Preparation of highly substituted carboxymethyl starch using a twin‐screw extruder

Carboxymethyl starch was prepared by reacting corn starch with sodium mono chloro acetate (SMCA) in a Brabender TSE‐20 co‐rotating twin screw extruder. The effects of the SMCA/starch ratio (theoretical degrees of substitutions 2.73, 3.62, and 4.53), aqueous ethanol/(starch + SMCA) ratio (0.13 and 0.25) and the screw configuration (0, 1, and 2 kneading blocks) on the degree of substitution (DS) and reaction efficiency were studied. A 3 × 2 factorial design with 3 levels of the starch/SMCA ratio and 2 levels of the aqueous ethanol/(starch + SMCA) ratio were used. This 3 × 2 factorial design was blocked, with the screw configuration as the blocking variable. The effects of the SMCA/starch ratio and the screw configuration were found to be significant. The carboxymethylated starches were characterized using FTIR, SEM, and XRD. The microstructure of the carboxymethylated starches, studied using SEM, revealed that the integrity of the starch granules was partially preserved at low aqueous ethanol levels when no kneading block was used. However, for all other reaction conditions either granule agglomeration or fusion was observed. XRD analysis indicated substantial loss of crystallinity in the carboxymethylated starches, irrespective of the damage to the granule structure. The highest DS and the highest reaction efficiency obtained were 1.54 and 0.42, respectively.     

Preparation of Starch Carbamates in Homogeneous Phase using Different Mixing Conditions

The preparation of starch carbamates of wrinkled pea starch in homogeneous phase catalysed by dibutyltin dilaurate in DMSO as solvent is described. The empfloyed isocyanates have linear alkyl chains with 7, 9, 11, 15 or 18 carbon atoms. Starch carbamates with equal degrees of substitution and different alkyl chains lengths were synthesised in a reaction flask. The preparation of carbamates with equal alkyl chain length and different degrees of substitution was also possible. The structures of the polymers were characterised by elemental analysis, IR‐ and ¹H‐NMR‐spectroscopy. The behaviour of the prepared starch carbamates under thermal loading was investigated by using Differential Scanning Calorimetry (DSC) and a hot press. In addition, for 1‐undecyl isocyanate the starch carbamate was prepared both in a kneader and an extruder. The differences in reaction conditions and the results were discussed.     

Starch conversion and expansion behaviour of wheat starch cooked with either; palm,soybean or sunflower oils in a co‐rotating intermeshing twin‐screw extruder

Wheat starch was extrusion cooked with the addition of three commercial vegetable oils, namely; palm oil, soybean oil and sunflower oil. The effects of the addition of the oils on the degree of starch conversion as well as extrudates expansion were investigated. In order to conduct a comparison between the three added oils, the barrel temperatures, material feed rate, water content and finally the screw speed were fixed. The three selected oils were added at concentrations varied from 1% to 8% on starch dry basis and the quantities added were controlled through the whole process. The results suggested that for the three vegetable oils used, the specific mechanical energy (SME) was decreased as the oil concentration increased up to 5% and further rise in concentration did not impart significant changes. This drop in the SME values was accompanied with a decrease in the extent of starch conversion. This was assessed by rapid viscosity analyser (RVA) viscosity and water solubility and absorbance measurements. The effect of the addition of oil on extradites’ sectional expansion was complex in which a significant increase until 5% oil concentration was reached and further increase of oil quantities resulted in a drastic reduction. This effect was observed for all three oils and no significant differences between oils were noticed. All extrudates exhibited a v‐type crystalline pattern which was ascribed to the amylose lipid complex formation. However, the crystallinity indices indicated no interference by the three oils to the complex formation. This suggested that the endogenous lipids naturally present in wheat starch were sufficient to complex the starch.     

Isocyanate‐free Route to Starch‐graft‐Polycaprolactone via Carbonyldiimidazole (CDI)‐mediated End Group Conversion

This paper reports on the synthesis of biodegradable starch‐graft‐poly ϵ‐caprolactone (starch‐g‐PCL) in two steps. First, poly ϵ‐caprolactone (PCL) was modified on the terminal groups by using carbodiimidazole (CDI) as coupling agent. Then, the starch graft copolymers with PCL were prepared through a carbonate bond using carboimidazole function. Monofunctional and bifunctional reactive end‐group PCL terminated with carboimidazole groups were prepared and reacted with hydroxyl groups of starch. The resulting starch‐g‐PCL copolymers were characterized by FT‐IR, NMR, HR‐MAS‐NMR, DSC, MEB and XRD.     

