The influence of temperature extremes on some quality and starch characteristics in bread, biscuit and durum wheat.
Labuschagne, M. T., Elago, O. & Koen, E. (2009). Journal of Cereal Science, 49(2), 184-189.
Environmental conditions during grain-fill can affect the duration of protein accumulation and starch deposition, and thus play an important role in grain yield and flour quality of wheat. Two bread-, one durum- and one biscuit wheat were exposed to extreme low (−5.5°C for 3 h) and high (32°C/15°C day/night for three days) temperatures during grain filling under controlled conditions for two consecutive seasons. Flour protein content was increased significantly in one bread wheat, Kariega, under heat stress. Cold stress significantly reduced SDS sedimentation in both bread wheats. Kernel weight and diameter were significantly decreased at both stress treatments for the two bread wheats. Kernel characteristics of the biscuit wheat were thermo stable. Kernel hardness was reduced in the durum wheat for the heat treatment. Durum wheat had consistently low SDS sedimentation values and the bread wheat high values. Across the two seasons, the starch content in one bread wheat was significantly reduced by both high and low temperatures, as is reflected in the reduction of weight and diameter of these kernels. In the durum wheat, only heat caused a significant reduction in starch content, which is again reflected in the reduction of kernel weight and diameter.
Biochemical Characterization of the Wheat Waxy A Protein and Its Effect on Starch Properties 1.
Demeke, T., Hucl, P., Abdel-Aal, E. S. M., Båga, M. & Chibbar, R. N. (1999). Cereal Chemistry, 76(5), 694-698.
Granule bound starch synthase1 (GBSS1) is a key enzyme in amylose biosynthesis and is encoded by the A, B and D GBSS1 wx loci in wheat. Wheat lines with mutations at the three GBSS1 loci have been identified. We have characterized and compared the grain starch of CDCW6 wheat line (null B and D for GBSS1) with PI235238 (null A and B for GBSS1), waxy (null A, B and D for GBSS1), and AC Reed (wild type wheat) grain starches. The grain starch of waxy, CDCW6, PI235238, and AC Reed lines contained ≈0, 12, 23, and 25% amylose (w/w), respectively. Waxy, partially waxy, and wild wheat grain starches showed significant differences in onset and peak transition temperatures as determined by differential scanning calorimetric analysis. Grain starches extracted from waxy, CDCW6, and PI235238 also had higher enthalpy of gelatinization values than did wild wheat starch. X-ray diffraction analysis revealed the highest crystallinity for starch extracted from waxy wheat, followed by CDCW6. The starch produced from the CDCW6 line may find special food and industrial applications because of its relatively low amylose concentration.
Amylose determination in genetically modified starches.
Gérard, C., Barron, C., Colonna, P. & Planchot, V. (2001). Carbohydrate Polymers, 44(1), 19-27.
The amylose contents of starches from various botanical origins (potato, smooth pea, wrinkled pea, wheat, maize) and from maize mutants [waxy (wx) , amylose extender (ae), dull (du), sugary-2 (su2), aewx, aedu, dusu2 and wxdu] were determined by size exclusion chromatography (SEC), iodine-binding capacity (IBC) measurements, differential scanning calorimetry (DSC) and complexation with concanavalin A. SEC (with a 2.6 x 200 cm column) on HW75 S gel was used as the reference method for analyzing the macromolecular composition of starches. Variations in the fine structure of amylopectin affected its reactivity in classical methods such as IBC and were probably responsible for erroneous values in determinations when this polymer was the only starch component studied. When starches were composed of two macromolecules, all methods gave similar results, but with some discrepancies in DSC. The elution volume for a third class of α-glucans detected in some maize mutant starches was between that of amylopectin and amylose. Only SEC gave accurate results in this case since all other tested methods showed higher apparent amylose contents.
Genetic elimination of a starch granule protein, SGP-1, of wheat generates an altered starch with apparent high amylose.
Yamamori, M., Fujita, S., Hayakawa, K., Matsuki, J. & Yasui, T. (2000). Theoretical and Applied Genetics, 101(1), 21-29.
