Studies on tuber starches. II. Molecular structure, composition and physicochemical properties of yam (Dioscorea sp.) starches grown in Sri Lanka

Thermal Properties and Dynamic Rheological Characterization of Dioscorea Starch Gels

Yam (Dioscorea. sp.) is an edible starchy tuber with potential for being a commercial source of starch for industrial purposes, but yam starch is underutilized. The dynamic oscillatory and thermal properties of yam starches from sixteen varieties each of Dioscorea. rotundata, Dioscora. alata, Dioscorea. bulbifera and one variety of Dioscorea. dumetorum from Nigeria were studied to determine their potential for industrial utilization. The storage modulus, loss modulus, damping factor and complex viscosity as a function of frequency (ω) of the dioscorea gels, as well as the onset temperature (To), peak gelatinization temperature (Tp), end of gelatinization (TC), and gelatinization enthalpy of the starches were determined by standard procedures. Results showed that all the dioscorea starches showed a typical elastic behavior with the magnitude of G' greater than G″ while tan δ < 1 in all varieties. Thus, the starch gels were more elastic than viscous. All the starch gels exhibited shear thinning characteristics and showed frequency (ω) independence characteristics of weak gels. D. rotundata varieties had the lowest ∆Hgel, while D. bulbifera varieties had the highest. The diversity of the visco-elastic and thermal properties of the yam starch gels from different varieties and species can be an advantage in their utilization in both food and non-food industries.

Physicochemical Properties of Wild Yam (Dioscorea villosa) Starch

Native starch extracted from wild yam (Dioscorea villosa) was evaluated for its intrinsic physicochemical properties. From the results, essential metals such as K, Ca, P, and Fe were detected along with some nonessential heavy metals below the WHO permissible limits. Bulk density was 0.13-0.63 g/mL. The water absorption capacity, oil absorption capacity, swelling power, and solubility of the starch were pH-responsive. Thermal profiles showed onset temperature, To (59.21 °C), peak temperature, Tp (60.22 °C), endset temperature, Tc (63.12 °C), gelatinization enthalpy, ΔHgel (0.54 J/g), temperature range of gelatinization, R (3.91 °C), and peak height index, PHI (1.87 J/g °C). Exhibiting a crystallite size of 0.03 nm, absorption peaks of 15.3119°, 24.4120°, and 18.4170°, corresponding to interplanar d-spacings of 3.7500 Ǻ, 5.14000 Ǻ, and 4.954610 Ǻ, were obtained. Evidence of C-H at 1338.1 cm-1, C-O at 640.0 cm-1, C-H stretch at 2829.7 cm-1, and a strong and broad O-H group at 3291.2 cm-1 were obtained. The starch granules had low particle sizes, were homogeneous, and were aggregates of irregular shapes. At a lower pH (2-4), the wild yam starch studied could be a potential absorbent material in the production of disposable diapers and female napkins and as biodegradable films due to its high hydrophobicity at a high pH (8-12).

Characteristics of physically modified starches

Starch is an abundant natural, non-toxic, biodegradable polymer. Due to its low price, it is used for various purposes in various fields such as the cosmetic, paper, and construction industries as well as the food industry. Due to recent consumer interest in clean label materials, physically modified starch is attracting attention. Manufacturing methods of physically modified starch include pregelatinization, hydrothermal treatment such as heat moisture treatment and annealing, hydrostatic pressure treatment, ultrasonic treatment, milling, and freezing. In this study, toward development of clean label materials, manufacturing methods and characteristics of physically modified starches were discussed.