High‐resolution Imaging of Starch Granule Structure using Atomic Force Microscopy

Atomic force microscopy (AFM) was carried out for the precise structural analysis of starch granules. AFM is a useful technique to obtain — under atmospheric conditions — high‐resolution images which are as good as those obtained by conventional scanning and transmission electron microscopy. The samples for observation by AFM do not require complicated preparations such as the drying and metal coating as in the case of electron microscopy. The AFM technique is suitable for the precise structural observation of bio‐materials in which damage caused by drying and heating must be avoided and the effect of the thickness of the metal coating must be considered. Several preparation methods for exposing the bare inner surface of starch granules were studied in the beginning. AFM structural analyses on the nanometer scale were carried out on starch granules from five different botanical sources which were prepared by a physical method. It was directly demonstrated that fine particles of approximately 30 nm in diameter existed inside each granule and occasionally formed a straight chain structure. These fine particles may correspond to the individual blocklet or single cluster which has been proposed in the starch structural model previously discussed.     

Starch Paste Stickiness is a Relevant Native Starch Selection Criterion for Wet‐end Paper Manufacturing

The correct choice of selection and quality criteria is critical for most starch applications. In this study, a set of different potato starches, selected for a large variation in natural phosphate content and final viscosity, was cationised and tested in a laboratory scale wet‐end paper manufacturing process. Analysis of further parameters expected to be critical for processing, including amylose content and starch granule size, was also performed. Since no significant correlation was found between any of these parameters and paper processing, further attempts were made to find structural or physico‐chemical explanations for the paper processing performance. Hence, several additional parameters of the starches were determined including amylopectin chain length pattern, phosphate substitution, molecular size distribution, pasting‐texture properties and fragility of the gelatinised granules. Among these parameters, the best correlation found to paper filler retention was stickiness of the starch as measured by texture analysis. The starches that performed best in the paper trials showed rapid granule bursts that could be readily estimated from the width of the pasting curve peaks. Light microscopy of non‐soluble remnant starch obtained after gelatinisation of starch under dilute conditions revealed a high proportion of broken granular structures. It is hypothesised that the degree of phosphorylation, together with a hitherto unknown molecular parameter that is related to starch granule fragility, determines starch paste stickiness, which in turn is an important parameter for wet‐end paper manufacturing.     

Starch as a Pore‐forming and Body‐forming Agent in Ceramic Technology

Wheat and corn starch can be used for the preparation of porous alumina ceramics via the SCC (starch consolidation casting) process, resulting in porosities ranging from > 20% to approx. 50% (using nominal starch contents of 10 – 50%, v/v), with open porosity dominating (closed porosity < 6.5%). The character of porosity and the shape of the pores corresponds to the starch granules used, but the pore size is determined by a complex interplay between starch swelling (during the body‐forming step) and pore shrinkage (during sintering of the ceramic). Typically, for low starch contents (e.g. nominal starch contents of around 10%, v/v) starch swelling is a significant effect, and the pores after sintering are larger than the size of the starch granules. For higher starch contents swelling is constrained (by limited space and/ or water availability), and the matrix shrinkage during sintering overcompensates the swelling effect, so that the final pores in the ceramic can be significantly smaller than the original starch granule size. In this paper it is shown how porosity is related to pore size. In particular, it is demonstrated that the porosity indirectly determined from image analysis (via the median pore size) is closely related to the porosity directly measured via the Archimedes method. On the other hand, mercury porosimetry measures the distribution of pore throat sizes. With increasing starch content in the suspension, the pore throat size in the as‐fired ceramic materials increases, resulting in a more open microstructure.     

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.     

Effects of starch alkenylsuccinylation on the grafting efficiency,paste viscosity,and film properties of alkenylsuccinylated starch‐g‐poly(acrylic acid)

Commercial cornstarch was alkenylsuccinylated with alkenylsuccinic anhydride to different degrees of substitution (DS) and then the products were graft‐copolymerized with acrylic acid for investigating the effects of starch alkenylsuccinylation on the graft copolymerization with vinyl monomer, as well as on paste viscosity and film properties of alkenylsuccinylated starch‐g‐poly(acrylic acid) (ASS‐g‐PAA). The number of carbon atom of alkenyl in alkenylsuccinates considered was 8 and 12, corresponding to octenylsuccinylation and dodecenylsuccinylation of starch, respectively. The graft copolymerization was accessed by grafting efficiency, grafting ratio, and conversion of monomer to polymer, and the film properties of ASS‐g‐PAA considered included tensile strength, breaking elongation, and work‐to‐break. Experimental results demonstrated that the alkenylsuccinylation showed marked effects on the copolymerization, paste viscosity, and film properties. It resulted in increased grafting efficiency, stable paste viscosity, and strong starch film. Carbon‐chain length of the alkenyl and DS value of the alkenylsuccinates also exhibited evident effects on the copolymerization and film properties. Octenylsuccinylation of starch before the copolymerization was superior to dodecenylsuccinylation in improving the efficiency and film properties. Low levels of octenylsuccinylation could be utilized to increase the efficiency of the copolymerization and improve the properties of starch film.     