A starch granule protein, SGP-1, is a starch synthase bound to starch granules in wheat endosperm. A wheat lacking SGP-1 was produced by crossing three variants each deficient in one of three SGP-1 classes, namely SGP-A1, -B1 or -D1. This deficient wheat (SGP–1 null wheat) showed some alterations in endosperm starch, meaning that SGP-1 is involved in starch synthesis. Electrophoretic experiments revealed that the levels of two starch granule proteins, SGP-2 and -3, decreased considerably in the SGP-1 null wheat though that of the waxy protein (granule-bound starch syn- thase I) did not. The A-type starch granules were deformed. Apparent high amylose level (30.8–37.4%) was indicated by colorimetric measurement, amperometric titration, and the concanavalin A method. The altered structure of amylopectin was detected by both high- performance size-exclusion chromatography and high-performance anion exchange chromatography. Levels of amylopectin chains with degrees of polymerization (DP) 6–10 increased, while DP 11–25 chains decreased. A low starch crystallinity was shown by both X-ray diffraction and differential scanning calorimetry (DSC) analyses because major peaks were absent. Abnormal crystallinity was also suggested by the lack of a polarized cross in SGP-1 null starch. The above results suggest that SGP-1 is responsible for amylopectin synthesis. Since the SGP-1 null wheat produced novel starch which has not been described before, it can be used to expand variation in wheat starch.
Chain‐length Distribution Profiles of Amylopectin Isolated from Endosperm Starch of Waxy and Low‐amylose Bread Wheat (Triticum aestivum L.) Lines with Common Genetic Background.
Yasui, T., Ashida, K. & Sasaki, T. (2009). Starch‐Stärke, 61(12), 677-686.
Large A-type endosperm starch granules were isolated from near-isogenic waxy and non-waxy lines and low-amylose mutant lines of bread wheat with a common genetic background. The amylose contents of A-type starch ranged from 2.6% to 23.6%. Amylopectin was isolated by concanavalin A (Con A) precipitation from the isolated starch. The λmax (range: 532-538 nm) and blue values at 680 nm (range: 0.026-0.037) of the iodine-amylopectin complex were not significantly different among the isolated amylopectins, indicating that amylopectins from non-waxy and low-amylose lines did not contain such long chains as amylose or extra-long chains of amylopectin affecting iodine complex properties. Chain-length distribution profiles measured by both high-performance size-exclusion chromatography (HPSEC) and high-performance anion-exchange chromatography (HPAEC) showed that the amylopectin structures of these lines were indistinguishable from each other. Extra-long chains were not detected in the amylopectins by HPSEC measurement. The side-chains measured by HPAEC were classified into four groups according to their degree of polymerization (DP), and the proportion of each group were in the following ranges: DP 6-12, 26.5-27.5%; DP 13-24, 43.6-44.1%; DP 25-36, 13.6-14.2%, and DP 37-60, 11.0-11.7%. The alleles on the Wx-D1 locus, i.e., Wx-D1a, Wx-D1d, Wx-D1f, and Wx-D1g, responsible for granule-bound starch synthase (GBSS I) biosynthesis had no influence on the properties of iodine-amylopectin complex and the chain-length distribution profiles of amylopectin.
Effect of gamma irradiation on the thermal and rheological properties of grain amaranth starch.
Kong, X., Kasapis, S., Bao, J. & Corke, H. (2009). Radiation Physics and Chemistry, 78(11), 954-960.
Physical properties of starch from two cultivars of gamma-irradiated grain amaranth with different amylose content were investigated. Pasting viscosities decreased continuously with the increase in dosages of irradiation. Furthermore, different irradiation dosages resulted in modification of the thermal properties and crystallinity of starch. Dynamic oscillation on shear was also employed, temperature and frequency sweeps showed that changes in storage modulus and loss modulus were significant, with Tibet Yellow producing more elastic gels as compared to Hy030 at different irradiation dosages.
Functional properties of hydroxypropylated, cross-linked, and hydroxypropylated cross-linked tuber and root starches.
Gunaratne, A. & Corke, H. (2007). Cereal Chemistry, 84(1), 30-37.
