Mutant genes at the r and rb loci affect the structure and physico-chemical properties of pea seed starches

Mutant genes at two loci, r and rb, known to encode genes affectingthe starch biosynthetic pathway, were studied for their effecton the structure and gelatinization of pea seed starches. Comparisonswere made using starches from four lines {RRRbRb, rrRbRb, RRrbrb,and rrrbrb), near-isogenic except for genes at these two loci.All the starches had C-type X-ray diffraction patterns, butdifferent contents of ‘A’ and ‘B’ polymorphs.The presence of a mutation at either locus increased the ‘B’polymorph content in the starches, although the influence ofthe r mutation was much greater than that of rb. Differenceswere discovered in the crystalline stucture of the rrRbRb starchwhich correlated with a high content of amorphous phase as wellas with the changes in amylopectin structure. In addition, changesin the crystalline structure of this sample correlated witha lack of co-operative transition during starch gelatinizationin excess water. The RRrbrb starch had a greatly increased enthalpyof gelatinization in excess water compared with the wild-typestarch. It is proposed that this effect is connected with specificcharge interactions between the molecules in the starch granule.The rrrbrb starch had parameters of crystalline structure andgelatinization which reflected the different influences of thetwo genes. With regard to gelatinization, this starch had relativelywide co-operative transition and low enthalpy and a very highpeak temperature of transition. Key words: Pisum sativum, starch structure, genetic effects, rugosus mutants     

Production of modified polymeric carbohydrates

The cloning of a gene responsible for the phosphorylation of glucans has made it possible to genetically engineer the phosphorylation level of starches in higher plants. Through the manipulation of starch synthase activity, it is now also possible to genetically tailor the chain-length distribution in the amylopectin. Both findings will lead to the development of novel starches utilized as a renewable resource. The production of fructans on a large scale can also be envisioned for the near future.     

Towards a more versatile alpha-glucan biosynthesis in plants

Starch is an important storage polysaccharide in many plants. It is composed of densely packed alpha-glucans, consisting of 1,4- and 1,4,6-linked glucose residues. The starch polymers are used in many industrial applications. The biosynthetic machinery for assembling the granule has been manipulated in many different ways to gain insight into the process of starch biosynthesis and to engineer starches with improved functionalities. With respect to the latter, two generic technologies with great potential have been developed: (i) introduction of new linkage types in starch polymers (1,3- and 1,6-linkages), and (ii) engineering granule-boundness. The toolbox to engineer this new generation of starch polymers is discussed.     

Improving starch for food and industrial applications

Progress in understanding starch biosynthesis, and the isolation of many of the genes involved in this process, has enabled the genetic modification of crops in a rational manner to produce novel starches with improved functionality. For example, potato starches have been created that contain unprecedented levels of amylose and phosphate. Amylose-free short-chain amylopectin starches have also been developed; these starches have excellent freeze-thaw stability without the need for chemical modification. These developments highlight the potential to create even more modified starches in the future.     

Mutan produced in potato amyloplasts adheres to starch granules

Production of water-insoluble mutan polymers in Kardal potato tubers was investigated after expression of a full-length (GtfI) and a truncated mutansucrase gene referred to as GtfICAT (GtfI without glucan-binding domain) from Streptococcus downei. Subsequent effects on starch biosynthesis at the molecular and biochemical levels were studied. Expression of the GtfICAT gene resulted in the adhesion of mutan material on starch granules, which stained red with erythrosine, and which was hydrolysed by exo-mutanase. In addition, GtfICAT-expressing plants exhibited a severely altered tuber phenotype and starch granule morphology in comparison to those expressing the full-length GtfI gene. In spite of that, no structural changes at the starch level were observed. Expression levels of the sucrose-regulated, AGPase and GBSSI genes were down-regulated in only the GTFICAT transformants, showing that GtfICAT expression interfered with the starch biosynthetic pathway. In accordance with the down-regulated AGPase gene, a lower starch content was observed in the GTFICAT transformants. Finally, the rheological properties of the GTFICAT starches were modified; they showed a higher retrogradation during cooling of the starch paste.     

