Thesis (MSc)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: 'Forelle' is one of three blushed pear cultivars produced in South Africa. A mandatory
minimum cold storage duration of 12 weeks at -0.5°C to ensure even ripening,
prevents 'Forelle' from being marketed earlier. Since earlier marketing can result in
premium prices (in excess of 50% morê per carton) research in recent years has been
directed at reducing this 12 week cold storage period. Intermittent warming
treatments, controlled atmosphere (CA) storage in combination with regular
atmosphere (RA) storage intervals, and ethylene treatments, have been tested as
alternatives to the 12 week cold requirement. However, none of these treatments
delivered a better internal quality in terms of mealiness and astringency.
Fruit harvested from the Warm Bokkeveld and Theewaterskloof areas at commercial
maturity were stored at -0.5°C for up to 21 and 22 weeks, respectively, to understand
the changes in ripening and mealiness of 'Forelle' pears after cold storage (Paper 1).
Samples were removed every third weev, placed at 15°C, and maturity factors, total
ACC concentration, ethylene production and respiration rates monitored every third
day for 12 days. Fruit from the Warm Bokkeveld and the Theewaterskloof areas
ripened after 6 and 7 weeks at -0.5°C, respectively. However, after 6 weeks of cold
storage followed by 6 days at 15°C, all fruit harvested in the Warm Bokkeveld, and
70 % of the fruit harvested in the Theewaterskloof area, were mealy. With extended
storage at -0.5°C (> 15 weeks) the incidence of mealiness declined in fruit from both
areas, but never disappeared, when evaluated at 15°C over 12 days.
Since harvest maturity affects the incidence of mealiness in other pear cultivars, the
effect of harvest maturity on 'Forelle' pears with regard to mealiness development
was examined (Paper 2). Fruit were harvested from the Ceres area, in weeks 8 (preoptimum),
10 (optimum), 12 and 14 (both post optimum). Maturity indices, juice
content, mealiness, total ACC content, ethylene production and internal ethylene were
monitored at harvest, after 6 weeks of storage at -0.5°C and again after 7 days at
15°C. Fruit harvested 2 weeks before commercial harvest (week 8) had the highest
total ACC concentration, ethylene production and the potential to ripen, but also
developed the highest incidence of mealiness (80%). However, fruit of all harvest
maturities (except where contamination with 1-MCP occurred) were mealy. It would appear that factor(s), other than harvest maturity, play a more important role in the
initiation of mealiness in 'Forelle' pears.
Although ethylene has been shown to shorten the cold requirement of 'Forelle', there
are conflicting reports as to its effectiveness in reducing mealiness. Consequently, the
aim of the third paper was to evaluate the effect of ethylene on ripening and mealiness
of 'Forelle' pears. Fruit harvested from the Elgin area at commercial maturity were
stored for 3 weeks at -0.5°C, treated with ethylene (100 Jl L.L·l
, 24h, 20°C) and held at
20°C for a further 2 days (without ethylene). Control fruit were held at 20°C for 3
days. Fruit were returned to -0.5°C for a further 3 weeks. After a subsequent 3 days at
20°C, flesh firmness was 4.6 kg in treated fruit compared to 6.1 kg for control fruit.
At this point all fruit treated with ethylene were mealy. Control fruit all exhibited
mealiness after a further 3 weeks at -0.5°C followed by 7 days at 15°C. Ethylene
treatment advanced fruit maturity, but did not prevent or alleviate mealiness.
Mealiness is a textural disorder recognized by a dry soft pulp. This has previously
been recorded in 'd'Anjou' pears, as a result of storing the fruit for too long at -1.1°C,
but has also been the result of a chilling injury in fruit like nectarines, kiwi and
persimmon. The role of storage temperature on ripening, and specifically mealiness,
of 'Forelle' was thus investigated (Paper 4). Fruit harvested from the Elgin area at
commercial maturity were stored at -0.5°C, 4.0°C and 7.5°C for 0, 3 and 6 weeks.
Samples were removed every third week, placed at 15°C, and maturity indices,
extractable juice content, mealiness, total ACC content, internal ethylene
concentration and ethylene production were monitored on removal and after 7 days.
Flesh firmness of the 4°C stored fruit was 0.5 kg lower than fruit stored at -0.5°C, on
removal from storage. Fruit stored at 4°C and 7.5°C ripened with little to no
mealiness (0 and 8% respectively) in contrast to fruit stored at -0.5°C (70% mealy).
