Chemical and Physical Characterisation of Grain Tef [Eragrostis tef (Zucc.) Trotter] Starch Granule Composition

Chemical and physical properties of starch granules isolated from five grain tef (Eragrostis tef) varieties were characterised and compared with those of maize starch. Endogenous starch lipids extracted with hot water‐saturated n‐butanol and total starch lipids extracted with n‐hexane after HCl hydrolysis were 7.8 mg/g (mean) and 8.9 mg/g (mean), respectively, slightly lower than in the maize starch granules. The starch phosphorus content (0.65 mg/g) was higher than that of maize starch but virtually the same as reported for rice starch. The starch granule‐swelling factor was lower than that of maize starch and extent of amylose leaching was higher. The starch X‐ray diffraction pattern was characteristic of A type starch with a mean crystallinity of 37%, apparently lower than the crystallinity of maize starch and more similar to that reported for rice and sorghum starches. The starch DSC gelatinisation temperature was high, like for other tropical cereals; T_o, T_p, T_c and ΔH were in the range 63.8—65.4, 70.2—71.3, 81.3—81.5 °C and 2.28—7.22 J/g, respectively. The lower swelling, apparently lower percentage crystallinity and lower DSC gelatinisation endotherms than maize starch suggest that the proportion of long amylopectin A chains in tef starch is smaller than in maize starch.     

Paste and Gel Properties and In Vitro Digestibility of Tef [Eragrostis tef (Zucc.) Trotter] Starch

Properties of tef starch from five varieties were compared with commercial maize starch. In most tef varieties the paste clarity (measured as % T) was similar to that of maize starch, but the paste was visually less white in colour. Tef starch gel texture was short and in most varieties was slightly firmer than that of maize starch. Tef starch adhesiveness was less than maize starch. Retrogradation extent of tef starch evaluated, as % gel syneresis under storage at 4 °C and ‐18 °C at 3, 7, 10 and 21 storage test days, was lower than that of maize starch. Storage with three freeze‐thaw cycles (‐18 °C 24 h; 23 °C 6 h) gave a similar trend. In tef starch initial digestion by α‐amylase and hydrolysis by mild HCl treatment was slightly higher than in maize starch, probably in part because of the smaller granule size and higher amorphous portion of tef starch. Alpha‐amylase degradation of tef starch granules was by surface erosion, probably due to the absence of surface pores in the granules.     

An SEC−MALLS Study of Molecular Features of Water‐soluble Amylopectin and Amylose of Tef [Eragrostis tef (Zucc.) Trotter] Starches

The molecular features of five tef starches along with those of commercial normal maize starch were investigated by size‐exclusion chromatography with multi‐angle laser light scattering‐differential refractive index detection (SEC/MALLS‐DRI) after solubilization in water by cooking in a household pressure cooker. The weight‐average molar mass ( ) and weight‐average root‐mean square radius of gyration (<R_g>_w) of the amylopectin (AP) of tef starches ranged from 10.1×10⁷ g/mol (156 nm) to 16.5×10⁷ g/mol (205 nm) with a mean of 13.9×10⁷ g/mol (186 nm). The AP of the tef starches was considerably smaller than that of maize starch ( = 19.6×10⁷ g/mol, <R_g>_w = 207 nm). These considerably smaller AP molecules in tef starches were most probably responsible for the low paste viscosity of tef starches as compared to maize starch. In most tef starches, the polydispersity index (PI) of the AP was broader than that of the AP of maize starch. The intermediate fraction (IN) 1.0−1.6, mean = 1.1) of most tef starches were similar to those of the IN of maize starch. The amylose (AM) (range 1.5×10⁶−3.0×10⁶ g/mol, mean = 2.2×10⁶ g/mol) and size (range 176−214 nm, mean = 191 nm) of most tef starches was also apparently similar to that of the maize starch ( = 2.3×10⁶ g/mol, <R_g>_w = 193 nm), but the polymer distribution was narrower. The AM−iodine complex of the tef starches had a λ_max range of 611−679 nm and the absorption shifted toward longer wavelengths by 8−14 nm as compared to the maize starch AM−iodine complex. The blue value (absorption at λ_max) for 1 mg/mL of tef AM had a range of 2.3−2.8 (mean = 2.5), whereas for the maize starch, the mean was 2.2. The branched nature of tef starches was also investigated by debranching with isoamylase and determination of chain lengths (DP_n) of the branches by size exclusion chromatography with refractive index detector (SEC‐RI). The AP in tef starches had a polymodal distribution with a periodicity similar to that of cereal starches. The branches had DP_n values of A = 11, B1 = 16, B2 = 46 (range 46−47), B3 = 70 (range 69−72) and B4 = 118 (range 113−123). The outer (A + B1) chains were shorter than those of maize starch AP with abundance (74%, w/w) only slightly less than that of the maize starch (75%, w/w). The slow rate of retrogradation, the slightly lower percent crystallinity, the lower gelatinization temperatures and the lower gelatinization enthalpy observed for tef starches (as compared to maize starch) are probably related to the shorter outer (A + B1) chain lengths of their amylopectin molecules, and may be the foundation of the comparably good keeping quality of tef injera, the main staple in the Ethiopian diet.     