A novel in situ atomic force microscopy imaging technique to probe surface morphological features of starch granules

The application of atomic force microscopy (AFM) for observing iodine complexes in starch has been limited due to limitations including granular sample fixation techniques and possible unintended reactions with embedding materials such as epoxy resins or adhesives. In this paper, a new method is described that employs an optical microscopic technique to ensure that the tip of the AFM is scanning a specified granule without any probe-induced particle movement by the AFM probe motion. The direct sprinkling of samples on a two-sided adhesive tape allows investigations in an in situ environment of the un-embedded starch granule surface and thus provides high-resolution images of granule morphology and phase changes of starches in the presence of humidity and with iodine vapor. These observations demonstrate that this novel in situ AFM imaging technique allows us to visualize the hair-like structures on the surface of granular starches when starches are exposed to iodine vapor under humid environments. This study reveals that the hair-like extensions on the starch granule surfaces are strongly dependent on the organization of the glucan polymers within corn or potato starch.     

Process optimization for the synthesis of octenyl succinyl derivative of waxy corn and amaranth starches

Modification of starch by dicarboxylic acid anhydrides to starch esters, containing both hydrophilic and hydrophobic groups are known to improve its emulsification properties, and can also be used for encapsulation after hydrolysis. Reports on the effect of process conditions on the extent of modification of starches by using n-octenyl succinic anhydride (n-OSA) are not readily available. In the present study, the process of manufacturing of OSA starches from waxy corn and amaranth starch were studied with respect to the OSA/starch ratio, pH, temperature and time of the reaction. The effects of these parameters were evaluated on the basis of degree of substitution (DS). The concluding conditions for amaranth-OSA starches was a reaction time of 6 h at 3% OSA/starch ratio at 30 °C and pH 8.0 at 25% starch concentration. For waxy corn-OSA starch, all parameters were identical except for the reaction time of 24 h. The maximum DS achieved for both the starches was 0.02. Emulsification capacity and oil absorption capacity of the OSA-modified starches were more or less similar within the parameter chosen and also independent of starch type.     

粉末X射线衍射图谱计算植物淀粉结晶度方法的探讨

植物淀粉有A-型、B-型和C-型3种晶体。以水稻(Oryza sativa)、马铃薯(Solanum tuberosum)、豌豆(Pisum sativum) 和莲藕(Nelumbo nucifera)淀粉为材料, 利用粉末X-射线衍射仪(XRD)调查了不同晶体类型淀粉的波谱特征, 探讨XRD波谱相对结晶度的计算方法。软件峰拟合法、软件曲线法、直线作图法和曲线作图法均可用于计算淀粉XRD波谱的相对结晶度, 以曲线作图法计算结果较为可靠。利用曲线作图法得出的结果表明, 稻米淀粉的结晶度与直链淀粉含量呈显著线性负相关, 酸解莲藕淀粉的结晶度与淀粉酸水解度呈显著线性正相关。酸水解使莲藕淀粉的C-型晶体转变为A-型晶体。上述研究结果为利用XRD分析植物淀粉晶体类型和计算相对结晶度提供了重要参考。     

Cold Plasma: an Alternative Technology for the Starch Modification

Cold plasma is an emerging novel non-thermal technology in the sector of food processing. In the present review we will discuss the recent scientific reports on properties of cold plasma treated starches. For industrial use native starch is subject to modification to enhance the properties. This paper reviews on the mechanism of starch modification by plasma reactive species, briefly discussing its effects on properties. The effect of cold plasma on starches depends on the type of feed gas, voltage applied and treatment time. The alteration in the properties is mainly due to depolymerization and cross linking of amylose and amylopectin side chains. After plasma treatment there is decrease in molecular weight, viscosity, and gelatinization temperatures. Plasma etching increased the surface energy and enhanced the hydrophilicity of the starch granules. We can conclude that cold plasma is as alternative technology to modify the properties of starch.     

