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).     

Improving the application of gibberellic acid to prolong dormancy of yam tubers (Dioscorea spp)

With the aim of reducing the cost and time needed to treat yam tubers with gibberellic acid (GA₃), this study compared several new methods of application with the established dipping procedure (150 mg kg^?1 for 1 h). Both GA₃‐containing soil paste (25 mg kg^?1) and gelatinized starch (860 mg kg^?1) were applied to tuber heads of Dioscorea alata and D cayenensis‐rotundata in the Ivory Coast. Soil paste, gelatinized starch and dipping consistently prolonged dormancy and reduced fresh matter losses by 23–39% in D cayenensis‐rotundata 3‐year means. Although dipping reduced the storage losses most efficiently, soil paste and gelatinized starch used considerably less GA₃. Both new treatments were easily prepared and quickly applied. Soil paste was most effective when the treatment was repeated before the end of dormancy. The third new method, spraying the tubers with a GA₃ solution (150 mg kg^?1), was not effective. In general, the optimal time of application was immediately post‐harvest. For D alata, treatment only 1 month after harvest was particularly ineffective, whereas D cayenensis‐rotundata tubers could be treated with some effect up to the end of dormancy. To achieve extended storage periods of healthy tubers of D cayenensis‐rotundata, GA₃ application may be recommended as post‐harvest practice. Copyright © 2003 Society of Chemical Industry     

Influence of light exposure, ethanol and copper(II) on the formation of a precursor for xanthylium cations from tartaric acid

The production of xanthylium cation pigments was greatly increased when an aged, tartaric acid buffered, 12% (v/v) aqueous ethanol solution was used in a model white wine system. This suggested the formation of a precursor to the pigments during the ageing of the tartaric acid solution. On examining factors responsible for the generation of tartaric acid oxidation products in wine-like solutions it was observed that on exposure of samples to sunlight, glyoxylic acid, a known precursor to xanthylium cations, was produced. The production of glyoxylic acid was achieved in both the absence and presence of ethanol and copper(II). Hydrogen peroxide was also detected in these solutions. The results were consistent with the presence of glyoxylic acid in the aged tartaric acid buffered, 12% (v/v) aqueous ethanol solution that had frequent aeration and periodic exposure to sunlight throughout its storage. Studies on the role of hydrogen peroxide in the production of glyoxylic acid were also investigated. On the addition of hydrogen peroxide to tartaric acid solutions, with heating at 45°C in darkness, glyoxylic acid was only determined in solutions without ethanol.     

Isolation, characterization and immunological activity of a polysaccharide from the fruit bodies of an edible mushroom, Sarcodon aspratus (Berk.) S. Ito.

A water-soluble polysaccharide (HCP) with a molecular mass of 6.7 × 10⁵ Da determined by high performance size-exclusion chromatography (HPSEC), was isolated from the fruit bodies of Sarcodon aspratus (Berk.) S. Ito., an edible mushroom. HCP was elucidated as a liner glucan with a backbone structure of (1 → 6)-linked-??-d-glucopyranosyl residues by interpretation of the composition analysis, methylation analysis, periodate oxidation experiment, FT-IR, and NMR spectroscopy. Immunological activity evaluation using H³-thymidine incorporation method revealed that HCP could significantly stimulate the proliferation of the cultured mice spleen lymphocyte in a dose-dependent manner. HCP might be a potential immunomodulator which can be used against pathogens and tumors in health-care food or medicine. This is the first report on the detailed structure elucidation of the polysaccharide from S. aspratus.     

Isolation and characterization of the volatile aroma compounds from the concrete headspace and the absolute of <Emphasis Type="Italic">Jasminum sambac</Emphasis> (L.) Ait. (Oleaceae) flowers grown in Egypt

The composition of the volatile fraction of Egyptian Jasminum sambac (L.) Ait. (Family: Oleaceae) flowers picked in July (the climax of the flowering season), was studied using GC/MS. The flowers’ concrete headspace (HS) volatiles had been analyzed by SPME (solid phase microextraction) and compared with those from the flowers’ absolute. The main volatile constituents of the concrete HS and the absolute, respectively, were: benzyl acetate (23.7 and 14.2%), indole (13.1 and 13.4%), E-E-α-farnesene (15.9 and 13.1%), Z-3-hexenyl benzoate (4.9 and 9.4%), benzyl alcohol (7.7 and 8.4%), linalool (10.6 and 6.3%), and methyl anthranilate (5.0 and 4.7%). The major volatile constituents of Egyptian J. sambac absolute are almost qualitatively similar but quantitatively different from those grown in other geographical regions. The proportion of some major volatile constituents at this investigation are also different from those reported in a previous investigation for Egyptian J. sambac. The study also revealed that, headspace-solid phase microextraction (HS-SPME), equipped with a polydimethylsiloxane (PDMS) fiber, can give an indication about the composition of some of the major volatile constituents of J. sambac, e.g., indole, methyl anthranilate and E-E-α-farnesene, directly from the concrete HS.     

Isolation,characterization and antioxidant capacity assessment of the bioactive compounds derived from Hypoxis rooperi corm extract (African potato)

The rhizome of the plant Hypoxis rooperi (“African potato”) is known for its traditional and ethnomedical uses in the treatment of benign prostatic hyperplasia and other diseases. We have characterized an extract derived from H. rooperi, isolated its major bioactive compound, hypoxoside, and obtained its aglycone, rooperol, by enzymatic digestion. Absorption, fluorescence emission and bidimensional NMR complete spectral data of these compounds were obtained. The antioxidant capacity of both compounds was fully analyzed through the thiobarbituric acid reactive substances (TBARS) and Trolox equivalent antioxidant capacity (TEAC) assays, and it was compared to catechins and olive biophenolics. Both compounds showed a strong antioxidant capacity, although rooperol exhibited a higher antioxidant activity against lipid peroxidation which correlated to its strong affinity for phospholipid membranes as derived from its extremely high lipid/water partition coefficient (K_p = 3.4 × 10⁴). The study of the lipophilic (EtOH) and hydrophilic (water) TEAC values revealed that more hydrophobic compounds, had greater lipophilic TEAC values than hydrophilic ones, probably indicating that lipophilic TEAC assay may be more reliable for these compounds. The H. rooperi extract also showed higher antioxidant efficacy compared to other strong antioxidant herbal extracts, such as olive leaf or green tea. Moreover, neither evidence of acute oral toxicity nor adverse effects were observed when the H. rooperi commercial extract containing 45% hypoxoside was used at a dosage of 2000 mg/kg. The results obtained in this work may contribute to understanding the biological activity described for these dicatechols and the African potato extract for food and cosmetic applications.