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Separation of taxol and related taxanes using supercritical fluidsVandana, Vishnu 08 1900 (has links)
No description available.
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Design of solvent systems for supercritical fluid and high pressure applicationsHafner, Kellye Padgett 05 1900 (has links)
No description available.
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Synthetic membranes for chiral separationsBorgsmiller, Karen McNeal 05 1900 (has links)
No description available.
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Mixed Matrix Membrane Chromatography for Bovine Whey Protein FractionationTuan Chik, Syed Mohd Saufi January 2010 (has links)
Whey protein fractionation is an important industrial process that requires effective large-scale processes. Although packed bed chromatography has been used extensively, it suffers from low processing rates due to high back-pressures generated at high flow rates. Batch chromatography has been applied but generally has a low efficiency. More recently, adsorptive membranes have shown great promise for large-scale protein purification, particularly from large-volume dilute feedstocks. A new method for producing versatile adsorptive membranes by combining membrane and chromatographic resin matrices has been developed but not previously applied to whey protein fractionation. In this work, a series of mixed matrix membranes (MMMs) were developed for membrane chromatography using ethylene vinyl alcohol (EVAL) based membranes and various types of adsorbent resin. The feasibility of MMM was tested in bovine whey protein fractionation processes.
Flat sheet anion exchange MMMs were cast using EVAL and crushed Lewatit® MP500 (Lanxess, Leverkusen, Germany) anion resin, expected to bind the acidic whey proteins β-lactoglobulin (β-Lac), α-lactalbumin (α-Lac) and bovine serum albumin (BSA). The MMM showed a static binding capacity of 120 mg β-Lac g⁻¹ membrane (36 mg β-Lac mL⁻¹ membrane) and 90 mg α-Lac g⁻¹ membrane (27 mg α-Lac mL⁻¹ membrane). It had a selective binding towards β-Lac in whey with a binding preference order of β-Lac > BSA > α-Lac. In batch whey fractionation, average binding capacities of 75.6 mg β-Lac g⁻¹ membrane, 3.5 mg α-Lac g⁻¹ membrane and 0.5 mg BSA g⁻¹ membrane were achieved with a β-Lac elution recovery of around 80%.
Crushed SP Sepharose™ Fast Flow (GE Healthcare Technologies, Uppsala, Sweden) resin was used as an adsorbent particle in preparing cation exchange MMMs for lactoferrin (LF) recovery from whey. The static binding capacity of the cationic MMM was 384 mg LF g⁻¹membrane or 155 mg LF mL⁻¹ membrane, exceeding the capacity of several commercial adsorptive membranes. Adsorption of lysozyme onto the embedded ion exchange resin was visualized by confocal laser scanning microscopy. In LF isolation from whey, cross-flow operation was used to minimize membrane fouling and to enhance the protein binding capacity. LF recovery as high as of 91% with a high purity (as judged by the presence of a single band in gel electrophoresis) was achieved from 150 mL feed whey.
The MMM preparation concept was extended, for the first time, to produce a hydrophobic interaction membrane using crushed Phenyl Sepharose™ (GE Healthcare Technologies, Uppsala, Sweden) resin and tested for the feasibility in whey protein fractionation. Phenyl Sepharose MMM showed binding capacities of 20.54 mg mL⁻¹ of β-Lac, 45.58 mg mL⁻¹ of α-Lac, 38.65 mg mL⁻¹ of BSA and 42.05 mg mL⁻¹ of LF for a pure protein solution (binding capacity values given on a membrane volume basis). In flow through whey fractionation, the adsorption performance of the Phenyl Sepharose MMM was similar to the HiTrap™ Phenyl hydrophobic interaction chromatography column. However, in terms of processing speed and low pressure drop across the column, the benefits of using MMM over a packed bed column were clear.
