Active modified atmosphere packaging, postharvest physiology, quality attributes and shelf life of minimally processed pomegranate arils (cv. Wonderful)

Banda, Kalenga (2015-03)

Thesis (MScAgric)--Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: Minimally processed fresh products have a short shelf life and marketable period and could therefore benefit from active modified atmosphere packaging (MAP) technology because it allows earlier establishment of suitable equilibrium atmospheres than passive MAP. However, there are limited studies that have explored the application of active MAP in minimally processed pomegranate arils. This study, therefore, investigated the effects of active MAP and storage conditions on postharvest physiology, quality attributes and shelf life of pomegranate arils (cv. Wonderful). In the first part of the study, the effects of storage temperature (5, 10 and 15 °C), relative humidity (76, 86 and 96%) and citric acid pre-treatment on transpiration rate (TR) of minimally processed pomegranate arils were investigated. In addition, the effects of storage temperature (5, 10, 15 and 20 ± 2 °C, and 90 ± 2 % RH) on respiration rate (RR) and quality attributes of citric acid treated and non-treated arils were determined in order to establish best storage conditions. Citric acid pre-treatment was only effective in reducing aril RR at 15 and 20 °C. Aril RRs were lowest at 5 °C throughout the 5 d storage duration and declined from 4.75 to 2.86 mL CO2 kg-1 h-1 and 4.86 to 2.7072 mL CO2 kg-1 h-1 for citric acid treated and non-treated arils, respectively. About twofold increase in RR was observed with increase in storage temperature from 5 to 15 °C and threefold when increased to 20 °C. Storing arils under low temperature condition (5 °C and 96 % RH) maintained the lowest transpiration rates (TR), with arils under these conditions suffering negligible moisture loss (~1%) after 9 d compared to 7 and 12% moisture loss for those stored under 86 and 76 % RH, respectively. The study further showed that citric acid pre-treatment had no significant effects on TR of arils at all the temperature and RH combinations. The effects of active MAP on postharvest physiology, quality attributes and shelf life of minimally processed pomegranate arils at 5 °C and 90 % RH were investigated using two independent experiments. In experiment 1, arils were packed in low barrier bi-axially oriented polyester (BOP) polymeric film under two active MAPs (5% O2 + 10% CO2 + 85% N2; 30% O2 + 40% CO2 + 30% N2), passive MAP and clamshell containers as control. In experiment 2, a high barrier polyethylene polymeric film (polylid) was used with arils packed in three active MAPs (5% O2 + 10% CO2 + 85% N2; 30% O2 + 10% O2 + 60% N2; 100% N2) and passive MAP as the control. Respiration rate, physico-chemical attributes, antioxidant properties (total anthocyanin, total phenolic and ascorbic acid content, and radical scavenging activity), microbial quality and sensory attributes were monitored every third day over a 12 d storage period. Equilibrium O2 (16-18%) and CO2 (7%) atmospheres were established after 3 d in the low barrier BOP in experiment 1; however, the recommended levels of gas composition (2-5 % O2 and 10-20% CO2) for MAP of minimally processed pomegranate arils were not reached. In contrast, O2 levels decreased and CO2 increased continuously, in pomegranate arils packaged in high barrier polylid film in experiment 2. Respiration rate of arils in both low barrier BOP film and high barrier polylid film were significantly affected by MAP and increased significantly (p < 0.05) with storage duration. Arils in clamshell containers maintained lower RR than other MAP treatments, while passive MAP had the highest in experiment 1. Arils in active MAPs with low O2 (5% O2 + 10% CO2 + 85% N2), high O2 (30% O2 + 10% CO2 + 60% N2) and passive MAP in the high barrier polylid film generally maintained similar RR levels throughout the 12 d storage duration. In contrast, RR of arils in 100% N2 was about 40% lower than that in other MAP treatments from day 6 until the end of storage. Furthermore, MAP with 100% N2 was effective in supressing ascorbic acid oxidation from day 6 until the end of storage. Total anthocyanin content (TAC) of arils fluctuated with storage duration across all the MAP treatments. At the end of 12 d storage duration, anthocyanin content of arils in experiment 1 was highest in clamshell packages (30.7 ± 0.9 mg C3gE/ 100ml) and lowest in passive MAP (26.7 ± 1.8 mg C3gE/ 100 ml). In the high barrier polylid film in experiment 2, arils in 100% N2 maintained higher TAC levels than other MAP treatments from day 9 until the end of storage. Similarly, radical scavenging activity of arils in the high barrier polylid film in experiment 2 was highest in 100% N2 while that in passive MAP was lowest from day 6 until the end of storage. Arils in in 100% N2 and high O2 atmospheres in both experiment 1 (30% O2 + 40% CO2 + 30% N2) and 2 (30% O2 + 10% CO2 + 60% N2) maintained lower aerobic mesophilic bacteria counts than other MAP treatments throughout the storage duration. However, shelf life was limited to 9 days for arils in 100% N2 based on overall acceptability and off-odour sensory scores, while arils in active MAP with high O2 scored above the acceptable limit by day 9. Arils in passive MAP in both films also remained acceptable until day 9, while those in clamshell packages were not acceptable beyond day 6.

