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Synthesis and selective derivatization of 1,2,4-triols as a model for fluorous tagging and separation of compounds in avocado oilChigondo, Fidelis January 2012 (has links)
M. Tech. Chemistry. / While there are existing methods for the analysis and authentication of avocado oil based on the composition of the saponifiable fraction, the projected growth in the market for avocado oil as heart healthy edible oil or for use in cosmetics and pharmaceuticals may lead some producers to cheat via adulteration with inferior vegetable oils of similar fatty acid composition. Thus new methods based on the analysis of the unsaponifiable fraction could be used to complement the existing methods of detecting undesirable additives. The aim is to develop a method of selective benzoylation of 1,2-diols and 1,2,4-triols based on the Martinelli protocol.
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Winter leaf yellowing in "Hass" avocadoMandemaker, Andries J. January 2007 (has links)
Thesis (M.Sc. Biological Sciences)--University of Waikato, 2007. / Title from PDF cover (viewed March 17, 2009) Includes bibliographical references (leaves 107-115)
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Chemical composition and vitamin B content of the Trapp and West Indian seeding avocados, varieties of the West Indian raceUnknown Date (has links)
May E. Winfield / Typescript / M.S. Florida State College for Women 1926 / Includes bibliographical references
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Management of avocado postharvest physiology.Blakey, Robert John. January 2011 (has links)
Avocados are an important horticultural crop in South Africa, especially in the provinces of
KwaZulu-Natal, Mpumalanga and Limpopo. The distance to traditional export markets,
phytosanitary restrictions to lucrative markets such as China, the USA and Japan and
increased competition in the European market have challenged the South African avocado
industry. The industry has responded with improved logistics and shipping, a co-ordinated
market access program and a global system to co-ordinate exports of avocados to the
European market. To remain competitive on the global market, further improvements and
innovations are required to improve the efficiency of postharvest operations. These
improvements and innovations should be guided by a greater understanding of postharvest
physiology. Avocados are a relatively new export crop, so there is still much to be learnt about
avocado postharvest physiology and the optimisation of postharvest management. In this
regard, reduced temperature storage (1°C) and modified humidity packaging (MHP) were
investigated for their effect on fruit physiology and quality, the effect of a water- and ABA-infusion
on ripening was examined and the effect of a cold chain break on fruit physiology and
quality determined; near-infrared spectroscopy was also examined for its potential for its use
in the avocado industry.
As an initial study, the relationships between individual sugars, protein and oil were
studied to understand the changes in avocado fruit during ripening. It was found that
mannoheptulose and perseitol were the predominant sugars at harvest, but declined to very
low levels during the first 10 days postharvest. The concentrations of glucose and fructose
increased, while sucrose declined slightly during ripening. The concentration of protein
increased sigmoidally during ripening, reflecting the increase in the ripening enzymes,
particularly cellulase and polygalacturonase. The oil content fluctuated slightly during
ripening. It is suggested that mannoheptulose and perseitol are important carbon and energy
sources during ripening. Glucose concentration was also found to increase earlier in fast
ripening fruit compared to slow ripening fruit, which is related to increased cellulase activity
and may be related to the ABA functioning.
Thereafter, storage and ripening trials in two consecutive seasons showed that 1°C
storage and the use of MHP for 28 days reduced mass loss, water loss, ethylene production,
respiration, softening and heptose consumption, without appreciably affecting fungal rots,
physiological disorders or external chilling injury, compared to fruit stored at 5.5°C and
regular atmosphere respectively. Also, the storage of fruit in MHP delayed the rise in the
activity of cellulase during ripening, compared to fruit not stored in MHP, but there was no
significant difference in the peak activity of cellulase, polygalacturonase or pectin
methylesterase.
