Gel texture and chain structure of amylomaltase-modified starches compared to gelatin

Amylomaltase (AM) (4-α-d-glucanotransferase; E.C. 2.4.1.25) from Thermus thermophilus was used to modify starches from various botanical sources including potato, high amylose potato (HAP), maize, waxy maize, wheat and pea, as well as a chemical oxidized potato starch (Gelamyl 120). Amylopectin chain length distribution, textural properties of gels and molecular weight of 51 enzyme and 7 non-enzyme-modified starches (parent samples) were analyzed. Textural data were compared with the textural properties of gelatin gels. Modifying starch with AM caused broadening of the amylopectin chain length distribution, creating a unimodal distribution. The increase in longer chains was supposedly a combined effect of amylose to amylopectin chain transfer and transfer of cluster units within the amylopectin molecules.Exploratory principal component analysis (PCA) data analysis revealed that the data were composed of two components explaining 94.2% of the total variation. Parent starches formed a cluster separated from that of the AM-modified starches.Extended AM treatments reduced the apparent molecular weight and the gel texture without changing the amylopectin chain length distribution. However, the gel texture was typically increased as compared to the parent starch. AM-modified HAP gels were about twice as hard as gelatin gels at identical concentration, whereas gels of pea starch were comparable to gelatin gels. Modifying Gelamyl 120 and waxy maize with AM did not change the textural properties. Branching enzyme (BE) (1,4-α-d-glucan branching enzyme; EC 2.4.1.18) from Rhodothermus obamensis was used in just one modification and in combination with AM. The combined AM/BE modification of pea starch resulted in starches with shorter amylopectin chains and pastes unable to form gel network even at concentration as high as 12.0% (w/w). The PCA model of all gel texture data gave suggestive evidence for starch structural features being important for generating a gelatin-like texture.     

Rheological Properties of Mixed Gels using Waxy and Non‐waxy Wheat Starch

Mixed starches with an amylose content of 5, 10, 18, 20, 23, and 25% were prepared by blending starches isolated from waxy and non‐waxy wheat at different ratios. The dynamic viscoelasticity of mixed 30% and 40% starch gels was measured using a rheometer with parallel plate geometry. The change in storage shear modulus (G′) over time at 5 °C was measured, and the rate constant of G′ development was estimated. As the proportion of waxy starch in the mixture increased, starch gels showed lower G′ and higher frequency dependence during 48 h storage at 5 °C. Since the amylopectin of waxy starch granules was solubilized more easily in hot water than that of non‐waxy starch granules, mixed starch containing more waxy starch was more highly solubilized and formed weaker gels. G′ of 30% and 40% starch gels increased steadily during 48 h. 30% starch gel of waxy, non‐waxy and mixed starches showed a slow increase in G′. For 40% starch gels, mixed starch containing more waxy starch showed rapidly developed G′ and had a higher rate constant of starch retrogradation. Waxy starch greatly influenced the rheological properties of mixed starch gels and its proportion in the mixture played a major role in starch gel properties.     

The Effects of Amylose and Starch Phosphate on Starch Gel Retrogradation Studied by Low‐field 1H NMR Relaxometry

Low‐field Nuclear Magnetic Resonance (23 MHz) was used to study the effects of the degree of phosphorylation, the amylose content and the amylopectin chain length distribution on gel retrogradation for a set of 26 starches, six of which were of crystal polymorph type A, 18 of type B and two of type C. The phosphate content ranged from 0 to 58.8 nmol Glc6P/mg and the amylose content from 0 to 72.1%. The starch pastes (13%, w/w) were measured before and after storage for six days at 35 °C. It was found that Principal Component Analysis (PCA) of the raw Carr‐Purcell‐Meiboom‐Gill (CPMG) relaxation curves from the two measurements (day 1 and day 7) could be used as a simple, illustrative way of describing the retrogradation. Three different behaviours were identified: One group of samples (mostly potato starches) slowly changed from a soft to a more rigid gel from day 1 to 7. A second group (mostly cereal starches) formed a rigid gel already before the first measurement and changed little after that. A third group comprised a few samples containing little or no amylose aged similarly to the first group of samples, but at a much slower rate. For the potato starches, a weak negative correlation (r = ‐0.63) was found between the degree of phosphorylation and the difference between the LF NMR relaxation curves of day 1 and day 7.     