Valorization and Development of Acorn Starch as Sustainable and High-Performance Papermaking Additive for Improving Bagasse Pulp and Paper Properties

Improving bagasse pulp and paper properties using forest-byproduct biomass, native Acorn starch (NAS), was compared with conventional wet-end additive cationic corn starch (CCS). The extracted acorn starch was characterized by SEM, XRD, and GPC. The results clearly showed irregular granular shape (6-12 μm) with rough surfaces, C_A-type XRD pattern, and 436.2 kDa molecular weights for NAS. The bagasse pulp retention and drainage as keys of operation performance and runnability were superior by NAS in comparison with CCS, while the lowest dosage of NAS (0.5%) showed superior results than the highest dosages of CCS (1% & 1.5%). The higher NAS adsorption onto the fiber surfaces compared to CCS could be concluded by higher water retention value (WRV) of the pulp together with higher density (up to 20%) and mechanical properties of the produced paper, e.g., tensile (up to 63%), burst (up to 37%) and tear (up to 11%) indices. NAS exploiting naturally as a papermaking additive would provide performance higher than commercial chemically-modified starch.

Structure and Processing Properties of Nine Yam (Dioscorea opposita Thunb) Starches from South China: A Comparison Study

In order to explore the processing and application potential of Chinese yam starch, nine kinds of Chinese yam starch (GY11, GY5, GY2, GXPY, LCY, SFY, MPY, SYPY, ASY) from South China were collected and characterized. The chemical composition, rheological properties, thermal properties, and in vitro starch digestion were compared, and the correlation between the structure and processing properties of these yam starches was analyzed using Pearson correlation. The results show that GY2 had the highest amylose content of 28.70%. All the yam starches were similarly elliptical, and all the yam starch gels showed pseudoplastic behavior. Yam starches showed similar pasting temperatures and resistant starch content, but SYPY showed the largest particle size (28.4 μm), SFY showed the highest setback (2712.33 cp), and LCY showed the highest peak viscosity (6145.67 cp) and breakdown (2672.33 cp). In addition, these yam starches also showed different crystal types (A-type, B-type, C-type), relative crystallinity (26.54-31.48%), the ratios of 1045/1022 cm-1 (0.836-1.213), pasting properties, and rheological properties, so the yam starches have different application potentials. The rheological and pasting properties were related to the structural properties of starch, such as DI, Mw, and particle size, and were also closely related to the thermodynamic properties. The appropriate processing methods and purposes of the processed products of these yam starches can be selected according to their characteristics.

Composition, morphology and physicochemical properties of starches derived from indigenous Ethiopian tuber crops: A review

Starch is a key food ingredient that can be extracted from roots, tubers, cereals, legumes and used in a variety of industrial applications. The issue of starch has received considerable critical attention. Most conventional sources of starch are being overexploited, it is necessary to investigate new botanical sources of starch to relieve pressure on traditional sources. Indigenous Ethiopian tuber crops can represent unexploited sources of starch with interesting characteristics in terms of potential uses as starch-based foods. It comes in a variety of shapes, sizes and properties allowing for a wide range of applications with high technological value in both the food and non-food industries. Compared to common starches, these starches have far fewer studies on their food and industrial applications. In the future, tubers grown Ethiopia could become another source of starch for the processor. This review summarizes current knowledge about the composition, structure, and physicochemical properties of Ethiopian tubers starches, intending to recommend future research to improve their use in the food industry. In the future, more in-depth work will be needed to reveal the mechanism of modification involved for structural change to use these starches for different purposes.

The Dioscorea Genus (Yam)-An Appraisal of Nutritional and Therapeutic Potentials

The quest for a food secure and safe world has led to continuous effort toward improvements of global food and health systems. While the developed countries seem to have these systems stabilized, some parts of the world still face enormous challenges. Yam (Dioscorea species) is an orphan crop, widely distributed globally; and has contributed enormously to food security especially in sub-Saharan Africa because of its role in providing nutritional benefits and income. Additionally, yam has non-nutritional components called bioactive compounds, which offer numerous health benefits ranging from prevention to treatment of degenerative diseases. Pharmaceutical application of diosgenin and dioscorin, among other compounds isolated from yam, has shown more prospects recently. Despite the benefits embedded in yam, reports on the nutritional and therapeutic potentials of yam have been fragmented and the diversity within the genus has led to much confusion. An overview of the nutritional and health importance of yam will harness the crop to meet its potential towards combating hunger and malnutrition, while improving global health. This review makes a conscious attempt to provide an overview regarding the nutritional, bioactive compositions and therapeutic potentials of yam diversity. Insights on how to increase its utilization for a greater impact are elucidated.

