Controlled peeling of the surfaces of starch granules by gelatinization in aqueous dimethyl sulfoxide at selected temperatures

Microscopic examination of starch granules in 90:10 (v/v) Me(2)SO-H(2)O indicated that the granules were slowly being gelatinized from their surfaces. The rate of gelatinization was dependent on two variables: (1) the amount of water in Me(2)SO and (2) the temperature. An increase of water in Me(2)SO and/or an increase in temperature increased the rate of gelatinization and vice versa. Specific ratios of Me(2)SO and H(2)O (85:15-95:5) and temperatures (0-15 degrees C) were found to give controlled sequential peeling/gelatinization of eight kinds of starch granules in 1-12h, with amounts of 10-25% gelatinization per hour. It was observed that the percent of starch granule remaining versus time gave curves that were linear and others that had linear parts separated by one or more abrupt changes. No two starches had a similar gelatinization curve for the same two conditions of the amount of water and the temperature. It is hypothesized that these curves reflect different structural characteristics for the individual kinds of starch granules.     

Influence of native starch's properties on starch nanocrystals thermal properties

Starch nanocrystals (SNC) are crystalline square-like platelet about 10 nm thick and 50-100 nm equivalent diameters. Depending on the botanic origin of starch these platelets show different features. The aim of the present study was (i) to assess the thermal stability of SNC in different processing conditions (i.e., excess water and dry) and (ii) to investigate the potential influence of botanic origin on thermal stability. The thermal properties of five types of starches (waxy maize, normal maize, high amylose maize, potato and wheat) and their corresponding SNC were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). SNC revealed two endothermic transitions. No correlation between melting temperature and botanic origin was found. However, a review of starch thermal properties allowed to postulate for the mechanism involved in SNC thermal transitions. It was also found that SNC can be used in wet processes below 100 °C and in dry processes below 150-200 °C to avoid melting.     

Influence of thickness on the mechanical properties for starch films

The aim of the present study was to investigate some mechanical properties of starch films. Starch is a natural common polymer in nature and the use of natural materials is increasing in the industries. In this study, the mechanical properties of starch plasticized with 30 parts by weight, of glycerol, are investigated. For the mechanical testing films of different thickness were used, the thickness varied between 0.5 and 2.5 mm. T_g was measured with a differential scanning calorimeter and with a dynamical mechanical analysis. The starch films were tested in tension and characterised in terms of stiffness, strength and failure strain. Fracture toughness was measured by single edge notch tests. Both stiffness and strength showed a strong dependence on film thickness, stronger then expected from linear fracture mechanics. This can be due to the different molecule orientation in the films, and due to the crystallinity of the films.     

Particle size distribution of rice flour affecting the starch enzymatic hydrolysis and hydration properties

Rice flour is becoming very attractive as raw material, but there is lack of information about the influence of particle size on its functional properties and starch digestibility. This study evaluates the degree of dependence of the rice flour functional properties, mainly derived from starch behavior, with the particle size distribution. Hydration properties of flours and gels and starch enzymatic hydrolysis of individual fractions were assessed. Particle size heterogeneity on rice flour significantly affected functional properties and starch features, at room temperature and also after gelatinization; and the extent of that effect was grain type dependent. Particle size heterogeneity on rice flour induces different pattern in starch enzymatic hydrolysis, with the long grain having slower hydrolysis as indicated the rate constant (k). No correlation between starch digestibility and hydration properties or the protein content was observed. It seems that in intact granules interactions with other grain components must be taken into account. Overall, particle size fractionation of rice flour might be advisable for selecting specific physico-chemical properties.     

Solution properties of starch nanoparticles in water and DMSO as studied by dynamic light scattering

Solution properties of starch nanoparticles dispersed in DMSO and in water were studied using dynamic light scattering. The particle size distribution had two main peaks in both solvents at all scattering angles studied. They were at around 40 and 300 nm, ascribed to isolated starch nanoparticles and their aggregates, respectively. From the excess scattering intensity by the 40-nm particles, the molecular weight of the nanoparticle was estimated as 2.2–2.6×10⁶ g/mol. When the concentration was increased, another peak appeared at around 1 μm. Raising the temperature from 25 to 65 °C did not change the distribution, indicating a purely entropic process in dynamic equilibrium of the aggregation. In DMSO, an oscillatory behavior was observed in the autocorrelation function at high temperatures.     

Banana starch: production, physicochemical properties, and digestibility—a review

The large quantity of green cull bananas has the potential of being used industrially and, thereby, to improve banana economics and eliminate the large environmental problem presented by banana waste. This review summarizes the present knowledge of the composition, structure, physiochemical properties, modifications, and digestibility of banana starches and provides suggestions for needed research to improve the utilization of green cull bananas.     

