Thermal and rheological properties of nixtamalized maize starch

The effect of nixtamalization process on thermal and rheological characteristics of corn starch was studied. Starch of raw sample had higher gelatinization temperature than its raw counterpart, because, the Ca(2+) ions stabilize starch structure of nixtamalized sample; however, the enthalpy values were not different in both samples. The temperature of the phase transition of the retrograded starches (raw and nixtamalized) were not different at the storage times assessed, but the enthalpy values of the above mentioned transition was different, indicating a lower reorganization of the starch structure in the nixtamalized sample. The viscoamylographic profile showed differences between both starches, since raw starch had higher peak viscosity than the nixtamalized sample due to partial gelatinization of some granules during this heat treatment. Rheological test showed that at low temperature (25 degrees C) the raw and nixtamalized starches presented different behaviour; however, the elastic characteristic was more important in the starch gel structure. The nixtamalization process produced changes in thermal and rheological characteristics becoming important in those products elaborated from nixtamalized maize.     

Effect of water-soluble and insoluble non-starch polysaccharides isolated from wheat flour on the rheological properties of wheat starch gel

Water-soluble (WSP) and insoluble non-starch polysaccharides (WIP) were isolated from wheat flour to evaluate the effects of WSP and WIP on starch gel properties. Isolated WSP and WIP were added to two types of isolated wheat starch with different amylose content at a concentration of 3% based on the dry weight of starch. 30% starch gels were prepared and stored at 5 °C for 1, 8, or 24 h. The dynamic viscoelasticity of 30% starch gels mixed with WSP and WIP was measured using parallel plate geometry, showing that WSP and WIP affected the elastic component of starch gels in opposite ways. Adding WIP increased the storage shear modulus (G′) of starch gels, while adding WSP decreased G′ and dramatically increased the loss tangent (tan δ=G″/G′).     

Physico-chemical and degradative properties of in-planta re-structured potato starch

Starch re-structured directly in potato tubers by antisense suppression of starch branching enzyme (SBE), granule bound starch synthase (GBSS) or glucan water dikinase (GWD) genes was studied with the aim at disclosing the effects on resulting physico-chemical and enzyme degradative properties. The starches were selected to provide a combined system with specific and extensive alterations in amylose and covalently esterified glucose-6-phosphate (G6P) contents. As an effect of the altered chemical composition of the starches their hydrothermal characteristics varied significantly. Despite of the extreme alterations in phosphate content, the amylose content had a major affect on swelling power, enthalpy for starch gelatinization and pasting parameters as assessed by Rapid Visco Analysis (RVA). However, a combined influence of the starch phosphate and long glucan chains as represented by high amylose or long amylopectin chain length was indicated by their positive correlation to the final viscosity and set back (RVA) demonstrating the formation of a highly hydrated and gel-forming system during re-structuring of the starch pastes. Clear inverse correlations between glucoamylase-catalyzed digestibility and amylopectin chain length and starch phosphate and lack of such correlation with amylose content indicates a combined structuring role of the phosphate groups and amylopectin chains on the starch glucan matrix.     

A rheological comparison between the effects of sodium caseinate on potato and maize starch

The differences in response of 1% potato and 4% maize starch pastes to sodium caseinate inclusion were investigated. Pasting of the starches was performed at 95 °C for l h in a range of concentrations of sodium caseinate. Caseinate levels as low as 0.01% dramatically reduced the swelling volume of potato starch and hence the viscosity of the system. Since sodium chloride addition shows similar effects, it appears that caseinate acts through a non-specific ionic strength effect. The influence of caseinate on maize starch was less clear since it depended on the solvent medium. In distilled, deionized water, there was an increase in viscosity with increasing caseinate concentration, which may simply be explained by a contribution of the caseinate to the viscosity of the continuous phase. However, in 0.1M, pH 7.0 buffer the results suggest that caseinate may inhibit retrogradation as the viscosity of the system after ageing is reduced by its inclusion. It is suggested that phase separation between starch and caseinate is encouraged at high salt concentrations. As a consequence, both starch granule swelling and subsequent retrogradation are discouraged by caseinate in the buffer system, but not when pasting is carried out in distilled, deionized water.     