In a separate experiment, fruit ripening was significantly affected by the infusion of ABA
in an aqueous solution. Water slightly reduced the variation in ripening while ABA reduced
the time to ripening and the variation; it is suggested that water stress and ABA are
intrinsically involved in the ripening processes and may act as a ripening trigger. The water
concentration in fruit was measured non-destructively using reflectance NIR; this model was
used to determine the maturity of fruit and the loss of water during cold storage.
In the cold chain break experiment, it was found that although fruit recovered after a
cold chain break, in terms of ethylene production and respiration, there was a loss in quality
because of severe shrivelling as a result of increased water loss. Fruit that were stored at 1°C
were generally of a better quality at ripeness, if the cold chain was broken, compared to fruit
stored at 5.5°C. In a follow-up experiment, it was found that significant changes occurred in
avocado physiology over a 6h period. The respiration rate of fruit significantly increased after
4h at room temperature and mannoheptulose declined by 32% in control fruit and by 16% in
ethephon-treated fruit after 6h. This demonstrates the potential for quality loss in a short
amount of time.
Furthermore, a model of avocado ripening is proposed, outlining the role of water, ABA,
ethylene, respiration, ripening enzymes and individual sugars. This study has contributed to
the understanding of avocado postharvest physiology and should aid in better management of
avocados for improved fruit quality and consumer satisfaction. / Thesis (Ph.D.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.
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Enhancement of 'Hass' avocado shelf life using ultra-low temperature shipping or 1-MCP treatment and cold chain management.Kok, Richard Dean. January 2011 (has links)
Avocados are becoming an increasingly important crop in South Africa, where the main producing areas include Limpopo, Mpumalanga and KwaZulu-Natal provinces. The South African avocado industry faces considerable challenges including increasing competition exporting avocados, particularly to the European market. The processes involved to export avocados has markedly improved over the past two decades, however there is always room for improvement and it is necessary to remain competitive on a global scale. Issues such as fruit being partially soft on arrival, quality defects and cold chain management breakdown are still present. It is necessary to investigate new aspects of cold storage such as extending the storage period and understanding the physiological aspects involved. To improvement such issues, an investigation was conducted on ultra-low temperature shipping (1°C) as well as the use of 1-MCP; the implementation of deliberate cold chain breaks to achieve a better understanding as to the quality influences involved; an extended storage period of 56 days to assess the quality issues and benefits involved; as well as investigating the physiological aspects involved with all above treatments on 'Hass' avocados. An initial study saw early-, mid- and late-season 'Hass' avocados stored at 1°C or 5.5°C for 28 days. Additional treatments included fruit treated and not treated with 1-MCP as well as waxed and unwaxed fruit. Storage at 1°C was comparable with 1-MCP treatment for both fruit softening in storage and extending the ripening period. Storage at 5.5°C resulted in partial in-transit ripening, if 1-MCP was not used. Early-season fruit incurred the most external chilling injury but overall levels were minimal and not concerning. Mid-season fruit were the most sound in terms of quality. It is suggested that 1°C can be used as a viable economic alternative to 1-MCP for long distance shipping of 'Hass' up to 28 days. The cold chain break trial included a 24 hour delay before cold storage, a deliberate 8 hour break at day 14 of cold storage where fruit were removed from cold storage and a control of 28 days cold storage where no break was involved. Early-, mid- and late-season 'Hass' avocados were stored at 1°C or 5.5°C for 28 days. Additional treatments included fruit treated and not treated with 1-MCP as well as waxed and unwaxed fruit. It was found that cold chain breaks do influence the amount of water loss, fruit softening and days taken to ripen. Storage at 1°C did not entirely negate the effects of cold chain breaks compared with 5.5°C, but did result in fruit which were harder at the end of storage and took longer to ripen. The use of 1-MCP also