The influence of Cu(II) ions on physicochemical properties of potato starch oxidised by hydrogen peroxide

The study investigates the influence of Cu(II) ions used as a catalyst on the effectiveness of potato starch oxidation by hydrogen peroxide, and compares the physicochemical properties of the modified starches. The starch was oxidised by H₂O₂ alone and with the addition of Cu(II) ions at three concentrations: 0.1, 0.2 or 0.3 g per 100 g d.m. of starch. The oxidised starches were examined for the content of carboxyl groups, carbonyl groups, amylose and copper, and for water‐binding capacity and water solubility at temperatures of 60 and 80°C. Colour parameters (L*a*b*), susceptibility to retrogradation, thermodynamic characteristics of pasting, intrinsic viscosity and pasting characteristic by RVA were also determined. The results indicate that the concentration of Cu(II) ions added as a catalyst has an effect on both the effectiveness of the oxidation process and the physicochemical properties of starch.     

Biochemical characterisation of a glycogen branching enzyme from Streptococcus mutans: Enzymatic modification of starch

A gene encoding a putative glycogen branching enzyme (SmGBE) in Streptococcus mutans was expressed in Escherichia coli and purified. The biochemical properties of the purified enzyme were examined relative to its branching specificity for amylose and starch. The activity of the approximately 75 kDa enzyme was optimal at pH 5.0, and stable up to 40 °C. The enzyme predominantly transferred short maltooligosyl chains with a degree of polymerization (dp) of 6 and 7 throughout the branching process for amylose. When incubated with rice starch, the enzyme modified its optimal branch chain-length from dp 12 to 6 with large reductions in the longer chains, and simultaneously increased its branching points. The results indicate that SmGBE can make a modified starch with much shorter branches and a more branched structure than to native starch. In addition, starch retrogradation due to low temperature storage was significantly retarded along with the enzyme reaction.     

Physicochemical,Morphological, Pasting,and Rheological Properties of Tamarind (Tamarindus indica L.) Kernel Starch

Starch was isolated from tamarind kernels, which are at present considered as waste. It was compared with corn and mung bean starch for its physicochemical, rheological, and morphological properties. Tamarind kernel starch showed significantly lower amylose content, light transmittance, solubility, and higher swelling power in comparison to corn and mung bean starch. The micrographs of tamarind kernel starch revealed its small oval shape granules with smooth surfaces. X-ray diffraction pattern of tamarind kernel starch was similar to corn starch with strong diffraction peaks at 15, 17, and 23° (2θ). Changes in storage modulus (G?), loss modulus (G??), and loss tangent (tan δ) during heating of starches showed the lowest peak G? for tamarind kernel starch, whereas the highest was observed for corn starch. Changes in G? and G?? during cooling, holding and subsequently heating were also studied. The frequency dependence of G? and G?? of starches measured at 25 and 95°C revealed their weak gel behavior. During cooling tamarind kernel starch showed lower increase in G? in comparison to other starches. Tamarind kernel starch was different from corn and mung bean starch in exhibiting highest peak, breakdown, and lowest setback viscosity. Tamarind seeds have potential as a relatively new, cheap, and underutilized source of starch in food applications.     

In situ Raman microscopy of starch granule structures in wild type and ae mutant maize kernels

A method developed for in situ imaging of starch granule structure in dry seeds has been applied to compare the starch granule structures found in wild type and ae mutant maize kernels. In the isogenic ae mutant the activity of the starch branching enzyme IIb is inhibited, which gives rise to a high amylose starch. The granule structures in the wild type samples have been found to be homogeneous, whereas those in the ae mutant are grossly heterogeneous within individual granules, between granules within individual cells, and between cells across the endosperm. The level of heterogeneity observed in situ appears to be more marked than that previously reported for studies on isolated ae mutant starches. Iodine/potassium iodide staining and polarised light microscopy have been used together with Raman microscopy, which has allowed high‐resolution mapping of the composition and physical state of the structures within the granules, to probe the origins of the heterogeneity of the starch structures. Although the mutation inhibits the activity of the branching enzyme within the granules, and both the composition and level of crystallinity within and between granules is variable, the major origin of the heterogeneity of the granule architecture appears to result from significant changes in the assembly and packaging of the crystalline structures within the granule. It is suggested that this arises due to the mutation of the starch branching enzyme introducing defects into the self‐assembly of the crystalline structure, resulting in an accumulation of defects and increased randomisation of the granule structure.     

