Acid phosphatase in the tubers of Dioscorea species and its purification from the white yam (D. rotundata poir)

Acid phosphatase activity was determined in 15 cultivars from four species of yam. A 12-fold purification of the enzyme from Dioscorea rotundata (cv. chikakwondo) gave a homogeneous preparation as demonstrated by polyacrylamide gel electrophoresis. This enzyme preparation has an apparent molecular weight of 115 000 ±2000 and an optimum activity at a pH of 5·20 and a temperature of 50°C. The K_m of the enzyme is 3·81 mM with disodium p-nitrophenylphosphate (p-NNP) as a substrate. The energy of activation, heat of activation, energy of inactivation and heat of inactivation are 7·0, 6·4, 4·41 and 4·34 kcal M^?1, respectively. Although it has very little activity with most organic phosphoric acid esters, it is significantly inhibited by Ca²⁺, Hg²⁺ and EDTA and activated by Mg²⁺. The enzyme has a half-life of 50,17 or 13 days, respectively, when stored at 6-8°C, 0°C or room temperature (29±2°C).     

Use of gibberellic acid to prolong dormancy and reduce losses during traditional storage of yams

The annual vegetative cycle of the yam (Dioscorea spp) necessitates a long period of storage. Losses during this period are high and are mainly due to germination. Trials on the effectiveness of gibberellic acid (GA₃) for controlling storage losses were carried out on the two main species of yam (D cayenensis rotundata and D alata) grown in the Ivory Coast. Methods of application at the apex adapted to the rural environment were tested. Treatment with GA₃ prolonged the dormancy period and thus reduced losses. This substance was effective at low concentration with a long soaking duration (75 mg litre⁻¹ for 2 h) and during a soaking of short duration with a higher concentration (0·5 h at 150 mg litre⁻¹). Because of its stability at ambient temperature, the solution was still active 3 days after being prepared and after reuse of the same dip six times. © 1998 SCI.     

Genetic diversity of organoleptic properties in water yam (Dioscorea alata L)

Improving the food quality of yams (Dioscorea spp) is an ongoing challenge to yam breeders and researchers. Forty accessions of D alata were evaluated for the suitability of their tubers for the preparation of two dominant food forms (boiled and pounded) as part of an effort to identify potential parents for use in genetic improvement. Trained panellists were presented with randomised, replicated and coded samples of boiled yam tuber pieces and asked to rate them for mealiness, colour, wetness, softness and taste. The sensory attributes considered for pounded yam (dough from boiled and pounded tubers) were consistency, colour, sheen, smoothness, stickiness, elasticity and hardness. Ratings were based on hedonic scales. Cluster analysis revealed groupings of accessions into eight and nine similarity clusters for boiled yam and pounded yam respectively. The mean scores for general preference were regressed on individual attribute scores. Mealiness, colour and taste were important in the general preference for boiled yam. Consistency, colour and stickiness determined the general preference for pounded yam. Of the accessions, 67% were identified as being suitable for preparation as a boiled vegetable, while 55% were assessed to be good for pounded yam, based on the respective quality attributes evaluated. © 2003 Society of Chemical Industry     

Effect of short-term storage on phenolic content,o-diphenolase and peroxidase activities of cut yam tubers (Dioscorea sp)

The effect of short-term storage on the protein, phosphorus and phenolic content as well as peroxidase and o-diphenolase activities of cut, harvested Jamaican yam (Dioscorea sp) tubers (D rotundata. D alata and D cayenensis) was studied. There was an initial increase in the total phenolic content up to the third week of storage followed by a gradual decrease to the sixth week. Phenolic content was found to be highest in D cayenensis followed by D rotundata and D alata. The activities of peroxidase (EC 1. 11. 1. 7) and o-diphenolase (EC 1. 10.3.1) increased steadily up to the third week of storage and thereafter decreased to the fifth week. The intensity and rapidity of browning in tubers when cut, correlated very closely with the tuber o-diphenolase and phenolic content levels while the onset of rotting correlated with the peroxidase activity levels in the species studied.     

Anti-Fenton reaction activity of three taxa of water yam (Dioscorea alata L.)

In the present study, we compared the anti‐Fenton reaction activity of three taxa of water yam (Dioscorea alata L.): DS2, TN2 and PSY [D. alata L. var. purpurea (Roxb.) M. Pouch]. Anti‐Fenton reaction activity was evaluated by measuring the damage inflicted on calf thymus DNA by copper ions combined with hydrogen peroxide with the use of an ethidium bromide binding assay and agarose gel electrophoresis. We found that extracts of tuber pulp from all three taxa of yam had significant anti‐Fenton reaction activity. The protection pattern of the three tuber pulp extracts was similar to that of EDTA, a typical divalent metal ion chelator, which displayed a significant protection lag‐phase. With the use of thin‐layer chromatography, we found that a common, major ansialdehyde‐sulphuric acid stained spot (possibly a polysaccharide mucilage) with an R_f of 0.09 may be the most likely contributor to the anti‐Fenton reaction activities of the yam tuber extracts investigated. The present study identifies the mechanism of the health benefit of the Dioscorea family. The copper‐chelating and absorbing capability of yam tuber pulp extracts may be useful in functional screening.     