Total ACC accumulation and ethylene production were higher for fruit stored at 4°C
and 7.5°C than fruit stored at -0.5°C. Storage temperature appears to playa role in the
development of mealiness.
Although storage temperatures influenced mealiness development, this research
should be repeated before this can recommended as a commercial treatment. The underlying mechanism of action in the development of mealiness should be
investigated.
By examining fruit grown in different climatical areas, harvested at different
maturities, treated with exogenous ethylene and stored at different temperatures, this
research has helped to a better understanding of the role of factors affecting ripening
and development of mealiness in 'Forelle'. / AFRIKAANSE OPSOMMING: Forelle' is een van drie blos peer kultivars wat in Suid Afrika geproduseer word. 'n
Minimum van 12 weke by -0.5°C opberging, is deur wetgewing vasgestel, om
eweredige rypheid van 'Forelle' te verseker. Vroeër bemarking van 'Forelle' kan
daartoe lei dat vrugte premium pryse, van 50% meer per karton behaal. Aangesien die
vasgestelde koue periode verhoed dat 'Forelle' vroeër bemark kan word, het onlangse
navorsing gefokus op vermindering van die vasgestelde opberging van 12 weke by
-0.5°C.
Afwisselende verwarmmgs behandelings gedurende koue opberging, beheerde
atmosfeer (BA) opberging in kombinasie met gewone atmosfeer (GA) opbergings
intervalle, en etileen behandelings, is _getoets as alternatiewe vir die 12 weke
opbergings vereiste by -0.5°C. Geen van die bogenoemde behandelings kon egter 'n
beter interne kwaliteit in terme van meleringheid en frankheid as 'n alternatief
verseker nie.
Die doel van die eerste proef was om die invloed van koue opberging by -0.5°C op
rypwording en melerigheid van 'Forelle' te bepaal. Vrugte is in die Warm Bokkeveld
and Theewaterskloof areas geoes tydens kommersiële oesrypheid, waarna hulle vir 21
en 22 weke, respektiewelik, by -0.5°C opgeberg is. Monsters is elke derde week vanaf
die -0.5°C koue opberging geneem en by 15°C geplaas, waarna rypheids indeksering,
totale ACC konsentrasie, etileen produksie and respirasie tempos elke derde dag vir
12 dae gemonitor is. Vrugte wat in dieWarm Bokkeveld en Theewaterskloof areas
geoes is, het rypgeword by 15°C, na 6 and 7 weke by -0.5°C, respektiewelik. Alle
vrugte vanaf die Warm Bokkeveld en 70% vrugte vanaf die Theewaterskloof area, het egter na die 6 en 7 weke by -0.5°C, respektiewelik, en 6 dae by 15°C, melerigheid
ontwikkel. Vrugte wat vir langer as 15 weke by -0.5°C opgeberg is, het in albei areas
'n afname in melerigheid getoon, maar die defek het nooit heeltemal verdwyn tydens
evaluasie by 15°C nie.
Oes rypheid affekteer die ontwikkeling van melerigheid in ander peer kultivars. Die
tweede proef was dus gefokus op dip. invloed van oes rypheid op 'Forelle' se
ontwikkeling van melerigheid. Vrugte is in die Warm Bokkeveld area geoes in week 8
(pre-optimum), 10 (optimum), 12 and 14 (albei post-optimum). Rypheids indekse,
uitdrukbare sapinhoud, meleringheid, totale ACC konsentrasie, interne etileen vlakke
en etileen produksie is gemonitor, na opberging vir 6 weke by -0.5°C en 7 dae by
15°C. Vrugte wat 2 weke voor kommersiële rypheid geoes is (week 8) het die hoogste
totale ACC konsentrasie en etileen produksie gehad, en het reeds die potensiaal gehad
om ryp te word. Die hoogste vlakke van melerigheid (80%) is ook in vrugte wat
tydens hierdie oes verkry is, waargeneem. Vrugte wat op alle tye geoes is, het
melerigheid ontwikkel, behalwe waar kontaminasie met 1-MCP plaasgevind het. Dit
wil voorkom asof 'n ander faktor 'n belangriker rol in die ontwikkeling van
melerigheid in 'Forelle' speel as oes rypheid.