Profiling Anthocyanins in Thai Purple Yams (Dioscorea alata L.)

Two accessions of Thai purple yam (Dioscorea alata) were investigated for their chemical constituents during tuber development when the vines were 3 to 8 months old. Yam tubers contained total phenolic compounds ranging between 100 and 385 mg gallic acid equivalent (GAE), flavonoids 60–160 mg catechin equivalent (CE), monomeric anthocyanin of 10–90 mg cyanidin-3-glucoside equivalent (CGE), 70 g starch, and 25–30 g amylose in 100 g yam tuber on a dried weight basis, depending on the accession and age of yam vine. LCMS-IT-TOF mass spectrometry revealed that anthocyanins in both accessions from 8-month-old vines had cyanidin or peonidin nucleus. Their glycosides were nonacylated, monoacylated, or diacylated with sinapic or ferulic acid. The major yam anthocyanins found in both accessions were alatanin C (cyanidin 3-(6-sinapoyl gentiobioside). This study revealed the insights on chemical components during tuber development and characteristics of alatanins for future selection and cultivation of purple yam tubers.

Development of biodegradable films based on purple yam starch/chitosan for food application

One of the most critical challenges for the food packaging industry to overcome is the development of biodegradable coatings from renewable sources. In this work, purple yam starch (PYS), chitosan (CS), and glycerol were blended to obtain biodegradable films for characterization as intended food coatings. The films had a homogeneous surface, and the amount of CS highly influenced the film thickness. Infrared spectroscopy indicated hydrogen bond interactions between PYS and CS in the films. Thermogram data suggested that glycerol contributed to the thermal stability of the films, due to its greater interaction with CS than to the PYS. Finally, the application of a YS/CS film on apples for 4 weeks was able to preserve the fruit quality, as weight loss from the coated apple was significantly lower than the uncoated apple (p = 0.44, Dunnet's posthoc test). YS/CS films have great prospects in the food packaging industry as a new biodegradable coating.

Physical, thermal and functional properties of flour derived from Ubi Gembili (Dioscorea esculenta L.) tubers grown in Indonesia

Gembili (Dioscorea esculenta L.) tuber is one of the important food sources in term of cultural, nutritional and economic perspectives for the people in the Africa, Caribbean islands, Asia, and Oceania regions. The tubers can be eaten after being boiled, roasted, fried or cooked. However, there is lack of information on the advanced utilizations of the tubers as raw material in the manufacture of modern foods. This study aims to characterize the physical, functional and thermal properties of Gembili flour, so that this information can be used as the basis in the development of novel foods. The microstructure, crystallinity, gelatinization temperature, swelling power and solubility of the flour were determined. The electron microscope observation revealed that Gembili flour consisted of smooth surface oval granules, which were light brown in color and having 23 µm average diameter. They are comprised of polygonals or some clusters of irregular fragments. Similar to most of tuber flours, Gembili flour also exhibited B-type crystallinity with approximately 31 ±3.7% crystallinity. The gelatinization temperature of Gembili flour was high and being comparable to that of cereal flour. The enthalpy of gelatinization of Gembili flour (9.52 ±0.80 J.g-1) was comparable to that of Dioscorea alata. Unfortunately, Gembili flour exhibited low swelling power (3.90 ±0.01 g.g-1). The Gembili flour granules were highly soluble in water (11.07 ±0.05%). Based on those reported properties, Gembili flour can be a suitable raw material for the manufacture of bakery, cookies, noodle and infant foods.