Comparison of the morphological,crystalline, and thermal properties of different crystalline types of starches after acid hydrolysis

A‐type maize starch, B‐type Fritillaria ussurensis, and C‐type Rhizoma dioscorea starches were hydrolyzed (32 days) with 2.2 N HCl. Regardless of the crystallinity level, starch with predominant B‐crystalline type was less susceptible to acid degradation than A‐type and C‐type starches, and initial rates of hydrolysis in B‐type was lower than others. The SEM and XRD results revealed that different types of starch displayed different hydrolysis mechanisms. The acid corrosion started from the exterior surface of A‐type and B‐type starches followed by the core of granules. However, the hydrogen ions primarily attacked the interior of the C‐type R. dioscorea starch granules and then the exterior. FT‐IR results confirmed that the amorphous regions in the starch granules were hydrolysed first. After 8–32 days of hydrolysis, the acid‐modified C‐type starch showed typical A‐type characteristics upon analysis of the XRD pattern. The average particle size of hydrolytic starch decreased with increasing hydrolysis time. The thermal results revealed that the hydrolytic starch showed lower ΔH than the native starch, while displaying higher peak width (T_c − T_o) value.     

Effect of amylose content and rice type on dynamic viscoelasticity of a composite rice starch gel

Amylose content is an important indicator to determine the utility of raw milled rice. Indica type rice with high amylose content is usually used for manufacturing rice noodles, while Japonica rice may be mixed partially to adjust the noodle texture. The effect of amylose and rice type on dynamic viscoelasticity of rice starch gel was investigated using a model starch composite in this study. The information will be helpful to control and obtain the required noodle texture by combination of different rice types. The results show that nonwaxy Indica and waxy Japonica rice starches in a composite mixture were incompatible and demonstrated their individual gelatinization behavior during heating. High amylose starch showed higher moduli and lower loss tangent values, as well as higher retrogradation rate. The starch gel made from Japonica rice starch showed a slow retrogradation rate even containing a similar amount of amylose to Indica starch. The storage modulus of the gel made from higher amylose rice was shown to be more independent of frequency. Not only amylose content but also chain length distribution in amylopectin affected the dynamic viscoelasticity of rice gel. Japonica rice starch, with fewer super-long chains in amylopectin, retrograded slower after gelatinization than Indica rice, thus the paste is too sticky for production of rice noodles.     

Physicochemical,morphological, structural,and thermal characteristics of starches separated from Bulbus fritillaria of different cultivars

The starches studied from the nine Fritillaria species had differently shaped and sized granules but all of them showed the presence of smooth, round, or elliptic‐shaped, indicating that the isolation process did not destroyed the starch granules. The nine Fritillaria starches presented different AM content, moisture content, ash content, particle size, swelling power, solubility, water absorption capacity and light transmittance. The starches isolated from Chuan‐Beimu species exhibited a higher amount of crude protein content and lower amount of AM than other the groups, which had lower swelling power, higher solubility and light transmittance. All the nine Fritillaria starches had an XRD pattern of the B‐type. In addition, F. hupehensis, F. walujewii and F. ussuriensis starches with fairly large‐sized or irregular granules had higher T_p and ΔH_gel values than that isolated from the four Chuan‐Beimu species. The results obtained yielded information about the possible behavior of these starches when being used in certain applications. Cluster analysis results showed that this classification method based on macromolecule chemical compounds (starch) is original and credible in the quality control of various Beimu. In addition, it provided more information to the authentication systematics taxonomy methods including morphological, histological and molecular biological techniques of Fritillaria species.     