A novel mixed mode interaction membrane was synthesized in a single membrane by incorporating a certain ratio of SP Sepharose cation resin and Lewatit MP500 anion resin into an EVAL base polymer solution. The mixed mode cation and anion membrane chromatography developed was able to bind basic and acidic proteins simultaneously from a solution. Furthermore, the ratio of the different types of adsorptive resin incorporated into the membrane matrix could be customised for protein recovery from a specific feedstream. The customized mixed mode MMM consisting of 42.5 wt% of MP500 anionic resin and 7.5 wt% SP Sepharose cationic resin showed a binding capacity of 7.16 mg α-Lac g⁻¹ membrane, 11.40 mg LF g⁻¹ membrane, 59.21 mg β-Lac g⁻¹ membrane and 6.79 mg IgG g⁻¹ membrane from batch fractionation of 1 mL LF-spiked whey. A tangential flow process using this membrane was predicted to be able to produce 125 g total whey protein per L membrane per h.
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Purification and characterization of s-adenosylmethionine synthetase from candida albicansJones, Ward M. January 1989 (has links)
S-Adenosylmethionine (SAM) synthetases isolated from both the yeast and hyphal-phase of the dimorphic fungus, C. albicans, were partially purified using DEAE cellulose ion-exchange column chromatography. Further characterization was accomplished using enzyme kinetics and specific enzyme effectors. SAM synthetase is the enzyme responsible for synthesis of SAM which is the major methyl group donor in the methylation of macromolecules. Kinetic studies on column samples, from both phases, were performed. The yeast-phase enzyme had apparent Km ranges for L-methionine and ATP of 1.06-1.42mM and 1.11-1.69mM, respectively. The hyphal-phase enzyme had apparent Km ranges for L-methionine and ATP of 1.34-2.66mM and 3.29-6.28mM, respectively. Effector studies (in vitro) indicate that 10% (v/v) dimethyl sulfoxide (DMSO) and 5mM cycloleucine inhibit SAM Synthetase from both phases, 24% and 46%, respectively. The methionine analogues DLmethionine sulfone, DL-methionine-DL-sulfoxide and L-methioninesulfoximine and sinefungin, an analog of SAM, had no effect on SAM synthetase activity. Although the data is inconclusive with respect to the existence of isozymes, the observed Km's of the yeast and hyphal-phases are different suggesting that isozymes may exist. Additionally, the yeast-phase DEAE column profile has a shoulder prior to the main peak of activity indicating that more then one form of the enzyme may be present. / Department of Biology
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Figures of merit for a direct injection nebulizer for flow injection analysis and liquid chromatography with inductively coupled plasma spectrometric detectionChakrabarty, Chitra L. January 1990 (has links)
A direct injection nebulizer was constructed in our laboratory and was evaluated as an interface between a liquid chromatography column and an inductively coupled plasma-atomic emission spectrometer (ICP-AES). Optimum operating conditions, detection limits, and reproducibility in water and in organic solvents were studied. The detection limits in water were similar to a commercially available device. The detection limits of elements in organic solvents were about ten times higher than those in water. The DIN-ICP system stave more uniform response towards different species of Phosphorus and osmium than did a Meinhard nebulizer-ICP system, even when great differences in volatilitN existed between the species. A Potential application to the speciation of cisplatin and its analogs was also investigated. / Department of Chemistry
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Polyphenols, ascorbate and antioxidant capacity of the Kei-apple (Dovyalis caffra) / Tersia de BeerDe Beer, Tersia January 2006 (has links)
There is a close relationship between the susceptibility to disease and nutritional state, in the
sense that an adequate diet enhances resistance to disease. There is an increasing interest in this
beneficial relationship among scientists, food manufacturers and consumers. The trend is
moving towards functional foods and their specific health benefits.
The results of numerous epidemiological studies and recent clinical trials provide consistent
evidence that diets rich in fruits and vegetables can reduce the risk of chronic diseases. These
protective effects are mediated through multiple groups of beneficial nutrients contained in the
fruits and vegetables, one of these being polyphenol antioxidants. The intake of the polyphenols
plays an important role in the reduction and prevention of coronary heart disease (CHD),
cardiovascular disease and cancer, as a consequence of their associated antioxidant properties.