Functional properties of some underexploited tuber and root starches (true yam, gourd yam, taro, lotus, and sweet potato) were investigated before and after hydroxypropylation, cross-linking, and hydroxypropylation and cross-linking using potato starch as the reference. Low swelling ability, poor viscosity development but high shear stability, gel hardness, and resistance to enzyme hydrolysis was observed in starches from true yam and gourd yam. The extent of retrogradation was also highest in these two starches. Most of the functional properties of lotus starch were similar to those of potato starch. Hydroxypropylation to a molar substitution level of ≈0.1 increased the swelling factor and susceptibility to α-amylase hydrolysis but decreased acid tolerance of paste viscosity, retrogradation, gelatinization parameters, gel hardness, and shear stability. Cross-linking decreased the swelling factor and amylose leaching, and increased shear stability and resistance to enzyme and acid tolerance. Cross-linking had very little influence on gelatinization and retrogradation properties but a larger effect on pasting properties. Increased or decreased peak viscosities and gel hardness values were noted for different cross-linked starches. Cross-linking of hydroxypropylated starches increased commonly desirable functional properties providing a wider range of potential applications.
Distribution of methyl substituents in amylose and amylopectin from methylated potato starches.
van der Burgt, Y. E. M., Bergsma, J., Bleeker, I. P., Mijland, P. J. H. C., van der Kerk-van Hoof, A., Kamerling, J. P. & Vliegenthart, J. F. G. (2000). Carbohydrate Research, 325(3), 183-191.
Granular potato starches were methylated in aqueous suspension with dimethyl sulfate to molar substitution (MS) values up to 0.29. Fractions containing mainly amylose or amylopectin were obtained after aqueous leaching of the derivatised starch granules. Amylopectin in these fractions was precipitated with Concanavalin A to separate it from amylose. Amylose remained in solution and was enzymatically converted into D-glucose for quantification, thereby taking into account the decreased digestibility due to the presence of methyl substituents. It was found that the MS of amylose was 1.6–1.9 times higher than that of amylopectin in methylated starch granules. The distributions of methyl substituents in trimers and tetramers, prepared from amylose- or amylopectin-enriched fractions, were determined by FAB mass spectrometry and compared with the outcome of a statistically random distribution. It turned out that substituents in amylopectin were distributed heterogeneously, whereas substitution of amylose was almost random. The results are rationalised on the basis of an organised framework that is built up from amylopectin side chains. The crystalline lamellae are less accessible for substitution than amorphous branching points and amylose.
New insights on the mechanism of acid degradation of pea starch.
Wang, S., Blazek, J., Gilbert, E. & Copeland, L. (2012). Carbohydrate Polymers, 87(3), 1941-1949.
The degradation of pea starch granules by acid hydrolysis has been investigated using a range of chemical and structural methods, namely through measuring changes in amylose content by both the iodine binding and concanavalin A precipitation methods, along with small angle X-ray scattering (SAXS), wide angle X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The relative crystallinity, intensity of the lamellar peak and the low-q scattering increased during the initial stages of acid hydrolysis, indicating early degradation of the amorphous regions (growth rings and lamellae). In the first 2 days of hydrolysis, there was a rapid decline in amylose content, a concomitant loss of precipitability of amylopectin by concanavalin A, and damage to the surface and internal granular structures was evident. These observations are consistent with both amylose and amylopectin being located on the surface of the granules and attacked simultaneously in the early stages of acid hydrolysis. The results are also consistent with amylose being more concentrated at the core of the granules. More extensive hydrolysis resulted in the simultaneous disruption of amorphous and crystalline regions, which was indicated by a decrease in lamellar peak intensity, decrease in interhelix peak intensity and no further increase in crystallinity. These results provide new insights into the organization of starch granules.
Physical properties of Amaranthus starch.
Kong, X., Bao, J. & Corke, H. (2009). Food Chemistry, 113(2), 371-376.
Physicochemical and functional properties of starches isolated from fifteen grain amaranth cultivars (Amaranthus spp.) produced in China were analysed in this study. Amaranth starches had low but diverse amylose contents, ranging from 4.7% to 12.5%. Wide variation was also found in physicochemical properties, such as swelling power, water solubility index, pasting, thermal and textural properties. Amylose content was significantly correlated with functional properties, including pasting, thermal and textural properties and appeared to be the important determinant for these properties. Correlations among pasting, thermal and textural parameters were also significant. Principal component analysis using 17 variables extracted four principal components that explained 88% of the total variance. The first component represented amylose content, pasting and gel textural properties and explained 59% of the total variance, while the second component represented the thermal properties and accounted for an additional 14.5% of the total variance.