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Sally Ann Crawford - One of the best experts on this subject based on the ideXlab platform.
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Synthesis of L-Ascorbic Acid
Advances in Carbohydrate Chemistry and Biochemistry, 2008Co-Authors: Thomas C. Crawford, Sally Ann CrawfordAbstract:Publisher Summary This chapter provides a summary of the methods developed for the synthesis of L-Ascorbic Acid. L -Ascorbic Acid is a white, crystalline solid melting at 192°C and having, in water, a specific rotation at the sodium D line of +24°. In solution, L -ascorbic Acid has a pK 1 of 4.17 and a pK 2 of 11.79. The more-Acidic proton has been shown by both chemical and physical methods to be that of the 3-hydroxyl group. The structure of L-Ascorbic Acid in solution has been studied by C-NMR spectroscopy, suggesting that a variety of tautomeric structures is possible. L-Ascorbic Acid has also been synthesized from D-galacturonic Acid —a hexose derivative not as readily available as D-glucose. In the chapter, the methods of preparation of precursors in the various syntheses are discussed. Many of the methods used for the preparation of analogs are based on the procedures used for the synthesis of L -ascorbic Acid. The synthesis and biological activity of a number of these analogs are reviewed in the chapter.
Marc Hendrickx - One of the best experts on this subject based on the ideXlab platform.
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thermal stability of l ascorbic Acid and ascorbic Acid oxidase in broccoli brassica oleracea var italica
Journal of Food Science, 2010Co-Authors: Ann Wambui Munyaka, Edna Edward Makule, Ann Van Loey, Marc HendrickxAbstract:ABSTRACT: The thermal stability of vitamin C (including L-Ascorbic Acid [l-AA] and dehydroascorbic Acid [DHAA]) in crushed broccoli was evaluated in the temperature range of 30 to 90 °C whereas that of ascorbic Acid oxidase (AAO) was evaluated in the temperature range of 20 to 95 °C. Thermal treatments (for 15 min) of crushed broccoli at 30 to 60 °C resulted in conversion of l-AA to DHAA whereas treatments at 70 to 90 °C retained vitamin C as l-AA. These observations indicated that enzymes (for example, AAO) could play a major role in the initial phase (that is, oxidation of l-AA to DHAA) of vitamin C degradation in broccoli. Consequently, a study to evaluate the temperature–time conditions that could result in AAO inactivation in broccoli was carried out. In this study, higher AAO activity was observed in broccoli florets than stalks. During thermal treatments for 10 min, AAO in broccoli florets and stalks was stable until around 50 °C. A 10-min thermal treatment at 80 °C almost completely inactivated AAO in broccoli. AAO inactivation followed 1st order kinetics in the temperature range of 55 to 65 °C. Based on this study, a thermal treatment above 70 °C is recommended for crushed vegetable products to prevent oxidation of l-AA to DHAA, the onset of vitamin C degradation. Practical Application: The results reported in this study are applicable for both domestic and industrial processing of vegetables into products such as juices, soups, and purees. In this report, we have demonstrated that processing crushed broccoli in a temperature range of 30 to 60 °C could result in the conversion of L-Ascorbic Acid to dehydroascorbic (DHAA), a very important reaction in regard to vitamin C degradation because DHAA could be easily converted to other compounds that do not have the biological activity of vitamin C.
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thermal stability of l ascorbic Acid and ascorbic Acid oxidase in broccoli brassica oleracea var italica
Journal of Food Science, 2010Co-Authors: Ann Wambui Munyaka, Edna Edward Makule, Ann Van Loey, Marc HendrickxAbstract:UNLABELLED: The thermal stability of vitamin C (including L-Ascorbic Acid [l-AA] and dehydroascorbic Acid [DHAA]) in crushed broccoli was evaluated in the temperature range of 30 to 90 degrees C whereas that of ascorbic Acid oxidase (AAO) was evaluated in the temperature range of 20 to 95 degrees C. Thermal treatments (for 15 min) of crushed broccoli at 30 to 60 degrees C resulted in conversion of l-AA to DHAA whereas treatments at 70 to 90 degrees C retained vitamin C as l-AA. These observations indicated that enzymes (for example, AAO) could play a major role in the initial phase (that is, oxidation of l-AA to DHAA) of vitamin C degradation in broccoli. Consequently, a study to evaluate the temperature-time conditions that could result in AAO inactivation in broccoli was carried out. In this study, higher AAO activity was observed in broccoli florets than stalks. During thermal treatments for 10 min, AAO in broccoli florets and stalks was stable until around 50 degrees C. A 10-min thermal treatment at 80 degrees C almost completely inactivated AAO in broccoli. AAO inactivation followed 1st order kinetics in the temperature range of 55 to 65 degrees C. Based on this study, a thermal treatment above 70 degrees C is recommended for crushed vegetable products to prevent oxidation of l-AA to DHAA, the onset of vitamin C degradation. PRACTICAL APPLICATION: The results reported in this study are applicable for both domestic and industrial processing of vegetables into products such as juices, soups, and purees. In this report, we have demonstrated that processing crushed broccoli in a temperature range of 30 to 60 degrees C could result in the conversion of L-Ascorbic Acid to dehydroascorbic (DHAA), a very important reaction in regard to vitamin C degradation because DHAA could be easily converted to other compounds that do not have the biological activity of vitamin C.
