Physicochemical Properties and Starch Digestibility of Autoclaved-Cooled Water Yam (Dioscorea alata L.) Flour

Water yam (Dioscorea alata L.) is suitable for resistant starch high flour because of its high amylose content. The purple, yellow, and white water yams were treated by autoclaving and cooling with one, two, and three cycles to obtain resistant starch. Water yam tubers were cooked in an autoclave for 15 min, and then cooled prior to drying. Autoclaving–cooling of water yams decreased protein, fat, dietary fiber, water soluble polysaccharide, dioscorin, and diosgenin but increased amylose and sugar. The treatments significantly raised resistant starch and reduced in vitro starch digestibility that depended on water yam types, and affected starch granule morphology.     

Starch properties of various potato (Solanum tuberosum L) Cultivars susceptible and resistant to low-temperature sweetening

Properties of starch granules isolated from different varieties and selections of potato (which vary in their degree of chill sweetening) were examined. Differential scanning calorimetry (DSC) showed an increase in resistance to gelatinisation of isolated starch granules which correlated (r = 0.911) with higher chip scores following storage at 4°C and 12°C. Varying water level content during DSC studies resulted in significantly lower water content required to produce two endotherms for starch isolated from varieties resistant to chill sweetening. These data strongly suggest that starch granule composition might be a factor differentiating the low temperature sweetening sensitive from resistant cultivars, and may provide a screening method for predicting chip colour of potatoes out of storage.     

Variability in starch physicochemical and functional properties of yam (Dioscorea sp) cultivated in Ivory Coast

An Erratum has been published for this article in Journal Of the Science of Food and Agriculture 85(5), 889 (2005). Native starches were extracted from 21 cultivars of four yam species representative of the yam population of Ivory Coast. They were first characterized for their proximate composition, starch physico‐chemical properties (amylose content, particle size distribution, crystallinity, thermal properties and intrinsic viscosity). Some functional properties (swelling, solubility and pasting behaviour and paste clarity) were then determined. Analysis of variance and principal component analysis showed that three homogenous groups could be distinguished, mainly based on starch physico‐chemical properties. The first group contained all yam starches of the D alata and the D cayenensis‐rotundata complex species. It was characterized by a large diameter grain (approximately 25 µm), a high amylose content (around 25% db), a high intrinsic viscosity (mean of 190 cm³ g^?1), and a high apparent viscosity and clarity of the paste. The second group contained the D esculenta varieties, characterized by a small granule size (diameter 6 µm), a low intrinsic viscosity (121 cm³ g^?1), a high gelatinization enthalpy change (19 J g^?1) and a low paste viscosity. The D dumetorum sample differed from the D esculenta group by having a pure A‐type crystalline form and an opaque paste. A multiple regression showed that the volume fraction of the dispersed phase and native granule size (or amylose content) could account for close to 80% of the variability of paste apparent viscosity. Gel clarity appeared mainly linked to granule size, small granules from D dumetorum and D esculenta giving the most opaque gels. Copyright © 2004 Society of Chemical Industry     

MICROSTRUCTURE OF BOILED YAM (DIOSCOREA SPP.) AND ITS IMPLICATION FOR ASSESSMENT OF TEXTURAL QUALITY

The effects of boiling on the microstructure of yams and their association with the textural quality of “boiled yam,” arguably the most common food product from yams, were studied using six varieties with variable cooking qualities from each of the two species, Dioscorea alata L. and D. rotundata Poir. Histological studies on raw yams showed parenchyma cells of both species to be three‐dimensional and polyhedral in shape, with starch granules loosely arranged in D. rotundata but densely packed in D. alata. Generally, there was cell separation and rounding off of cells in cooked yams of D. rotundata varieties, whereas cell separation was only partial with no rounding off in D. alata. Mealy boiled yams showed complete cell separation and the “rounding off” phenomenon, whereas the waxy ones showed partial retention of textural cell integrity. These relative changes in microstructure of yam when boiled could serve as indicators of textural quality in boiled yam.     

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.     