Starch Granule‐Associated Proteins and Polypeptides: A Review

This paper reviews current information regarding the (non‐gluten) proteins which are naturally located in and on starch granules, and which are termed starch granule associated proteins (SGAPs). At least ten major SGAPs can be extracted from most starches and have molecular weights in the range of approximately 5 to 149 kDa. A substantial number of these proteins are located at the starch granule surface, where their presence in association with that of other minor granule components (such as lipids), appears to significantly influence the overall properties of both starch granules and starchy products. The different extraction conditions which can be exploited to selectively remove SGAPs are detailed. Although some SGAPs may serve as supplementary storage proteins, the majority of SGAPs are believed to be starch biosynthetic enzymes, a proportion of which remain trapped within the growing granule structure. The identity and quantities of the biosynthetic enzymes varies with botanical source, genetic variety and even with time. Current knowledge regarding the identities, compositions, locations, properties and functions of several of the more common SGAPs (e.g. the ∼15 kDa friabilin/puroindoline proteins, the ∼30 kDa protein, and the ∼60 kDa starch granule‐bound starch synthase (SGBSS) protein) are reviewed in detail.     

Molecular Fractionation of Starch in Nycodenz‐Dimethyl Sulfoxide by Density‐Gradient Ultracentrifugation

Starches from various origins (normal corn, waxy corn, high‐amylose corn, normal rice, waxy rice, potato and tapioca) were fractionated by density‐gradient ultracentrifugation at 124,000×g, using a gradient of Nycodenz (0–40%, w/w) in 90% dimethyl sulfoxide (DMSO). The fractions of different densities were collected from a centrifuge tube, and then analyzed by the phenol‐sulfuric acid method and iodine‐binding test. Amylose and amylopectin were clearly separated by the density‐gradient centrifugation within 6 h of centrifugation in the total carbohydrate vs. density profile. The amylose content in the starches, measured from the centrifugation for 6 h, agreed with the values reported in the literature, and the content of intermediate fraction (5–13%) was also measured. Amylopectin quickly reached a density region (1.22–1.23 g/mL) with a sharp and stable peak, whereas amylose showed a band in a broad density range, moving toward higher density as the centrifugation continued. The buoyant density of amylose became similar to that of amylopectin after extensive centrifugation. Because the sedimentation rate of amylose was much lower than that of amylopectin, both starch chains are effectively fractionated in the gradient medium, and the iodine‐binding property of the fractionated starches provides valuable information on the chain conformation of starch.     

Influence of Chain Length on α‐1,4‐D‐Glucan Recrystallization and Slowly Digestible Starch Formation

Short‐chain α‐(1,4)‐D ‐glucan samples were generated by debranching of potato amylopectin and fractionation on gel permeation chromatography. The collected fractions were gathered to generate two samples with an average DP_n of 32 and 42, respectively. The samples were recrystallized at −80 and 1°C for three days (10%, w/w) and the resulting structures and related digestibility were assessed. The results revealed that the slowly digestible starch (SDS) content was affected by both chain length and recrystallization temperature. The highest SDS level (49%) was obtained at −80°C from the sample with the lowest average DP_n. Its structure showed B‐type polymorphic crystallites with a substantial amorphous part and a melting temperature of 85°C. Such a melting temperature was close to that already reported in the literature and appears characteristic of recrystallized SDS structures.     

Laboratory‐scale Dry/Wet‐Milling Process for the Extraction of Starch and Gluten from Wheat

A laboratory‐scale process is presented for the manufacture of starch and gluten from wheat. Main feature of this process is that whole wheat kernels are crushed dry between smooth rolls prior to wet disintegration in excess water in such way that gluten formation is prevented and fibres can be removed by sieving. Centrifugation of the endosperm suspension yields a dough which can be separated into starch and gluten using an established batter process. The results suggest that starch recovery is increased in comparison to a conventional wheat flour process without a concomitant decrease in protein recovery. Although starch purification was omitted, a total starch with a low protein content is obtained. On the other hand, the protein content of the gluten fraction is rather low due to difficulties in removing the starch. Despite this, the effect on dough mechanical properties by the addition of gluten obtained from wet‐milled wheat is comparable to the effect of gluten from flour.     

