Department of Horticulture

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Browsing Department of Horticulture by Author "Banda, Kalenga"

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    Active modified atmosphere packaging, postharvest physiology, quality attributes and shelf life of minimally processed pomegranate arils (cv. Wonderful)
    (Stellenbosch : Stellenbosch University, 2015-03) Banda, Kalenga; Opara, Umezuruike Linus; Caleb, Oluwafemi James; Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.
    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.