AFRIKAANSE OPSOMMING: Vars produkte wat minimaal verwerk is het ’n kort raklewe en kan net vir ’n kort tydperk bemark word. Daar is dus voordeel te trek uit gemodifiseerde atmosfeer verpakking (MAP) tegnologie, want dit maak dit moontlik om vroeër as die geval is met passiewe MAP, ’n toepaslike ewewigatmosfeer te vestig. Tot dusver is daar egter min studies oor die toepassing van MAP op minimaal verwerkte granaat arils gedoen. In hierdie studie was die fokus dus op die effek van aktiewe MAP en stoortoestande op die na-oes fisiologie, gehalte kenmerke en raklewe van granaat arils (Kultivar Wonderful). In die eerste deel van die studie is die effek van stoortemperatuur (5, 10 and 15 °C), relatiewe humiditeit (76, 86 and 96%) en voorafbehandeling met sitroensuur op die transpirasie-tempo van minimaal verwerkte granaat arils ondersoek. Die effek van stoortemperatuur (5, 10, 15 en 20 ± 2 °C, en 90 ± 2 % RH) op die respirasie-tempo en gehalte kenmerke van sitroensuur behandelde, en nie-behandelde arils is bepaal, om sodoende die beste stoortoestande vas te stel. Behandeling met sitroensuur was net effektief in die verlaging van die arils se respirasie-tempo by 15 en 20 °C. Arils se respirasie-tempo was tydens die 5 dae stoortydperk op sy laagste by 5 °C en het afgeneem van 4.75 tot 2.86 mL CO2/kg per uur en 4.86 tot 2.7072 mL CO2/kg per uur vir onderskeidelik behandelde en nie-behandelde arils. Die transpirasie-tempo het ongeveer twee voudig gestyg met ´n vernaging in temperatuur van 5 °C tot 15 °C en drie voudig toegeneem met ´n verderenvelhoging in temperatuur tot 20 °C. Die stoor van arils teen lae temperature (5 °C en 96 % RH) het gelei tot die laagste transpirasie-tempo. Onder hierdie toestande het die arils ook min vog (~1%) na 9 dae verloor, in vergelyking met arils wat 7% en 12% vog verloor het as dit teen 86% and 76 % RH onderskeidelik gestoor is. Daar is verder gevind dat sitroensuur behandeling geen noemenswaardige effek op die transpirasie koers van die arils by al die temperature en lugvoggehalte kombinasies gehad het nie. Die effek van die aktiewe MAP op die na-oes fisiologie, gehalte kenmerke en raklewe van minimaal verwekte granaat arils teen 5 °C and 90 % RH is deur middel van twee onafhanklike eksperimente ondersoek. In eksperiment 1 is die arils in lae versperring biaksiaal-georiënteerde poliester (BOP) polimeriese film onder twee aktiewe MAP tegnologieë (5% O2 + 10% CO2 + 85% N2; 30% O2 + 40% CO2 + 30% N2), passiewe MAP, en “clamshell” houers as kontrole verpak. In eksperiment 2 is ’n hoë versperring polietileen polimeriese film gebruik (polimeriese deksel) en is met die arils in drie aktiewe MAP tegnologië (5% O2 + 10% CO2 + 85% N2; 30% O2 + 10% O2 + 60% N2; 100% N2) verpak met ’n passiewe MAP as kontrole. Die respirasie-tempo, fisio-chemiese kenmerke, antioksidant kenmerke (totale antosianien, totale fenoliese en