Some characteristics and a comparison 6f the activities of o-dihydroxyphenoloxidase activity from five yam (Dioscorea spp.) species

o-Dihydroxyphenoloxidase (E.C. 1.14.18.1) (o-DPOase) was extracted from acetone-extracted freeze-dried yam tubers, and fractionated by (NH₄)₂SO₄ precipitation and chromatography on DEAE-cellulose to give two forms from Dioscorea alta L. (cv. UM680) and three forms from D. rotundata Poir. (cv. Nwopoke). Polyacrylamide gel electrophoresis revealed one of the forms from each species to contain two protein bands with o-DPOase activity. o-DPOase from D. alata showed activity with catechol, (+)-catechin, (?)-epicatechin and chlorogenic acid, but not with tyrosine, as substrate, o-DPOase from D. rotundata showed activity only with catechol and (+)-catechin. K_m values for D. rotundata enzymes, calculated assuming a two-substrate reaction, were between 0.2 and 0.8 mM for oxygen and 70 and 120 mM for catechol. The enzyme was most active between pH 5.5 and pH 7.0, and showed slight activation after holding for 2 minutes at 40 or 50°C. After heating to above 60°C the enzyme showed evidence of irreversible denaturation. Theo-DPOase activity extracted from ten cultivars of five species of D. alata L., D. bulbifera L., D. cayenensis Lam., D. dumetorum Pax, and D. rotundata Poir. were compared.     

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     

Macromolecular characteristics of ten yam (Dioscorea spp) starches

Starches from ten yam (Dioscorea) species were compared with those of maize, wheat, potato and cassava, and characterized by high‐performance size‐exclusion chromatography coupled with multiangle laser light scattering. Treatment with 95% (v/v) dimethylsulphoxide and microwave heating in a high‐pressure vessel led to complete dissolution of the starch samples. For yam starches, M?_w were between 1.88 × 10⁸ and 3.27 × 10⁸ g mol^?1 and R?_G were between 258 and 396 nm. The hydrodynamic coefficients of amylopectins were between 0.36 and 0.44, indicating that those of maizes and esculenta 5 and dumetorum yam species had particularly highly branched structures. Multidimensional analysis of the macromolecular characteristics of yam starches indicated three classes: dumetorum cultivar (Dioscorea dumetorum), esculenta 5 cultivar (Dioscorea esculenta) and the other eight yam starches, including cultivars of Dioscorea alata and Dioscorea cayenensis‐rotundata species. Some yam starches were also leached at 90 °C. The macromolecular characteristics of the leached fractions confirmed the previous typology. Copyright © 2003 Society of Chemical Industry     

Physico‐chemical characteristics of non‐irradiated and γ‐irradiated yams cultivars (Dioscorea rotundata,Dioscorea alata) and sweet potato (Ipomoea batatas (L) Lam)

Physico‐chemical (pasting) properties of non‐irradiated (fresh) and γ‐irradiated yam cultivars and sweet potato were determined using Rapid Visco Analyser (RVA). Generally, pasting characteristics of the commodities decreased significantly with increased γ‐irradiation dose. Non‐irradiated sweet potato showed significantly higher peak (45.79), trough (35.25), breakdown (10.54), final (75.21) and setback (39.96) viscosities (in RVU) than γ‐irradiated samples. Also, peak time (6.97 min) and pasting temperature (50.18 RVU) significantly reduced with increased γ‐irradiation dose of tubers. The pasting properties of non‐irradiated and γ‐irradiated sweet potato showed similar but clearer trend compared with yam flours. Also, non‐irradiated and γ‐irradiated Dioscorea rotundata and Dioscorea alata showed significantly higher values of each of the pasting characteristics than values noted in sweet potato. Aside from the TDr 03/00196, peak time did not vary significantly with γ‐irradiation dose.     

Nutritional quality of yam (Dioscorea dumetorum and D rotundata) flours for growing rats

The digestibility and metabolism of diets based on flours prepared from raw, boiled or steamed tubers of the sweet yam (Dioscorea dumetorum) were evaluated in growing albino rats by the balance method in comparison with diets containing similar flours from the popular white yam (D rotundata). The results show that whatever their method of preparation, flours from D dumetorum promote higher growth rate and have higher nutritional value in the growing rat than corresponding D rotundata flours. This can be attributed to the good digestibility of D dumetorum starch which facilitates digestibility and absorption of nitrogen and other nutrients. Moisture-heat treatment of tubers before processing into flour improves the nutritional value, especially for D rotundata.     

