Studies on nucleotides and related compounds in plants. V. Isolation and identification of bracken nucleotides

The presence of acid-soluble nucleotides was demonstrated in bracken rhizomes. Cold trichloroacetic acid extracts of bracken had to be submitted to some eight purification steps prior to analysis. Of the nucleotide material held by an anion exchange resin uridine derivatives (UMP, UDP-glucose, UDP-galactose, UDP-xylose, UDP-arabinose, UDP-glucuronic acid and a trace of UDP) accounted for some 80% of the total. The remainder comprised guanosine (12%; GMP, GDP-mannose and GDP-fucose) and adenosine (8%; mainly ATP) compounds. A comparison of the sugar composition of the nucleotide material with that of associated soluble carbohydrates present in the rhizome (mucilage, glycoside and sucrose) is also included.     

Studies on nucleotides and related compounds in plants. I. Isolation and identification of starch grain nucleotides

The presence of nucleotide material in whole starch grains was confirmed and the amounts of individual constituents present in a variety of starches were determined quantitatively. A rapid method for the isolation of starch grains from potato tubers to limit contamination by cell-sap nucleotides was developed. This technique enabled reproducible nucleotide patterns to be obtained from comparable batches of starch. Of the material held by a strong anion-exchange resin above pH 7.5, the adenine nucleotides were quantitatively dominant, only traces of UMP and GMP being detected. The relative amounts of AMP, ADP and ATP in the various starches fluctuated. ADP-glucose was the only sugar-containing nucleotide encountered and UDP-glucose, although looked for, appeared to be absent in all cases.     

Studies on nucleotides and related compounds in plants. III. Adenine and adenosine ratios in starch from potatoes held under prescribed conditions

Adenine is the sole base and adenosine is the sole nucleoside in potato starch extracts. The levels of these metabolites remain constant in stored potato starch over several months. In starch samples obtained from potatoes under differing physiological conditions the ratio of adenine to adenosine fluctuates. When potatoes are in an active state of growth the adenosine levels in the starch are low and the ratio of adenine to adenosine is consequently high (approx 8–12). Starch from physiologically inactive potatoes has an adenine: adenosine ratio of 1.5:2.5. When potatoes are held at 0 °C the levels of adenine and adenosine in the starch fall, but there is no striking change in the ratio of these two metabolites.     

Studies on nucleotides and related compounds in plants. IV. Synthesis of N6-benzyladenosine phosphate derivatives of possible relevance to starch grain formation

The chemical synthesis of gramme quantities of a range of N⁶-substituted adenine nucleotides (cytokinins) required primarily for studies on starch grain biosynthesis is undertaken. The direct conversion of preformed samples of AMP, ADP, ATP, ADP-N-acetylglucosamine and ADP-mannose is successfully accomplished in yields ranging from 19 to 35% using DEAE-cellulose and 70% aqueous methanol solutions of ammonium carbonate for their isolation from original nucleotide material. For the synthesis of N⁶-benzylADP-α-glucose and N⁶-benzylADP-β-glucose recourse had to be made to the morpholidate procedure and the products were thus obtained in yields of 42 to 48% as isolated from DEAE-cellulose with 70% aqueous methanol solutions of ammonium acetate at pH 5. The substituted adenine compounds were treated with the potato tuber preparation shown previously, to mobilise adenine from a range of adenine nucleotides. As with other nucleotides tested dephosphorylation readily occurred, but cleavage of the nucleoside releasing N⁶-substituted adenine could not be detected, thus emphasising the specificity of the adenyl-cleaving activity of the potato tuber preparation.     

Lipids of potato tubers. II. Lipid-degrading enzymes in different varieties of potato tuber

The levels of two lipid-degrading enzymes, namely a hydrolytic enzyme (lipolytic acyl hydrolase) and an oxidising enzyme (lipoxygenase) were measured in tubers from 23 varieties of potato at harvest. Twenty-two varieties had very high levels of the hydrolytic enzyme, ranging from 5 to 50 jumol of substrate hydrolysed/ min/g of fresh weight of tuber. One variety, Desiree, contained a much lower level of this enzyme (0.06 to 0.2 units/g fresh weight). All varieties contained high levels of lipoxygenase activity in the range of 1 to 25 μmol of 0₂ consumed/min/g fresh weight of tuber, with linoleic acid as substrate. The combined action of these enzymes in the degradation of potato tuber lipids is discussed.     

