Thesis (MScAgric)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: Red colour development on bi-coloured apples and pears ensures better prices for
producers. The use of postharvest irradiation to improve colour has been successful on
apples, and the objectives of this thesis were to optimise conditions during irradiation for
apples and to evaluate the effects of irradiation on pears.
'Cripp's Pink' apples responded to postharvest irradiation with high-pressure sodium
(HPS) lights by developing a red blush, whereas the response to irradiation with UV 8
plus incandescent lights was less effective. '8raeburn' apples held at -0.5°C for 4 or 8
weeks prior to irradiation showed a decrease in hue angle and an increase in
anthocyanin concentration after 72 hours of irradiation with HPS lamps. In 'Forelle'
pears treated in the same way, neither colour development nor anthocyanin synthesis
was affected by irradiation.
'8raeburn' and 'Cripp's Pink' apples picked weekly for 5 weeks until the optimum harvest
date were irradiated with HPS lights. A significant increase in fruit colour was only
measured in mature fruit of both cultivars.
'Cripp's Pink' apples were harvested from two production areas with different
microclimates, namely, Ceres and Grabouw, and stored for 0, 2 or 5 days at -0.5 °C
before irradiation for 120 hours at either 6°C or 20°C. Fruit from Ceres that were
irradiated immediately after harvest developed better colour at 6 °C than at 20°C. The
differences between fruit irradiated at the two temperatures were no longer significant
after 5 days of cold storage prior to irradiation. Fruit from Grabouw consistently
developed better colour when irradiated at 6°C than at 20°C. Colour development slightly after 5 days of cold storage prior to irradiation. In another experiment, fruit from
both areas were stored at -0.5°C for 20 days before irradiation at either 6°C or 6/20°C.
The fluctuating temperature regime resulted in decreases in hue angle of 70° and 65° for
the fruit from Grabouw and Ceres, respectively. The decreases were smaller (±200)
when fruit were irradiated at 6°C.
The hue angle value of well-coloured 'Cripp's Pink' apples held at 3rC under HPS lights
for 144 hours increased from 29.3° to 48.3°, and anthocyanin concentration decreased
from 739.9 IJg·g·1to 283.6 IJg·g·1. Control fruit held at the same temperature in the dark
did not show any change in hue angle value or anthocyanin concentration.
'Bon Rouge' and 'Red d' Anjou', two full red pear cultivars, irradiated with HPS lights for
72 hours, showed no significant changes in hue angle. 'Forelle' pears, harvested with or
without attached leaves, were irradiated with HPS at two temperature regimes, 20°C and
200/6°C. The resulting decreases in hue angle were attributed to yellowing and not red
colour formation.
In conclusion, the response of apples to postharvest irradiation was affected by maturity
and temperature, while pears failed to respond at all. / AFRIKAANSE OPSOMMING: Rooikleurontwikkeling van twee-kleur appels en pere verseker beter pryse vir die
produsente. Na-oesbestraling om kleur te verbeter is al suksesvol uitgevoer op appels,
en die doelwit van hierdie tesis was om die kondisies vir appels gedurende bestraling te
optimaliseer en om die effek van bestraling op pere te evalueer.
'Cripp's Pink' appels het reageer op na-oesbestraling met hoëdruk-natriumligte (HDN)
deur 'n rooi blos te ontwikkel, terwyl die reaksie op bestraling met UV-B plus
gloeilamplig minder effektief was. 'Braebum' appels opgeberg by -O.5aC vir 4 of 8 weke
voor bestraling het 'n afname in die kleurskakeringswaarde getoon, asook 'n toename in
antosianienkonsentrasie na 72 uur se bestraling met HDN ligte. 'Forelle' pere wat
dieselfde behandeling ontvang het, het geen kleurontwikkeling en geen
antosianienontwikkeling getoon na bestraling nie.
'Braebum' en 'Cripp's Pink' appels wat weekliks geoes is vir 5 weke tot die optimum
oesdatum is bestraal met HDN ligte. Slegs die volwasse vrugte van beide kultivars het
'n betekenisvolle toename in kleur getoon.
'Cripp's Pink' appels is geoes in twee produksie areas met verskillende mikroklimate,
naamlik Ceres en Grabouw. Vrugte is opgeberg vir 0, 2 of 5 dae by -O.5aC voor
bestraling vir 120 uur by of 6aC of 20aC. Vrugte van Ceres wat onmiddellik na oes
bestraal is het beter kleur ontwikkel by 6aC as by 20aC. Kleurontwikkeling by vrugte
bestraal by 6 of 20aC het nie verskil wanneer vrugte vooraf opgeberg was by -~5ac vir 5 dae nie. Vrugte van Grabouw het konstant beter kleur pntwikkel wanneer bestraling by
6°C eerder as 20°C plaasgevind het. In die volgende eksperiment, was beide die vrugte
van Ceres en Grabouw vir 20 dae opgeberg by -o.soC voor bestraling by 6°C of
6°/20°C. Die flukturerende temperatuur regime het afnames van 70° en 65° in
kleurskakeringswaarde getoon vir die vrugte van Grabouw en Ceres, respektiewelik.
Die afname was kleiner (±200)wanneer vrugte by 6°C bestraal is.
'Cripp's Pink' appels wat goed gekleur was en opgeberg is by 3rC terwyl dit blootgestel
is aan HDN ligte vir 144 uur, het 'n toename van 29.30 tot 48.3° getoon vir die
kleurskakeringswaarde, en antosianienkonsentrasie het afgeneem van 739 I'g.g-1 tot
283.6 I1g.g-1. Die kontrole vrugte opgeberg by dieselfde temperatuur in die donker het
geen verandering in beide die kleurskakeringswaarde of die antosianienkonsentrasie
getoon nie.
'Bon Rouge' en 'Red d' Anjou', twee volrooi peerkultivars, is bestraal met HDN ligte vir
72 uur en het geen betekenisvolle verandering in kleur getoon nie. 'Forelle' pere, geoes
met of sonder 'n aangehegte stingelsegment, is bestraal met HDN ligte by twee
verskillende temperatuur regimes, nl. 20°C of 20/6°C. Die afname in
kleurskakeringswaarde is aan vergeling toegeskryf eerder as aan rooikleurontwikkeling.
Ter opsomming, die reaksie van appels op na-oes bestraling is beïnvloed deur rypheid
en temperatuur, terwyl pere geen reaksie getoon het nie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/51878 |
| Date | 04 1900 |
| Creators | Marais, Evelyn |
| Contributors | Holcroft, D. M., Jacobs, G., Stellenbosch University. Faculty of Science. Dept. of Horticultural Sciences. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 131 p. : ill. |
| Rights | Stellenbosch University |
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