An oligonucleotide array to detect genetically modified events in potato

For rapid and simultaneous detection of transgenic elements in genetically modified (GM) food crops, we explored DNA array technology. Forty-four oligonucleotide 23-to 31-mers were selected to use in an array on the basis of melting temperature and sequence specificity. Selected oligonucleotides consisted of DNA fragments corresponding to structural and regulatory elements and selectable markers used in developing transgenic crops, such as potato. Other oligonucleotides represented endogenous genes from potato to serve as positive controls and from heterologous crops, such as soybean and canola, to serve as negative controls. Amino-terminated oligonucleotides were hand-spotted on activated nylon membrane with a commercial spotting device. Target DNA was isolated from foliage of transgenic and nontransgenic crops, including potato, and labeled with digoxigenin-dUTP by random priming following restriction digestion to reduce DNA fragment size. Hybridization signals were visualized by an alkaline phosphatase anti-DIG-Fab conjugate and the chemiluminescent substrate, CDP-star. We detected the presence or absence of transgenic elements in transgenic and nontransgenic potato samples. Preliminary studies demonstrated that more specific and sensitive hybridization signals were generated from an oligonucleotide probe array than from a PCR product array. We anticipate that oligonucleotide probe arrays will be useful for regulatory monitoring of transgenic events.     

Influence of cross-linked potato starch treated with POCl3 on DSC, rheological properties and granule size

Differential scanning calorimetry (DSC), rheological measurements and granule size analyses were performed to characterize the influence of phosphorylation substitution levels on the properties of cross-linked potato starch. Phosphorus oxychloride (POCl₃) was used to produce the cross-linked potato starch. The levels of the reagent used for the reaction ranged between 40 and 5000 ppm (dwb). Storage (G′) and loss (G″) moduli were measured for a 5% (w/w) gelatinized starch dispersion stored at 20 °C for 24 h after heating at 85 °C for 30 min. The samples from 80 to 500 ppm were recognized as ‘strong gel'systems, whereas native potato starch showed ‘weak gel'behavior. Steady shear and dynamic viscoelastic properties of gelatinized starch dispersion were compared. Furthermore, granule mean diameter was measured by laser scattering for a 1% (w/w) dispersion heated at 85 °C for 30 min. The granules in the 100 ppm sample swelled to a maximum of about 2.6 times the native starch granule mean diameter.     

Effects of genetically modified starch metabolism in potato plants on photosynthate fluxes into the rhizosphere and on microbial degraders of root exudates

A high percentage of photosynthetically assimilated carbon is released into soil via root exudates, which are acknowledged as the most important factor for the development of microbial rhizosphere communities. As quality and quantity of root exudates are dependent on plant genotype, the genetic engineering of plants might also influence carbon partitioning within the plant and thus microbial rhizosphere community structure. In this study, the carbon allocation patterns within the plant-rhizosphere system of a genetically modified amylopectin-accumulating potato line (Solanum tuberosum L.) were linked to microbial degraders of root exudates under greenhouse conditions, using (13)C-CO(2) pulse-chase labelling in combination with phospholipid fatty acid (PLFA) analysis. In addition, GM plants were compared with the parental cultivar as well as a second potato cultivar obtained by classical breeding. Rhizosphere samples were obtained during young leaf developmental and flowering stages. (13)C allocation in aboveground plant biomass, water-extractable organic carbon, microbial biomass carbon and PLFA as well as the microbial community structure in the rhizosphere varied significantly between the natural potato cultivars. However, no differences between the GM line and its parental cultivar were observed. Besides the considerable impact of plant cultivar, the plant developmental stage affected carbon partitioning via the plant into the rhizosphere and, subsequently, microbial communities involved in the transformation of root exudates.     

Isolation of genetically modified potato plant containing the gene of defensive peptide from Amaranthus]

The plants of potato (Solanum tuberosum L., var. Desire) have been transformed with a pH22Kneo vector carrying the gene ac2, encoding the fungicidal peptide (defensin) from the seed of amaranth (Amaranthus caudatus L.). The transformation involved co-cultivation of potato stem explants (excised from aseptically grown plants) and Agrobacterium tumefaciens on solid MS medium. Factors affecting in vitro regeneration of the explants and the transformation efficiency were optimized. Regenerated potato plants harboring the amaranth defensin gene were selected by two traits, growth and ability to form roots on kanamycin-supplemented MS medium. The transgenic state was confirmed PCR analysis of ac2 in tissues of the kanamycin-resistant plants. The transgenic organisms thus obtained differed from the original ambiol-treated plants in growth patterns and proton translocation across the plasma membrane of the tuber cells.     