had advantageous effects with respect to significantly lengthening the ripening period, even when a cold chain break occurred, compared with fruit not treated with 1-MCP. As results of the study differed in some respects to those of previous studies, it is recommended that further work be conducted to determine what fruit or pre-harvest factors affect the fruit physiological changes which take place when cold chain breaks occur. Having the option to make use of an extended storage period would be of benefit to the industry if delays occur and fruit have to be maintained under cold storage. Extended storage of South African avocados, especially at the end of the season would also allow for the option of strategically holding back fruit from the export market in order to extend the supply period. It would not only benefit export options, but would also be highly beneficial to local pre-packers, as it would reduce the need to import fruit from the Northern hemisphere production areas during the South African off-season. Early-, mid- and late-season 'Hass' avocados were stored at 1°C or 5.5°C for 56 days. Additional treatments included fruit treated and not treated with 1-MCP as well as waxed and unwaxed fruit. The combination of 1°C with the use of 1-MCP resulted in a good shelf life as well as maintenance of internal quality and integrity. External chilling injury is of concern for early-season fruit, however, mid- and late-season fruit did not incur extensive damage. It is, therefore, advised that fruit placed in extended storage are marketed through the 'Ready ripe' program to mask any chilling injury on the 'Hass' fruit. Avocados are renown as a "healthy food" due to their nutritional value as well as containing relatively high concentrations of antioxidants. The fruit also contain high amounts of C7 sugars which can act as antioxidants. Additionally, C7 sugars and other antioxidants play important roles in fruit quality. Therefore, it is important to understand how varying storage conditions and treatments affect the levels of these physiological parameters. Treatments of cold chain break/delay included a deliberate 8 hour break at day 14 of cold storage where fruit were removed from cold storage, a 24 hour delay before cold storage and a control of 28 days where no break was involved. A 56 day extended storage period was also used. Early-, mid- and late-season 'Hass' avocados were stored at 1°C or 5.5°C for 28 days. Additional treatments included fruit treated and not treated with 1-MCP as well as waxed and unwaxed fruit. The use of 1-MCP maintained higher levels of antioxidants, ascorbic acid and C7 sugars for both the 28 day and the 56 day storage periods. The 24 hour delay had a
tendency to increase consumption of anti-oxidant and sugar reserves. The use of 1°C resulted in antioxidant and ascorbic acid levels decreasing while maintaining higher sugar levels. Overall, high stress imposed on fruit decreased reserves resulting in poor quality fruit. The use of 1°C and 1-MCP treatments maintained fruit quality. / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.
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Effect of postharvest silicon application on 'hass' avocado (Persea americana Mill.) fruit quality.Kaluwa, Kamukota. January 2010 (has links)
The South African avocado industry is export-orientated with forty percent of total
production sold overseas. The avocado fruit is a highly perishable product with a
relatively high rate of respiration which results in the quick deterioration of fruit
quality. Good phytosanitary procedures are a necessity in ensuring good product
quality. Due to the threat of pests and diseases becoming resistant to the
conventional chemicals currently used to control them, there has been a great
need to diversify from their usage.
Silicon (Si), being the second most abundant element (28%) in the earth’s crust
after oxygen, is a major constituent of many soils and has been associated with
disease resistance in plants for a long time. It has been used in a number of crop
species to provide resistance against pathogenic agents. In some horticultural
crops Si has been found to offer protection against fungal infections by
strengthening cell walls, thus making it more difficult for the fungi to penetrate and
colonize the plant. The aim of this research was to investigate the effects of postharvest
silicon application on the quality of ‘Hass’ avocado fruit. The specific
objectives included investigating the effect of silicon on the ripening pattern as well
as the metabolic physiology of the avocado fruit.