The structure and properties of different types of starch exposed to UV radiation: A comparative study

The effect of UV-irradiation on four different types of native starch (corn, waxy corn, wheat and potato) have been investigated. Although the changes in the chemical structure of starch specimens were small, indicating good photostability, the samples lost adsorbed water and their crystallinity degree decreased after irradiation. Moreover, a drop in average molecular weight occurred in samples (with the exception of potato starch) as a result of main chain scission. The variations in the properties of investigated specimens of various origin were related to the differences in their structure and macromolecular arrangement. The lowest photostability among the four starches was exhibited by potato starch.     

Film blowing of thermoplastic starch

Thermoplastic starch materials are often based on a combination of starch, glycerol and water. In the present study, two potato starch grades were employed; a native (natural) grade and an oxidised and hydroxypropylated grade of the native material, in order to produce the thermoplastic material. The primary aim of the study was to identify possible routes for film blowing thermoplastic starch on a laboratory scale by a suitable choice of processing conditions, amount of glycerol and moisture content. With an appropriate combination of these parameters, the thermoplastic material based on the modified starch could be film blown in a satisfactory manner. Film blowing of material based on the natural starch was significantly more difficult. The difficulties encountered were mainly related to a sticky surface of the film, insufficient tenacity and foaming. The processing window for thermoplastic starch (related to film blowing) is briefly outlined and discussed.     

Influence of dimethylsulfoxide on tylosin production in Streptomyces fradiae

The polyketide aglycone, tylactone (protylonolide), does not normally accumulate during tylosin production in Streptomyces fradiae, suggesting that the capacity of the organism to glycosylate tylactone exceeds the capacity for polyketide synthesis. Consistent with this model, tylosin yields were significantly increased (due to bioconversion of the added material) when exogenous tylactone was added to fermentations. However, tylosin yield improvements were also observed (albeit at lower levels) in solvent controls to which dimethylsulfoxide (DMSO) was added. At least in part, the latter effect resulted from stimulation of polyketide metabolism by DMSO. This was revealed when the solvent was added to fermentations containing the tylA mutant, S. fradiae GS14, which normally accumulates copious quantities of tylactone. Journal of Industrial Microbiology & Biotechnology (2001) 27, 46–51. Received 18 March 2001/ Accepted in revised form 29 May 2001     

Properties of quinoa and oat spaghetti loaded with carboxymethylcellulose sodium salt and pregelatinized starch as structuring agents

Spaghetti based on quinoa or oat were manufactured using two different structuring agents, carboxymethylcellulose sodium salt (CMC) and pregelatinized starch at three different percentages (0.1%, 0.2%, 0.3% and 10%, 20%, 30%, respectively). The dough rheological properties were determined using a capillary rheometer, the mechanical characteristics of dry spaghetti by a dynamic mechanical analyzer and the sensorial parameters by a trained panel. Elongational and shear viscosity declined or increased when CMC was added to quinoa and oat based dough, respectively. The stress at break for dry non-conventional spaghetti increased for oat spaghetti added with CMC and pregelatinized starch, whereas decreased for quinoa spaghetti. The sensorial parameters of dry and cooked spaghetti in quinoa and oat base were strongly affected by addition of CMC and pregelatinized starch as it was not possible to produce spaghetti in base either quinoa or oat without using the tested structuring agents.     

Properties of a plasticised starch blend. Part 1: Influence of moisture content on fracture properties

The effect of moisture content on tensile and fracture properties of a plasticised starch/high molecular weight polyol blend was investigated. A wide range of mechanical behaviour was achieved by varying slightly the water uptake of this material. At low moisture content, the Young’s modulus was 3800 MPa and the yield stress, 54 MPa. When the moisture content reached 15 wt%, their values dropped, respectively, to around 1500 MPa and 21 MPa. As the material behaviour varies greatly over the moisture content range, two fracture mechanics techniques were employed: the linear elastic fracture mechanics approach to characterise brittle behaviour and the essential work of fracture method to investigate a more ductile material. At low moisture content, the measured strain energy release rate at fracture, J_Q was very low and showed little dependency on the moisture content. As the moisture content increases, the material becomes increasingly ductile and displayed a brittle-to-ductile transition at 12% of moisture content, which corresponded to the glass transition temperature of the added polyol.     

