Metal content, bioaccumulation, translocation, and health risk assessment of root vegetables grown in KwaZulu-Natal small-scale farms of South Africa.

Metal uptake by vegetables is becoming a threat to the life of consumers. Therefore, continuous monitoring of metals in vegetables and soils is becoming a necessity. In this study, the occurrence of 18 metals in amadumbe (Colocasia esculenta L.), sweet potatoes (Ipomoea batatas L.), potatoes (Solanum tuberosum L.), and carrots (Daucus carrota L.) grown in small-scale South African agricultural farms was monitored using inductively coupled plasma-optical emission spectroscopy. All the 18 investigated elements were detected in soils and different vegetative plants parts. Bioaccumulation factors indicated the transfer of selected metals from soils into the plant roots. Toxic metals Cd, Cr, and Pb had their concentrations exceeding the maximum permissible levels set by the World Health Organization in the edible parts of all root vegetables. Cd and Pb varied between 18.89 and 19.19 mg kg-1 and 10.46 and 11.46 mg kg-1, respectively, while Cr remained constant at 16.78 mg kg-1. The exact metals together with As and Ni had their total hazard quotients exceeding the threshold value of 1, which indicated that the daily consumption of the investigated root vegetables is likely to pose health risks to both adults and children. Therefore, this study points out to a possibility of toxic health effects that could arise when these vegetables are consumed daily.

Cocoyam (Colocasia esculenta) modulates some parameters of testosterone propionate-induced rat model of benign prostatic hyperplasia.

The increased global prevalence of benign prostatic hyperplasia (BPH) and the promising potentials of functional foods in ameliorating it led to this study which reported the effect of aqueous ethanol extract of cocoyam (Colocasia esculenta) tuber on some biochemical indices in testosterone propionate (TP) induced benign prostatic hyperplasia (BPH) rats. Thirty male albino rats were randomly assigned into 6 groups of 5 rats each. Group 1 (negative control) received 3 mg/kg of TP and normal saline, group 2 (positive control) received 3 mg/kg of TP and 5 mg/kg of finasteride; groups 3, 4, and 6 rats received 3 mg/kg of TP and 100, 200 and 400 mg/kg of ethanol extracts of cocoyam respectively while group 5 (normal control) received olive oil + normal saline. The study lasted for 28 days. The negative control had increased prostate weight (p < 0.05), decreased body weight gain, prostatic superoxide dismutase, catalase and glutathione concentrations; no differences (p > 0.05) in the serum total cholesterol, triacylglycerol, Very Low Density Lipoprotein, High Density Lipoprotein, Low Density Lipoprotein concentration but increased (p < 0.05) prostate levels of interleukin 10, prostate specific antigen, testosterone, total proteins and malondialdehyde relative to the normal control. Finasteride or the C. esculenta tuber extract modulated most of these parameters as corroborated by histology of the prostate. The percentage yield of the C. esculenta tuber extract was 1.56% and 23 phenolic compounds were characterized in the tuber. The study showed the potentials of C. esculenta tuber in the management of BPH.

Optimization of oxalate-free starch production from Taro flour by oxalate oxidase assisted process.

Taro (Colocasia esculenta) starch is known to possess unique physical and functional properties such as low amylose content, A-crystalline form, small granules, higher swelling power, etc. Due to the presence of significant amount of calcium oxalate crystals, the food industry is reluctant to explore this unique and cheap starch source for various food applications. Traditional processes utilizing various physical and chemical methods to remove oxalate content of starch inevitably change its physical and functional properties. However, using oxalate oxidase can effectively remove oxalates without altering the unique properties of starch. Hence, an attempt was made to optimize oxalate oxidase assisted starch extraction process from taro flour using response surface methodology. A central composite design comprising 20 experimental trials with 10 cube points augmented with six axial points and four replicates at the center point was applied. A mathematical model was developed to show the effect of taro flour concentration, enzyme load and incubation time on the oxalate removal. Validity of the model was experimentally verified and found that 98.3% of total oxalates can be removed under optimal conditions. This is the first report of optimization of the production of starch from taro flour using microbial oxalate oxidase.