Composition, Granular Structure, and Pasting Properties of Native Starch Extracted from Plectranthus edulis (Oromo dinich) Tubers

Chemical composition, granular morphology and pasting properties of native starch extracted from tubers of Plectranthus edulis were analyzed. Starch was extracted from tubers of 6 accessions collected from 4 different areas in Ethiopia. Particle size analysis (PSA) and cryo-scanning electron microscope (cryo-SEM) imaging were used to examine the granular morphology and visualize the starch paste, respectively. Pasting properties, water absorption, and gelation capacity were compared. A wide range was found for the amylose (14.2% to 23.9%), calcium (216 to 599), potassium (131 to 878), and phosphorus (1337 to 2090) contents (parts per million per dry matter). PSA showed a bimodal distribution containing small spherical (14.6 μm) and large ellipse-shaped (190.4 μm) granules. Major differences were found for the pasting with peak viscosities differing from 3184 to 7312 mPa⋅s. Starch from accessions Chencha and Inuka showed a difference in packing density as clearly seen through cryo-SEM image at 75% of the peak viscosity (PV), and the granular integrity was mainly responsible for the significant difference in their PV and breakdown. Principal component analysis revealed 2 distinct groups: native starch extracted from accessions at the Wolayta zone (Inuka, Lofua, and Chenqoua) and other accessions (Jarmet, Arjo white, and Chencha). The study revealed the potential of P. edulis starch for its application in food industries. However, the inherent variation due to environmental conditions on physicochemical properties of the starch needs further investigation.

PRACTICAL APPLICATION

Plectranthus edulis is cultivated in considerable amounts throughout Ethiopia, which makes it a valuable starch source. Due to its low tendency to retrograde, it could be applied in food industry as an equivalent for the current starch sources. Moreover, the low amylose content makes it preferable for an application in refrigerated foods as this unique quality trait prevents syneresis in end products during storage. Based on the significantly higher pasting temperature of the studied P. edulis starch extracts, it can form an alternative for potato starch, which is less suitable for its use in pasteurized foods.

Synergistic rheological behavior and morphology of yam starch and Auricularia auricula-judae polysaccharide-composite gels under processing conditions

Polysaccharides from Auricularia auricula-judae (AP) have unique functionalities. The influence of AP-blending ratios (0.1-0.8%), temperature, pH, and ionic strength on the rheological interactions of yam starch (YS)-AP blends (YA, 6%) was investigated. YA gels showed shear-thinning behavior with flow-behavior indices of 0.28-0.37 and greater pseudoplasticity in the presence of 0.8% AP. With incremental AP addition, the viscosity and consistency indices significantly increased, whereas the activation energy decreased from 7.55 to 5.12 kJ/mol (p < 0.05). YA gels exhibited excellent thickening and heat tolerance and behaved as weak gels over an AP concentration range of 0.1-0.4% but as true gels at higher concentrations (e.g. 0.8%). The viscosity/elasticity of the combinations weakened with NaCl addition or extreme pH values. A complex 3-dimensional network structure of the YA system was confirmed by scanning electron microscopy. These results indicated that AP has great potential for functional applications in the starchy food industry.

Starch Characteristics Linked to Gluten-Free Products

The increasing prevalence of coeliac disease (CD) and gluten-related disorders has led to increasing consumer demand for gluten-free products with quality characteristics similar to wheat bread. The replacement of gluten in cereal-based products remains a challenge for scientists, due to its unique role in network formation, which entraps air bubbles. When gluten is removed from a flour, starch is the main component left. Starch is used as gelling, thickening, adhesion, moisture-retention, stabilizing, film forming, texturizing and anti-staling ingredient. The extent of these properties varies depending on the starch source. The starches can additionally be modified increasing or decreasing certain properties of the starch, depending on the application. Starch plays an important role in the formulation of bakery products and has an even more important role in gluten-free products. In gluten-free products, starch is incorporated into the food formulation to improve baking characteristics such as the specific volume, colour and crumb structure and texture. This review covers a number of topics relating to starch; including; an overview of common and lesser researched starches; chemical composition; morphology; digestibility; functionality and methods of modification. The emphasis of this review is on starch and its properties with respect to the quality of gluten-free products.

