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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/16456 |
| Date | 12 1900 |
| Creators | Van Wyk, Angelique A. (Angelique Ann) |
| Contributors | Barry, G.H., Huysamer, M., University of Stellenbosch. Faculty of Agrisciences. Dept. of Horticulture. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | viii, 128 leaves : ill. (some col.) |
| Rights | University of Stellenbosch |
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