Avocado fruit were obtained from two locations in the KZN Midlands (Everdon
Estate in Howick and Cooling Estate in Wartburg). Fruit were treated with different
forms of Si (potassium silicate (KSil), calcium silicate (CaSil), sodium silicate
(NaSil) and Nontox-silica® (NTS)) at concentrations ranging from 160 ppm to 2940
ppm. After dipping for 30 minutes in the silicon treatments, the fruit were stored at
-0.5°C, 1°C, 5°C or at room temperature (25°C). Energy dispersive x-ray (EDAX)
analysis was then conducted on the exocarp and mesocarp tissues to determine
the extent of silicon infiltration within each treatment. Firmness measurements,
ethylene evolution and CO2 production were recorded as fruit approached
ripening. The CO2 production of fruit that were stored at room temperature was
analysed daily until they had fully ripened, while fruit from cold storage were
removed weekly to measure respiration. Mesocarp tissue from each fruit was
extracted using a cork borer and subsequently freeze-dried and stored for
physiological analysis. The freeze-dried mesocarp tissue was then finely ground
and later analysed for sugar content, total anti-oxidant capacity (TAOC), total
phenolic (TP) content and phenylalanine ammonia lyase (PAL) activity using their
respective assays. Statistical analyses were carried out using GenStat® version
11 ANOVA. Treatment and storage temperature means were separated using
least significant differences (LSD) at 5% (P = 0.05). The experimental design in
this study was a split-plot design with the main effect being storage temperature
and the sub-effect being treatments. Each replication was represented by a single
fruit.
EDAX analysis revealed that Si passed through the exocarp into the mesocarp
tissue in fruit treated with high concentrations of silicon, i.e., KSil 2940 ppm.
Significant differences (P < 0.001) were observed in temperature means with
regards to firmness. Fruit treated with KSil and NTS only and stored at 5°C were
firmer than fruit stored at other temperatures. Fruits treated with Si in the form of
KSil 2940 produced the least amount of CO2, while non-treated fruits (Air) had the
highest respiration rate. Fruit stored at room temperature (25°C) produced
significantly higher amounts of CO2 and peaked much earlier than fruit stored at
other temperatures. Ethylene results showed that there were differences (P <
0.05) between temperature means with the highest net ethylene being produced
by fruit stored at 25°C. There were also significant differences amongst treatment
means (P < 0.001), with fruits treated with KSil 2940 ppm producing the least
ethylene.
There were significant differences (P < 0.001) in temperature means with regards
to the total phenolic concentration with fruits stored at 1°C having the highest TP
concentration (26.4 mg L-1 gallic acid). Fruit treated with KSil 2940 ppm had the
highest total phenolic concentration whilst the control fruit (Air and Water) had the
lowest. There were also differences (P < 0.05) in storage temperature means with
respect to the total antioxidant capacity. Fruit stored at -0.5°C had the highest
TAOC (52.53 μmol FeSO4.7H2O g-1 DW). There were no significant differences in
TAOC (P > 0.05) with regards to treatment means although fruit treated with KSil
2940 ppm and stored at -0.5°C showed the highest TAOC of 57.58 μmol
FeSO4.7H2O g-1 DW. With regards to the concentration of major sugars in
avocado, mannoheptulose and perseitol (mg g-1), no significant differences (P >
0.05) were observed in temperature means. However, fruit stored at -0.5°C had
the highest concentration of these C7 sugars compared with fruit stored at other
temperatures. There were significant differences in treatment means (P < 0.001)
showing that fruit treated with KSil 2940 ppm had the highest concentration of both
mannoheptulose (18.92 mg g-1) and perseitol (15.93 mg g-1) in the mesocarp
tissue.
Biochemical analyses showed differences (P < 0.05) in storage temperature
means with respect to PAL enzymatic activity. Fruit stored at 5°C had the highest
PAL activity (18.61 mmol cinnamic acid g-1 DW h-1) in the mesocarp tissue
compared with fruit stored at other temperatures. There were significant
differences in treatment means (P < 0.001) with regard to PAL activity. Fruit
treated with KSil 2940 ppm had the highest PAL activity (23.34 mmol cinnamic
acid g-1 DW h-1).