The bone‐protective effect of a Taiwanese yam (Dioscorea alata L. cv. Tainung No. 2) in ovariectomised female BALB/C mice

BACKGROUND: Yam products have been marketed for treating postmenopausal syndromes. This study investigated the effects of Dioscorea alata L. cv. Tainung No. 2 (TNG yam) on the bone density of ovariectomised (OVX) female BALB/c mice and the mechanism whereby TNG yam exerted this effect. Sham and OVX control groups were fed a control diet while remaining OVX mice were randomly allocated into experimental diets, i.e. yam (630 g TNG powder kg^?1), E2 (20 mg 17β‐oestradiol kg^?1), or genistein (2 g genistein kg^?1) diet. After 12 weeks of feeding, the uterine weight, indices of bone mass and caecal short chain fatty acids were determined. RESULTS: Neither a yam nor genistein diet restored the OVX‐induced uterine atrophy as did the E2 diet. The femoral and lumbar bone mineral density (BMD) of mice fed the yam diet was greater than those of the sham group, respectively (P < 0.05 vs OVX control), while the lumbar BMD of yam and sham groups were similar (P > 0.05 vs sham). The femoral ash and calcium content in the yam group was significantly greater than that in the OVX control group, respectively (P < 0.05 vs OVX control). The total short chain fatty acid content in the caecum, only enhanced in the yam group, was not correlated with the calcium content of either bone or the plasma calcium level. CONCLUSION: TNG yam prevented loss of BMD and improved bone calcium status without stimulating uterine hypertrophy in OVX BALB/c mice. TNG yam may be beneficial for postmenopausal women for preventing bone loss. Copyright © 2008 Society of Chemical Industry     

Iron,nickel, copper,zinc and cadmium content of two cultivars of white yam (Dioscorea rotundata) and their source soils

The determination by atomic absorption spectroscopy of the iron, nickel, copper, zinc and cadmium content of two cultivars of white yam (Dioscorea rotundata Pair) and their source soil from three farms, and also of random samples of the cultivars from five geographical areas in Kaduna and Plateau states of Nigeria, is reported. The analyses show all the metals except Fe to be in trace amounts in the tissues of both cultivars; the barks contain two to four times more. The iron content was found to be about 20 times higher in the bark than in the tissue. Less than 0.7% of the metals present in the soil could be extracted with NH₄NO₃ solution. Yam bark, which contains reasonable amounts of the above metals, could be useful as cattle feed. Yam tissue, having a high content of Zn compared with Cd, could be recommended for the diet of hypertensive patients.     

Biochemical aspects of wound healing in yams (Dioscorea spp)

The effects of wounding on the activities of certain enzymes and on the concentrations of selected metabolites were investigated in the tubers of white yam (Dioscorea rotundata). Lipolytic acyl hydrolase activity decreased and disappeared after 4 days whereas the activity of lipoxygenase, peroxidase and polyphenol oxidase increased to a maximum after 1, 4 and 5 days, respectively. The activities of lipoxygenase and polyphenol oxidase were much higher in the proximal half of the tubers than in the distal portion. The increase in lipoxygenase activity at the wound site was a localised phenomenon. The application of the antibiotic, tetracycline, during the early stages of wound healing substantially reduced the increase in the activities of polyphenol oxidase and lipoxygenase. The concentration of free amino acids, total polyphenols and ascorbate increased in response to wounding. Free amino acids steadily declined after 24 h following wounding.     

Uncooked Taiwanese yam (Dioscorea alata L. cv. Tainung No. 2) beneficially modulated the large bowel function and faecal microflora in BALB/c mice

This study investigated the effects of an uncooked Taiwanese yam, Dioscorea alata L. cv. Tainung No. 2, on faecal characteristics, faecal microflora, short‐chain fatty acid (SCFA) levels in the caecal content and faeces, and morphological and proliferation indices of the caecal and colonic crypts in BALB/c mice. Mice were randomly allocated to consume a control diet or a 25 or 50% (w/w) yam diet for 21 days. Faecal wet and dry masses increased with increasing proportions of dietary yam. Both yam diets similarly increased faecal moisture content and decreased faecal pH as compared with the control diet. The yam diets increased total bacteria and bifidobacteria counts and decreased Clostridium perfringens counts in faeces. The 50% yam diet, but not the 25% yam diet, increased total SCFA concentration in the caecal content. However, both yam diets increased total SCFA output in faeces. Both yam diets also promoted crypt depth, width and proliferation indices in the caecum; in contrast, they only promoted crypt width in the distal colon. In conclusion, the 25 and 50% yam diets increased the faecal mass and SCFA output, modulated the faecal microflora and thickened the mucosa lining of the caecum in BALB/c mice. Copyright © 2007 Society of Chemical Industry     