Argonic performance and field resistance of genetically modified,virus-resistant potato plants

Time consuming potato breeding programmes for virus resistances may be shortened by engineering virus resistance in existing cultivars or advanced breeding lines. Under field conditions genetically modified potato plants expressing viral coat protein genes of potato virus X, Y and potato leaf roll virus showed improved resistance up to near immunity. Despite the occurence of variation in the level of virus resistance and in phenotypic identity, in all cases true to type transgenic clones with improved virus resistance could be selected. These results indicate that improving potato cultivars or advanced breeding lines, by selectively adding new traits while preserving intrinsic properties, is commercially feasible.     

Compression molding and tensile properties of thermoplastic potato starch materials

The mechanical and melt flow properties of two thermoplastic potato starch materials with different amylose contents were evaluated. The materials were prepared by mixing starch, glycerol, and water, mainly in the weight proportions of 10:3:4.5. Compression molding was used to produce sheets/films with a thickness in the range of 0.3-1 mm. After conditioning at 53% relative humidity (RH) and 23 C, the glycerol-plasticized sheets with a higher amylose content (HAP) were stronger and stiffer than the normal thermoplastic starch (NPS) with an amylose content typical for common potato starch. The tensile modulus at 53% RH was about 160 MPa for the high-amylose material and about 120 MPa for the plasticized NPS. The strain at break was about 50% for both materials. The stress at break was substantially higher for the HAP materials than for the NPS materials, 9.8 and 4.7 MPa, respectively. Capillary viscometry at 140 C showed that the high-amylose material had a higher melt viscosity and was more shear-thinning than the NPS. Dynamic mechanical measurements indicated a broad transition temperature range for both types of starch material. The main transition peaks for glycerol-plasticized starch were located at about room temperature with the transition for the HAP material being at a somewhat higher temperature than that of the NPS material with a lower amylose content. It was also noted that the processing conditions used during the compression molding markedly affected the mechanical properties of the starch material.     

Transformation of Acinetobacter sp. BD413 with DNA from commercially available genetically modified potato and papaya

AIM: To estimate the likelihood of transfer of kanamycin-resistance gene (nptII) from commercially available genetically modified (GM) plants. METHODS AND RESULTS: Acinetobacter sp. BD413 carrying a plasmid containing an inactivated nptII gene was treated with DNA derived from GM potato and GM papaya. Kanamycin-resistant transformants were obtained at a frequency of 10-30 microg(-1) DNA. Calculation of the results suggested that 6-9 x 10(4) molecules of genomic DNA from GM plants were needed to obtain one transformant. However, such transformation events were not detectable in the absence of the plasmid in the host strain. CONCLUSIONS: Acinetobacter sp. BD413 was transformed with DNA derived from GM potato and GM papaya, in the presence of an inactivated nptII gene on a plasmid. However, the frequency of such events in the natural environment on wild-type strains, while evidently low, remains unknown. SIGNIFICANCE AND IMPACT OF THE STUDY: Our results may help to evaluate potential risks associated with the use of antibiotic-resistance determinants as genetic markers in GM plants. Complete risk assessment must consider factors other than transformation frequency alone, including the natural background of antibiotic resistance present in bacterial populations, and the spectrum and clinical use of the antimicrobial agents in question.     