Municipal wastewater treatment potential and metal accumulation strategies of Colocasia esculenta (L.) Schott and Typha latifolia L. in a constructed wetland.

This paper elucidates phytoremediation potential of two wetland plants (Colocasia esculenta (L.) Schott and Typha latifolia L.) for municipal wastewater treatment using constructed wetland (CW) mesocosms. The concentrations (mg L-1) of chemical oxygen demand (COD), total kjeldahl nitrogen (TKN), Cu, Cd, Cr, Zn, and Pb in municipal wastewater were higher than permissible Indian standards for inland surface water disposal; however, Mn and Ni were within the permissible limits. The pollutant removal efficiencies of planted CWs varied as electrical conductivity (EC) 67.8-71.4%; COD 70.7-71.1%; TKN 63.8-72.3%; Cu 75.3-83.4%; Cd 73.9-83.1%; Mn 74.1-74.5%; Cr 64.8-73.6%; Co 82.2-84.2%; Zn 63.3-66.1%; Pb 71.4-77.9%; and Ni 76-80%. Mass balance analysis revealed that the loss of metals from wastewater was equivalent to net accumulation in plants and natural degradation of metals. Metal accumulation strategies of plants were investigated using bioconcentration factor (BCF) and translocation factor (TF) of metals which indicated that both plants could be employed for phytostabilization (BCF > 1 and TF < 1) of Cu, Cd, Co, Pb, and Ni and phytoextraction (BCF > 1 and TF > 1) of Mn and Zn. The study demonstrated that a reduction of pollutants (except Pb) was observed within permissible levels (BIS) and suggested disposal of municipal wastewater into the inland surface water bodies after 20 days of treatment. The study concluded that both the plants could potentially be used for an efficient municipal wastewater treatment using constructed wetlands.

Leaf water 18 O and 2 H maps show directional enrichment discrepancy in Colocasia esculenta.

Spatial patterns of leaf water isotopes are challenging to predict because of the intricate link between vein and lamina water. Many models have attempted to predict these patterns, but to date, most have focused on monocots with parallel veins. These provide a simple system to study, but do not represent the majority of plant species. Here, a new protocol is developed using a Picarro induction module coupled to a cavity ringdown spectrometer to obtain maps of the leaf water isotopes (18 O and 2 H). The technique is applied to Colocasia esculenta leaves. The results are compared with isotope ratio mass spectrometry. In C. esculenta, a large enrichment in the radial direction is observed, but not in the longitudinal direction. The string-of-lakes model fails to predict the observed patterns, while the Farquhar-Gan model is more successful, especially when enrichment is accounted for along the radial direction. Our results show that reticulate-veined leaves experience a larger enrichment along the axis of the secondary veins than along the midrib. We hypothesize that this is due to the lower major/minor vein ratio that leads to longer pathways between major veins and sites of evaporation.

Structural analysis and binding properties of isoforms of tarin, the GNA-related lectin from Colocasia esculenta.

The lectins, a class of proteins that occur widely in animals, plants, fungi, lichens and microorganisms, are known for their ability to specifically bind to carbohydrates. Plant lectins can be classified into 12 families including the Galanthus nivalis agglutinin (GNA)-related lectin superfamily, which is widespread among monocotyledonous plants and binds specifically to mannose, a behavior that confers remarkable anti-tumor, anti-viral and insecticidal properties on these proteins. The present study characterized a mitogenic lectin from this family, called tarin, which was purified from the crude extract from taro (Colocasia esculenta). The results showed that tarin is a glycoprotein with 2-3% carbohydrate content, composed of least 10 isoforms with pIs ranging from 5.5 to 9.5. The intact protein is a heterotetramer of 47kDa composed of two non-identical and non-covalently associated polypeptides, with small subunits of 11.9kDa and large subunits of 12.6kDa. The tarin structure is stable and recovers or maintains its functional structure following treatments at different temperatures and pH. Tarin showed a complex carbohydrate specificity, binding with high affinity to high-mannose and complex N-glycans. Many of these ligands can be found in viruses, tumor cells and insects, as well as in hematopoietic progenitor cells. Chemical modifications confirmed that both conserved and non-conserved amino acids participate in this interaction. This study determined the structural and ligand binding characteristics of a GNA-related lectin that can be exploited for several different purposes, particularly as a proliferative therapeutic molecule that is able to enhance the immunological response.