Variation in glycoalkaloid concentration of potato tubers harvested from mature plants

Individual tubers from mature plants of cultivars Pentland Dell and Estima were harvested from experimental plots in two successive years and analysed for α‐solanine, α‐chaconine and total glycoalkaloid concentration (α‐solanine and α‐chaconine combined) using high‐performance liquid chromatography. Mean tuber glycoalkaloid concentration per plant was strongly affected by genotype and was much higher in plants of Pentland Dell (10.0 and 16.3 mg per 100 g fresh weight in 1994 and 1995, respectively) than Estima (4.0 and 4.3 mg per 100 g fresh weight in 1994 and 1995, respectively). The variation between plants in mean tuber glycoalkaloid concentration, expressed as coefficient of variation, was similar for the two cultivars in both years. Variation within plants was higher for cultivar Pentland Dell than Estima for both years but it was statistically significant only in 1995. Tuber position within a plant had no effect on glycoalkaloid concentrations in tubers of similar size. An inverse relationship between total glycoalkaloid concentration and tuber fresh weight of individual tubers was found for both cultivars and small tubers of Pentland Dell (20–40 g fresh weight) exceeded the safety limit of 20 mg per 100 g fresh weight. The pattern of glycoalkaloid accumulation differed between genotypes and appeared related to tuber growth. The implications of these results in terms of food safety are discussed. © 1999 Society of Chemical Industry     

Lipids of potato tubers. I. Lipid and fatty acid composition of tubers from different varieties of potato

Tubers from 23 varieties of potato were obtained at harvest and analysed for total lipid content, lipid composition and distribution of component fatty acids. The total lipid content was similar for all varieties (approx. 0.1% of the fresh weight) and no significant differences were observed between varieties in the individual lipid components. The polyunsaturated fatty acids, i.e. linoleic and linolenic acids, represented 51 to 60 and 13 to 24%, respectively, of the total fatty acids. An inverse relationship between linoleic acid and linolenic acid was observed resulting in a very similar proportion of the combined polyunsaturated fatty acids for all varieties (70 to 76% of total fatty acids). The results are discussed in relation to the role of lipids in the potato tuber.     

An enzyme-linked immunosorbent assay for total glycoalkaloids in potato tubers

An antiserum raised against a solanine-bovine serum albumin conjugate has been characterised and shown to be specific for the glycoalkaloids found in commercially available potatoes. The antiserum has been employed at high dilution in an enzyme-linked immunosorbent assay (ELISA) for the glycoalkaloids. The assay is sensitive and precise and has many advantages over alternative procedures currently employed. Potato sample preparation is minimal and no recovery factors are required.     

寡雄蛋白处理对马铃薯块茎活性氧代谢及病程相关蛋白的诱导

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Lipids of potato tubers. Effects of storage temperature on total,polar and sterol lipid content and fatty acid composition of potato tubers

Potato tubers (Majestic and Bintje varieties) were stored at 5 and 20 °C for up to 24 weeks. Only minor differences were observed in lipid composition of tubers stored at the two temperatures. Linolenic acid levels were slightly lower in the 10 °C stored tubers, although no significant differences were found in the proportions of the total polyunsaturated fatty acids of tubers at 5 and 20 °C. The effects on the fatty acid composition of Pentland Crown potatoes of short term storage at 30 °C are reported. It is concluded from this and from previous papers in this series that neither the choice of potato variety, nor of storage temperature for a given variety, is likely to reduce the polyunsaturated fatty acid content of potato sufficiently to avoid the problems experienced commercially in the oxidative degradation of polyunsaturated fatty acids to produce off-flavours in potato products. The large changes in the proportions of the different classes of sterol lipids which have been reported to occur in potatoes during storage were not confirmed by the present studies.     

Chlorogenic acids and related compounds in medicinal plants and infusions

The consumption of plant infusions for prevention and treatment of health disorders is a worldwide practise. Various pharmacological activities inherent to medicinal plants have been attributed to their phenolic composition, including chlorogenic acids (CGA). Studies have shown potential beneficial properties of CGA to humans such as antioxidant, hepatoprotective, hypoglycaemic. In the present study, the CGA composition of 14 dried medicinal plants was determined by HPLC-UV and LC-DAD–ESI-MS. The plants with the highest CGA contents were Ilex paraguariensis, Bacharis genistelloides, Pimpinella anisum, Achyrochine satureioides, Camellia sinensis, Melissa officinalis and Cymbopogon citratus, with 84.7 mg/100 g–9.7 g/100 g, dry weight. Plant infusions were prepared (at 0.5%) in order to evaluate the actual consumption of CGA through these beverages. Total CGA contents in the infusions were similar to those in the methanolic extracts and indicated that a satisfactory extraction occurs during the preparation of infusions. These CGA-rich plants deserve attention regarding the pharmacological properties attributed to CGA.     

Lipids of potato tubers. 3. Effect of growth and storage on lipid content of the potato tuber

The effect of physiological changes on the lipid content of six varieties of potato tubers was studied. No significant varietal differences were observed. A marked decrease occurred in the amount of total lipid and fatty acids during the initial weeks of growth, followed by a levelling off during maturation and subsequent storage at 5 ºC. After 6 months' storage, the early maturing varieties revealed a large degree of sprouting with an accumulation in both total lipid and fatty acid content. Palmitic, linoleic and linolenic acids represented 95% of the fatty acids and throughout these studies the relative proportions of the major fatty acids remained constant. Chromatographic analysis demonstrated very little change in the polar lipids, but minor trends among the neutral lipid classes were detected. In the early stages of growth of the tuber the triglyceride level fell rapidly, but later, following the break of dormancy in the stored tuber, there was a regeneration of triglyceride accompanied by a noticeable rise in sterol and carotenoid content.     