Effect of grain tef [Eragrostis tef (Zucc.) Trotter] flour substitution with flaxseed on quality and functionality of injera

Injera from tef substituted with two flaxseed forms at 3%, 6% and 9% and control injera showed substitution had a significant effect on injera proximate, energy, titratable acidity (TA), total phenolics (TP) contents and sensory acceptability. Flaxseed forms had influence on moisture, fibre, total carbohydrate (TC) and TA. With 9% flour and whole flaxseed substitution, percentage energy, moisture, ash, crude protein, fibre and TA increase were 3.5, 27.3, 25.9, 20.4, 114.3 and 10.1, respectively. TC and pH were high for control. In all injera samples, condensed tannins and free fatty acid were insignificant. With an increase in the flaxseed substitution, most sensory acceptance increased, whereas injera eyes and colour decreased and appeared superior for control (100% tef injera). The 9% flaxseed‐substituted injera showed good proximate nutritional and energy contents of functional potential of high in dietary fibre, alpha linolenic acid, lignans, proteins and TP of anti‐oxidant nature.     

Physico‐chemical Characterization of Floridean Starch of Red Algae

The current work reports on isolation and physico‐chemical characterization of floridean starch from three species of agarophytic macro red algae. As determined by ¹H‐NMR spectroscopy, the average chain length and degree of branching frequency of this starch were 18 and 4.8, respectively. According to its amylopectin chain length distribution obtained by Dionex analysis, the crystalline polymorph of floridean starch from the red alga Gracilariopsis lemaneiformis was deduced to be C‐type and this was further supported from its X‐ray crystallographic pattern. Enzymatic analysis of its glucose 6‐phosphate content showed that floridean starch had a low level of covalently linked phosphate (1 nmol per milligram starch) and this was further confirmed by ³¹P‐NMR. The absorbance peak of floridean starch with iodine occurred at 527—530 nm and the blue value was low (0.1), indicating the absence of amylose, which was confirmed by differential scanning calorimetry (DSC). Floridean starch exhibited low gelatinization temperature, low viscosity, high clarity and little or no retrogradation upon repetitive freeze‐thaw cycles, as studied by DSC and rapid viscosity analysis (RVA). These results are discussed in light of the functional properties and the structure of floridean starch.     