Optimization of Lactobacillus acidophilus cultivation using taro waste and evaluation of its biological activity.

In this study, taro waste (TW) was utilized for Lactobacillus acidophilus BCRC 14079 cultivation and the anti-tumor and immune-modulatory properties of heat-killed cells (HKCs), cytoplasmic fraction (CF), and exopolysaccharide (EPS) were evaluated. The optimum liquefaction enzyme dosage, temperature, and time determined by Box-Behnken design response surface methodology (BBD-RSM) were 9 mL/L of α-amylase, 79.2 °C, and 5 h of reaction, respectively. The optimum temperature and reaction time for saccharification were determined as 60 °C and 3 h. The optimum medium, CGMY1 medium, constitutes of TW hydrolysate containing 37 g/L of glucose, 25 g/L of corn gluten meal (CGM), and 1 g/L of yeast extract (YE). Results of MTT assay showed that HKCs and EPS from CGM medium exhibited the highest anti-proliferative in HT-29 (IC50 of HKCs, 467.25 µg/mL; EPS, 716.10 µg/mL) and in Caco-2 cells (IC50 of EPS, 741.60 µg/mL). Luciferase-based NF-ΚB and COX-2 systems indicated HKCs from CGM medium stimulated the highest expression of luciferin in both systems. The luciferase activities by using 100 and 500 µg/mL of HKCs from CGM were 24.30- and 45.83-fold in NF-ΚB system and 11.54- and 4.93-fold in COX-2 system higher than the control. In conclusion, this study demonstrated the potential of TW medium for L. acidophilus cultivation and the production of non-viable probiotics with enhanced biological activities.

Effects of Amendments on Growth and Uptake of Cd and Zn by Wetland Plants, Typha angustifolia and Colocasia esculenta from Contaminated Sediments.

A pot study was conducted to compare the effects of amendments (CaHPO4 and cow manure) on growth and uptake of Cd and Zn from contaminated sediments by two wetland plant species, Typha angustifolia and Colocasia esculenta. Contaminated sediments (Cd 33.2 mg kg(-1) and Zn 363 mg kg(-1)) were collected from Mae Tao basin, Mae Sot district, Tak province, Thailand. The experiment consisted of 4 treatments: control (uncontaminated sediment), Cd/Zn, Cd/Zn + 5% CaHPO4, and Cd/Zn + 10% cow manure. Plants were grown for 3 months in the greenhouse. The addition of CaHPO4 resulted in the highest relative growth rate (RGR) and highest Cd accumulation in both T. angustifolia and C. esculenta while the lowest RGR was found in C. esculenta grown in the cow manure treatment. Both plant species had higher concentrations of metals (Cd, Zn) in their belowground parts. None of the amendments affected Zn accumulation. C. esculenta exhibited the highest uptake of both Cd and Zn. The results clearly demonstrated the phytoremediation potential of C. esculenta and the enhancement of this potential by CaHPO4 amendment.

Essential and toxic metals in taros (Colocasia esculenta) cultivated in the Canary Islands (Spain): evaluation of content and estimate of daily intake.

Taros are a staple in the diet of many people around the world, and they are an excellent source of minerals. Monitoring the levels of metals in food provides basic information that is useful from the perspectives of safety, regulation, and nutrition. Forty-two samples of taros were randomly obtained from supermarkets, vegetable markets, and farmer's plots on the island of Tenerife (Canary Islands, Spain). The edible portion (pulp) was the only part considered for analysis. Flame atomic absorption spectrometry (FAAS) was used to determine the contents of Na, K, Ca, Mg, Cu, Fe, Mn, and Zn. The levels of Cr, Ni, Cd, and Pb were determined using graphite furnace atomic absorption spectrometry (GFAAS). Mean concentrations (mg/kg) were 565.6 Na, 2947 K, 231.4 Ca, 364.5 Mg, 1.224 Cu, 3.818 Fe, 1.408 Mn, 2.242 Zn, 0.044 Cr, 0.021 Ni, 0.003 Cd, and 0.006 Pb. The mean concentrations of Cd and Pb were well below the accepted European Commission limits (0.1 mg/kg weight for both metals, respectively). Daily consumption of taro (10.41 g taro/person/day) contributes to the dietary intake of essential metals and trace elements, mainly Mg (1.265% in adult women and 1.084% in adult men) and Cu (1.182% for adult men and women). The average daily intakes of Cd (0.031 µg/day) and Pb (0.062 µg/day) from taro were below the legislated respective tolerable weekly intakes (TWIs). Thus, the samples analyzed were considered safe to eat based on their metal concentrations and legislated allowable intakes.