This research has demonstrated the beneficial effects, particularly applications of
2940 ppm Si in the form of KSil. This treatment successfully suppressed the
respiration rate of avocado fruit. Biochemical analyses of total antioxidants, total
phenolics and PAL activity in the mesocarp tissue have shown the usefulness of Si
in improving the fruit’s metabolic processes. The C7 sugars (D-mannoheptulose
and perseitol) also seem to be more prevalent in avocado fruit treated with Si
(particularly KSil 2940 ppm) than in non-treated fruit. This suggests that an
application of Si to avocado fruit can aid in the retention of vital antioxidants (C7
sugars). / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.
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Evaluation of edible films and coatings for extending the postharvest shelf life of avocadoMaftoon Azad, Neda. January 2006 (has links)
No description available.
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Evaluation of edible films and coatings for extending the postharvest shelf life of avocadoMaftoon Azad, Neda. January 2006 (has links)
The focus of this thesis is to develop pectin-based edible films for application of fruits and vegetables to extend their post harvest shelf life. Preliminary research demonstrated that edible coatings could effectively extend the shelf life of based avocado and peach. The respiration rate, moisture loss, firmness, chemical parameters and color changed in a lower rate in coated fruits as compared with the control. Pectin-based film formulations were then evaluated to identify the proper type and concentration of pectin, lipids and plasticizers in the film. The effects of pectin, beeswax and sorbitol concentration on water vapor permeability, mechanical properties and opacity of the films were then evaluated using response surface methodology to identify appropriate levels of different components. Results of studies on film structure revealed that water vapor permeability increased by pectin and sorbitol concentration and was decreased by beeswax concentration. Mechanical properties were mainly affected by pectin and sorbitol concentration. Beeswax was the most influential factor that affected opacity which increased with increasing beeswax concentration. / In order to successfully employ these films, their adsorption behavior, thermal and thermomechanical properties were evaluated as a function of moisture content and sorbitol concentration. The adsorption behavior was strongly influenced by sorbitol concentration. Moisture content and sorbitol concentration increased the films elongation at break, but decreased tensile strength, modulus of elasticity and Tg, and increased water vapor permeability of the films. Finally, avocado was coated with a pectin-based film and the associated quality changes were evaluated during storage. From storage studies, kinetic parameters (rate constants) and activation energy were quantified to help model the quality changes in avocado quality as function of storage temperature and time. Pectin-based coating resulted in slowing down the rate of quality changes in avocado at each storage temperature. In general, most changes were well described by some form of zero or first order rate. Temperature sensitivity of rate constant was adequately described by the Arrhenius model. / A hyperspectral imaging technique was also used to gather additional tools for following quality changes associated with stored avocados. Artificial neural network (ANN) concepts were evaluated as alternated models for predicting quality changes in coated and non-coated avocados during storage at different temperature. Modeling of quality changes in avocado indicated that compared to conventional mathematical models, ANN has more feasibility to predict of these changes. Models developed for firmness, weight loss and total color difference had better fitness than respiration rate. / Finally, the effect of coating on disease severity and different properties of avocados infected by Lasiodiplodia theobromae was studied. The coated fruits demonstrated slower rate of disease progress, respiration rate, softening and color changes. Respiration rate, firmness and color parameters were sensitive to coating and disease severity, and thus these parameters could successfully used to predict fruit quality from disease in coated and uncoated avocados.
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Measuring the effectiveness of research and development on avocado, Persea Americana Mill, in South AfricaDe Graaf, Johan 05 May 2011 (has links)
No research method has yet been identified to best measure South African avocado R&D effectiveness. The research question was which criteria were best in measuring R&D effectiveness and what was the level of satisfaction with these criteria.
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Measuring the effectiveness of research and development on avocado, Persea Americana Mill, in South AfricaDe Graaf, Johan 05 May 2011 (has links)
No research method has yet been identified to best measure South African avocado R&D effectiveness. The research question was which criteria were best in measuring R&D effectiveness and what was the level of satisfaction with these criteria.
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