Effect of Yam (Dioscorea alata Compared to Dioscorea japonica) on Gastrointestinal Function and Antioxidant Activity in Mice

ABSTRACT:  Effects of Chinese yam ( Dioscorea alata) and Japanese yam ( Dioscorea japonica ) on gastrointestinal functions including intestinal microflora and intestinal enzymes' activities, as well as antioxidant protection against lipopolysaccharide (LPS)-induced oxidative damage, in Balb/cA mice were examined. In part I, mice were fed yam-supplemented diet for 4 or 8 wk, and killed with carbon dioxide. In part II, mice were fed yam-supplemented diet for 4 wk, and followed by intraperitoneal LPS treatment (i.p. 4 mg/kg bodyweight). The intake of Chinese yam and Japanese yam significantly changed intestinal microflora, in which the colony numbers of Bifidobacterium and Lactobacillus were increased and the colony numbers of Clostridium perfringens were decreased ( P < 0.05). The intake of both Chinese and Japanese yams also significantly elevated the activity of leucine aminopeptidase and lipase ( P < 0.05), and the activities of sucrase and maltase were increased only in 20% yam-treated groups ( P < 0.05). The preintake of yam significantly alleviated subsequent LPS-induced oxidative injury by decreasing lipid oxidation level and fibronectin production and elevating superoxide dismutase activity ( P < 0.05). Both Chinese and Japanese yams contained dietary fibers, polyphenols, and flavonoids, which may contribute to the observed gastrointestinal function and antioxidant protection. These results suggest that both Chinese yam and Japanese yam were beneficial for intestinal health and oxidation prevention.     

Factors affecting the in-vitro establishment of Jamaican yams (Dioscorea spp) from nodal pieces

Factors such as inorganic ammonium, growth regulator supplements, propagule type and subculture period affecting the in-vitro establishment of Dioscorea cayenensis and D trifida have been examined. The results indicate that for D cayenensis, transfer of whole plantlets to fresh initiation media prior to cutting into nodal segments and transfer to establishment media was beneficial. Addition of 800 mg litre^?1 NH₄NO₃ to basal medium (BM) containing 0.5 mg litre^?1benzylamino purine (BAP) caused a significant improvement in nodal numbers and resulted ir. 11.8 propagules per original explant after 8 weeks or 184.1 propagules after 16 weeks in-vitro. Rapid establishment of D trifida cv Short Neck Yampie depended on the original explant source. Explants obtained from small tuber vines grew faster on establishment than those obtained from leafy cuttings. Initiation on BM supplemented with 0.5 mg litre^?1 kinetin (BM0.5K) and establishment on BM supplemented with 0.5 mg litre^?1 BAP (BM0.5BAP) produced the optimum result for the vines obtained from small tubers (24.0 propagules after 8 weeks of culture). For explants obtained from leafy cuttings, initiation on BM0.5BAP and establishment on BM0.5K gave optimum results (15.8). Quick establishment of initiated plantlets shown by increased shoot response and high multiplication rates were achieved in this study.     

A study of weight loss of stored yam (Dioscorea cayenensis) as affected by the ventilation of the storage locations

Investigation of the effect of ventilation on the storage losses of yam (Dioscorea cayenensis L) was carried out. The tubers were stored in three ventilation locations (1.4%, 3.8% and exposed ventilation) in two storage environments. It was found that the higher the ventilation level, the greater the weight loss. Exposed tubers that were subjected to direct heating and cooling of the sun and rain, respectively, rotted away; the high temperature involved preventing the sprouting of the tubers. Tubers in the 1.4% and 3.8% ventilation levels outside took a longer time to sprout than those stored inside.     

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     

Effect of Hydroxypropylation on the Properties of White Yam (Dioscorea rotundata) Starch

Starch isolated from white yam (Dioscorea rotundata) was subjected to hydroxypropylation under different conditions. Corresponding increases were observed between the molar substitution (MS) and the volume of propylene oxide added to the reaction mixture. After hydroxypropylation, a slight reduction in the intensity of the peak at 2θ = 19.6° was observed and the doublet peak at 23.8°, which was present in native starch, was no longer seen. Hydroxypropylation enhanced the free swelling capacity (FSC) and solubility. Setback and retrogradation of native starch declined after hydroxypropylation. Turbidity of native starch paste and syneresis were higher with storage time. The results also indicate that enzymatic digestibility improved as the MS increased, while the reverse was observed for starch paste turbidity, syneresis, setback and retrogradation. This study presents relevant information that could strategically position D. rotundata starch and its hydroxypropylated derivatives for industrial applications.