Influence of di‐functional versus multi‐functional chain extenders on the foamability of a potato starch‐based biopolymer

This study examines the effectiveness of di‐functional versus multi‐functional glycidyl ether chain extenders (CE) for improving the foamability of a commercial blend of hydrolyzed potato starch and polylactic acid, Solanyl® 30R (Solanyl Biopolymers Inc.). The blend was reactively modified in bulk using CEs at concentrations ranging from 0.5–2.5 wt% within a twin‐screw extruder operating at 170°C and 150 RPM. Thermal and rheological analysis of the modified blends found that only one multi‐functional polymeric CE was effective for altering the molecular structure of the blend while both significantly improved the foamability of the material. The two di‐functional CEs did not produce detectable changes in melt elasticity for the blend but again had a notable influence on improved foamability. Foamability was evaluated based on improvements to the material that increased foam stability (i.e. higher cell densities and smaller bubbles), and the results in this study suggested that these CEs influenced bubble expansion in ways other than simply causing rheological change.     

Starch Phosphate Hydrogels. Part I: Synthesis by Mono‐phosphorylation and Cross‐linking of Starch

Starch‐based hydrogels were synthesized by cross‐linking monostarch monophosphates (MSMP) with different di‐ and tricarboxylic acids such as succinic, adipic or citric acid. Phosphorylation of starch was performed in a semi‐dry process using a mixture of primary and secondary sodium phosphates. The phosphorus content and degree of substitution of phosphate groups (DS_P) of the resulting MSMP were determined using a photometric method. For structural characterization of starch phosphates ³¹P NMR was used. Investigations showed that MSMP hydrogels were strong water absorbing polymer networks with a free swelling capacity (FSC) of up to 185 g water / g dry hydrogel.     

The Relationship Between Wheat Flour and Starch Pasting Properties and Starch Hydrolysis: Effect of Non‐starch Polysaccharides in a Starch Gel System

Non‐starch polysaccharides (NSPs) and celite (used as inert filler) were incorporated into wheat flour and wheat starch paste preparations at levels of 1, 2.5, and 5% in both addition and replacement modes. Pasting properties of gums were compared using a Rapid Visco Analyser. Use of guar gum and locust bean gum elevated the peak and final viscosities of the resulting pastes (when used in either addition or replacement modes), whereas arabic gum significantly reduced the peak and final viscosity properties of the pastes. Samples which comprised wheat starch yielded higher peak and final viscosity characteristics compared to wheat flour containing samples, however higher breakdown and setback values were observed for samples using wheat flour as a base compared to wheat starch. The firmness of the gels (as determined using a texture analyser) increased with the use of wheat starch compared to wheat flour. Little significant difference was observed between NSP used and mode of application (replacement or addition). In vitro starch degradation was conducted on the wheat flour gels. Guar gum and locust bean gum reduced the amount of starch degradation in these gels, whereas arabic gum and celite increased the amount of starch hydrolysis (or were similar to the control). The rate of starch hydrolysis appears to be related to the viscosity altering behaviour of the NSPs in a starch‐rich system. The results indicate that selection of NSPs is important as gum arabic has the potential to increase starch hydrolysis compared to the control.     

Properties of Steam‐Treated Arrowroot (Maranta arundinacea) Starch

Arrowroot starch was steam‐treated (ST) by subjecting to pressure steaming at 1.03 bar for 15 min, after preconditioning the moisture content in the samples to 15, 25 and 30%. A control sample (9.8% H₂O) without any added moisture was also treated in a similar way. The steam‐treated samples and the unmodified sample were analysed for apparent and soluble amyloses (expressed as blue value), intrinsic viscosity, swelling and solubility at 90 °C, and cold water solubles. The thermal decomposition pattern of the samples was studied on a differential thermal analyser (DTA) and the X‐ray diffraction pattern on a Philips X‐ray diffractometer. The enzyme susceptibility of the unmodified and steam‐treated samples was examined with reference to α‐amylase. In general, steam‐treated samples showed appreciable changes in the above properties compared to the unmodified one, as well as to the sample steam‐treated without any added moisture.     

挤压机作为生化反应器的应用

对挤压机作为连续式生化反应器用于以蛋白质、淀粉和纤维等聚合物为基质的生物原料进行生物或化学反应这一领域内的应用作了研究 ,并对挤压机作为生化反应器在结构方面提出了一些自己的设计思路