Properties of starches of some West African yams

The tuber starches of several species and varieties of yam (Dioscorea) grown as food crops in West Africa were examined. The granule sizes were investigated, and the forms of the starch granules are illustrated in photographs. Amylose contents were also measured, together with ‘pasting temperatures’, viscous properties and gel strength. The granules of D. rotundata and D. alata were large (10–70 μ) while those of D. esculenta and D. dumetorum were much smaller (1–5 μ). The starch of D. rotundata gave the most viscous solutions, but that of D. alata gave the strongest gel. Pasting temperatures ranged between 76° and 85°.     

Comparative analysis of starch properties of different root and tuber crops of Sri Lanka

The physicochemical properties of starches of six different root and tuber crop species grown mainly in Sri Lanka showed significant differences among the tested crop species and varieties. The median granule size of starch of tested root and tuber crop species varied from 33.5 to 10.2 μm. The largest granule size and the highest blue value were given by the canna, Buthsarana, and yam species, in that order. The amylose content of cassava was higher than those of sweet potato and many yams. High peak viscosities, high breakdown, and high final viscosities were observed in yams, and, generally, such starch showed a high swelling power. According to the correlation analysis, these pasting properties would mainly be due to their larger starch granule size. Based on the thermal properties, cassava starch showed less energy requirement for gelatinization and thus gelatinized at lower temperatures. Furthermore, a higher susceptibility of raw cassava starch toward fungal glucoamylase was observed. The low enzyme digestibility of raw yam starch would be due to its large granules. Correlation analysis showed that the blue value and starch granule size were important in determining the pasting, thermal, and other properties of starch.     

Changes in flour gelatinisation of trifoliate yam (Dioscorea dumetorum) tubers after harvest

BACKGROUND: Changes in the properties of starch during postharvest hardening of trifoliate yam (Dioscorea dumetorum) tubers need to be investigated. In this work the starch gelatinisation kinetics of D. dumetorum cv. Yellow stored under prevailing tropical ambient conditions (0.98–2.32 kg vapour per 100 m³ airflow) for 0, 2, 7, 14, 21 and 28 days was studied using a 3 × 5 factorial experiment with three cooking temperature (75, 85 and 95 °C) and five cooking times (0, 5, 10, 20 and 40 min). Samples were also evaluated for starch properties and gelatinisation temperature. RESULTS: Storage of D. dumetorum tubers caused starch damage. However, the starch gelatinisation temperature was between 70 and 75 °C irrespective of the tuber storage duration. The starch gelatinisation reaction followed first‐order kinetics defined by the relationship ln(1 ? α) = ? k_Gt. The gelatinisation rate was significantly influenced (P≤0.05) by cooking temperature and increased with tuber storage duration. The activation energy also increased with tuber storage duration. CONCLUSION: Although the gelatinisation temperature of D. dumetorum starch was not influenced by tuber storage, the starch gelatinisation process was affected by tuber storage duration, since tuber storage involved a greater need of energy for starch gelatinisation, which may be an effect of the postharvest hardening phenomenon. Copyright © 2008 Society of Chemical Industry     

Morphological,thermal, rheological and retrogradation properties of potato starch fractions varying in granule size

The physicochemical properties of small, medium and large starch granules separated from four potato cultivars were investigated to reveal whether functional properties differed among the various size classes of the starches. Large‐size fractions showed higher amylose content and light transmittance and lower swelling power than small‐size fractions. The granules from the three fractions had diameters of 5–20, 25–40 and 40–85 µm respectively. The large and medium granules were ellipsoidal to irregular or cuboidal while the small granules were spherical or ellipsoidal in shape. The transition temperatures and gelatinisation temperature range of the fractionated starches increased while the enthalpy of gelatinisation decreased with decreasing granule size. Rheological parameters such as peak storage (G′) and loss (G″) moduli increased in the order small‐, medium‐ and large‐granule starches when subjected to temperature sweep testing. The breakdown in peak G′ during the heating cycle and retrogradation during storage were found to be highest for large‐ and lowest for small‐size fractions. The differences in functional properties among the different size fractions suggested that the granule size distribution is an important parameter that can influence the behaviour of potato starch during processing. Copyright © 2004 Society of Chemical Industry     

