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REGULATION OF DEGREENING AND REGREENING OF CITRUS PEEL WITH SELECTED CARBOHYDRATE AND NITROGEN COMPOUNDS IN VITRO.Ahmed, Omer Khidir January 1986 (has links)
The regulation of citrus fruit color by various concentrations of sugars, sugar metabolites, and nitrogen compounds was investigated in peel segments of Citrus paradisi Macf. (cv. Marsh) cultured on modified media of Murashige and Tucker. Green and yellow peel segments were cultured for degreening and regreening studies, respectively, and chlorophyll level in the individual peel segments was measured with a reflectometer. Degreening was significantly promoted by 150 mM sucrose, 300 mM glucose and fructose, or 50 mM citrate but not by 300 mM of the hexoses galactose and mannose, 300 mM of the pentoses xylose and ribose, or 25, 50, and 100 mM succinate. Regreening was significantly inhibited by 150 mM sucrose, 300 mM glucose and fructose, or 50 mM citrate and malate. Succinate and α-ketoglutarate at concentrations of 50 mM did not inhibit regreening. The inhibition of regreening by 300 mM sucrose was reduced by 33 percent with the glycolytic inhibitor iodoacetic acid at 1 mM but not by DL-glyceraldehyde at 50 mM. Neither ethanol nor potassium bicarbonate inhibited regreening, suggesting that the regulation of citrus fruit color is specific to sugars or sugar metabolites. However, pyruvate did not promote degreening or inhibit regreening because it was probably not absorbed from the media by the flavedo of the peel. These results suggest that sucrose, glucose, fructose, and citrate maintain carotenoid synthesis and accumulation in both cultured green and yellow peel segments but cause the loss of chlorophyll from green peel segments. Treatment of either the green or yellow segments with sucrose or citrate may increase the partitioning of these compounds into the mevalonic acid pathway to provide carbon for synthesis or carotenoids, resulting in degreening of the green peels and maintaining the yellow color in the yellow peels. Malonate inhibited regreening when incorporated in media at concentrations of 4 mM. This inhibition was reversed by 60 mM glutamine but not by 5 mM glutamine or KNO₃. The action of malonate on regreening may be a specific effect of malonate on plastid development rather than by modifying the partitioning of sugar metabolites into the carotenoid synthetic pathway.
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AN IN VITRO STUDY OF THE EFFECT OF GIBBERELLIC ACID ON DEGREENING AND REGREENING OF CITRUS FRUIT.Garray, Hamad Elnill Bashir. January 1984 (has links)
No description available.
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A study of introduced clones of sweet orange (Citrus sinensis) and postharvest degreening of 'Valencia late' oranges in Kenya /Kiuru, Paul D. N. (David Ngugi) January 1994 (has links)
The performance of eleven 'Valencia Late' and nine 'Washington Navel' orange (Citrus sinensis) clones all on rough lemon (Citrus jambhiri) rootstock was evaluated. Significant differences in trunk cross sectional area, plant canopy volume, cumulative yield and yield efficiency were found between clones of different citrus cultivars. Some clones such as VL106, VL139, VL185 and WN204 appeared to be promising in terms of good growth characteristics and high yield, and could therefore be used for the national performance trials. Studies on post-harvest degreening of 'Valencia Late' oranges were also carried out at Matuga Regional Research Sub-Centre (Kenya) in a series of experiments. Fully mature fruits were dipped for three minutes in 0, 500, 1000, 1500, 2000, 2500 and 3000 ppm concentrations of ethephon. Fruits wrapped in aluminum foil shrivelled less and retained their firmness and freshness. Rind brightness increased by dipping of fruits in ethephon (2000) ppm giving a good colour change. Dipping fruits a second time three days after the first dip did not have any significant effect on colour change. (Chemical names used: (2-Chloroethyl)phosphonic acid (ethephon).
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A study of introduced clones of sweet orange (Citrus sinensis) and postharvest degreening of 'Valencia late' oranges in Kenya /Kiuru, Paul D. N. (David Ngugi) January 1994 (has links)
No description available.
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Preharvest manipulation of rind pigments of Citrus spp.Le Roux, Smit 12 1900 (has links)
Thesis (MscAgric (Horticulture))--University of Stellenbosch, 2006. / Rind colour is one of the main cosmetic preferences consumers use when purchasing citrus
(Citrus spp.) fruit. To enhance the cosmetic quality of citrus fruit, attempts were made to
stimulate preharvest chlorophyll degradation and carotenoid biosynthesis to obtain a deeper,
more uniform, orange rind colour in early-maturing citrus cultivars. As part of a larger study
to stimulate rind colour enhancement, an initial study was conducted on ‘Eureka’ lemon [C.
limon (L.) Burm. f.] nursery trees to determine the concentration of various gibberellin
biosynthesis inhibitors required to obtain a biological response in citrus trees, as measured by
vegetative growth. Thereafter, different concentrations of prohexadione-calcium (ProCa;
Regalis®) were applied at various stages of fruit development on early-maturing citrus
cultivars to establish the concentration and timing of ProCa required to improve rind colour
by enhancing chlorophyll degradation and carotenoid biosynthesis. In addition, a search to
enhance rind colour development of early-maturing citrus cultivars was conducted by
screening various nutritional, hormonal and possible physiological stress-inducer products
and some combination treatments thereof.