Macromolecular properties of cepacian in water and in dimethylsulfoxide

Cepacian is the exopolysaccharide produced by the majority of the so far investigated clinical strains of the Burkholderia cepacia complex. This is a group of nine closely related bacterial species that might cause serious lung infections in cystic fibrosis patients, in some cases leading to death. In this paper the aggregation ability and the conformational properties of cepacian chain were investigated to understand its role in biofilm formation. Viscosity and atomic force microscopy studies in water and in mixed (dimethylsulfoxide/water) solvent indicated the formation of double stranded molecular structures in aqueous solutions. Inter-residue short distances along cepacian chain were investigated by NOE NMR, which showed that two side chains of cepacian were not conformationally free due to strong interactions with the polymer backbone. These interactions were attributed to hydrogen bonding and contributed to structure rigidity.     

Effects of organic solvents on protein structures: Observation of a structured helical core in hen egg-white lysozyme in aqueous dimethylsulfoxide

A partly folded state of hen egg-white lysozyme has been characterized in 50% DMSO. Low concentrations of DMSO (<10%) have little effect on the overall folded conformation of lysozyme as seen from ¹H NMR chemical shift dispersion. At increasing DMSO concentrations (>10%) a cooperative transition of the structure to a new, partially folded state is observed. This transition is essentially complete by ∼50% DMSO. NMR studies show an overall decrease in chemical shift dispersion with marked broadening of many resonances. A substantial number of backbone and side chain–side chain NOEs suggests the presence of secondary and tertiary interactions in the intermediate state. Tertiary organization of the aromatic residues is also demonstrated by enhanced near-UV circular dichroism and limited exposure of tryptophans as monitored by iodide quenching of fluorescence. The intermediate state exhibits enhanced binding to hydrophobic dyes. Further, the structural transition from this state to a largely unfolded conformation is cooperative. H/D exchange rates of several amide protons and four indole protons of tryptophans (W28, W108, W111, and W123), measured by refolding from 50% DMSO at different time intervals reveal that protection factors are high for the helical domain, whereas NH groups in the triple stranded antiparallel β-sheet domain are largely solvent-exposed. An ordered hydrophobic core in the intermediate state comprising of helix A, helix B, and helix D is consistent with the high protection factors observed. The structured intermediate in 50% DMSO resembles the early kinetic intermediate observed in the refolding of hen egg white lysozyme, as well as a molten globule state of equine lysozyme at low pH. The results demonstrate the potential use of nonaqueous structure perturbing solvents like DMSO to stabilize partially folded conformations of proteins. Proteins 29:492–507, 1997. © 1997 Wiley-Liss, Inc.     

Unusual rheological properties of a new associative polysaccharide in salt media

New amphiphilic polysaccharides based on alginate-grafted-Poly (ε-caprolactone) or alg-g-PCL bearing two kinds of PCL chains with different molar masses (1250 and 530 gmol⁻¹) with various amounts from 3% to 15% were prepared. Rheological properties in aqueous solutions of such systems have been investigated as a function of polymer concentration, added salt and temperature in semi-dilute regime. Strong hydrophobic intermolecular associations were clearly demonstrated in pure water whatever the PCL chain length and extend of modification. Increasing polymer concentration, grafting rate and/or PCL chains length can lead to a structured liquid behaviour. Rheological properties of the most organized system have been found independent to the temperature (until 60 °C). In salt media, a strong dependence of hydrophobic interactions to the length of PCL chains was observed. For M_PCL = 1250 g.mol⁻¹ the screening of charges promotes the establishment of intermolecular interactions and leads to a strong physical gel for the highest grafting rates. For M_PCL = 530 g mol⁻¹, ionic strength leads to a decrease of rheological properties when increasing grafting rate. This result may indicate an increase of hydrophobic clusters even in the entangled regime. This unusual behaviour opens the ways for the preparation of suitable hydrogels for drug release.     

Banana starch structure and digestibility

It is well known that raw banana starch is a good source of resistant starch. Less is known, however, regarding the digestion property of gelatinized banana starch. In this study, banana starch cooked for 20 min in excess water had a significant fraction of slowly digestible starch (19%), as well as resistant fraction (27%). Amylopectin is thought to be responsible for its slow digestion property, since banana starch studied here has a relatively low amylose content of 11.2%. Chain-length distribution analysis revealed that banana amylopectin has a significantly different structure from corn or potato amylopectin in that it has a higher proportion of very long chains. Retrogradation studies support the view that banana starch retrogrades at a substantially faster rate than corn or potato starch leading to less digestible cooked starch. Additionally, banana starch has unique pasting properties making it behave like a chemically lightly cross-linked starch. Banana starch is unique, both nutritionally and functionally, to warrant further investigation on potential commercial uses.     