Fruits contain an array of polyphenols with antioxidant capacity. Polyphenols may be classified
in two broad groups namely: flavonoids and non-flavonoids. Flavonoid subgroups in fruits are
further grouped as catechins, anthocyanins, procyanidins and flavonol among others. Phenolic
acids occur as hydroxylated derivatives of benzoic acid and cinnarnic acid, and are classified as
non-flavonoids. Polyphenols have redox properties allowing them to act as reducing agents,
hydrogen donators and singlet oxygen quenchers, and thus contribute to the antioxidant capacity
of fruits and vegetables. Because of the numerous beneficial effects attributed to these
antioxidants, there is renewed interest in finding vegetal species with high phenolic content and
relevant biological activities.
In view of the importance of these substances towards health and food chemistry, this study will
focus on the polyphenol and Vitamin C characterisation and quantification of an indigenous
South African fruit, the Kei-apple (Dovyalis cafra), thought to have antioxidant properties. Due
to the fact that polyphenol content influences the colour, taste and possible health benefits of the
fruit / processed food product, this study will supply valuable information to industry in choosing
the best fruit processing methods to attain the desired end product. The exploitation of
indigenous South African fruits (Marula and Kei-apple) is receiving increasing prominence, not
only due to their health benefits, but also the opportunities these present to rural based
economics. Furthermore, this research will serve as a platform for further research on the Kei-apple
and other indigenous South African fruits with possible health benefits.
Aims: The overall aim of this study is the quantification and characterisation of various nutritionally
important antioxidants (polyphenols and ascorbate) in the Kei-apple fruit in its entirety, as well
as in its individual fruit components (peel, flesh and seeds). In addition, the total antioxidant
capacity of the entire fruit and the various fruit components will be determined in the
unfractionated and fractionated fruit extracts. Gas chromatography coupled mass spectrometry
(GC-MS) characterisation of the individual polyphenol components will also be analyzed in
order to speculate on possible specific health benefits which the Kei-apple may possess.
Methods: The study was designed to ensure that a representative fruit sample was collected.
Approximately 100 kg Kei-apples were picked in the month of November 2004 from the
Bloemhof area in South Africa. A sample of 50 fruits was rinsed and separated into the various
components (peel, flesh and seeds). An additional 50 fruits were randomly selected, cleaned and
used in their entirety for data representative of the entire fruit. The sample extracts were
prepared, after being grounded and lyophilized, by a method described by Eihkonen et al.
(1999) using 70% aqueous acetone. The C18-fractionation on the fruit and separated fruit
components resulted in four fractions containing (1) phenolic acids; (2) procyanidins, catechins
and anthocyanin monomers; (3) flavonols and (4) anthocyanin polymers.
The total polyphenol content of the fruit and fruit components as well as the above mentioned
C18-fractions were determined by Folin-Ciocalteu's method (Singleton & Rossi, 1965). Both
free and total ascorbate concentrations in these samples were determined as described by Beutler
(1984), in addition to total sugar content of these via standard methods. Apart from their
nutritional interest, both these measurements are necessary for the correction of the total
polyphenol concentrations. The total antioxidant capacity of the entire fruit and various fruit
components was determined by measuring the oxygen radical absorbance capacity (ORAC) and
ferric reducing antioxidant power (FRAP) of the unfractionated and fractionated extracts. Using
GC-MS analysis, the various individual polyhenol compounds contributing to the total
polyphenol content of the Kei-apple was separated, identified and quantified.
This quantitative data was captured and statistically analysed. The analysis of variation was
performed using the Tukey Honest Significant Difference test for post-hoc comparison. ORAC,
FRAP and polyphenol Pearson correlation analyses were performed using Statistics (Statsoft
Inc., Tulsa, Oklahoma, USA) with significance set at P ≤ 0.05.