Physicochemical properties and micro-structural characteristics in starch from kudzu root as affected by cross-linking

Kudzu starch was cross-linked with sodium trimetaphosphate (STMP) at different temperatures, time and of STMP concentrations in this work. The cross-linked starches (CLSs) were fractionated further into cross-linked amylose and amylopectin in order to compare the effect of cross-linking on the microstructure. According to scanning electron microscope (SEM), CLSs displayed the resemble appearance of spherical and polygonal shapes like NS. X-ray diffraction (XRD) revealed that amylose of native starch (A), NS and CLS displayed a combination of A-type and B-type structure, while that was not found in amylose of cross-linked starch (CLA). The deconvoluted fourier transform infrared (FT-IR) indicated that crystal structure of kudzu starch was losing with the proceeding of cross-linking reaction. The CLSs exhibited a higher retrogradation and freeze-thaw stability than NS. This was accompanied by a significant decrease in sedimentation, transparency, swelling power and solubility.

Variety Difference in Molecular Structure, Physico-chemical and Thermal Properties of Starches from Pigmented Rice

Starches isolated from three different pigmented rice varieties (Chak-hao Amubi, Chak-hao Poireiton, and Chak-hao Angangba) and investigated for their molecular structure and physico-chemical properties including amylose content, morphology, crystallinity, pasting viscosity, color, thermal property, swelling power and solubility. Significant differences were detected in physico-chemical and functional properties (p≤0.05) of rice starches. The amylose content results revealed that Chak-hao Angangba (1.93 %) and Chak-hao Poireiton (1.98 %) are waxy rice, and Chak-hao Amubi (3.16 %) is a very low-amylose rice. The morphology of rice starch granules shown polyhedral edges with an irregular shape; and the XRD patterns of rice starches exhibited A-type crystalline patterns with peaks at 2θ=15.1°, 17.1°, 18.2° and 23.0°. Waxy rice starches shown higher peak viscosity and enthalpy with lower gelatinization temperatures than very low amylose rice starches. The pasting viscosity, swelling power and solubility crystallinity of rice starches were varied significantly (p≤0.05). Finally, the present study provides knowledge for the utilization of starches isolated from three pigmented rice varieties grown in North-Eastern part of India that would be relevant for both domestic and industrial applications.

Effects of removal of surface proteins on physicochemical and structural properties of A- and B-starch isolated from normal and waxy wheat

The effects of protein removal on the physicochemical and structural properties of normal and waxy wheat and their A- and B-type granule fractions were investigated. No evident changes were observed in the morphological, birefringence pattern and X-ray diffraction pattern after treatment, but there was evidence showing that the relative crystallinity, swelling power and percentage syneresis of all samples were significant increased. Protein removal treatment increased the peak, setback, final viscosity, breakdown viscosity of normal and waxy native wheat starch, and their A- and B-type starch granule fractions, whereas it decreased the pasting temperature, peak time and trough viscosity. Meanwhile, the thermal transition temperatures (To, Tp, Tc) and gelatinization temperature range (ΔTr) of normal and waxy wheat and their isolated A- and B-type granules were increased, but the enthalpy decrease slightly. The different genetic factors and amylose content in normal and waxy wheat starch and their A- and B-type wheat starch granules fractions were related to the different physicochemical and structural characteristics of those starches.

Effects of Dioscoreae Rhizoma (SanYak) on Peripheral Neuropathy and its Safety

Objectives:

This study aimed to evaluate the evidence available in the literature for the safety and efficacy of Dioscoreae Rhizoma(DR) for the treatment of peripheral neuropathy.

Methods:

Literature searches were performed in MEDLINE and three Korean medical databases up to April 2013. All studies evaluating the effects on peripheral neuropathy or the safety of DR monopreparations were considered.

Results:

Three studies - DR extract per os (po) on diabetic neuropathy in mice, DR extract injection on the peripheral sciatic nerve after crush injury in rats and DR extract injection to patients with peripheral facial paralysis proved that DR treatments were effective for the treatment of nerve injuries.