Structural characterization and properties of starch/konjac glucomannan blend films

In this work, a series of glycerol-plasticized pea starch/konjac glucomannan (ST/KGM) blend films was prepared by a casting and solvent evaporation method. The structure, thermal behavior, and mechanical properties of the films were investigated by means of Fourier Transform Infrared Spectroscopy, wide-angle X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, and tensile testing. The results indicated that strong hydrogen bonding formed between macromolecules of starch (ST) and konjac glucomannan (KGM), resulting in a good miscibility between ST and KGM in the blends. Compared with the neat ST, the tensile strength of the blend films were enhanced significantly from 7.4 to 68.1 MPa with an increase of KGM content from 0 to 70 wt%. The value of elongation at break of the blend films was higher than that of ST and reached a maximum value of 59.0% when the KGM content was 70 wt% and 20% of glycerol as plasticizer. The incorporation of KGM into the ST matrix also led to an increase of moisture uptake for the ST-based materials. The structure and properties of pea starch-based films were modified and improved by blending with KGM.     

Physicochemical properties and in vitro digestibility of flour and starch from pea (Pisum sativum L.) cultivars

Flours and isolated starches from three different cultivars (1544-8, 1658-11 and 1760-8) of pea grown under identical environmental conditions were evaluated for their physicochemical properties and in vitro digestibility. The protein content, total starch content and apparent amylose content of pea flour ranged from 24.4 to 26.3%, 48.8 to 50.2%, and 13.9 to 16.7%, respectively. In pea starches, the 1760-8 showed higher apparent amylose content and total starch content than the other cultivars. Pea starch granules were irregularly shaped, ranging from oval to round with a smooth surface. All pea starches showed C-type X-ray diffraction pattern with relative crystallinity ranging between 23.7 and 24.7%. Pea starch had only a single endothermic transition (12.1-14.2 J/g) in the DSC thermogram, whereas pea flour showed two separate endothermic transitions corresponding to starch gelatinization (4.54-4.71 J/g) and disruption of the amylose-lipid complex (0.36-0.78 J/g). In pea cultivars, the 1760-8 had significantly higher setback and final viscosity than the other cultivars in both pea flour (672 and 1170 cP, respectively) and isolated starch (2901 and 4811 cP). The average branch chain length of pea starches ranged from 20.1 to 20.3. The 1760-8 displayed a larger proportion of short branch chains, DP (degree of polymerization) 6-12 (21.1%), and a smaller proportion of long branch chains, DP ≥ 37 (8.4%). The RDS, SDS and RS contents of pea flour ranged from 23.7 to 24.1%, 11.3 to 12.8%, and 13.2 to 14.8%, respectively. In pea starches, the 1760-8 showed a lower RDS content but higher SDS and RS contents. The expected glycemic index (eGI), based on the hydrolysis index, ranged from 36.9 to 37.7 and 69.8 to 70.7 for pea flour and isolated pea starch, respectively.     

Thermal and structural properties of unusual starches from developmental corn lines

Starches from exotic corn lines were screened by using differential scanning calorimetry (DSC) to find thermal properties that were significantly different from those exhibited by starches from normal Corn Belt lines. Two independent gelatinization transitions, one corresponding to the melting of a peak at 66 °C and the other to a peak melting at 69 °C, were found in some starches. The melting characteristics were traced to two separate types of granules within the endosperm. Strong correlations were found between DSC properties and proportion of large granules with equivalent diameter ≥17 μm. Starches with a lower peak onset gelatinization temperature (T_oG), had a lower normalized concentration of chains with a degree of polymerization (dp) of 15–24 and/or a greater normalized concentration of chains with a dp of 6–12. These studies will aid in understanding structure–thermal property relationships of starches, and in identifying corn lines of interest for commercial breeding.     

Physical, chemical and microscopic characterization of a new starch from chayote (Sechium edule) tuber and its comparison with potato and maize starches

In this work, the chayote tuber starch (CHS) was isolated and its chemical composition and its physical and microscopic characteristics were determined, and compared with potato (PS) and maize (MS) starches. The starch content in chayote tubers (728 g kg⁻¹ dry weight) was similar to potato tubers (700 g kg⁻¹ dry weight), with a high level of purity (>98%), while its phosphorous content was higher (0.15%) than PS (0.08%) and MS (0.01%). Starch granules were oval, irregular, truncated and rounded with sizes between 7 and 50 μm with smooth surfaces. CHS dispersions (1% and 4%, w/w) showed higher viscosity (75 and 1715 mPa s), than PS (350% and 50% lower) and MS (715% and 600% lower). The gelatinization temperature (65 to 74 °C) was similar in CHS and PS. The pasting properties (RVA) of the starches suggest that CHS showed better characteristics than the commercial potato and maize starches. Therefore, CHS could be used as a thickening agent and a substitute to PS in food dispersions where a high viscosity is needed.