Thomas C. Crawford - One of the best experts on this subject based on the ideXlab platform.
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Synthesis of L-Ascorbic Acid
Advances in Carbohydrate Chemistry and Biochemistry, 2008Co-Authors: Thomas C. Crawford, Sally Ann CrawfordAbstract:Publisher Summary This chapter provides a summary of the methods developed for the synthesis of L-Ascorbic Acid. L -Ascorbic Acid is a white, crystalline solid melting at 192°C and having, in water, a specific rotation at the sodium D line of +24°. In solution, L -ascorbic Acid has a pK 1 of 4.17 and a pK 2 of 11.79. The more-Acidic proton has been shown by both chemical and physical methods to be that of the 3-hydroxyl group. The structure of L-Ascorbic Acid in solution has been studied by C-NMR spectroscopy, suggesting that a variety of tautomeric structures is possible. L-Ascorbic Acid has also been synthesized from D-galacturonic Acid —a hexose derivative not as readily available as D-glucose. In the chapter, the methods of preparation of precursors in the various syntheses are discussed. Many of the methods used for the preparation of analogs are based on the procedures used for the synthesis of L -ascorbic Acid. The synthesis and biological activity of a number of these analogs are reviewed in the chapter.
Roberto Viola - One of the best experts on this subject based on the ideXlab platform.
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Synthesis of L-Ascorbic Acid in the phloem
BMC Plant Biology, 2003Co-Authors: Robert D Hancock, Diane Mcrae, Sophie Haupt, Roberto ViolaAbstract:Background Although plants are the main source of vitamin C in the human diet, we still have a limited understanding of how plants synthesise L -ascorbic Acid (AsA) and what regulates its concentration in different plant tissues. In particular, the enormous variability in the vitamin C content of storage organs from different plants remains unexplained. Possible sources of AsA in plant storage organs include in situ synthesis and long-distance transport of AsA synthesised in other tissues via the phloem. In this paper we examine a third possibility, that of synthesis within the phloem. Results We provide evidence for the presence of AsA in the phloem sap of a wide range of crop species using aphid stylectomy and histochemical approaches. The activity of almost all the enzymes of the primary AsA biosynthetic pathway were detected in phloem-rich vascular exudates from Cucurbita pepo fruits and AsA biosynthesis was demonstrated in isolated phloem strands from Apium graveolens petioles incubated with a range of precursors ( D -glucose, D -mannose, L -galactose and L -galactono-1,4-lactone). Phloem uptake of D -[U-^14C]mannose and L -[1-^14C]galactose (intermediates of the AsA biosynthetic pathway) as well as L -[1-^14C]AsA and L -[1-^14C]DHA, was observed in Nicotiana benthamiana leaf discs. Conclusions We present the novel finding that active AsA biosynthesis occurs in the phloem. This process must now be considered in the context of mechanisms implicated in whole plant AsA distribution. This work should provoke studies aimed at elucidation of the in vivo substrates for phloem AsA biosynthesis and its contribution to AsA accumulation in plant storage organs.
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accumulation of l ascorbic Acid in tuberising stolon tips of potato solanum tuberosum l
Journal of Plant Physiology, 1998Co-Authors: Roberto Viola, D Vreugdenhil, H V Davies, Linda SommervilleAbstract:Summary Swelling stolon tips (diameter >2mm) and small developing tubers of up to 7.5 mm diameter from glasshouse-grown potato plants (cv. Desiree) contained 5–7 fold more L-Ascorbic Acid (AsA) compared with non-swelling stolon tips (diameter
Zbigniew Czarnocki - One of the best experts on this subject based on the ideXlab platform.
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enantioselective synthesis of r laudanosine and r glaucine from l ascorbic Acid
Tetrahedron-asymmetry, 1996Co-Authors: Zbigniew Czarnocki, Jozef Mieczkowski, Marek ZiolkowskiAbstract:Abstract L -Ascorbic Acid 1 was converted into L -gulonolactone 2 by catalytic hydrogenation. Treatment of 2 with 3,4-dimethoxyphenylethyl amine 3 afforded amide 4 , which in several steps was transformed into the title alkaloids in good enantiomeric excesses. Also, chromium(III) oxide is proposed as an effective catalyst for the conversion of ( R )-(−)-laudanosine into ( R )-(−)-glaucine.
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Enantioselective synthesis of (R)-(−)-laudanosine and (R)-(−)-glaucine from L-Ascorbic Acid
Tetrahedron-asymmetry, 1996Co-Authors: Zbigniew Czarnocki, Jozef Mieczkowski, Marek ZiółkowskiAbstract:Abstract L -Ascorbic Acid 1 was converted into L -gulonolactone 2 by catalytic hydrogenation. Treatment of 2 with 3,4-dimethoxyphenylethyl amine 3 afforded amide 4 , which in several steps was transformed into the title alkaloids in good enantiomeric excesses. Also, chromium(III) oxide is proposed as an effective catalyst for the conversion of ( R )-(−)-laudanosine into ( R )-(−)-glaucine.