Photosynthetic costs and benefits of abaxial versus adaxial anthocyanins in Colocasia esculenta 'Mojito'.

MAIN CONCLUSION: Anthocyanins in upper (adaxial) leaf tissues provide greater photoprotection than in lower (abaxial) tissues, but also predispose tissues to increased shade acclimation and, consequently, reduced photosynthetic capacity. Abaxial anthocyanins may be a compromise between these costs/benefits. Plants adapted to shaded understory environments often exhibit red/purple anthocyanin pigmentation in lower (abaxial) leaf surfaces, but rarely in upper (adaxial) surfaces. The functional significance of this color pattern in leaves is poorly understood. Here, we test the hypothesis that abaxial anthocyanins protect leaves of understory plants from photo-oxidative stress via light attenuation during periodic exposure to high incident sunlight in the forest understory, without interfering with sunlight capture and photosynthesis during shade conditions. We utilize a cultivar of Colocasia esculenta exhibiting adaxial and abaxial anthocyanin variegation within individual leaves to compare tissues with the following color patterns: green adaxial, green abaxial (GG), green adaxial, red abaxial (GR), red adaxial, green abaxial (RG), and red adaxial, red abaxial (RR). Consistent with a photoprotective function of anthocyanins, tissues exhibited symptoms of increasing photoinhibition in the order (from least to greatest): RR, RG, GR, GG. Anthocyanic tissues also showed symptoms of shade acclimation (higher total chl, lower chl a/b) in the same relative order. Inconsistent with our hypothesis, we did not observe any differences in photosynthetic CO2 uptake under shade conditions between the tissue types. However, GG and GR had significantly (39 %) higher photosynthesis at saturating irradiance (A sat) than RG and RR. Because tissue types did not differ in nitrogen content, these patterns likely reflect differences in resource allocation at the tissue level, with greater nitrogen allocated toward energy processing in GG and GR, and energy capture in RG and RR (consistent with relative sun/shade acclimation). We conclude that abaxial anthocyanins are likely advantageous in understory environments because they provide some photoprotection during high-light exposure, but without the cost of decreased A sat associated with adaxial anthocyanin-induced shade syndrome.

Comparative Metabolome and Transcriptome Analyses Reveal the Regulatory Mechanism of Purple Leafstalk Production in Taro (Colocasia esculenta L. Schott).

Taro is a plant in the Araceae family, and its leafstalk possesses significant botanical and culinary value owing to its noteworthy medicinal and nutritional attributes. Leafstalk colour is an essential attribute that significantly influences its desirability and appeal to both breeders and consumers. However, limited information is available about the underlying mechanism responsible for the taro plant's colouration. Thus, the purpose of the current study was to elucidate the information on purple leafstalks in taro through comprehensive metabolome and transcriptome analysis. In total, 187 flavonoids, including 10 anthocyanins, were identified. Among the various compounds analysed, it was observed that the concentrations of five anthocyanins (keracyanin chloride (cyanidin 3-O-rutinoside chloride), cyanidin 3-O-glucoside, tulipanin (delphinidin 3-rutinoside chloride), idaein chloride (cyanidin 3-O-galactoside), and cyanidin chloride) were found to be higher in purple taro leafstalk compared to green taro leafstalk. Furthermore, a total of 3330 differentially expressed genes (DEGs) were identified by transcriptome analysis. Subsequently, the correlation network analysis was performed to investigate the relationship between the expression levels of these differentially expressed genes and the content of anthocyanin. There were 18 DEGs encoding nine enzymes detected as the fundamental structural genes contributing to anthocyanin biosynthesis, along with seven transcription factors (3 MYB and 4 bHLH) that may be promising candidate modulators of the anthocyanin biosynthesis process in purple taro leafstalk. The findings of the current investigation not only provide a comprehensive transcriptional code, but also give information on anthocyanin metabolites as well as beneficial insights into the colour mechanism of purple taro leafstalk.