Characterization of Cassava Starch Attributes of Different Genotypes

The genetic variation of starch of Indonesian cassava genotypes with various morphological characteristics of roots and eco‐geographical origin was characterized and compared. The morphological characteristics of the roots of 71 collected cassava genotypes were classified into yellow and white for flesh colors, purple, pink, light brown, yellow, cream and white for cortex colors, dark brown and light brown for external colors, as well as conical and cylindrical for root shapes. Starch samples extracted from 17 genotypes showed that the amylose content varied from 17.1 to 21.3%. The mean particle size was around 7.3 to 9.7 µm, and the gelatinization onset temperature was in the range of 63.5‐66.1°C. Seven genotypes were analyzed in more detail for their physicochemical properties. The granule size distribution was in the range of 3.2 µm to 17.6 µm for d10 and d90 (i.e. 90% of the granules were bigger than 3.2 μm and 90% were smaller than 17.6 μm), respectively, and the median granule size was around 7.7‐10.8 µm. The gelatinization temperatures of the different cassava starches were in the range of 63.5‐66.1°C. The phosphate content varied from 23.5‐25.3 nmol/mg starch. Particle size distribution and gelatinization temperature as well as the phosphate content of the starch of the selected seven genotypes also showed minor differences among the genotypes. The swelling power of all starches showed some differences between genotypes, but the profiles were similar. The opacity of starch of all the tested genotypes increased twofold within six days, but no large differences among the different genotypes could be detected except for the genotype Ketan. Strength of the gels, which are indicated with force, adhesiveness, cohesiveness, and elasticity, also did not show large differences.     

In vitro Digestibility of Raw Starches Extracted from five Yam (Dioscorea spp.) Species Grown in Jamaica

Starch granules from Round leaf yellow yam, Negro yam, Sweet yam, Bitter yam and Chinese yam grown in Jamaica were isolated and characterized. The amylose content, granular size, crystallinity, and digestibility by α‐amylase were determined. The granules obtained were of three crystalline types. Round leaf yellow yam, Negro yam and Sweet yam were found to be type‐B, while Chinese yam and Bitter yam were type‐C and type‐A, respectively. Round leaf yellow yam had the highest amylose content (26.5%) while Chinese yam had the lowest (11.1%). The granule size varied between 1–3 μm for Chinese yam and 16–42 μm for Round leaf yellow yam. Significant variations in digestibility of the granules were observed. Raw starches from Chinese yam and Bitter yam were the most susceptible to α‐amylase digestion (porcine pancreatic α‐amylase, pH 5.5, 0.02% CaCl₂, 40°C, 24 h) with 21.27 ± 0.01% and 18.11 ± 0.02% degradation, respectively, while Round leaf yellow yam, Negro yam and Sweet yam starches were the least susceptible, with 13.74 ± 0.03%, 14.98 ± 0.08%, and 15.32 ± 0.04% enzymatic degradation, respectively.     

Fundamental and Derived Properties of Yam (Dioscorea Spp.) Starch Powders and Implications in Tablet and Capsule Formulation

A comparative investigation of the fundamental and derived properties of starches from some species of yam (Dioscorea spp.) was conducted with a view to establishing their suitability as excipients in tablet and capsule formulations. Variations were observed in the mean granular diameter of the starches obtained from the different Dioscorea species. Granular diameter ranged from 5.4 µm (Chinese yam) to 34.5 µm (Round leaf yellow yam). Chinese yam and Bitter yam had the highest specific surface area (625.91 m²/kg and 258.76 m²/kg, respectively) while Round leaf yellow yam and Negro yam had the lowest (117.4 m²/kg and 154.34 m²/kg, respectively). Chinese yam had the lowest granular volume (6.00 µm³), surface area (5.67 µm²) and granule surface‐mean diameter (6.74 µm), while Round leaf yellow yam had the largest mean granular diameter, highest granular volume (35.2 µm³), surface area (34.8 µm²) and granule surface mean diameter (35.88 µm). Particle size distribution plots of Chinese yam, Round leaf yellow yam and Negro yam displayed a Gaussian size distribution pattern while Bitter yam displayed a negatively skewed distribution. The variations observed in the granular size and shape may influence the observed derived properties of the starches.     