Influence of Delayed Harvest Time on Physico‐chemical Properties of Sweetpotato Starch

Eight varieties of sweetpotato [Ipomoea batatas (L.) Lam] were transplanted in June, and harvested in October, November, December 1999 and January 2000. Starch content and starch properties of the tuberous roots were compared on delaying the harvest date. The shoot tops got blighted in early December and chilling injury rate of roots (average of eight varieties) increased up to 76.7% in January with decrease in temperature. Starch contents in October (24.0 g/100 g fresh weight, fw) and November (25.0 g/100 g fw) were almost the same, but the content decreased remarkably in December (21.2 g/100 g fw) and January (15.5 g/100 g fw). In December and January, the sucrose content of the roots had higher values. Hardness and leaked water percentage (LWP) of the starch gels remarkably increased from November to December (hardness: 76.4 to 112.3 g, LWP: 6.6 to 10.9%). On the contrary, the changes in amylose content and pasting properties of the starches were not consistent with decrease in temperature. This suggests that the effect of low temperature on these properties is insignificant after the growth period of sweetpotato. There were significant differences among the varieties in terms of starch retrogradation. The selection of varieties such as Kyushu 123 with the lowest percentage of retrogradation and Kyukei90142‐8 with the lowest chilling injury rate will help to lengthen the storage time in the field at least until December.     

Evaluation of Vitreous and Starchy Syrian Durum (Triticum Durum) Wheat Grains: The Effect of Amylose Content on Starch Characteristics and Flour Pasting Properties

The physiochemical composition of durum wheat cultivars was studied in order to investigate the influence of vitreousness on the chemical composition of starch and its thermal and pasting properties. Six durum wheat lines were chosen and grown in northern Syria. Grains of each cultivar were visually sorted according to the degree of vitreousness into fully vitreous and fully starchy fractions. Amylose/amylopectin ratio and total starch was determined using Megazyme methods, while thermal and pasting properties were determined using DSC and RVA. Starchy kernels were higher in total starch than vitreous kernels but showed a decreased amylose content. Negative linear relations were found between amylose content, and both peak viscosity and breakdown. Trends in variation of gelatinisation characteristics were observed between vitreous and starchy kernels from the same cultivar, with higher total enthalpy being associated with starchy grains compared with vitreous grains of the same line.     

Physicochemical Properties of Starch in Sago Palms (Metroxylon sagu) at Different Growth Stages

This study was aimed to examine the physicochemical properties of starch extracted from two different points (base and mid heights) of the sago palms trunks (Metroxylon sagu) of different physiological growth stages namely, ‘Plawei’, ‘Bubul’, ‘Angau Muda’, ‘Angau Tua’ and ‘Late Angau Tua’ stages. The physicochemical properties of sago starch studied were the morphology of starch, amylose content, particle size and distribution profile, pasting, thermal and retrogradation profiles. The results showed significant differences in the amylose and amylopectin content as well as in the granule sizes of starch from the different growth stages. Variation was observed in the proportions of granule sizes and pasting properties of starch from base and mid heights of the different growth stages while slight or insignificant differences was observed in the thermal properties of sago starch.     

Starch–fenugreek (Trigonella foenum-graecum L.) polysaccharide interactions in pure and soup systems

The effect of replacement of varying levels of a fenugreek polysaccharide (FP) product (0.1–0.9%) on 5% wt/wt corn starch cream soups and pure starch systems was investigated. Pasting, textural and viscoelastic characteristics along with granule size and sensory properties were determined. Significant changes were revealed with increasing FP replacement, with the effects being more pronounced on the soup formulations compared to the effects on pure starch/fenugreek systems.     

Comparison between ultra-homogenisation and ultrasound for extraction of phenolic compounds from teff (Eragrostis tef (Zucc.))

This study investigated the effect of the solvent composition on the extraction of phenolic compounds from teff grains and compared the efficiency between the techniques homogeniser-assisted extraction (HAE) and ultrasound-assisted extraction (UAE). The solvents used were water, ethanol and methanol, and the response analysed was the total phenolic content (TPC). The quantitative profile of polyphenols extracted was also determined by ultra-performance liquid chromatography–tandem mass spectrometry (UPLC-TQD). According to the optimisation, the maximum response was estimated at solvent ratios of 51:40:9 and 49:26:25 (water/ethanol/methanol, v/v/v) for HAE and UAE, respectively. Under optimal conditions, the extraction technique did not significantly influence the TPC extracted, but the TFC (total flavonoid content) and the antioxidant capacity were significantly higher when UAE was used. The phenolic acids p-coumaric and protocatechuic and the flavonoids quercetin, rutin and myricetin were the main polyphenols extracted. Both techniques studied were efficient in extracting polyphenols from whole teff grains.     