Modulation of MRSA virulence gene expression by the wall teichoic acid enzyme TarO.

Phenol-soluble modulins (PSMs) and Staphylococcal protein A (SpA) are key virulence determinants for community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA), an important human pathogen that causes a wide range of diseases. Here, using chemical and genetic approaches, we show that inhibition of TarO, the first enzyme in the wall teichoic acid (WTA) biosynthetic pathway, decreases the expression of genes encoding PSMs and SpA in the prototypical CA-MRSA strain USA300 LAC. Mechanistically, these effects are linked to the activation of VraRS two-component system that directly represses the expression of accessory gene regulator (agr) locus and spa. The activation of VraRS was due in part to the loss of the functional integrity of penicillin-binding protein 2 (PBP2) in a PBP2a-dependent manner. TarO inhibition can also activate VraRS in a manner independent of PBP2a. We provide multiple lines of evidence that accumulation of lipid-linked peptidoglycan precursors is a trigger for the activation of VraRS. In sum, our results reveal that WTA biosynthesis plays an important role in the regulation of virulence gene expression in CA-MRSA, underlining TarO as an attractive target for anti-virulence therapy. Our data also suggest that acquisition of PBP2a-encoding mecA gene can impart an additional regulatory layer for the modulation of key signaling pathways in S. aureus.

Crystal structure of tarocystatin-papain complex: implications for the inhibition property of group-2 phytocystatins.

Tarocystatin (CeCPI) from taro (Colocasia esculenta cv. Kaohsiung no. 1), a group-2 phytocystatin, shares a conserved N-terminal cystatin domain (NtD) with other phytocystatins but contains a C-terminal cystatin-like extension (CtE). The structure of the tarocystatin-papain complex and the domain interaction between NtD and CtE in tarocystatin have not been determined. We resolved the crystal structure of the phytocystatin-papain complex at resolution 2.03 Å. Surprisingly, the structure of the NtD-papain complex in a stoichiometry of 1:1 could be built, with no CtE observed. Only two remnant residues of CtE could be built in the structure of the CtE-papain complex. Therefore, CtE is easily digested by papain. To further characterize the interaction between NtD and CtE, three segments of tarocystatin, including the full-length (FL), NtD and CtE, were used to analyze the domain-domain interaction and the inhibition ability. The results from glutaraldehyde cross-linking and yeast two-hybrid assay indicated the existence of an intrinsic flexibility in the region linking NtD and CtE for most tarocystatin molecules. In the inhibition activity assay, the glutathione-S-transferase (GST)-fused FL showed the highest inhibition ability without residual peptidase activity, and GST-NtD and FL showed almost the same inhibition ability, which was higher than with NtD alone. On the basis of the structures, the linker flexibility and inhibition activity of tarocystatins, we propose that the overhangs from the cystatin domain may enhance the inhibition ability of the cystatin domain against papain.

Impact of soil quality on elemental uptake by, and distribution in, Colocasia esculenta (Amadumbe), an edible root.

