Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Modified atmosphere packaging (MAP) is a dynamic process of altering gaseous composition
inside a package. It relies on the interaction between the respiration rate (RR) of the
produce, and the transfer of gases through the packaging material. These two processes are
dependent on numerous factors such as storage temperature, film thickness and surface
area, produce weight as well as free headspace within the pack. Therefore, in order to
achieve the desired modified atmosphere in a given package, it is important to understand
the three basic disciplines of MAP, namely produce physiology, polymer engineering, and
converting technology.
In this study the effects of storage conditions and duration on physiological responses i.e.
respiration (RR) and transpiration rate (TR) of two pomegranate cultivars ‘Acco’ and
‘Herskawitz’, were investigated and mathematical models were developed to predict these
physiological responses at given time and storage conditions. The result of this study
showed that RR of whole pomegranate fruit was significantly higher than that of fresh arils,
and that temperature had a significant impact on the RR of both whole fruit and fresh arils.
The influence of time, and the interaction between temperature and time also had significant
influences on RR of fresh pomegranate arils. These findings highlight the significance of
maintaining optimal cold-storage condition for packaged arils or whole fruit along the supply
chain. In addition, mathematical models based on the Arrhenius-type equation and the
power function equation coupled with Arrhenius-type equation accurately predicted the
effect of temperature and the influence of time and temperature on the RR of fresh
pomegranate arils for both cultivars. Furthermore, the results of experimental and model prediction studies showed that both
relative humidity (RH) and storage temperature had significant effects on TR. RH was the
variable with the greatest influence on TR, and it was observed that arils were best kept at
5°C and 96% RH to maintain quality for 8 days. The applicability of the transpiration model
developed was validated based on prediction of TR of pomegranate arils under different
combinations of storage conditions. The model adequately predicted TR and provides a
useful tool towards understanding the rate of water loss in fresh pomegranate arils as
affected by storage conditions and duration. The effect of passive-MAP engineering design parameters as a function of produce weight
contained, storage temperature and duration on fresh pomegranate arils was investigated.
The result showed that produce weight of aril content, temperature and the interaction
between temperature and time had slight but insignificant effects on measured
physicochemical quality attributes. However, headspace gas concentration was significantly
influenced by produce weight and storage temperature. Oxygen (O2) composition decline
below 2% after day 3 and 5 at 15 and 10 ºC, respectively, while samples at 5 °C did not
reach below 2% throughout the study. On the other hand, CO2 levels increased significantly
during storage for all packaging conditions. This study showed the importance of a
systematic approach to the design of optimal MAP systems. At lowest storage temperature
the inability to achieve desired modified atmosphere (MA) required for optimal storage of
arils despite the increase in produce weight, suggests that the use of active gas modification
(gas flushing with recommended atmosphere) would be necessary. However, the present
results show that at higher temperature macro/micro perforations would be required on
the polymeric films used in the present study in order to avoid critical levels of O2 and CO2. The influence of passive MAP, storage temperature and duration on volatile composition
and evolution of packaged pomegranate arils was investigated. The results showed that
changes in aroma compounds were dependent on cultivar differences, storage condition and
duration. Using GC-MS analysis of pomegranate juice HS-SPME extracts, a total of 18 and 17
volatiles were detected for ‘Herskerwitz’ and ‘Acco’, respectively. Furthermore, flavour life
(7 days) was shorter than the postharvest life (10 days) for both cultivars. There was a
decrease in volatile composition during the storage period (aldehydes < alcohols < esters)
while the concentration (%) and composition of ethyl esters increased with storage time.
These results highlight the need for a more precise definition of flavour shelf life for MApackaged
pomegranate arils and other packaged fresh produce. The importance of
maintaining optimal cold storage condition, selection of appropriate packaging materials and
a systematic approach to the design and application of MAP systems has also been shown. / AFRIKAANSE OPSOMMING: Gemodifiseerde atmosfeer-verpakking (GAV) is ’n dinamiese proses waartydens die
gassamestelling binne-in ’n verpakking gewysig word. Dit berus op die wisselwerking tussen
die respirasietempo (RT) van die produkte en die oordrag van gasse deur die
verpakkingsmateriaal. Hierdie twee prosesse is van verskeie faktore soos
bergingstemperatuur, dikte van die film en oppervlakte, gewig van die produkte asook vry
boruimte binne-in die pakkie afhanklik. Om dus die gewenste gemodifiseerde atmosfeer in ’n
gegewe verpakking te verkry, is dit belangrik om die drie fundamentele dissiplines van GAV
te begryp, naamlik produkfisiologie, polimeerontwerp, en omsettingstegnologie.
