Investigating physiological and quality response of pomegranate fruit to controlled atmosphere storage

Mugode, Luke (2017-03)

Thesis (PhD (Food Sc ))--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: Pomegranate (Punica granatum) is a highly valued crop with a huge economic potential. It is very nutritious with numerous bioactive compounds with the potential to prevent a certain type of cancers and other health conditions. The fruit can also be processed into various industrial products. In South Africa, the pomegranate industry is growing rapidly due to the rising demand from local and international markets. However, owing to its high perishability, the shelf life is limited to less than eight weeks under cold storage conditions. In light of this, a study of ‘CA’ storage as a supplementary postharvest treatment was investigated. The ‘CA’ storage is a system that involves altering and maintaining an atmospheric gas composition different from that of room air (79% N2, 20% O2, and 0.03% CO2) to levels generally, with O2 below 8% and CO2 above 1% supplemented with low temperature and relative humidity above 90%. The primary objective of this study was to investigate the physiological and quality response of pomegranate (weight loss, shrivel, decay, colour, texture, incidences of disorders and decay) to different ‘CA’ treatments and storage temperatures. In addition, to assess the overall quality (total soluble solids, pH, acidity, antioxidant properties, aroma volatility compounds and sensory analysis) including respiration and development of a model for predicting the transpiration rate with the view to optimise the ‘CA’ storage requirements for ‘Wonderful’ and ‘Bhagwa’ pomegranates. The results showed that the selected pomegranate cultivars responded differently to ‘CA’ storage conditions. More importantly, it was observed that by increasing CO2 and/or decreasing O2 concentrations under ‘CA’ resulted in opposite effects on quality attributes. Despite the variation in response, the shelf life of the whole pomegranate fruit was extended by five months more after harvest with a minimal loss of physiological properties (weight loss, physiological disorders, colour, and texture) and quality. Furthermore, the notable fluctuation of quality attributes (TSS, aroma volatility compounds and antioxidants) under ‘CA’ conditions depended highly on cultivar, storage temperature, gas composition and storage duration. In addition, a mathematical model developed based on respiratory heat energy reliably predicted the transpiration rate, with an accuracy of R2 = 0.97. In conclusion, the study proposes a goal-oriented optimisation strategy focussing on the market-driven quality expectation with a negligible compromise on some attributes. The concept was validated using a general linear model (statistical tool) which showed that atmosphere under CAs minimised the weight loss with minimal physiological and quality loss of attributes in addition to extending the shelf life for than two-fold compared to room air. These findings highlight both importance and challenges in finding optimal ‘CA’ for the storage of fresh horticultural produce.

AFRIKAANSE OPSOMMING: Granate (Punica granatum) is ’n waardevolle vrug met baie ekonomiese potensiaal. Dit is baie voedsaam en daar is baie bioaktiewe samestellings wat die potensiaal besit om sekere tipes kanker en ander ongesteldhede te verhoed. Die vrug kan ook in sekere industriële produkte gebruik word. Die granaatindustrie in Suid-Afrika groei tans vinnig as gevolg van die groeiende vraag na granate in plaaslike en internasionale markte. Maar omdat granate baie onderhewig is aan bederf, is die raklewe daarvan beperk tot minder as agt weke as dit onder koel toestande geberg word. Daarom is berging onder beheerde atmosfeeer toestande ‘CA’ ondersoek. Die ‘CA’ -berging behels verandering endie behoud van ’n atmosferiese gas samestelling wat verskil van dié van normale lug (79% N2, 20% O2, and 0.03% CO2) tot vlakke waar die O2 onder 8% en die CO2 bokant 1%, die temperature laag en die lugvoggehalte bo 90% is. Die hoofdoel met hierdie studie was om die fisiologiese en gehalte respons van granate (verlies aan gewig inkrimping, aftakeling, kleur, tekstuur, en siektetoestande) tot verskillende ‘CA’ behandeling en bergingtemperature te ondersoek. Verder is daar gepoog om die algehele gehalte (oplosbare vastestowwe, pH, suurinhoud, antioksidantkenmerke geur en sensoriese ontleding) insluitende respirasie te assesseer en om ’n model vir die voorspelling van die uitwasemingkoers te bou om sodoende die ‘CA’ berging van die kultivars, ‘Wonderful’ en ‘Bhagwa te verbeter. Die resultate het bewys dat die verskillende tipes granate verskillend op ‘CA’ berging reageer. Meer belangrik is die feit dat die verhoging van CO2 en/of die vermindering van O2 konsentrasies teenoorgestelde uitwerkings op die gehalte van die vrug het. Ten spyte van die verskillende reaksies is die raklewe in die geheel met vyf maande na die oes verleng en met minimale verlies aan fisiologiese kenmerke (verlies aan gewig, fisiologiese probleme, kleur en tekstuur) en gehalte. Verder is daar bevind dat die fluktuasies in gehalte (TSS, geur, vlugtigheidsamestellings en antioksidante) onder bergingstoestande tot ’n groot mate afhang van die kultivar, bergingstemperatuur, komposisie van die gas en die duur van die berging. Verder is ’n wiskundige model ontwikkel wat baseer is op respiratoriese hitte energie wat die uitwasemingskoers koers met ’n akkuraatheid van R2 = 0.97. voorspel. Daar is tot die slotsom gekom dat daar van ’n doelgerigte optimasie strategie gebruik gemaak moet word met die fokus op markverwagtings en met toegewens in sommige onbelangrike opsigte. ’n Lineêre model (statistiese instrument) is gebruik om die konsep te valideer. Daar is bevind dat berging onder beheerde atmosfeer tieatande lei tot minimale verlies aan gewig, kenmerke en gehalte en dat dit die raklewe twee keer meer as normale lug. Hierdie bevindinge beklemtoon die belangrikheid sowel as die uitdagings na die soeke van ‘n optimale ‘CA’ vir vars hortologie produkte.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/101395
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