Rheological and calorimetric properties of corn‐, wheat‐, and cassava‐ starches and soybean protein concentrate composites

The effect of soy protein concentrate (SPC) on the rheological and calorimetric properties of corn, wheat, and cassava starches was assessed. SPC increased T_o values and decreased the ΔH of all tested starches, which could be related to lower availability of water for starch gelatinization and/or to the interactions between SPC and amorphous regions of starch granules. SPC and sugar addition modified the viscosity parameters (obtained through a rapid visco‐analyser) of starch pastes, which was attributed to an increase in solid content and to the interaction of proteins with the starch dispersed phase. Frequency sweeps were carried out with a rheometer on gels containing starch, SPC, and sucrose. SPC raised storage and loss modulus, producing more consistent starch gels. Besides, penetration tests showed that SPC steadily increased starch gel firmness. Scanning electron micrographs showed that protein concentrate produced gels with closer structures. Summarizing, the starch and SPC in the gels obtained were expected to be arranged in a two‐phase system. Results showed that it is possible to achieve different textures for starch dessert formulations.     

Effects of the Barley amo1 and wax Genes on Starch Structure and Physicochemical Properties

Starch structural mutants showing abnormal endosperm characteristics have been used for investigating the effects of the mutation on structure and physicochemical properties of starches. Inbred lines of barley cultivars ‘Shikoku Hadaka 97’ and ‘Glacier AC38’ were used to investigate the impact of amo1 and waxy genes on starch properties. The amo1 type starch had high apparent amylose content and low starch content. The amo1+waxy type starch contained very little amylose. The content of long chains of amylopectin as detected with high‐performance size‐exclusion chromatography (HPSEC) was decreased, and that of amylopectin chains with the degree of polymerization (DP) of 12‐36 was increased in amo1 and amo1+waxy type starches. The amo1 and amo1+waxy type starches exhibited high gelatinization temperatures and low gelatinization enthalpies.     

Rate of Hydroxypropylation of Starches as a Function of Reaction Time

To determine the course of the hydroxypropylation reaction as a function of reaction time, waxy corn, normal corn, potato, and wheat starches were reacted with propylene oxide under normal reaction conditions. Amounts of leached material and MS values of both leached and granular molecules were determined over the course of reaction. For waxy and normal corn starches, the extent of reaction increased linearly from 0 to 12 h, after which the reaction proceeded at an ever decreasing rate, reaching zero at about 30 h of reaction. The initial rate of reaction was determined by reacting waxy corn starch with a greater amount of propylene oxide (10×normal concentration) so that there would be no slowing of the reaction due to loss of reagent. Results confirmed that the initial reaction rate was linear. The hypothesis that, as derivatization proceeds, granules are opened up, resulting in ever increasing rates of reaction was not substantiated. Amounts and MS values of leached molecules from waxy and normal corn starches increased continuously over the course of the reaction. For potato and wheat starches, MS values of the granular starch also increased continuously over the entire reaction period. Amounts of leached molecules from potato starch were greater than those from wheat starch, with the amount leached at 30 h from potato starch being slightly more than that from normal and waxy corn starches and that from wheat starch being considerably less.     

Chemical and Physical Properties of Kiwifruit (Actinidia deliciosa) Starch

Chemical and physical properties of kiwifruit (Actinidia deliciosa var. ‘Hayward’) starch were studied. Kiwifruit starch granules were compound, irregular or dome‐shaped with diameters predominantly 4–5 µm or 7–9 µm. Kiwifruit starch exhibited B‐type X‐ray diffraction pattern, an apparent amylose content of 43.1% and absolute amylose content of 18.8%. Kiwifruit amylopectins, relative to other starches, had low weight‐average molecular weight (7.4×10⁷), and gyration radius (200 nm). Average amylopectin branch chain‐length was long (DP 28.6). Onset and peak gelatinization temperatures were 68.9°C and 73.0°C, respectively, and gelatinization enthalpy was high (18.5 J/g). Amylose‐lipid thermal transition was observed. Starch retrograded for 7 d at 4°C had a very high peak melting temperature (60.7°C). Peak (250 RVU), final (238 RVU) and setback (94 RVU) viscosity of 8% kiwifruit starch paste was high relative to other starches and pasting temperature (69.7°C) was marginally higher than onset gelatinization temperature. High paste viscosities and low pasting temperature could give kiwifruit starch some advantages over many cereal starches.     

