Determining optimum storage conditions for pomegranate fruit (cv. Wonderful)

Arendse, Ebrahiema (2014-04)

Thesis (MScFoodSc )--Stellenbosch University, 2014.


ENGLISH ABSTRACT: The development of science-based management tools and appropriate postharvest handling protocols are required for the determination of optimal storage performance of pomegranate fruit. The South African pomegranate industry experiences considerable fruit quality losses due to the lack of knowledge on optimal storage and handling practices. The cultivar ‘Wonderful’ is the widely grown in South Africa; however, to date there is currently limited scientific knowledge on the storage requirements. To develop quality standards for the export market, knowledge of optimum storage conditions are required to provide an understanding of postharvest quality attributes and consumer organoleptic perceptions. The overall aim of this research was to provide science-based management tools for the storage performance of pomegranate fruit (cv. Wonderful). The research reported in Chapter 3 focused on the physiological responses of pomegranate fruit at different storage temperatures. Commercially harvested fruit were stored at 5±0.7°C, 7.5±0.3°C and 10±0.5°C with 92±2% RH and at room temperature (21±3°C, 65±6% RH) for 5 months. Fruit respiration and physiological disorders during long term storage were investigated. During storage, low temperatures evidently resulted in lower respiration rates; however, respiration rate increased gradually after 2 months resulting in higher respiration rates at 5°C than 7.5°C after 3 month storage period. Overall, fruit became more susceptible to internal and external disorders as storage period progressed. Storage of fruit longer than 2 months at 5°C resulted in chilling injury and this was observed over the 5 month storage period. Fruit stored at 21°C and 10°C were discarded after 1 and 4 months, respectively, due to complete fruit loss to decay and peel shrinkage. Furthermore, the severity of browning increased with storage temperatures, although this became more severe at 5°C after 3 months. Therefore, to maintain a relatively low respiration rate and minimize physiological disorders, the cv. Wonderful should be stored at 5°C and >92% RH for storage period up to 3 months. In Chapter 4, the effects of temperature and storage duration on pomegranate fruit quality and mechanical properties were conducted. This study revealed that weight loss increased with rise in temperature and storage duration with the primary source of moisture loss being the fruit skin (peel), which resulted in significant reduction in peel thickness with prolonged storage period. The CIE (L*, a*, b* and C*) colour parameters of fruit and arils decreased during storage. However, the hue (hº) for whole fruit increased as a result of browning incidence, and decreased in arils suggesting an increase in redness. Significant increases in total soluble solids (TSS), pH, TSS:TA and BrimA were observed with significant decreases in titratable acidity (TA) occurring throughout the storage period. Storage temperature and duration significantly affected majority of the investigated mechanical properties. Puncture resistance, fruit and aril compression strength decreased with storage temperature and duration. These findings showed that fruit may be stored between 2 to 3 months at 5°C to ensure the best internal and external quality attributes. The studies in Chapter 5 investigated the effects of storage temperature and duration on phytochemical and antioxidant properties. Fresh pomegranate juice was assessed for concentrations of total phenolic compounds, total anthocyanin and ascorbic acid. The antioxidant property of the fruit juice was tested against 2, 2-diphenyl–1–picryl hydrazyl (DPPH). The results showed that total phenolic and total anthocyanin concentration increased up to 3 months of storage at 5°C, 7.5°C, 10°C and 21°C and decreased gradually over time. For antioxidant activity, storage of fruit at 5°C, 7.5°C and 10°C significantly (p< 0.05) reduced the radical scavenging activity of juice by more than 56% when stored beyond 2 months. Furthermore, ascorbic acid concentration gradually declined with increasing storage duration, resulting in reduced juice antioxidant capacity. These findings are beneficial to pomegranate export industries, especially where fruit are stored for long for use in health-promoting purposes. The research conducted in Chapter 6 focused on determining suitable storage conditions based on the combination of instrumental measurements and sensory attributes. During storage, individual fruit were evaluated by trained sensory panel based on the overall appearance, taste and aril texture. Discriminant analysis at different storage temperatures was used to distinguish fruit from each other at 2 months of storage with sensory attributes such as overall pomegranate flavour (R2 = 0.56), total anthocyanin (R2 = 0.46) and Chroma (C*) colour index (R2 = 0.37). Discriminant analysis further showed that storage time rather than storage temperature led to the reduction in overall quality when storing fruit beyond 2 months. Based on sensory attributes, suitable storage temperature and duration were found to be 5°C and 2 months when overall flavor were highly rated; thereafter, significant reductions in overall appearance, aril and kernel texture were observed. Furthermore, the proposed storage conditions were supported with instrumental measurements, which revealed a decline in important fruit attributes such as total phenolics, total anthocyanin, aril colour and aril texture after 2 months of storage. Overall, this study provides science-based tools required for developing cold chain handling protocols needed to manage the long supply chain of ‘Wonderful’ pomegranate fruit grown in South Africa.