In this study the elemental distribution of selected essential (Ca, Mg, Al, Mn, Cu, Fe, Co, Cr, Zn, Ni and Se) and the non-essential (Pb, Hg and As) elements were determined in the bulb and peel of Amadumbe (Colocasia esculenta) samples from eight different sites in KwaZulu-Natal, South Africa. The concentration of Se and As in the soil and in the Amadumbe bulbs were below the detection limit of 0.09 µg g⁻¹. The total and bioavailable concentrations of the elements in conjunction with pH, soil organic matter (SOM) and cation exchange capacity (CEC) were determined in the soil samples from the eight sites. Statistical analysis was done to evaluate the impact of soil quality parameters on the chemical composition of the Amadumbe root. The results show accumulation or exclusion of certain elements by the bulb as evidenced by the noticeable increase or decrease of the concentrations of elements, respectively. Ca and Mg were found to be major elements in the range (2000-12000 µg g⁻¹), whilst Mn, Zn, Fe and Al were found to be minor elements in the range (20-400 µg g⁻¹). A general trend observed was that the plant favours the absorption of Zn over Cu. A positive correlation between Mg & Ca, Cu & Fe and Co & Ni was also observed. Statistical analysis revealed that the plant tended to accumulate Mg, Ca, Co, Cr and Pb whilst it excluded Hg and Fe, to a lesser extent.

Stable isotope natural abundances (δ13C and δ15N) and carbon-water relations as drought stress mechanism response of taro (Colocasia esculenta L. Schott).

Taro (Colocasia esculenta L. Schott) is an important staple food crop in tropical and developing countries, having high water requirements. The purpose of this study was to evaluate the feasibility of using carbon and nitrogen isotopic composition (δ13C and δ15N) as a physiological indicator of taro response to drought, and elucidation of the relationship between the water use efficiency (WUE) under drought conditions and carbon isotope discrimination (Δ13C). As an alternative to WUE determination, obtained by measuring plant growth and water loss during an entire vegetative cycle, we have used Δ13C to determine the tolerance of C3 taro plants to drought. Seven taro accessions from Madeira, Canary Islands and the Secretariat of the Pacific Community (Fiji) collections were grown under greenhouse conditions and subjected to different watering regimes during a one-year cycle. Total plant biomass (TPB), WUE and δ15N were determined at the whole-plant level (WP). Corms and shoots were evaluated separately for nitrogen content (N), δ13C, Δ13C and δ15N. WUE showed positive correlation with TPB (r = 0.4) and negative with Δ13C (r = -0.3); Corm δ15N showed positive correlations with WP δ15N (r = 0.6) and corm N (r = 0.3). Accordingly, the taro plants with enhanced WUE exhibited low Δ13C and δ15N values as a physiological response to drought stress. The approach used in the present study has developed new tools that could be used in further research on taro response to environmental stresses.

Environmental behavior of paclobutrazol in soil and its toxicity on potato and taro plants.

The environmental behavior of paclobutrazol in soil and its toxicity were studied by field investigation and an outdoor pot experiment, and the residue of paclobutrazol was detected by gas chromatography-mass spectrometry. Field investigation has found that the residual paclobutrazol in the former succession crop could severely inhibit the growth of succeeding crops of potato; with migration and transformation of residual paclobutrazol in the soil, the stems of potato were thickened with residual amount of 1.23 mg kg-1, the growth was slow, and the height of potato in soil with residual amount of 1.34 mg kg-1 and the control was significantly different. The degradation dynamics of paclobutrazol fits with the first-order degradation kinetics, although T1/2 of paclobutrazol of the taro planting soil was 30.14-46.21 days and the residual paclobutrazol remained detectable even on day 120 after application. Taro leaves were sensitive to the stress of paclobutrazol pollution; the taro leaf thickness increased, the leaf area decreased, the chlorophyll content per area unit of taro leaf showed an obvious increased trend, and SOD and CAT activities and MDA and proline content increased significantly. Paclobutrazol promoted the tillering of taro, and the taro seedlings were dwarfed by 58.01, 63.27, and 75.88% at different concentrations. It indicated that taro had strong stress response ability under paclobutrazol pollution.

Recovery of energy from Taro (Colocasia esculenta) with solid-feed anaerobic digesters (SOFADs).