Physico‐chemical characterization of starches extracted from potatoes of the group Phureja

Starch was extracted from twenty‐four accessions of Group Phureja cultivated diploid potatoes, and from two commercial potato (Solanum tuberosum) varieties. Extracted starch samples were characterized and compared to industrial potato starch. Starch from Phureja generally exhibited smaller granule sizes and lower phosphorus content than starch from commercial potatoes. Amylose content and thermal properties (gelatinization temperature and enthalpy) were however in the same range for both groups. Starches from Phureja displayed very distinct pasting behavior from that of commercial potato. The former exhibited lower initial pasting viscosity but higher shear resistance. This may be related to lower starch granule size, causing lower swelling power and solubility. Iodine complexation results seem to indicate that phureja potatoes have higher proportion of amylopectin long chains. Phureja thus appears to be a promising new source of starch with specific physico‐chemical and functional properties intermediate between industrial potato and cereal starches.     

Physico‐chemical and functional properties of starch isolated from ginger spent

Studies were carried out on starch isolated from ginger spent, obtained after the extraction of oleoresin, to explore the possibility of its use as a food ingredient. AM content was found to be 25.5%. SEM showed the granules were disc‐shaped as well as ovoid with a smooth surface. The average granule size was 22.5 ± 3.5 µ in length and 16.9 ± 4.8 µ in width with thickness of ∼3 µ. Ginger spent starch exhibited a high gelatinization temperature (88°C), peak viscosity (678 Brabender units (BU)) and cold paste viscosity (777 BU). It also possessed low paste clarity and higher freeze–thaw stability. Dynamic rheological properties of ginger spent flour, measured using parallel plate geometry showed that the storage modulus (G′) increased and loss modulus (G″) decreased as a function of frequency. Starch from ginger spent flour with high gelatinization temperature and low in vitro starch digestibility (45%) is suitable to use for development of speciality food formulations.     

Granule Integrity and Starch Solubility During Slow,Extended Pasting of Maize Starch — the Second Viscosity Peak

Maize starch granule integrity and starch solubilisation at specific intervals during a relatively long pasting profile—which is known to exhibit biphasic peak viscosity character—was studied by microscopy and high‐performance size‐exclusion chromatography, respectively. Maize starch granules, although swelling and leaching components, remained mainly intact until the second viscosity peak when they lost integrity and formed a relatively homogenous paste. The second viscosity peak coincided with a decrease in starch content in solution and amylose going out of solution was mainly responsible for this decrease. It is suggested that the loss of granule integrity during the second viscosity peak increases the potential for amylose to form complexes with lipids at this stage. It is further suggested that the second viscosity peak is due to the formation and breakdown of superstructures of amylose‐lipid complexes.     

The Effects of Environmental Conditions on the Structural Features and Physico‐chemical Properties of Starches

The effects of environmental factors on the structural features and physico‐chemical properties of starch (from various botanical sources) have been investigated over many decades. A close study of published data on the effects of environmental factors, especially growth temperature, reveals discrepancies with regard to its effects on the composition and properties of the major components of starch, namely amylose and amylopectin. These discrepancies can in part be explained on the basis of the different experimental protocols used by the various investigators to provide environmental variation although it is clear that environmental factors do influence the deposition and composition of starch granules. However, the effects of environmental conditions on the physical properties of starches are more easily reproduced and are consequently better understood. This review is an up to date survey of current knowledge in this area and draws extensively on the authors' own research.