AFRIKAANSE OPSOMMING: Die ontwikkeling van wetenskap-baseerde beheerinstrumente en toepaslike na-oes hanteringsmetodes is nodig vir die vasstelling van die optimale stoorprestasie van granate. Die Suid-Afrikaanse granaatindustrie ondervind groot vrug kwaliteit verliese as gevolg van die gebrek aan kennis oor optimale stoor en hantering praktyke. Die kultivar Wonderful is die wyd gegroei in Suid-Afrika, maar tot hede daar is tans beperk wetenskaplike kennis oor die stoor vereistes. Om gehaltestandaarde vir die uitvoermark te ontwikkel word kennis van die optimale stoortoestande benodig sodat ’n begrip van die na-oes gehalte-kenmerke en verbruiker se organoleptiese persepsies gevorm kan word. Die oorhoofse doelwit van die navorsing is om wetenskap-baseerde beheerinstrumente vir die stoor van granate (bv. Wonderful) te verskaf. Die navorsing wat in Hoofstuk 3 beskryf word is gerig op die fisiologiese respons van granate op verskillende bergingtemperatuur. Kommersieel-gekweekte vrugte is by 5±0.7°C, 7.5±0.3°C en 10±0.5°C met 92±2% RH en by kamertemperatuur by (21±3°C, 65±6% RH) vir 5 maande gestoor. Die respirasie van die vrugte en die fisiologiese ongesteldhede gedurende langtermyn stoor word ondersoek. Gedurende stoor het die laer temperature gelei tot laer respirasie koerse; maar respirasie koers het geleidelik na 2 maande verhoog wat lei tot hoër respirasie koerse by 5°C as teen 7.5°C na ’n 3-maande stoorperiode. Algehele, vrugte het egter meer vatbaar geword vir interne en eksterne ongesteldhede hoe langer die stoortydperk geduur het. Die stoor van vrugte langer as 2 maande teen 5°C lei tot skade as gevolg van verkoeling en dit is oor die 5 maande stoor tydperk waargeneem. Vrugte wat teen 21°C en 10°C gestoor is moes na onderskeidelik 1 tot 4 maande as gevolg van verlies wat die gevolg was van swam skade en skil krimping, weggegooi word. Die erns van die verbruining het verhoog toe die stoortemperature verhoog, alhoewel dit meer geraak het teen 5°C na 3 maande. Om dus ’n betreklik lae respirasie koers en min fisiologiese probleme te verseker, moet die kultivaar Wonderful teen 5°C en >92% RH vir 3 maande gestoor word. In Hoofstuk 4 word die effek van temperatuur en die duur van stoor op die gehalte van die granate en die meganiese eienskappe gemeet. Daar is bevind dat gewigsverlies met verhoogte toename in temperatuur en langer stoorperiodes toeneem en dat die hoofbron van verlies aan vog die skil van die vrug is. Die gevolg hiervan is ’n betekenisvolle reduksie in die dikte van die skil na ’n lang stoorperiode. Die CIE (L*, a*, b* and C*) kleur parameters van vrugte en granaatpitte het tydens stoor verminder. Die tint, (hº) van die hele vrug het as gevolg van verbruining, verhoog en het verminder in granaatpitte wat daarop dui vermeerdering in rooiheid. Daar was betekenisvolle verhogings in die totale oplosbare vaste stowwe (TSS), pH, TSS:TA en BrimA is opgemerk met betekenisvolle vermindering in asiditeit waarvan die waarde bepaal kan word (TA) en wat tydens die stoortydperk