Etileen is bewys om die vereiste koue opberging vir 'Forelle' te kan verkort, maar
daar is konflik oor die effektiwiteit van etileen op die verlaging van melerigheid in
'Forelle'. Die doel van die derde proef was dus om die effek van eksterne etileen
behandeling op rypheid en melerigheid van 'Forelle' te toets. Vrugte wat in die Elgin
area by kommersiële oesrypheid geoes is, is vir 3 weke gestoor by -0.5°C, met etileen
behandel (100 Il L.L-1, 24h, 20°C) en vir 'n verdere 2 dae by 20°C gehou (sonder
etileen). Kontrole vrugte is vir 3 dae by 20°C gehou. Daarna is vrugte weer vir 'n
verdere 3 weke by -0.5°C opgeberg. Na 'n verdere 3 dae by 20°C, was vlees fermheid
van etileen behandelde vrugte 4.6 kg .n vergelyking met 6.1 kg vir die kontrole
vrugte. Alle vrugte wat met etileen behandel is, was melerig op hierdie stadium. Die
kontrole vrugte het ook almal melerig geword, maar slegs na 'n verdere 3 weke by
-0.5°C en 7 dae by 15°C. Etileen behandeling het dus die rypheid van 'Forelle'
bevorder, maar het nie melerigheid voorkom nie.
Melerigheid is 'n tekstuur probleem, wat gekenmerk word aan sagte droë pulp.
Hierdie tekstuur probleem is voorheen waargeneem in 'd'Anjou' pere wat te lank by
-Ll=C opgeberg is, maar is ook kenmerkend by vrugte soos nektariens, kiwi en
persimmon wat aan koue skade ly. Lie gevolg is dat die effek van opbergings
temperatuur op 'Forelle' rypwording en melerigheid getoets moes word. Vrugte is
geoes van die Elgin area tydens kommersiële oesrypheid en gestoor by -0.5°C, 4.0°C
en 7.5°C vir 0, 3 en 6 weke. Vrug monsters is geneem, na verwydering van
bogenoemde stoor temperature en na 7 dae by 15°C, waarby rypheids indekse,
uitdrukbare sapinhoud, meleringheid, totale ACC konsentrasie, interne etileen vlakke
en etileen produksie gemonitor is. Vlees fermheid van vrugte wat vir 6 weke by 4°C
opgeberg was, was 0.5 kg laer as vrugte wat by -0.5°C opgeberg was. Vrugte wat by
4°C and 7.5°C vir 6 weke gestoor is en by 15°C ryp geword het, het min tot geen
melerigheid ontwikkel (0 and 8%, respektiewelik) nie. Vrugte wat by -0.5°C
opgeberg was het egter hoë vlakke van melerigheid bereik (70% melerig). Totale
ACC akkumulasie en etileen produksie was hoër vir vrugte wat by 4°C en 7.5°C
gestoor was, teenoor vrugte wat gestoor was by -0.5°C. Dit wil voorkom asof na-oes
opbergings temperature wel 'n rol speel in die ontwikkeling van melerigheid.
Alhoewel dit voorkom asof na-oes temperature wel 'n rol speel in die ontwikkeling
van melerigheid in 'Forelle' pere, is meer basiese navorsing nodig om die meganisme
van werking in melerigheid ontwikkeling te verstaan. Na-oes temperatuur as 'n faktor
wat melerigheid kan beïnvloed, moet oor 'n reeks van seisoene nagevors word.
Laasgenoemde is van uiterste belang aangesien die invloed van seisoenale variasies
op melerigheid nog nie gekwantifiseer is nie.
Die navorsing was gefokus daarop om vas te stel watter faktore 'n fisiologiese rol
speel in rypwording en melerigheid van 'Forelle' pere. Deurdat vrugte van twee areas
met verskillende klimate, vrugte met verskye oesryphede, ekterne etileen behandeling,
en vrugte van verskillende opbergings temperature ondersoek is, het hierdie navorsing
gehelp om 'n beter begrip te vorm van die rol van hierdie faktore op die rypwording
en die ontwikkeling van melerigheid in 'Forelle'.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53038 |
| Date | 12 1900 |
| Creators | Martin, Elke Monica |
| Contributors | Holcroft, D. M., Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 123 pages : illustrations |
| Rights | Stellenbosch University |
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