Transformation of carbohydrate and nitrogen compounds in potato tubers during drying: The influence of virus diseases

The influence of virus diseases on the concentrations of starch, total sugars, reducing sugars and nitrogen compounds was investigated in fresh and dried potato tubers. Virus disease hinders carbohydrate transformation and enhances nitrogenous transformation.     

Lipids of potato tubers. IV. Effect of growth and storage on the lipid-degrading enzymes of the potato tuber

Six varieties of potato were chosen to investigate the activity of lipolytic acyl hydrolase and lipoxygenase during tuber growth in the field, and subsequent storage at 5 ºC. Apart from an increase in the initial stages of growth, both enzymes displayed relatively consistent levels of activity throughout the life cycle of the tuber. The hydrolase showed an overall slight increase with time and there was a slight decline in lipoxygenase activity during storage. Throughout the physiological stages studied, the activities of both enzymes remained at levels characteristic for a given variety.     

Nonyl alcohol vapour in potato stores during sprout suppression. II.—Physical factors in the uptake of nonyl alcohol vapour by potato tubers

A study was made of some physical factors which influence the uptake by potato tubers of nonyl alcohol, used for sprout suppression in commercial storage. The saturation concentration of nonyl alcohol vapour in air was determined over the relevant temperature range. Investigation of the interactions between potato tubers and mixtures of air, nonyl alcohol vapour and water vapour showed that the tubers reached equilibrium with the alcohol vapour most rapidly in dry air at the higher of two temperatures investigated. The weight of alcohol taken up by the tuber was greater in dry air and was proportional to the square of the applied alcohol vapour concentration. A sudden rise in humidity caused a rapid release of some alcohol from a treated tuber, while a drop in humidity caused a rather slower uptake. The results suggest that part of the nonyl alcohol is absorbed by the bulk of the potato and part adsorbed on the surface of the skin. The relevance of the results to commercial potato storage practice is discussed.     

Indirect gas chromatographic determination of IPC and CIPC in potato tubers

A sensitive and reproducible method for the determination of the sprout-inhibitors IPC and CIPC in potatoes has been developed. Both substances were hydrolyzed in acidic medium and corresponding anilines were determined after acetylation by means of gas chromatography using flame ionization detector. The detection limit for both compounds was 0.01 mg · kg^?1.     

Transformation of carbohydrate and nitrogen compounds in potato tubers during drying: Part 1—The influence of tritox applied in cultivation of potatoes upon transformations of carbohydrate and nitrogen compounds during potato drying

The influence of tritox on the concentrations of starch, saccharose, reducing sugars and nitrogen compounds, is investigated in fresh and dried potato tubers. Tritox hinders carbohydrate transformations and enhances nitrogenous transformations. These effects may be enzyme-mediated.     

Effects of cooking methods on polyphenols,pigments and antioxidant activity in potato tubers

Potato tubers, which are one of the richest sources of antioxidants, are always cooked before human consumption. The objective of this study was to understand the effects of various domestic cooking methods, i.e., boiling, microwaving and baking on total phenolics, flavonoids, flavonols, lutein, anthocyanins and antioxidant activities in 5 cultivars and 9 advanced selections with different skin and flesh colors after 6 months of storage. The three cooking methods reduced the levels of these compounds and the percentage of DPPH (2,2-Diphenyl-1-pikryl-hydrazyl) radical scavenging activity in all the cultivars and selections. Boiling minimized these losses. Red fleshed tubers contained more flavonoids, whereas purple tubers contained more flavonols. Despite severe loss of these compounds due to cooking, both the flesh types retained larger amounts of all these compounds due to higher initial levels. Decline in the radical scavenging activity is directly related to loss of these compounds due to cooking treatments in all white and colored flesh tubers. Red and purple fleshed tubers exhibited greater radical scavenging activity than yellow and white fleshed tubers after each of the cooking treatments. Correction procedures were introduced to exclude interfering compounds (ascorbic acid, other oxidizing agents and reducing sugars) in Folin-Ciocalteu Reagent (FCR) assay of estimating total phenolics in potato.     

Studies on curcumin and curcuminoids VII. Chromatographic separation and quantitative analysis of curcumin and related compounds

Summary Chromatographic analysis of curcumin and structurally related compounds is described. The poor reproducibility of the quantitative analyses is due to the interaction between the 1,3-dicarbonyl group of the molecules and the solid chromatographic support. By careful selection of the chromatographic conditions a succesful quantitative analysis could be achieved.

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Studien über Curcumin und Curcuminoide. VII. Chromatographische Trennung und quantitative Analyse von Curcumin und verwandten Verbindungen

Zusammenfassung Die chromatographische Trennung von Curcumin und verwandte Verbindungen wird beschrieben. Die schlechte Reproduzierbarkeit der quantitativen Analyse ist durch eine Interaktion zwischen der 1,3-Dicarbonylgruppe und dem chromatographischen Trägermaterial bedingt. Durch gründliche Wahl der chromatographischen Bedingungen kann eine quantitative Analyse durchgefürt werden.