Effects of time/temperature treatments on potato (Solanum tuberosum) starch: a comparison of isolated starch and starch in situ

Previously, time/temperature treatments of starch have been performed mainly on starch/water systems. In this study the same time/temperature treatments were applied to starch/water systems and to potato starch in situ. Two potato varieties (Solanum tuberosum cultivars Asterix and Bintje) were used. The effect of time/temperature treatments on gelatinisation behaviour was evaluated using differential scanning calorimetry (DSC). A blanching process was simulated by heating samples to 74 °C and then cooling them to 6 °C. A DSC scan showed that starch was completely gelatinised after this treatment. Retrogradation of amylopectin increased during storage at 6 °C from 0 to 24 h after blanching. Annealing of starch, with the aim of altering cooking properties, was performed by heating samples to temperatures below the gelatinisation onset temperature. Treating samples at 50 °C for 24 h caused a shift in gelatinisation onset temperature of 11–12 °C for isolated starch and 7–11 °C for in situ samples. The extent of the annealing effect depended on the difference between onset and annealing temperatures, and prolonged treatment time increased the effect. Starch/water systems and tissue samples behaved similarly when exposed to time/temperature treatments. The most apparent difference was the shift of gelatinisation to higher temperatures in tissue samples. Copyright © 2003 Society of Chemical Industry     

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.     

Gelatinisation properties of native and annealed potato starches

The relationship between the gelatinisation parameters of native and annealed starches extracted from ten different potato varieties grown at the same site at the same time was studied. The objective was to identify how native gelatinisation temperatures and enthalpies impacted on annealed starch gelatinisation parameters. Prior to ANN, the initial onset (T_o), peak (T_p) and conclusion (T_c) gelatinisation temperatures ranged from 58.71 to 62.45, 62.52 to 66.05 and 68.67 to 72.27°C, respectively, which increased to 66.15 to 69.12, 70.22 to 72.30 and 76.21 to 77.44°C, respectively, post ANN. Overall, the greater the initial gelatinisation temperatures the smaller the increment (ΔGT) post ANN. Comparable enthalpy values pre‐ and post‐ANN were 15.13 to 18.37 and 15.76 to 18.37 J/g, respectively. These data indicate that the more ‘perfect’ the crystallites were before ANN the less they could be enhanced by the ANN process and that against a constant background of α‐glucan structure, the pattern (rate) of starch deposition might be the primary differentiator of starch architecture across the varieties.     

The physicochemical and binder properties of starch from Persea americana Miller (Lauraceae)

Avocado starch was extracted from the kernels of the fruit Persea americana Miller (Fam. Lauraceae) and evaluated for its potential as an alternative to maize starch as a pharmaceutical excipient. Its physicochemical and thermal properties were evaluated and compared with those of maize starch. Granules prepared with avocado and maize starch pastes as binder were evaluated for their flow, friability and compaction characteristics. The average yield of starch extracted from the fresh kernels of P. americana was 20.5 ± 0.55% w/w. The scanning electron micrograph (SEM) showed that avocado starch has two characteristic granule shapes; triangular and circular both having an approximate equal distribution. The triangular shaped granules are larger (28 to 32 µm) than the circular (6 to 9 µm). The foaming capacity of avocado starch was 19.05 ± 0.6%, its swelling, moisture uptake and paste clarity were generally lower than that of the maize starch. Avocado starch gel exhibited an extent of syneresis after freeze–thaw that increased cumulatively with increase in number of freeze–thaw cycles. The glass transition (T_g) and gelatinisation temperatures for avocado starch were higher than that of maize starch. The melting temperatures (T_m), ash value, as well as the various densities of avocado starch showed similarities with those of maize starch. The granules prepared with avocado starch pastes as binder showed superior compactibility and mechanical strength to those of maize starch but with similar flow characteristics. Avocado starch generally showed distinct physicochemical and binder properties with some similarities to the standard maize starch.     