plaasvind. Stoortemperatuur en die duur van die stoor het ’n groot invloed gehad op die meganiese kenmerke wat ondersoek is. Weerstand teen priken die kompressie krag van die vrugte en die granaatpitte het met verhoogde temperatuur en duur van stoor afgeneem. Hierdie bevindinge het getoon dat vrugte kan gestoor word tussen 2 tot 3 maande by 5°C die beste interne en eksterne kwaliteit eienskappe om te verseker. In hoofstuk 5 is die effek van stoortemperatuur en duur op die fitochemiese en antioksidant kenmerke ondersoek. Vars granaatsap is ondersoek en ramings is gemaak t.o.v. totale konsentrasies van fenoliese samestellings, totale antosianiene en askorbinesuur. Die antioksidant kenmerke van die vrugtesap is getoets vir met 2, 2-diphenyl–1–picryl hydrazyl (DPPH). Daar is bevind dat die totale fenoliese en totale antosianiene konsentrasies tot by 3 maandemaande van stoor teen 5°C, 7.5°C, 10°C and 21°C toegeneem het en toe mettertyd afgeneem het. Wat betref antioksidant aktiwiteit, is daar gevind dat die stoor van vrugte teen 5°C, 7.5°C en 10°C die radikale reinigingsaktiviteite van die sap betekenisvol (p< 0.05) met meer as 56% verminder as dit vir meer as 2 maande gestoor word. Verder, askorbiensuur konsentrasie geleidelik afgeneem met toenemende stoor duur, wat lei tot verlaagde sap antioksidant kapasiteit. Hierdie bevindings is van belang vir die granaatuitvoerindustrie, veral waar vrugte vir 'n lang tydperk gestoor vir gebruik in gesondheids-bevordering doeleindes. Die navorsing wat in hoofstuk 6 beskryf is, het gefokus op die vasstelling van geskikte stoortoestande baseer op ’n kombinasie van instrumentale meting en sensoriese kenmerke. Gedurende stoor word individuele vrugte deur ’n opgeleide panel evalueer t.o.v. voorkoms, smaak en tekstuur van die granaatpitte. Diskriminantontleding teen verskillende stoor temperature is gebruik om vrugte na 2 maande stoor vrugte t.o.v sensoriese kenmerke soos algehele granaat smaak. (R2 = 0.56), totale antosianiene (R2 = 0.46) en Chroma (C*) kleur indeks (R2 = 0.37) te onderskei. Diskriminantontleding het verder getoon dat die duur van die stoor en nie die stoortemperatuur nie, gelei het tot die reduksie in algehele gehalte as die vrugte vir langer as 2 maande gestoor word. Gegrond op sensoriese eienskappe is geskik stoor temperatuur en duur gevind word by 5°C en 2 maande wanneer algehele geur was as hoog beoordeel; en daarna, is aansienlike vermindering in die algehele voorkoms, en die tekstuur van die granaatpitte afgeneem. Hierdie voorgestelde stoortoestande word ook ondersteun deur instrumentele meting, wat ’n afname in belangrike kenmerke soos totale fenologie, totale antosianiene en die kleur en tekstuur van die granaatpitte na ’n 2 maande stoorperiode toon. In die geheel verskaf die bevindinge van hierdie studie wetenskap-baseerde instrumente vir die ontwikkel van koue-ketting hantering protokol vir die bestuur van die lang verskaffingsketting van Wonderful granate wat in Suid-Afrika gekweek word.

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