Formation of starch spherulites: Role of amylose content and thermal events

Commercial maize starches and potato starches of two cultivars differing in physicochemical composition (granule size distribution; amylose to amylopectin ratio) and crystallinity were heated to 180 °C and then cooled by fast quench using a differential scanning calorimeter (DSC), in order to produce spherulitic starch morphologies. Among the raw maize starches, waxy maize starch had highest relative crystallinity (49%) whereas a lowest crystallinity of 33–39% was calculated for high-amylose maize starches. Potato starches showed a relative crystallinity of 50%. The temperatures and enthalpies of gelatinisation and melting varied among all the starches. High-amylose maize starches showed higher transition temperatures of gelatinisation (T_gel), whereas waxy maize starch had lowest T_gel and enthalpy of gelatinisation (ΔH_gel). Similarly, a considerable variation in parameters related with crystalline melting (T_m1, T_m2 and ΔH_m1, ΔH_m2) was observed for different starches. The superheated gels of different starches treated using DSC were subjected to polarised microscopy, to confirm the formation of spherulites. Both the high-amylose starch gels showed the presence of spherulites exhibiting birefringence and a weak crystalline pattern. No birefringence was observed for waxy maize starch gel, while potato starch gels had some birefringence. The particle size distribution of high-amylose maize starch gels analysed through Zetasizer showed the sizes of spherulitic particles fall in the range of 300 nm–900 nm. The scanning electron micrographs of the dried high-amylose maize starch gels showed the presence of round spherulites consisting of several aggregated spherulitic particles. Amylose content and melting of crystallites during heating play an important role during recrystallisation of amylose (spherulite morphologies).     

Characteristics of pores in native and hydrolyzed starch granules

Low‐temperature nitrogen adsorption and mercury porosimetry were applied for analyzing effect of α‐amylolysis upon the porosity of granules of native corn, wheat, rice, and potato starches. Specific surface area (S_BET), porosity, pore size distribution, total pore area, and mean pore radius were determined for native and digested granules. It was found that native starch granules are macroporous materials with a small participation of mesopores. In the case of native starches, the highest value of S_BET was obtained for rice starch (1.27 m²/g) and the lowest – for potato starch (0.14 m²/g). Pore size distribution curves obtained by nitrogen adsorption showed peaks in the range of diameters 2–3 nm (for all starches) and 100–200 nm (for corn and rice starches). After 60 min of enzyme action, surface area of all starches doubled in comparison to native ones. Arising of the new pores was also noted. The results of mercury porosimetry measurements showed that rice starch had the highest total area of pores and porosity but the lowest mean pore radius among all native starches. The pore size distribution curves for all starches exhibited solely one peak corresponding to the dominant group of pores of the radii in the range 0.5–8 µm, dependent on the starch source. There were also much smaller peaks situated within the range of 3–30 µm. After α‐amylolysis of corn and rice starches, the average radius of the dominant group of pores diminished. No substantial changes in the pore radii could be noted for potato starch.     

Characteristics of native and enzymatically hydrolyzed common wheat (Triticum aestivum) and dicoccum wheat (Triticum dicoccum) starches