Conclusions:

In conclusion, we found the DR has a strong positive potential for the treatment of peripheral neuropathy, but studies addressing direct factors related to the nerve still remain insufficient.

Physicochemical properties of flours and starches derived from traditional Indonesian tubers and roots

Flours and starches isolated from traditional tubers and roots grown in Indonesia have physical and chemical properties suitable for certain food applications. Compared to other flour samples, cassava and canna flours contained the highest amount of total starch (TS) (77.4 and 77.1 %, respectively). Taro starch had the lowest amount of TS among other starch samples with 75.4 %. The highest amount of amylose was observed from yam and canna flours (25.2 and 23.2 %, respectively). Among starch samples, canna starch contained the highest amylose content (30.4 %), while taro had the lowest (7.6 %). In terms of protein content, arrowroot flour had the highest amount (7.7 %), in contrast to cassava flour which had the lowest (1.5 %). Compared to other flours, canna and konjac flour were the most slowly digested which indicated by their high amount of resistant starch (RS). Canna starch had the highest swelling power and viscosity than other starches and flours. The clearest paste was observed from cassava flour and starch as opposed to konjac starch which was the most opaque paste.

Characterization of rice starches extracted from Indian cultivars

Physicochemical, morphological and pasting properties of starches isolated from four rice cultivars grown in India were studied. The amylose content ranged between 4.7 and 30.2% of starch, highest in K332 starch and lowest in SR1 starch. Swelling power, water solubility and water absorption capacity of starches increased with increase in temperature from 50 to 90 °C at 10 °C intervals. Highest swelling and water absorption was found in SR1 and lowest in K332 starches but reverse was observed in case of solubility that was highest for K332 and lowest for SR1 starch. The microstructure of starch granules from different rice cultivars showed the presence of mainly polyhedral granules having average size in the range of 4.0–5.2 µm. K332 showed the presence of smallest granules, whereas SR1 starch showed the presence of largest granules. X-ray diffraction pattern of rice starch from different cultivars showed typical A-type crystallinity. Pasting properties of starches differed significantly. Pasting temperature was highest for K332 and lowest for SR1, while peak viscosity was highest for aromatic rice and lowest for K448 starches. Higher setback was observed in K332 and lowest in SR1.

Comparison of the gelatinization behavior of organic and conventional spelt starches assessed by thermal and rheological analyses

The objective of this study was to compare gelatinization properties and molecular composition of starches extracted from locally grown organic and conventional spelt using thermal, rheological, and SEC analyses, along with Concanavalin A method. Organic and conventional spelt was planted in six replicated plots, and the extracted starch was analyzed for their gelatinization properties. DSC showed that the gelatinization temperature ranged from 56.7 to 68.8 °C with an average peak of 62.4 °C, with no evidence for statistical difference in gelatinization properties between treatments. Rheological behavior variation among samples was more pronounced than that between the two growing conditions. The amylose content ranged from 23.0% to 29.8%. There was no significant difference in the molecular weight of amylose and amylopectin irrespective of the plot locations, although a significant difference was found between the amylopectin molecular weight of organic and conventional spelt starches when analyzed collectively. The organic spelt starch studied may substitute the conventional starch when gelatinization behavior is considered.

Physicochemical properties of wheat-canna and wheat-konjac composite flours

Physicochemical properties of composite flours made of wheat from low to high protein contents and canna or konjac at different levels of substitution (0, 25, 50, 75, and 100 %) were prepared and analyzed. Compared to that of wheat flour alone, increasing levels of canna inclusions significantly increased the amount of resistant starch (RS) but decreased the protein content of composite flours. This substitution did not alter the total starch (TS), amylase and amylopectin contents of these mixtures. Changes in physicochemical properties were also observed in wheat-konjac composite flours. Increasing amounts of konjac flour decreased the TS, amylase, amylopectin, and protein content of the mixtures, but increased the amount of RS. Substitution of wheat flour with 75 % of canna or konjac flours in HPWC (High Protein Wheat-Canna), HPWK (High Protein Wheat-Konjac), and LPWK (Low Protein Wheat-Konjac) increased the swelling power of these mixtures at 80 and 90 °C. In general, substitution of wheat flour with up to 50 % of canna or konjac flours did not cause any other observable decline. In addition, the substitution of wheat flour with canna or konjac flours increased the gelatinization temperature of all composite flours.