Thermal properties of new varieties of yam starches

Starches isolated from yam varieties of Dioscorea alata and Dioscorea cayenensis‐rotundata species were prepared at different time–temperature conditions and characterised by DSC, amperometric iodine titration, light microscopy and rheology and compared to native and chemical modified tapioca starches. The observation by light microscopy showed different morphologies of the granules when heated above 100°C and the tendency for disintegration decreased in the order native tapioca starch > yam starch > modified tapioca starch. Differences between yam and tapioca starches were also revealed by DSC. Yam starch enthalpy is higher than tapioca starch, but the peak temperature is low. However, the significant differences between yam and the other tested starches were found in terms of their rheological behaviour. The viscosity of yam starch was very stable at high temperatures on the viscograph. With this property, yam starch can be used as thickening and gelling agent in food.     

Effect of temperature on the synthesis,composition and physical properties of potato microtuber starch

Potato microtubers (cv Maris Piper) were grown at 10, 16 and 24°C in total darkness for 28 days. Soluble and insoluble starch synthase, ADPglucose pyrophosphorylase, sucrose synthase and fructokinase were assayed in extracts of the microtubers and, in the case of soluble and insoluble starch synthase, activity was found to be particularly sensitive to increasing growth temperature. The starch content of the microtubers increased slightly with increasing growth temperature, but with little effect on the number of granules per microtuber and a small increase in the average granule size. The microtuber starch granules were much smaller than those found in commercial potato starch (c 8–9 μm modal diameter compared to c 21 μm). Although the amylose content of the microtuber starches tended to increase with increasing growth temperature, the phosphorus content was variable. Gel permeation chromatographic elution profiles of native and debranched microtuber and a commercial potato starch showed that no differences could be detected in either amylose or amylopectin molecular size, polydispersity or unit chain distribution of amylopectin (which contained two major unit chain fractions at DP 21 and 56). The onset, peak and conclusion temperatures of the DSC gelatinisation endotherm increased linearly as a function of growth temperature whilst the enthalpy of gelatinisation decreased. It is suggested that elevated temperature during starch biosynthesis facilitates ordering of amylopectin double helices into crystalline domains. © 1998 SCI.     

Potato starches: variation in composition and properties between three genotypes grown at two different sites and in two different years

Starch granules were isolated from three distinct potato (Solanum tuberosum L) genotypes, cvs Glamis and Record and line 86Q35(8), grown at two different sites in 1996 and 1997. Differences in the chemical compositions of the granules were investigated using blue values of the starch–iodine complexes as indicators of amylose contents and from phosphorus contents. The physical properties determined were starch damage, swelling power, turbidity, granule size distribution, viscosity data and profile, and gelatinisation temperatures as well as enthalpy of gelatinisation. The differences in the blue values of the starch–iodine complexes were significant for genotype (P < 0.001) but not for site or year. Highly significant differences in starch granule phosphorus contents were found both between genotypes (P < 0.001) and between sites (P < 0.001), but the differences between years were less significant (P < 0.01). Genotype 86Q35(8) had nearly twice the starch phosphorus content of the other two genotypes. Significant differences were also found between genotypes in terms of granule size distributions (P < 0.01), with 86Q35(8) having a modal granule size smaller than that of the other two genotypes. The viscosity data and profiles, measured at 48 g l⁻¹, showed that samples of starch granules isolated from genotype 86Q35(8), irrespective of the site or year, behaved similarly to each other. However, the profiles obtained from starch granules derived from Glamis and Record depended on the site and year and were distinctly different from the profiles obtained from starch granules isolated from 86Q35(8). On the other hand, the differential scanning calorimetric data recorded no consistent differences in the gelatinisation temperatures and enthalpy of gelatinisation between genotype, site and year. The prospects of using specific potato genotypes as sources of starch for particular uses are discussed. © 2000 Society of Chemical Industry