The compositional, structural, and enzymatic digestibility of starches isolated from common wheat and dicoccum wheat were determined to find out the possible reason for hypoglycemic nature of dicoccum wheat. The gelatinization temperature range (65±3 °C) as well as the elution profile of both the starches on Sepharose CL-2B gel were comparable, but the peak (PV, 233 RVU) and set back viscosity (SB, 140 RVU) of dicoccum wheat starch were higher than common wheat starch (PV, 211 RVU; SB, 113 RVU) as recorded in rapid visco-analyser (RVA). The degree of crystallinity (DOC: 29%) and the thermal energy (TE: 142.35 J) of dicoccum wheat starch were considerably higher than the DOC (23%) and TE (67.82 J) of the common wheat starch. The starches were digested with alpha-amylase (human salivary), beta-amylase (barley malt), pullulanase (Klebsiella pneumoniae), and amyloglucosidase (Aspergillus niger), and the solubilized fraction was separated from the undigested fraction (residue) by centrifugation. Characterization of the sugars in the solubilized fraction from alpha-amylase were glucose, maltose, and oligosaccharides of 3–7 DP, maltose from beta-amylase, maltotriose from pullulanase and glucose from amyloglucosidase. However, the molecular weight (M _w) of the residues from the enzymatic digestion of dicoccum wheat starch was slightly higher than that of the common wheat starch. The microscopic examination of residues also exhibited a few bigger chunks in case of dicoccum wheat starch and a large number of smaller sized pieces in the case of common wheat starch. Since, starch is the major component of wheat, these parameters may help to explain subtle differences in the digestibility that exist between common wheat and dicoccum wheat.     

Physicochemical and Biochemical Characterization of Starch Granules Isolated of Pigmented Maize Hybrids

In this study, the morphological and physicochemical of pigmented maizes as well as the initial characterization of the corresponding starch granule enzymes are described. Starch granules were isolated from blue, black, and white maize. They were analyzed using scanning electron microscopy, particle size distribution, pasting characteristics, sorption isotherms, differential scanning calorimetry, and two‐dimensional gel electrophoresis. The morphology of the starch granules of pigmented maizes was different from the granules of white maize; the pattern was related to the endosperm type of these varieties. The average starch granule size was higher for black than for white and blue maizes. The average gelatinization temperature was similar in the three starches, but the pigmented maizes had higher gelatinization enthalpy; black maize starch showed the lowest enthalpy of retrogradation. These results indicated that the starches from the three maizes analyzed had different organization level. Black maize starch showed the highest peak viscosity followed by white and blue maize starches. In the gel electrophoresis three starch granules presented one main spot at pI of 5 and MW of 60 kDa that corresponds to the granule‐bound starch synthase. Blue and white starches presented some spots near 97 kDa at pI of 5.3–5.7 (white maize) and 5.1–5.5 (blue maize), spots that were not observed for black maize starch. The morphological and physicochemical characteristics of maize starch are related to the enzymes involved in its biosynthesis.     

Studies on Dioscorea rotundata Starch Properties

Starch from six clonal selections of Dioscorea rotundata was isolated by standard procedure. The yield was between 20–24%. Various properties of these starches were compared. Granule size, 2% viscosity, peak viscosity, clarity, sol stability, total and soluble amylose contents were studied and only small variations were observed in the properties except paste viscosities among the clonal selections. The phosphorus content of Dioscorea starch was found to be three times as much as cassava starch, but low compared to potato starch. The higher gel strength of D. rotundata starch paste compared to cassava gel may be attributed to the phosphate linkages among the starch molecules in the granules.     

Physicochemical Properties of Pin Oak (Quercus palustris Muenchh.) Acorn Starch

Physicochemical properties of acorn (Quercus palustris) starch were studied. Acorn starch granules were spherical or ovoid, with diameters ranging from 3–17 μm. Acorn starch exhibited A‐type X‐ray diffraction pattern, an apparent amylose content of 43.4% and absolute amylose content of 31.4%. Relative to other A‐type starches, acorn amylopectin had a comparable weight‐average molar mass (3.9×10⁸ g/mol), gyration radius (288 nm) and density (16.3 g mol⁻¹nm⁻³). Average amylopectin branch chain‐length corresponded to DP 25.5. Onset gelatinization temperature was 65.0°C and peak gelatinization temperature was considerably higher (73.7°C). The enthalpy change of gelatinization was very high compared to non‐mutant starches (20.8 J/g). An amylose‐lipid thermal transition was not observed. Starch retrograded for 7 d at 4°C had very high peak melting temperature (54.2°C) relative to other A‐type starches. Final (260 RVU) and setback (138 RVU) viscosity of an 8% acorn starch paste was high relative to other starches and pasting temperature was 71.5°C.