Results and discussion: This study determined the presence of various nutritionally important antioxidants (polyphenols
and ascorbate), the total antioxidant capacity in the entire fruit as well as in the individual fruit
components (peel, flesh and seeds) and their polyphenol sub group fractions.
Total phenol content: The Kei-apple, in its entirety, has a polyphenol concentration of 943 ±
20.3 mg GAE/100g dry weight. Comparison of the individual fruit components showed the
seeds to have the highest total polyphenol concentration with 1990 ± 31.3 mg GAE/100g dry
weight, followed by that of the peel, 1126 ± 45.8 mg GAE/100g dry weight and then that of the
flesh, 521 ± 1.01 mg GAE/100g dry weight.
Total, L-ascorbic (ASC) and L-dehydroascobic (DHA) concentration: The total ascorbate of
Kei-apple fruit is 517 ± 0.92 mg/100g dry weight. In contrast to the polyphenol content, the
flesh of the Kei-apple had significantly the highest concentration of total ascorbate 778 ± 1.20
mg/100g dry weight, Gascorbic 241 ± 21.0 mg/100g dry weight, as well as Gdehydroascobic
537 ± 22.2 mg/100g dry weight. The ratio of Lascorbic acidltotal ascorbate for the flesh, entire
fruit, peel and seed is 0.31,0.43,0.49,0.95, respectively, indicating the seeds are the most stable
source of biologically active Vitamin C, with 95% of the total ascorbate occurring as G
ascorbate. This is also in line with the total polyphenol content of these components, confirming
a polyphenol sparing effect on ascorbate.
C18-fractionation extracts: Solid phase (C18) fractionation of the Kei-apple fruit and fruit
components showed that the fruit, peels and seeds consist predominantly of phenolic acids,
followed by procyanidin, catechin and anthocyanin monomers and thereafter varying amounts of
anthocyanin polymers and flavonols.
Antioxidant capacity: The antioxidant capacity of the entire fruit and individual fruit
components as determined by ORAC, (r=0.76) and FRAP, (r=0.95) significantly correlated with
the total polyphenol content, as well as to each other (r=0.88), indicating both to be good
predictors of antioxidant capacity.
GC-MS polyphenol characterisation of the Kei-apple: Caffeic acid and hydro-p-coumaric
acid were seen to be the phenolic acids occurring in the highest concentrations in the Kei-apple
fruit. The majority of these are concentrated in the flesh and in the case of caffeic acid, also in
the peel. The order of predominance of other major non-flavonoid components in the whole fruit
analysis are m-hydroxybenzoic acid > p-hydroxyphenyl acetic acid > 3-methoxy-4-
hydroxyphenylpropionic acid > p-coumaric acid. The peel of the Kei-apple, apart from caffeic
acid, has exceptionally high concentrations of ferulic acid and also serves as a source of
protocatechuic acid. Syringic acid was most prominent in the seeds. Although the total
flavonoid concentration in the Kei-apple was low, taxifolin and catechin were identified and the
seeds almost entirely accounting for these.
Conclusion: From this study it was concluded the Kei-apple is a rich source of antioxidant compounds
(polyphenols and ascorbate), with a strong antioxidant capacity, and hence may be associated
with health promotion properties, particularly in the prevention of cancer, cardiovascular disease,
and neurodegeneration. Additionally, due to the increased scientific and commercial interest in
this fruit, it is essential to take into consideration the various factors (agronomic, genomic, pre- and
post harvest condition and processing) and tissues. This might affect the chemical
composition of the final marketed product, which may play a significant role in determining the
polyphenol and ascorbate composition and bioactivity of these compounds during food
processing procedures. Hence, the polyphenol composition of the various fruit components
should be taken into consideration when selecting a method of fruit processing into the desired
end product. / Thesis (M.Sc. (Nutrition))--North-West University, Potchefstroom Campus, 2007.