askorbiensuursuur inhoud en radikale opruiming aktiwiteit), mikrobiale gehalte en sensoriese kenmerke is elke derde dag oor ’n 12 dae stoortydperk gemonitor. In eksperiment 1 is ewewig O2 (16-18%) en CO2 (7%) atmosfeer na drie dae in die lae versperring BOP atmosfeer bereik; maar die aanbevole gassamestellings vlakke (2-5 % O2 and 10-20% CO2) vir die MAP van minimaal verwerkte granaat arils is nie bereik nie. In kontras hiermee het die O2 en CO2 vlakke in die granaat arils wat in eksperiment 2 in hoë versperring polietileen film verpak is aanmekaar vermeerder en verminder. Die respirasie-tempo van die arils in beide die lae versperring BOP film en in die hoë versperring polietileen film is deur MAP ge-affekteer en het heelwat (p < 0.05) tydens stoor vermeerder. In eksperiment 1 het arils in “clamshell” houers ’n laer respirasie-tempo behou terwyl passiewe MAP die hoogste telling getoon het. Arils in aktiewe MAP met lae O2 (5% O2 +10% CO2 + 85% N2), hoë O2 (30% O2 + 10% CO2 + 60% N2) en passiewe MAP in the hoë versperring polietileen film het gewoonlik dieselfde respirasie-tempo gedurende die 12 dag stoortydperk behou. Die respirasie-tempo van arils in 100% N2 was vanaf dag 6 tot aan die einde van die stoortydperk omtrent 40% laer as die van die arils wat ander MAP behadelings ondergaan het. Verder was die MAP behandeling met 100% N2 vanaf dag 6 tot aan die einde van die stoortydperk effektief wat betref die onderdrukking van askorbiensuur oksidasie. Die totale antosianien inhoud (TAC) van arils het ge-fluktueer in die geval van al die MAP behandelings tydens stoor. In eksperiment 1 was die antosianie inhoud van die arils aan die einde van die 12-dag stoortydperk op sy hoogste in die “clamshell” pakette (30.7 ± 0.9 mg C3gE/ 100ml) en op sy laagste in passiewe MAP (26.7± 1.8 mg C3gE/ 100 ml). In die hoë versperring polietileen film in eksperiment 2, het arils in 100% N2 vanaf dag 9 tot by die einde van die stoortydperk hoër TAC vlakke as by ander MAP behandelings behou. In eksperiment 2 was die vry radikaal opruiming aktiwiteit van die arils in die hoë versperring polietileen film die hoogste in 100% N2 terwyl dit in die passiewe MAP vanaf dag 6 tot aan die einde van die stoortydperk die laagste was. Arils in 100% N2 en hoë O2 atmosfere in beide eksperiment 1 (30% O2 +40% CO2 + 30% N2) en 2 (30% O2 + 10% CO2 + 60% N2) het laer aerobiese mesofiliese bakterie tellings gedurende die stoortydperk behou. Die raklewe van arils in 100% N2 was beperk tot 6 dae wat betref algehele aanvaarbaarheid en reuk tellings, terwyl die tellings van arils in aktiewe MAP met hoë O2 teen dag 9 onaanvaarbaar hoog was. Arils in passiewe MAP het in beide films aanvaarbaar gebly tot by dag 9, terwyl die arils in “clamshell” pakette na dag 6 onaanvaarbaar was.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/96621
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