Physicochemical characteristics and fine structure of high-amylose wheat starches isolated from Australian wheat cultivars

High-amylose starch is a source of resistant starch (RS) which have great impact on human health like dietary fiber. Nowadays, high-amylose wheat has been produced by genetic backcrossing, which enhances apparent amylose content and generates altered amylopectin. In this study, the high-amylose wheat starches isolated from various high-amylose wheat cultivars grown in Australia were characterized for understanding their physicochemical properties and fine structure of starch. The physicochemical characteristics of the high-amylose wheat starches are significantly different among the cultivars. Amylose contents of these cultivars were in a range of 28.0–36.9%, which is significantly higher than that of the normal wheat starch (25.6%). The high-amylose wheat starches also had higher blue value but lower λ_max than the normal wheat starch. Gelatinization temperature of the high-amylose wheat starches is higher than that of the normal wheat starch but transition enthalpy is lower. X-ray diffraction showed that the high-amylose wheat starch had C-type crystals close to A-type crystal. Pasting properties of the high-amylose wheat starches were varying depending on the cultivars. However, almost high-amylose wheat starches had lower peak and final viscosities and higher setback viscosity than did the normal wheat starch. Fine structure of amylose and amylopectin was different among the high-amylose wheat cultivars and related to the physicochemical properties of starch. These results help to understand well the characteristics of the high-amylose wheat starches before application for food processing.     

Studies of the retrogradation process for various starch gels using Raman spectroscopy

The retrogradation of untreated wild-type starches (potato, maize, and wheat), waxy maize starches, and one pregelatinized, modified amylose-rich starch was investigated continuously using Raman spectroscopy. The method detects conformational changes due to the multi-stage retrogradation, the rate of which differs between the starches. The pregelatinized, modified amylose-rich starch shows all stages of retrogradation in the course of its Raman spectra. In comparison to amylose, the retrogradation of amylopectin is faster at the beginning of the measurements and slower in the later stages. The untreated starches can be ranked in the order of their rate of retrogradation as follows: potato>maize>wheat.     

Draft genome sequence of Streptomyces coelicoflavus ZG0656 reveals the putative biosynthetic gene cluster of acarviostatin family α-amylase inhibitors

Aims: The aims of this study are to obtain the draft genome sequence of Streptomyces coelicoflavus ZG0656, which produces novel acarviostatin family α‐amylase inhibitors, and then to reveal the putative acarviostatin‐related gene cluster and the biosynthetic pathway. Methods and Results: The draft genome sequence of S. coelicoflavus ZG0656 was generated using a shotgun approach employing a combination of 454 and Solexa sequencing technologies. Genome analysis revealed a putative gene cluster for acarviostatin biosynthesis, termed sct‐cluster. The cluster contains 13 acarviostatin synthetic genes, six transporter genes, four starch degrading or transglycosylation enzyme genes and two regulator genes. On the basis of bioinformatic analysis, we proposed a putative biosynthetic pathway of acarviostatins. The intracellular steps produce a structural core, acarviostatin I00‐7‐P, and the extracellular assemblies lead to diverse acarviostatin end products. Conclusions: The draft genome sequence of S. coelicoflavus ZG0656 revealed the putative biosynthetic gene cluster of acarviostatins and a putative pathway of acarviostatin production. Significance and Impact of the Study: To our knowledge, S. coelicoflavus ZG0656 is the first strain in this species for which a genome sequence has been reported. The analysis of sct‐cluster provided important insights into the biosynthesis of acarviostatins. This work will be a platform for producing novel variants and yield improvement.     

Effect of acid–alcohol treatment on the molecular structure and physicochemical properties of maize and potato starches

The molecular structure and physicochemical properties of acid–alcohol treated maize and potato starches (0.36% HCl in methanol at 25 °C for 1–15 days) were investigated. The yields of the modified starches were ranging from 91 to 100%. The average granule size of modified starches decreased slightly. The solubility of starches increased with the increase of treatment time, and the pasting properties confirmed the high solubility of modified starches. The gelatinization temperatures and range of gelatinization increased with the increase of treatment time except T_o (onset temperature) of maize starch. Molecular structures of modified starches suggested the degradation of starches occurred mostly within the first 5 days of treatment, and degradation rate of potato starch was higher than maize starch both in amylopectin and in amylose. Maize starch was found less susceptible to acid–alcohol degradation than potato starch.     