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CHARACTERIZATION OF VOLATILE ORGANIC COMPOUNDS RELEASED BY STORED GRAIN INSECTSTHIRUPPATHI, SENTHILKUMAR 13 September 2010 (has links)
Detecting the presence of insects at low densities can avoid total deterioration of stored grains because corrective actions can be implemented early. Tribolium castaneum (Herbst) and Cryptolestes ferrugineus (Stephens) are the major insect pests of the Canadian grain handling industry. Identification of the volatile organic compounds released by insects can be used to detect insects in stored grains. An attempt was made to identify the volatile organic compounds released by T. castaneum and C. ferrugineus by headspace analysis. The volatiles in the head space of vials with insects, insects and wheat flour, and insects and wheat, were analyzed using a GC-MS coupled with an automatic headspace sampler. Wheat with fifteen percent moisture content was used in this study along with two different insect densities. Feasibility of the automatic headspace sampler in headspace analysis was found to be positive. The sampler can do sample conditioning, absorption, trap cleaning and desorption of the volatiles into the GC-MS and speed up the process. The samples extracted at 20 strokes with 1000 µL per stroke, and desorbed at 250°C gave a clear peak of compounds.
The amount of volatiles produced by T. castaneum adults varied based on insect densities, the concentration of Methyl-1, 4-benzoquinone; Ethyl-1, 4-benzoquinone; and 1-Tridecene released by ten adult insects were 355, 390 and 530 µg/L compared to 300,310 and 210 µg/L of Methyl-1, 4-benzoquinone; Ethyl-1, 4-benzoquinone; and 1-Tridecene produced by five adult insects. Extreme high and low temperature leading to death produced very high amounts of volatiles compared to insects kept at 35°C. The larvae of the T. castaneum insects did not produce any volatiles at ambient condition as well as at extreme cold and warm conditions.
The C. ferrugineus adults did not produced any detectable amount of volatiles even at the higher insect density after up to 3 days. The results of the combination of T. castaneum and C. ferrugineus insects gave the same volatile organic compounds as produced by T. castaneum insects alone. The 1-Tridecene produced by T. castaneum was not reported previously in other studies.
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Polyphenols, ascorbate and antioxidant capacity of the Kei-apple (Dovyalis caffra) / Tersia de BeerDe Beer, Tersia January 2006 (has links)
There is a close relationship between the susceptibility to disease and nutritional state, in the
sense that an adequate diet enhances resistance to disease. There is an increasing interest in this
beneficial relationship among scientists, food manufacturers and consumers. The trend is
moving towards functional foods and their specific health benefits.
The results of numerous epidemiological studies and recent clinical trials provide consistent
evidence that diets rich in fruits and vegetables can reduce the risk of chronic diseases. These
protective effects are mediated through multiple groups of beneficial nutrients contained in the
fruits and vegetables, one of these being polyphenol antioxidants. The intake of the polyphenols
plays an important role in the reduction and prevention of coronary heart disease (CHD),
cardiovascular disease and cancer, as a consequence of their associated antioxidant properties.
Fruits contain an array of polyphenols with antioxidant capacity. Polyphenols may be classified
in two broad groups namely: flavonoids and non-flavonoids. Flavonoid subgroups in fruits are
further grouped as catechins, anthocyanins, procyanidins and flavonol among others. Phenolic
acids occur as hydroxylated derivatives of benzoic acid and cinnarnic acid, and are classified as
non-flavonoids. Polyphenols have redox properties allowing them to act as reducing agents,
hydrogen donators and singlet oxygen quenchers, and thus contribute to the antioxidant capacity
of fruits and vegetables. Because of the numerous beneficial effects attributed to these
antioxidants, there is renewed interest in finding vegetal species with high phenolic content and
relevant biological activities.