We present studies on solid-feed anaerobic digesters (SOFADs) in which chopped Colocasia esculenta was fed without any other pretreatment, in an attempt to develop an efficient means of utilizing the semi-aquatic weed that is otherwise an environmental nuisance. Two types of SOFADs were studied. The first type had a single vessel with two compartments. The lower portion of the digester, 25% of the total volume, was separated from the upper by a perforated PVC disk. The weed was charged from the top and inoculated with anaerobically digested cow dung-water slurry. The fermentation of the weed in the digester led to the formation of volatile fatty acids (VFAs) plus some biogas. The bioleachate, rich in the VFAs, passed through the perforated PVC disk and was collected in the lower compartment of the digester. The other type of digesters, referred to as anaerobic multi-phase high-solids digesters (AMHDs), had the same type of compartmentalized digester unit as the first type and an additional methaniser unit. Up-flow anaerobic filters (UAFs) were used as methaniser units, which converted the bioleachate into combustible biogas consisting of approximately 60% methane. All SOFADs developed a consistent performance in terms of biogas yield within 20 weeks from the start. Among the two types of digesters studied, the AMHDs were found to perform better with a twofold increase in biogas yield compared to the first type of digesters.

Thermodynamic criteria analysis for the use of taro starch spherical aggregates as microencapsulant matrix.

Spherical aggregates can be obtained from taro starch by spray-drying without using bonding agents. Accurate information about thermal issues of spherical aggregates can provide valuable information for assessing the application as encapsulant. Spherical aggregates of taro starch were obtained by spray-drying and analyzed using dynamic vapour sorption. The use of the Guggenheim, Anderson and de Boer (GAB) model indicated a Type II isotherm pattern with weaker interactions in the multilayer region. Differential enthalpy and entropy estimates reflected a mesoporous microstructure, implying that energetic mechanisms dominate over transport mechanisms in the sorption process. The limitation by energetic mechanisms was corroborated with enthalpy-entropy compensation estimates. The diffusivity coefficient was of the order of 10-8 m2·s-1, which is in line with results obtained for common materials used for encapsulation purposes. The thermodynamic properties and the lack of a bonding agent indicated the viability of spherical aggregates of taro starch for encapsulation of biocompounds.

Thermal and chemical denaturation of Colocasia esculenta tuber agglutinin from α2ß2 to unfolded state.

The major tuber storage protein of Colocasia esculenta, is a monocot mannose-binding, widely used dietary lectin, containing two polypeptides of 12.0 and 12.4 kDa. By both gel filtration and dynamic light scattering at pH 7.2, the lectin has a α2ß2 form of apparent molecular mass of 48.2 kDa and a hydrodynamic radius of 6.1 ± .2 nm; however, at pH 3, it migrates as αß and has a reduced hydrodynamic radius of 4.6 ± .3 nm. Our circular dichroism spectroscopy studies show that the lectin retains approximately 100% of its secondary structure between pH 2-8, going down to ~90% for extreme acidic/alkaline conditions. The fluorescence emission maxima of 346 to 350 nm for pH 4 to 10 show that the tryptophan residues are relatively exposed. The unfolding is a simple two-state process, N4 ↔ 4U, as seen in our denaturation scan profiles. These denaturation profiles, monitored separately by fluorescence, far-UV CD, and near-UV CD, are completely super imposable. Analyses of these profiles provide an estimate of several thermodynamic parameters at each guanidinium chloride concentration, including the melting temperature Tg, which is 346.9 K in 0 M, but lowers to 321.8 K in 3.6 M. Dimeric and tetrameric interfaces observed in the crystal structure for the same protein are used to rationalize solution data in some detail.

Mercury uptake and accumulation by four species of aquatic plants.

The effectiveness of four aquatic plants including water hyacinth (Eichornia crassipes), water lettuce (Pistia stratiotes), zebra rush (Scirpus tabernaemontani) and taro (Colocasia esculenta) were evaluated for their capabilities in removing mercury from water. The plants were exposed to concentrations of 0 mg/L, 0.5 mg/L or 2 mg/L of mercury for 30 days. Assays were conducted using both Microtox (water) and cold vapor Atomic Absorption Spectroscopy (AAS) (roots and water). The Microtox results indicated that the mercury induced acute toxicity had been removed from the water. AAS confirmed an increase of mercury within the plant root tissue and a corresponding decrease of mercury in the water. All species of plants appeared to reduce mercury concentrations in the water via root uptake and accumulation. Water lettuce and water hyacinth appeared to be the most effective, followed by taro and zebra rush, respectively.