玉米淀粉生物合成及其遗传操纵

淀粉是许多植物重要的储藏物质。淀粉突变体以及转基因植物中淀粉变异的特点使我们对淀粉生物合成的过程有了较深入的了解,许多研究的结果揭示了玉米淀粉的生物合成涉及4类酶--ADPG焦磷酸化酶、淀粉合成酶、淀粉分支酶和去分支酶。随着编码这些酶的基因的克隆,利用转基因技术对淀粉合成过程进行遗传操纵业已成为可能,并且在提高淀粉产量以及不同特性淀粉品质的种质资源创新等方面展示出巨大的潜力。 Abstract:Starch is the most important source of calories and a vital storage component in plants.The characterization and production of starch variants from mutation and with transgenic technology has improved our understanding of the synthesis of starch granule.In starch biosynthesis in plants,four enzymes,including ADP-glucose pyrophosphorylase,starch synthase,starch branching enzyme and starch debranching enzyme,are widely accepted from an enormous amount of research aimed primarily at enzyme characterization.As many genes encoding the enzymes and their multiple isoforms in starch biosynthesis pathway have been isolated,genetic manipulation of the starch biosynthesis pathway shows to be a practical way by which starch quantity is increased and starch with novel properties can be created.     

Physicochemical and functional properties of starches from sorghum cultivated in the Sahara of Algeria

Pure starches were isolated from white and red sorghum cultivated in Tidikelt, a hyper arid region situated in south Algeria. Amylose content, X-ray pattern and rheological properties of starches were examined. The amylose content in white sorghum starch (27.1%) was slightly higher than that in red sorghum (24.8%). The swelling power and the solubility behavior of both starches were nearly similar below 65 °C. At higher temperatures, starch isolated from the white sorghum cultivar showed higher swelling power and lower solubility index than pigmented sorghum starch. The pasting properties of starches determined by RVA, Rapid Visco Analyser showed different viscosity peaks. Red sorghum starch had a higher value (4731 cP) than white sorghum starch (4093 cP). For both sorghum, X-ray diffractograms exhibit an A-type diffraction pattern, typical of cereal starches and the relative degrees of crystallinity were estimated at 22.72% and 28.91%, respectively, for local white and red sorghum starch. DSC analysis revealed that sorghum starches present higher temperatures at the peak (70.60 and 72.28 °C for white and red sorghum starches, respectively) and lower gelatinization enthalpies (9.087 and 8.270 J/g for white and red sorghum starches, respectively) than other cereal starches.The results showed that physicochemical and functional properties of sorghum cultivar starches were influenced by the genotype and the environment.     

Extraction of starches from tuber crops using ammonia

Ammonia solution (0·03 ) was used to extract starch from various tuber crops by the conventional settling method. It was found that there was noticeable improvement in the yield of starch from Colocasia (6–16%), while it fell for sweet potato starch and remained almost the same for the other starches. The various properties of starch, thus extracted, were compared with those for starch obtained by water extraction. It was found that total amylose of all starches were unaffected while the ‘soluble amylose’ was slightly suppressed for Colocasia starch extracted with ammonia solution. Peak viscosity was found to be increased to a large extent for Colocasia and Dioscorea esculenta starches by ammonia extraction, while it was lowered for sweet potato starch. The swelling volume of Colocasia starch extracted with ammonia was similarly enhanced by 25%, but the Dioscorea esculenta starch did not show such a tendency. Sweet Potato starch suffered a reduction in swelling volume. Phosphorus content was found to be independent of the extraction medium.     