In view of the importance of these substances towards health and food chemistry, this study will
focus on the polyphenol and Vitamin C characterisation and quantification of an indigenous
South African fruit, the Kei-apple (Dovyalis cafra), thought to have antioxidant properties. Due
to the fact that polyphenol content influences the colour, taste and possible health benefits of the
fruit / processed food product, this study will supply valuable information to industry in choosing
the best fruit processing methods to attain the desired end product. The exploitation of
indigenous South African fruits (Marula and Kei-apple) is receiving increasing prominence, not
only due to their health benefits, but also the opportunities these present to rural based
economics. Furthermore, this research will serve as a platform for further research on the Kei-apple
and other indigenous South African fruits with possible health benefits.
Aims: The overall aim of this study is the quantification and characterisation of various nutritionally
important antioxidants (polyphenols and ascorbate) in the Kei-apple fruit in its entirety, as well
as in its individual fruit components (peel, flesh and seeds). In addition, the total antioxidant
capacity of the entire fruit and the various fruit components will be determined in the
unfractionated and fractionated fruit extracts. Gas chromatography coupled mass spectrometry
(GC-MS) characterisation of the individual polyphenol components will also be analyzed in
order to speculate on possible specific health benefits which the Kei-apple may possess.
Methods: The study was designed to ensure that a representative fruit sample was collected.
Approximately 100 kg Kei-apples were picked in the month of November 2004 from the
Bloemhof area in South Africa. A sample of 50 fruits was rinsed and separated into the various
components (peel, flesh and seeds). An additional 50 fruits were randomly selected, cleaned and
used in their entirety for data representative of the entire fruit. The sample extracts were
prepared, after being grounded and lyophilized, by a method described by Eihkonen et al.
(1999) using 70% aqueous acetone. The C18-fractionation on the fruit and separated fruit
components resulted in four fractions containing (1) phenolic acids; (2) procyanidins, catechins
and anthocyanin monomers; (3) flavonols and (4) anthocyanin polymers.
The total polyphenol content of the fruit and fruit components as well as the above mentioned
C18-fractions were determined by Folin-Ciocalteu's method (Singleton & Rossi, 1965). Both
free and total ascorbate concentrations in these samples were determined as described by Beutler
(1984), in addition to total sugar content of these via standard methods. Apart from their
nutritional interest, both these measurements are necessary for the correction of the total
polyphenol concentrations. The total antioxidant capacity of the entire fruit and various fruit
components was determined by measuring the oxygen radical absorbance capacity (ORAC) and
ferric reducing antioxidant power (FRAP) of the unfractionated and fractionated extracts. Using
GC-MS analysis, the various individual polyhenol compounds contributing to the total
polyphenol content of the Kei-apple was separated, identified and quantified.
This quantitative data was captured and statistically analysed. The analysis of variation was
performed using the Tukey Honest Significant Difference test for post-hoc comparison. ORAC,
FRAP and polyphenol Pearson correlation analyses were performed using Statistics (Statsoft
Inc., Tulsa, Oklahoma, USA) with significance set at P ≤ 0.05.
Results and discussion: This study determined the presence of various nutritionally important antioxidants (polyphenols
and ascorbate), the total antioxidant capacity in the entire fruit as well as in the individual fruit
components (peel, flesh and seeds) and their polyphenol sub group fractions.
Total phenol content: The Kei-apple, in its entirety, has a polyphenol concentration of 943 ±
20.3 mg GAE/100g dry weight. Comparison of the individual fruit components showed the
seeds to have the highest total polyphenol concentration with 1990 ± 31.3 mg GAE/100g dry
weight, followed by that of the peel, 1126 ± 45.8 mg GAE/100g dry weight and then that of the
flesh, 521 ± 1.01 mg GAE/100g dry weight.