Effect of sugars on the thermal and rheological properties of sago starch

Studies have been undertaken to investigate the effect of sugars on the thermal and rheological properties of sago starch. Sugars were found to increase the gelatinization temperature T_gel, and gelatinization enthalpy ΔH. T_gel and ΔH increased in the following order: control (water alone) < ribose < fructose < glucose < maltose < sucrose. The increase in ΔH was greater for 50% starch compared to 10% starch samples. The swelling factors in the presence of sugar were higher compared to the control for sugar concentrations below 25% but were lower at sugar concentration greater than 25%. These effects are discussed in terms of the antiplaticizing effect of the sugars compared to water, the influence of sugar–starch interactions and also the effect of the sugars on water structure. The storage modulus G′, the rate constant of gelation k, and the gel strength were significantly reduced in the presence of sugars. Generally G′ and k decreased in the following order: control (water alone) > hexose > disaccharide > pentoses. This has been attributed to the reduced proportion of amylose leached following gelatinizatison. In the presence of hexoses the freeze–thaw stability of starch gels decreased while in the presence of disaccharides and pentoses the freeze–thaw stability was slightly improved. © 1999 John Wiley & Sons, Inc. Biopoly 50: 401–412, 1999     

Gel formation in mixtures of high amylopectin potato starch and potato starch

The effects of starch granules on the rheological behaviour of gels of native potato and high amylopectin potato (HAPP) starches have been studied with small deformation oscillatory rheometry. The influence of granule remnants on the rheological properties of samples treated at 90 °C was evident when compared with samples treated at 140 °C, where no granule remnants were found. The presence of amylose in native potato starch gave to stronger network formation since potato starch gave higher moduli values than HAPP, after both 90 and 140 °C treatments. In addition, amylose may have strengthened the network of HAPP because higher moduli values were obtained when native potato starch was added to the system. The moduli values of the mixtures also increased with increasing polysaccharide concentration in the system, which is due to an increment in the polysaccharide chain contacts and entanglements. Finally, it was found that a mixture of commercial amylose from potato starch and HAPP resulted in lower values of G′ compared to native potato starch. This indicates that the source of amylose is important for the properties in a blend with native amylopectin.     

Comparison of tuber proteomes of potato varieties, landraces, and genetically modified lines

Crop improvement by genetic modification remains controversial, one of the major issues being the potential for unintended effects. Comparative safety assessment includes targeted analysis of key nutrients and antinutritional factors, but broader scale-profiling or "omics" methods could increase the chances of detecting unintended effects. Comparative assessment should consider the extent of natural variation and not simply compare genetically modified (GM) lines and parental controls. In this study, potato (Solanum tuberosum) proteome diversity has been assessed using a range of diverse non-GM germplasm. In addition, a selection of GM potato lines was compared to assess the potential for unintended differences in protein profiles. Clear qualitative and quantitative differences were found in the protein patterns of the varieties and landraces examined, with 1,077 of 1,111 protein spots analyzed showing statistically significant differences. The diploid species Solanum phureja could be clearly differentiated from tetraploid (Solanum tuberosum) genotypes. Many of the proteins apparently contributing to genotype differentiation are involved in disease and defense responses, the glycolytic pathway, and sugar metabolism or protein targeting/storage. Only nine proteins out of 730 showed significant differences between GM lines and their controls. There was much less variation between GM lines and their non-GM controls compared with that found between different varieties and landraces. A number of proteins were identified by mass spectrometry and added to a potato tuber two-dimensional protein map.     

Gene transfer from genetically modified food

The current debate about the safety of genetically modified food includes some important scientific issues where more scientific data would aid the robustness of safety evaluation. One example is the possibility of gene transfer, especially from genetically modified plant material.     

Specificity of starch synthase isoforms from potato.

In higher plants several isoforms of starch synthase contribute to the extension of glucan chains in the synthesis of starch. Different isoforms are responsible for the synthesis of essentially linear amylose chains and branched, amylopectin chains. The activity of granule-bound starch synthase I from potato has been compared with that of starch synthase II from potato following expression of both isoforms in Escherichia coli. Significant differences in their activities are apparent which may be important in determining their specificities in vivo. These differences include affinities for ADPglucose and glucan substrates, activation by amylopectin, response to citrate, thermosensitivity and the processivity of glucan chain extension. To define regions of the isoforms determining these characteristic traits, chimeric proteins have been produced by expression in E. coli. These experiments reveal that the C-terminal region of granule-bound starch synthase I confers most of the specific properties of this isoform, except its processive elongation of glucan chains. This region of granule-bound starch synthase I is distinct from the C-terminal region of other starch synthases. The specific properties it confers may be important in defining the specificity of granule-bound starch synthase I in producing amylose in vivo.