Investigation of Structural Transformations During the Manufacturing of Expanded Snacks for Reformulation Purposes

In this paper, we investigate the functionality of potato-based ingredients present in indirectly expanded snacks via careful analysis of their transformation during processing. This research is driven by the desire of industry to develop similar snacks for upcoming markets, where the potato-based ingredients are replaced by other starch sources, which are locally available and at a lower cost. For a range of reformulated snacks, the transformations of starchy ingredients are analysed with a wide variety of experimental methods, like DSC, XRD, and XRT. Our analysis shows that ingredients undergo little transformations during extrusion, which is indeed intended to be mild. During frying native tuber starches (potato and tapioca starch) fully gelatinize, while cereal starches show little gelatinization and swelling. Despite the gelatinization of tuber starches, the particulate character of ingredients is retained. Replacement of pregelatinized potato starch with other starches shows little change in structure. The evolution of the structure of the reformulated snacks are analysed with the CDS formalism. We conclude that gel formers and hard fillers present in the analysed formulations had little functionality regarding texture or structure. For texture, it appears to be required that the matrix composes of a bicontinuous structure of soft fillers, namely gelatinized tuber starches and potato dehydrates. Both these ingredients can be replaced by other tuber-starch sources if the aggregation of the two soft fillers can be prevented. Commercial availability of tuber flours can still be an issue.

     

Fusion proteins comprising the catalytic domain of mutansucrase and a starch-binding domain can alter the morphology of amylose-free potato starch granules during biosynthesis

It has been shown previously that mutan can be co-synthesized with starch when a truncated mutansucrase (GtfICAT) is directed to potato tuber amyloplasts. The mutan seemed to adhere to the isolated starch granules, but it was not incorporated in the starch granules. In this study, GtfICAT was fused to the N- or C-terminus of a starch-binding domain (SBD). These constructs were introduced into two genetically different potato backgrounds (cv. Kardal and amf), in order to bring GtfICAT in more intimate contact with growing starch granules, and to facilitate the incorporation of mutan polymers in starch. Fusion proteins of the appropriate size were evidenced in starch granules, particularly in the amf background. The starches from the various GtfICAT/SBD transformants seemed to contain less mutan than those from transformants with GtfICAT alone, suggesting that the appended SBD might inhibit the activity of GtfICAT in the engineered fusion proteins. Scanning electron microscopy showed that expression of SBD-GtfICAT resulted in alterations of granule morphology in both genetic backgrounds. Surprisingly, the amf starches containing SBD-GtfICAT had a spongeous appearance, i.e., the granule surface contained many small holes and grooves, suggesting that this fusion protein can interfere with the lateral interactions of amylopectin sidechains. No differences in physico-chemical properties of the transgenic starches were observed. Our results show that expression of granule-bound and “soluble” GtfICAT can affect starch biosynthesis differently.     

Divergent evolutionary pattern of starch biosynthetic pathway genes in grasses and dicots

Starch is the most widespread and abundant storage carbohydrate in crops and its production is critical to both crop yield and quality. In regard to the starch content in the seeds of crop plants, there is a distinct difference between grasses (Poaceae) and dicots. However, few studies have described the evolutionary pattern of genes in the starch biosynthetic pathway in these two groups of plants. In this study, therefore, an attempt was made to compare evolutionary rate, gene duplication, and selective pattern of the key genes involved in this pathway between the two groups, using five grasses and five dicots as materials. The results showed 1) distinct differences in patterns of gene duplication and loss between grasses and dicots; duplication in grasses mainly occurred before the divergence of grasses, whereas duplication mostly occurred in individual species within the dicots; there is less gene loss in grasses than in dicots, 2) a considerably higher evolutionary rate in grasses than in dicots in most gene families analyzed, and 3) evidence of a different selective pattern between grasses and dicots; positive selection may have occurred asymmetrically in grasses in some gene families, for example, ADP-glucose pyrophosphorylase small subunit. Therefore, we deduced that gene duplication contributes to, and a higher evolutionary rate is associated with, the higher starch content in grasses. In addition, two novel aspects of the evolution of the starch biosynthetic pathway were observed.