Total, L-ascorbic (ASC) and L-dehydroascobic (DHA) concentration: The total ascorbate of
Kei-apple fruit is 517 ± 0.92 mg/100g dry weight. In contrast to the polyphenol content, the
flesh of the Kei-apple had significantly the highest concentration of total ascorbate 778 ± 1.20
mg/100g dry weight, Gascorbic 241 ± 21.0 mg/100g dry weight, as well as Gdehydroascobic
537 ± 22.2 mg/100g dry weight. The ratio of Lascorbic acidltotal ascorbate for the flesh, entire
fruit, peel and seed is 0.31,0.43,0.49,0.95, respectively, indicating the seeds are the most stable
source of biologically active Vitamin C, with 95% of the total ascorbate occurring as G
ascorbate. This is also in line with the total polyphenol content of these components, confirming
a polyphenol sparing effect on ascorbate.
C18-fractionation extracts: Solid phase (C18) fractionation of the Kei-apple fruit and fruit
components showed that the fruit, peels and seeds consist predominantly of phenolic acids,
followed by procyanidin, catechin and anthocyanin monomers and thereafter varying amounts of
anthocyanin polymers and flavonols.
Antioxidant capacity: The antioxidant capacity of the entire fruit and individual fruit
components as determined by ORAC, (r=0.76) and FRAP, (r=0.95) significantly correlated with
the total polyphenol content, as well as to each other (r=0.88), indicating both to be good
predictors of antioxidant capacity.
GC-MS polyphenol characterisation of the Kei-apple: Caffeic acid and hydro-p-coumaric
acid were seen to be the phenolic acids occurring in the highest concentrations in the Kei-apple
fruit. The majority of these are concentrated in the flesh and in the case of caffeic acid, also in
the peel. The order of predominance of other major non-flavonoid components in the whole fruit
analysis are m-hydroxybenzoic acid > p-hydroxyphenyl acetic acid > 3-methoxy-4-
hydroxyphenylpropionic acid > p-coumaric acid. The peel of the Kei-apple, apart from caffeic
acid, has exceptionally high concentrations of ferulic acid and also serves as a source of
protocatechuic acid. Syringic acid was most prominent in the seeds. Although the total
flavonoid concentration in the Kei-apple was low, taxifolin and catechin were identified and the
seeds almost entirely accounting for these.
Conclusion: From this study it was concluded the Kei-apple is a rich source of antioxidant compounds
(polyphenols and ascorbate), with a strong antioxidant capacity, and hence may be associated
with health promotion properties, particularly in the prevention of cancer, cardiovascular disease,
and neurodegeneration. Additionally, due to the increased scientific and commercial interest in
this fruit, it is essential to take into consideration the various factors (agronomic, genomic, pre- and
post harvest condition and processing) and tissues. This might affect the chemical
composition of the final marketed product, which may play a significant role in determining the
polyphenol and ascorbate composition and bioactivity of these compounds during food
processing procedures. Hence, the polyphenol composition of the various fruit components
should be taken into consideration when selecting a method of fruit processing into the desired
end product. / Thesis (M.Sc. (Nutrition))--North-West University, Potchefstroom Campus, 2007.
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Chromatographic Behavior of Peptides Containing Oxidized Methionine in Reversed-phase Chromatography: Application to Cyclolinopeptides in Flaxseed Oil and Linear Tryptic PeptidesLao, Ying January 2014 (has links)
The thesis consists of two parts targeting the characterization of chromatographic behavior of linear tryptic and cyclic peptides containing oxidized methionine (Met) in reversed-phased chromatography. The retention order of methionine-containing peptide analogues was observed to be the same in both studies: Met oxide < Met dioxide < Met. For linear tryptic peptides, the magnitude of the retention time shift may vary dramatically: from –9 % to +0.36 % acetonitrile. Particularly, large negative retention time shifts are found mostly associated with methionine being in the hydrophobic face of an amphipathic helix. Contrary to previously reported observations, I demonstrate for the first time that methionine oxidation may increase peptide hydrophobicity, this occurs only when methionine is in the N3 position of the N-capping stabilization motif preceding an amphipathic helix. In the second study, the effect of peak splitting was observed for some Met oxide-containing cyclolinopeptides, which most likely appear due to diastereomerization.
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