Physicochemical, functional, and macromolecular properties of waxy yam starches discovered from "Mapuey" (Dioscorea trifida) genotypes in the Venezuelan Amazon

"Mapuey" tubers in Venezuela are staple food for indigenous peoples from the Caribbean coast and Amazon regions. Noticeable differences between genotypes of yam starches were observed. Granules were large, triangular, or shell-shaped with monomodal particle size distribution between 24.5 and 35.5 μm. Differential scanning calorimetry (DSC) analyses revealed onset gelatinization temperatures from 69.1 to 73.4 °C with high gelatinization enthalpy changes from 22.4 to 25.3 J g(-1). All X-ray diffractograms of starches exhibit B-type crystallinity. Crystallinity degrees varied from 24% to 40%. The highest crystallinity was found for the genotype having the highest amylose content. Iodo-colorimetric, amperometric, and DSC amylose determinations varied from 1.4 to 8.7%, 2.2 to 5.9%, and 1.4 to 3.5% for Amazonian genotypes, in comparison with commercial Mapuey starches: 12.0, 9.5, and 8.7%, respectively. Solubility and swelling power at 90 °C varied from 2.1 to 4.4% and 20.5 to 37.0%, respectively. Gel clarity fluctuated from 22.4 to 79.2%, and high rapid visco analyzer (RVA) viscosity was developed at 5% starch suspension (between 1430 and 2250 cP). Amylopectin weight average molar mass M(w), radius of gyration R(G), hydrodynamic coefficient ν(G), and apparent molecular density d(Gapp) were determined using high-performance size exclusion chromatography (HPSEC) and asymmetrical flow field flow fractionation (A4F) techniques coupled with multiangle laser light scattering (MALLS) on the Dioscorea trifida genotypes exhibiting the lowest and highest amylose contents. Amylopectins showed very similar molecular conformations. M(w) values were 1.15 × 10(8) and 9.06 × 10(7) g mol(-1) using HPSEC and A4F, respectively, thus, 3-5 times lower than those reported with the same techniques for other yam species, and very close to those of potato and cassava amylopectins. This discovery of a new natural amylose-free starch in the neglected yam "Mapuey" could present some potential for the food industry.

Isolation and physicochemical characterisation of starch from cocoyam (Colocasia esculenta) grown in Malawi

BACKGROUND

The aim of this study was to determine the physicochemical properties of starches isolated from Malawian cocoyams and compare them with those of cassava and corn starches.

RESULTS

The purity of the isolated starches varied from 851 to 947 g kg(-1) and pH from 4.93 to 6.95. Moisture, ash, protein, fat and amylose contents ranged from 104 to 132, 0.3 to 1.5, 3.5 to 8.4, 0.9 to 1.6, and 111 to 237 g kg(-1), respectively. Cocoyam starches gave higher potassium and phosphorus but lower calcium levels than the other starches. The shape of starch granules varied from spherical to polygonal with cocoyam starches displaying smaller-sized granules than cassava and corn starches. Cocoyam starches gave a higher wavelength of maximum iodine absorption and blue value but lower reducing capacity values than cassava and corn starches. The extent of acid hydrolysis of the starches also differed. Cocoyam starches exhibited amylopectin molecules of higher molecular weights but amylose molecules of lower molecular weights than cassava and corn starches. Cocoyam starches exhibited lower water absorption capacity and swelling power, paste clarity and viscosity but higher solubility, gelatinisation temperatures and retrogradation tendencies than cassava and corn starches.

CONCLUSIONS

The physicochemical properties of native Malawian cocoyam starches vary among the different accessions and differ from those of cassava and corn starches.