In hierdie studie is die gevolge van bergingstoestande en -duur op fisiologiese reaksie,
met ander woorde, respirasie- (RT) en transpirasietempo (TT) van twee geselekteerde
granaatkultivars ‘Acco’ en ‘Herskawitz’, ondersoek en wiskundige modelle is ontwikkel om
ons in staat te stel om hierdie fisiologiese reaksies by gegewe tyd- en bergingstoestande te
voorspel. Die resultaat van hierdie studie het aangetoon dat die respirasietempo (RT) van
heel granaatvrugte aansienlik hoër was as die RT van vars arils, en temperatuur het
beduidende uitwerking op RT van beide heel vrugte en vars arils gehad. Die invloed van tyd,
en die wisselwerking tussen temperatuur en tyd het ook ’n beduidende invloed op die RT
van vars granaatarils gehad. Hierdie bevinding beklemtoon die belang van die handhawing van
optimale koelbewaringstoestande vir verpakte arils of heel vrugte met die aanvoerketting
langs. Daarbenewens wiskundige modelle wat gebaseer op die Arrhenius-tipe vergelyking en
die magsfunksie-vergelyking gepaard met Arrhenius-tipe vergelyking, die uitwerking van temperatuur en die invloed van tyd en temperatuur op die RT van vars granaatarils vir beide
kultivars onderskeidelik voldoende en akkuraat voorspel.
Afgesien die resultate van eksperimentele en modelvoorspellings die studies aangetoon
dat beide relatiewe humiditeit (RH) en bergingstemperatuur ’n beduidende uitwerking op
TT het. RH was die veranderlike met die grootste invloed op TT, en it was waargeneem dat
dit die beste was om arils teen 5°C en 96% RH te bewaar (8 dae). Die toepaslikheid van die
transpirasiemodel wat ontwikkel is, is bevestig op grond van voorspelling van TT van
granaatarils onder verskillende kombinasies van bergingstoestande. Die model het TT
voldoende voorspel en sou ’n bruikbare instrument wees ten einde die waterverliestempo in vars granaatarils en ander vars produkte, soos deur bergingstoestande en duur beïnvloed,
te begryp.
Die uitwerking van passiewe-GAV ontwerpparameters as ’n funksie van gewig van die
produkte, bergingstemperatuur en duur op vars granaatarils is ondersoek. Dit het aan die lig
gebring dat gewig van die produkte, temperatuur en die wisselwerking tussen temperatuur
en tyd ’n geringe maar onbeduidende uitwerking op gemete fisikochemiese gehalteeienskappe
gehad het. Die gaskonsentrasie in die boruimte is betekenisvol beïnvloed deur
gewig van die produkte en bergingstemperatuur. Die O2-samestelling het tot benede 2%
gedaal na 3 en 5 dae by 15 en 10 ºC, onderskeidelik, terwyl monsters by 5 °C deur die
studie heen nooit laer as 2% was nie. Aan die ander kant, CO2-vlakke het gedurende berging
betekenisvol verhoog wat betref alle verpakkingstoestande. Hierdie studie het die
belangrikheid van ’n sistematiese benadering by die ontwerp van ’n optimale GAV-stelsel
aangetoon. By die laagste bergingstemperatuur dui die onvermoë om die gewenste
gemodifiseerde atmosfeer (GA) wat vir optimale berging van arils benodig word, te verkry –
ondanks die toename in die gewig van die produkte – daarop dat die gebruik van aktiewe
gasmodifisering (gasspoeling met aanbevole atmosfeer) nodig sou wees. Egter die huidige
uitslae aangetoon dat by hoër temperatuur, sou makro/mikroperforasies op die
polimeerfilms wat gebruik word in die onderhawige studie egter nodig wees ten einde
kritiese vlakke van O2 en CO2 te verhoed. Die invloed van passiewe GAV, bergingstemperatuur en duur op onstabiele samestelling
en evolusie van verpakte granaatarils is ondersoek. Die resultate aangetoon dat
veranderinge in aromaverbindings afhanklik was van kultivarverskille, bergingstoestande en
duur. Met behulp van GC-MS-analise van granaatsap HS-SPME-ekstrakte, het ons ’n totaal
van 18 en 17 vlugtige stowwe vir ‘Herskawitz’ en ‘Acco’, onderskeidelik bespeur. Verder het
ons waargeneem dat die smaakleeftyd (7 dae) korter was as die na-oesleeftyd (10 dae) vir
beide kultivar. Daar was ’n afname in vlugtige samestelling (aldehiede < alkohole < esters)
terwyl die konsentrasie (%) en samestelling van etielesters het met bergingstyd verhoog.
Hierdie resultate het die aandag gevestig op die behoefte aan ’n meer presiese definisie
van geur-raklewe vir GA-verpakte granaatarils en ander verpakte vars produkte. Die belang
van die handhawing van die optimale koelbewaringstoestand, seleksie van geskikte
verpakkingsmateriaal en ’n sistematiese benadering tot die ontwerp van ’n optimale GAVstelsel,
is ook beskryf.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/80198 |
| Date | 03 1900 |
| Creators | Caleb, Oluwafemi James |
| Contributors | Opara, U. L., Manley, M., Mahajan, P. V., Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | ix, 204 p. : ill. |
| Rights | Stellenbosch University |
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