Multiple applications of gibberellin biosynthesis inhibitors on ‘Eureka’ lemon nursery trees
significantly reduced internode length and hence vegetative growth. Regalis® applied at 4 to
8 g·L-1 and Sunny® (uniconazole) applied at 10 to 20 mL·L-1 had the greatest effect in
reducing internode length, and were therefore identified as potential candidates for further
field studies to test their effect on rind colour enhancement of citrus fruit.
The late, double applications (6 plus 3 weeks before anticipated harvest) of ProCa applied at
400 mg·L-1 consistently improved rind colour of all Citrus spp. tested. However, these effects were more pronounced after harvest, as ethylene degreening and cold-storage stimulated
additional chlorophyll degradation, unmasking the carotenoids, resulting in overall better
coloured fruit. In most instances in this study, ProCa stimulated chlorophyll degradation
allowing the underlying carotenoids to be expressed. Therefore, the improvement of rind
colour of citrus fruit following the application of a gibberellin biosynthesis inhibitor (400
mg·L-1 ProCa applied 6 plus 3 weeks before harvest) supports the hypothesis that there may
be a relationship between vegetative vigour and rind colour development of citrus fruit.
Preharvest applications of boric acid, Thiovit® (elemental sulphur), ammonium thiosulphate
(ATS) and half the recommended rate of Ethrel® (48% ethephon) in combination with
Thiovit® and ATS stimulated chlorophyll degradation in both orange- and yellow-rinded
fruit, and ColourUp® (neutralised calcium carbonate) and Figaron® (ethyclozate) stimulated
chlorophyll degradation only in orange-rinded fruit. Boric acid and the Thiovit®-ATSEthrel
® combination treatment stimulated carotenoid biosynthesis in orange-rinded fruit,
thereby improving the carotenoid to chlorophyll ratio. The screening of chemical products
which stimulate chlorophyll degradation in combination with chemical products which
stimulate carotenoid biosynthesis warrants further evaluation.
Worldwide, research on rind colour improvement has received attention for several decades,
particularly during the 1980s. Yet, rind colour still remains a problem at the beginning of
certain seasons. In the present study, the approach to improving rind colour was to manipulate
rind pigments through the reduction of vegetative vigour, which was hypothesised to be an
antagonist of chloro-chromoplast transformation. To this end, the preharvest application of
prohexadione-calcium stimulated chlorophyll degradation and carotenoid biosynthesis in
citrus fruit rinds. Furthermore, preharvest applications of various chemical products provides a novel approach to stimulate chlorophyll degradation and carotenoid biosynthesis. Together,
the results of this study provide potential commercial treatments that will result in deeper,
more uniform orange rind colour, thereby meeting consumer needs.
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Time-temperature interaction on postharvest rind colour development of CitrusVan Wyk, Angelique A. (Angelique Ann) 12 1900 (has links)
Thesis (MScAgric)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Rind colour is one of the most important external quality characteristics of citrus fruit and
plays an important role in purchasing decisions by consumers. Consumers perceive brightlycoloured
fruit to be sweet and mature, whereas citrus with a green rind is perceived to be sour
and immature. However, there is a poor correlation between rind colour and internal quality,
contradicting what is generally assumed by the fruit-buying public. In general, a bright
orange rind colour improves consumer acceptance. Thus, it is important to ensure that the
rind of citrus fruit is well-coloured on arrival at the market.
Various pre-harvest cultural practices and postharvest techniques can be applied to improve
rind colour. Degreening with ethylene gas is the most commonly used postharvest technology
to improve rind colour, but has various negative side-effects. Degreened fruit are more prone
to decay, have rinds which appear dull and flaccid, have been reported to develop off-flavours
and have a shorter shelf-life period. Therefore, it is necessary to find alternatives to ethylene
degreening and to extend shelf-life of citrus fruit.
Under normal orchard conditions, rind colour development is associated with low night
temperatures, usually experienced during autumn or following the passing of a cold front. To
simulate cold front conditions, a hydrocooler and cold room were used to rapidly drop fruit
temperature to 4 ºC for 6 hours, and then fruit were incubated at 20 to 22 ºC for 72 hours.
This “cold shock” treatment of ‘Nules Clementine’ mandarin improved rind colour to a level
similar to that of degreened fruit in the 2002 season due to a decrease in chlorophyll content
and increase in carotenoid content. However, this result could not be repeated. Storage temperature is one of the most important postharvest factors affecting rind colour.
Citrus fruit shipped to export markets requiring low temperatures (-0.6 ºC) for pest
disinfestations purposes have been reported to arrive with poor rind colour. Shipping under
low temperatures results in poor rind colour of fruit on arrival in the market. To comply with
the USA’s phytosanitary requirement for imported citrus, fruit is held at -0.6 ºC for a
minimum of 22 days. The effect of shipping at various temperatures (-0.6 ºC or 4.5 ºC),
durations and the influence of initial rind colour, “orange” or “yellow”, on fruit colour upon
arrival in the market was evaluated. Fruit shipped at a higher temperature (4.5 ºC) had a
marginally better rind colour than fruit shipped at -0.6 ºC. The perceived loss of rind colour
following shipping at sub-zero temperatures is probably due to carotenoid degradation.
