to the strong interactions between RS and TPLs during pasting/gelatinization. Subsequently, the coupling constants of samples A (the gelatinized sample of the blend of 16% TPLs and RS) and B (the blend of 16% TPLs and gelatinized RS sample) in 1H-NMR measurements were found to be the difference. Sample A had two coupling constants, 26h JHH = 82.08, 100.77 Hz and 6h JHH = 35.57 Hz, whereas Sample B had one larger coupling constant, 9h JHH = 140.24 Hz. This implied that these two samples differed in H–H interaction and interaction strength of sample A may be stronger than that of sample B. More important is, sample A had clearly broadened O–H stretching and frequency red-shifts of C–O–H bending as compared with sample B in quantitative FT–IR analysis. The overall results indicate that TPLs and RS can have hydrogen bonding interaction during gelatinization.

The HRMAS-NMR tool in foodstuff characterisation

High resolution magic angle spinning, that is, HRMAS, is a quite novel tool in NMR spectroscopy; it offers the almost unique opportunity of measuring intact tissues disguised as suspended or swollen in a deuterated solvent. The feasibility of (1)H-HRMAS-NMR in foodstuff characterisation has been exploited, but in spite of this, its applications are still limited. Metabolic profiling and biopolymer composition and aggregation are the topics investigated until now for raw vegetables, meat and processed foodstuff. Almost all known studies are reported in the next pages.

Analysis of acid-soluble glycogen in pork extracts of two PRKAG3 genotypes by 1H liquid-state NMR spectroscopy and biochemical methods

Meat extracts with acid-soluble glycogen (macroglycogen) from M. longissmus dorsi of carriers and noncarriers of the PRKAG3 mutation (RN(-) and rn(+) genotype) were analyzed by both (1)H liquid-state NMR spectroscopy and a biochemical method. The (1)H NMR analysis revealed that shorter polymers (dimers, trimers, etc.) of α-1,4-linked glucose were generated 24-48 h post-mortem. This is not possible to elucidate with the biochemical method, by which only the total amount of hydrolyzed glucose residues is determined. The shorter polymers were primarily formed in carriers of the PRKAG3 mutation, suggesting different post-mortem glycogen degradation mechanisms in the two genotypes.

Review: Starch Matrices and the Glycemic Response

Starch is the most important source of energy for humans, and it is present in many products derived from cereals, legumes and tubers. Interestingly, some of these food products can have different metabolic effects (e.g. change of postprandial blood glucose concentration) although the total amount of starch is the same. This review focuses on a microstructural perspective of the glycemic response, in search of an alternative and complementary explanation of this phenomenon. Several starch and food microstructures are responsible for the change in starch bioaccessibility. Aspects such as the characterization of the microstructure of starchy products and, its relation to the metabolic problem, the crucial role of the food matrix and other components in the ingested meal, and the gaps in our present knowledge are discussed.

Starch phosphorylation--maltosidic restrains upon 3'- and 6'-phosphorylation investigated by chemical synthesis, molecular dynamics and NMR spectroscopy

Phosphorylation is the only known in vivo substitution of starch, yet no structural evidence has been provided to explain its implications of the amylosidic backbone and its stimulating effects on starch degradation in plants. In this study, we provide evidence for a major influence on the glucosidic bond in starch specifically induced by the 3-O-phosphate. Two phosphorylated maltose model compounds were synthesized and subjected to combined molecular dynamics (MD) studies and 950 MHz NMR studies. The two phosphorylated disaccharides represent the two possible phosphorylation sites observed in natural starches, namely maltose phosphorylated at the 3'- and 6'-position (maltose-3'-O-phosphate and maltose-6'-O-phosphate). When compared with maltose, both of the maltose-phosphates exhibit a restricted conformational space of the alpha(1-->4) glycosidic linkage. When maltose is phosphorylated in the 3'-position, MD and NMR show that the glucosidic space is seriously restricted to one narrow potential energy well which is strongly offset from the global potential energy well of maltose and almost 50 degrees degrees from the Phi angle of the alpha-maltose crystal structure. The driving force is primarily steric, but the configuration of the structural waters is also significantly altered. Both the favored conformation of the maltose-3'-phosphate and the maltose-6'-phosphate align well into the 6-fold double helical structure of amylopectin when the effects on the glucosidic bond are not taken into account. However, the restrained geometry of the glucosidic linkage of maltose-3'-phosphate cannot be accommodated in the helical structure, suggesting a major local disturbing effect, if present in the starch granule semi-crystalline lattice.