Postharvest physiology and effects of modified atmosphere packaging and anti-browning treatment on quality of pomegranate arils and aril-sac (CV. Bhagwa)

Aindongo, Wilhelmina Vulikeni (2014-04)

Thesis (MScFoodSc)--Stellenbosch University, 2014.

Thesis

ENGLISH ABSTRACT: Knowledge of postharvest quality attributes of minimally processed packaged fruit is essential in order to establish the optimum shelf life period. The aim of this study was to investigate the effects of Passive-modified atmosphere packaging (MAP) on the quality of minimally processed pomegranate (cv. Bhagwa) arils and aril-sacs. These began by understanding the physiological processes i.e. respiration and transpiration rates of the whole fruit, arils and aril-sacs. The respiration rates (RR) of whole fruit, aril-sacs and arils were studied at 5, 10, 15 and 22°C, and comparisons were made among these fruit fractions. A high RR was observed in aril-sacs compared to whole fruit and arils across all storage temperatures. A 74.5% decrease in RR was observed when storage temperature was reduced from 22°C to 5°C. A significant increase in RR occurred from day 3 of storage across all fruit fractions and storage temperatures. The transpiration rates (TR) of arils and aril-sacs were studied at storage conditions of 5, 10 and 15°C and 76, 86 and 96% relative humidity (RH), and was found to increase with increase in temperature and decrease in relative humidity, with lowest TR occurring in fruit fractions stored at 5°C and 96% RH showing lower TR. Arils had high TR compared to aril-sacs, and this may be related to high surface area to volume ratio of exposed arils. The effects of modified atmosphere packaging and application of anti-browning agents on quality of arils and aril-sacs stored at 5°C were studied. Compared to clamshell packaging, Passive-MAP using POLYLID® 107 polyethylene (PE) polymeric film showed greater positive effects in maintaining the quality and extends the shelf life of the arils and aril-sacs. Furthermore, the anti-browning agents used controlled browning on the cut-surfaces of the peel of the aril-sacs and reduced microbial growth in both arils and aril-sacs. When the effects of MAP and anti-browning were combined, aril-sacs stored better than arils. These treatments extended the shelf life of aril-sacs to 12 days while arils lasted up to 9 days. The water vapour transmission rate (WVTR) of pomegranate fruit membrane was evaluated at cold storage (5°C, 90% RH) and room condition (18.7°C, 70% RH). A high WVTR occurred in membranes stored at room condition, compared to those stored at cold storage. Further studies are warranted to improve our understanding of the biophysical properties of pomegranate membranes in relation to possible exchange of water vapour and gases between the aril-sacs. In summary, the use of MAP in combination with anti-browning agents showed a high potential in maintaining the quality of pomegranate arils and aril-sacs and consequently increase their shelf-life.

AFRIKAANSE OPSOMMING: Kennis van naoes- gehalte-eienskappe van minimaal geprosesseerde verpakte vrugte is essensieel ten einde optimum rakleeftyd te bepaal. Die doel van hierdie studie was om die gevolge van passiewe gemodifiseerde atmosfeerverpakking (GAV) op die gehalte van arils en arilsakkies van minimaal geprosesseerde granaat (kv. Bhagwa) te ondersoek. ʼn Aanvang is gemaak deur die fisiologiese prosesse, m.a.w. respirasie- en transpirasietempo’s van die hele vrugte, arils en arilsakkies, te begryp. Die respirasietempo’s (RT) van hele vrugte, arilsakkies en arils is by 5, 10, 15 en 22°C bestudeer, en vergelykings is getref tussen hierdie vrugdele. ʼn Hoë RT is waargeneem by arilsakkies in vergelyking met hele vrugte en arils oor alle bergingstemperature heen. ʼn Afname van 74.5% RT is waargeneem toe bergingstemperatuur van 22°C na 5°C verminder is. ʼn Beduidende toename in RT het van dag 3 van berging af oor alle vrugdele en bergingstemperature heen voorgekom. Die transpirasietempo’s (TR) van arils en arilsakkies is by bergingstoestande van 5, 10 en 15°C en 76, 86 en 96% relatiewe humiditeit (RH) bestudeer, en daar is bevind dat dit verhoog met ’n toename in temperatuur en ʼn afname in relatiewe humiditeit, met die laagste TR wat voorkom by vrugdele geberg by 5°C en 96% RH wat dus laer TR toon. Arils het hoë TR gehad in vergelyking met arilsakkies, en dit kan verband hou met die verhouding van hoë oppervlakarea tot volume blootgestelde arils. Die gevolge van gemodifiseerde atmosfeerverpakking en aanwending van middels vir die voorkoming van verbruining op gehalte van arils en arilsakkies geberg teen 5°C is bestudeer. In vergelyking met verpakking in toeknipbakkies (clamshell packaging), het passiewe GAV waarby POLYLID® 107 poliëtileen- (PE) polimeriese film gebruik is, groter positiewe gevolge by die behoud van gehalte getoon, en die rakleeftyd van die arils en arilsakkies is verleng. Daarbenewens het die middels vir die voorkoming van verbruining beheerde verbruining op die sny-oppervlakke van die skil van die arilsakkies gebruik en mikrobiese groei in beide arils en arilsakkies verminder. Toe die gevolge van GAV en die voorkoming van verbruining gekombineer is, het arilsakkies beter as arils geberg. Hierdie behandelings het die rakleeftyd van arilsakkies tot 12 dae verleng terwyl arils tot 9 dae gehou het. Die waterdamptransmissiespoed (WDTS) van granaatvrugtemembraan is geëvalueer by koel berging (5°C, 90% RH) en kamertoestande (18.7°C, 70% RH). ʼn Hoë WDTS het voorgekom by membrane wat by kamertoestande geberg is in vergelyking met dié wat in koelbewaring geberg is. Verdere studies is geregverdig vir verbetering van ons begrip van die biofisiese eienskappe van granaatmembrane in verhouding met moontlike uitruiling van waterdamp en atmosfere tussen die arilsakkies.

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