Therefore, initial rind colour plays a critical role in final product quality. Depending on
market destination and shipping temperature, pale-coloured fruit should not be packed for
markets sensitive to rind colour.
Holding temperature after shipping can be effectively used to improve the rind colour of fruit
arriving in the market with undesirable rind colour. An intermediate holding temperature of
between 11 and 15 ºC resulted in the greatest improvement in rind colour after 2 weeks. A
high holding temperature (20 ºC) caused colour degradation, whereas a low holding
temperature (4.5 ºC) resulted in the maintenance of rind colour. By selecting the correct
holding temperature, even after shipping at sub-zero temperatures, final colour can be
improved. / AFRIKAANSE OPSOMMING: Tyd-temperatuur interaksie op na-oes skilkleur ontwikkeling by sitrus
Skilkleur is een van die belangrikste eksterne kwaliteitseienskappe van die sitrusvrug en spëel
ʼn belangrikke rol in wat verbruikers koop. Verbruikers verwag dat heldergekleurde vrugte
soet en ryp sal wees, terwyl sitrus met ʼn groen skil geassosieer word met onrypheid en ʼn suur
smaak. In teenstelling hiermee is daar egter ʼn swak korrelasie tussen skilkleur en interne
kwaliteit. Aangesien ʼn heldergekleurde oranje skil verbruikersaanvaarding verbeter, is dit dus
belangrik om te verseker dat die sitrusvrug ʼn goeie skilkleur het teen die tyd wat dit die mark
bereik.
Verskeie voor-oes bestuurspraktyke en na-oes tegnieke kan toegepas word om die skilkleur te
verbeter. Ontgroening met etileen gas is die tegnologie wat mees algemeen gebruik word om
skilkleur na oes te verbeter, maar dit het egter verskeie newe effekte tot gevolg. Ontgroende
vrugte is meer vatbaar vir bederf en verwelkde skille met ʼn dowwe voorkoms. Afsmaake kan
voorkom en ʼn verkorte rakleeftyd is al gerapporteer. Dit is dus noodsaaklik om ʼn alternatief
vir etileen ontgroening te ontwikkel en die rakleeftyd van sitrusvrugte te verleng.
Onder normale boordomstandighede word skilkleur ontwikkeling geassosieer met lae nag
temperature wat gewoonlik in die herfs of na ʼn kouefront ondervind word. Om soortgelyke
omstandighede na te boots, was ʼn “hydrocooler” en koelkamers gebruik om die temperatuur
vinnig te laat daal tot by 4 °C en dit vir 6 uur daar te hou. Die vrugte was dan by 20 tot 22 °C
geinkubeer vir 72 uur. Hierdie “koueskok” behandeling van ‘Nules Clementine’ mandaryn
het skilkleur verbeter tot ʼn vlak vergelykbaar met ontgroende vrugte in die 2002 seisoen wat ontstaan het weens ʼn verlaging in chlorofil en ʼn toename in die karotinoïed inhoud van die
skil.
Opbergingstemperatuur is een van die belangrikste na-oes faktore wat skilkleur beinvloed.
Sitrusvrugte wat verskeep word na uitvoermarkte wat lae temperature (-0.6 °C) vir
disinfestasie vereis arriveer soms by die mark met ʼn swak skilkleur. Om die fitosanitêre
vereistes vir die invoer van sitrus deur die VSA na tekom, was vrugte vir ʼn minimum van 22
dae by -0.6 °C gehou. Die effek van verskeping by verskeie temperature (-0.6 °C of 4.5 °C),
tydperke en die invloed van aanvanklike skilkleur, “oranje” of “geel” was geevalueer by
aankoms in die mark. Vrugte wat by hoër temperature (4.5 °C) verskeep was het ʼn effens
beter skilkleur as vrugte by -0.6 °C getoon. Die verlies in skilkleur wat waargeneem word na
verskeping onder vriespunt kan moontlik toegeskryf word aan karotenoiëd afbraak. Daarom
speel aanvanklike skilkleur ʼn kritieke rol in finale produk kwaliteit. Die finale mark
bestemming en verskepingstemperatuur sal bepaal of swakgekleurde vrugte verpak kan word.
Opbergingstemperatuur na verskeping kan effektief gebruik word om die skilkleur van vrugte
wat swak gekleur was met aankoms by die mark te verbeter. Matige temperature tussen 11 en
15 °C het na 2 weke die beste verbetering in skilkleur gelewer. Hoër temperature (20 °C) het
skilkleur nadelig beinvloed, terwyl lae temperature skilkleur behou het. Deur die korrekte
temperatuur te kies, selfs na verskeping by temperature onder vriespunt, kan uiteindelike
skilkleur steeds verbeter word.
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