Unpacking the influence of internal packaging on cooling characteristics and postharvest quality of pomegranate fruit

[摘要] ENGLISH SUMMARY: Plastic films (liners) are commonly used inside packages of pomegranates. Liners can create modified atmosphere around fruit (MAP) and minimize fruit moisture loss. However, the barrier nature of liners affects cooling characteristics by increasing resistance to airflow (RTA), delaying cooling and promoting condensation, leading to fruit spoilage. During this research the impact of liners on the characteristics and postharvest quality of pomegranate fruit during cold storage and subsequent shelf life was investigated. The role and impact of liner perforations was highlighted. The effect on RTA by non-perforated 'Decco', micro-perforated Xtend®, macro-perforated 'Decco' liners (2 mm × 70 and 4 mm × 18) and macro-perforated high density polyethylene (HDPE) liners (2 mm × 54 and 4 mm × 36), was studied in a wind tunnel. Generally, fruit stack packed with non-perforated 'Decco' and micro-perforated Xtend® liners increased the RTA of the no-liner packed fruit by 175.7 and 238.4 %, respectively. However, using macro-perforated 2 and 4 mm 'Decco' liners increased the RTA of the no-liner packed fruit by only 69.2 and 113.6 %, respectively.The impact of non-perforated 'Decco' and micro-perforated Xtend® liners on cooling characteristics was carried using a forced-air cooling (FAC) setup. The 7/8 cooling time of fruit stack packed with no-liner was 3.5 ± 0.2 h, compared to 8.1 ± 0.1 h with non-perforated 'Decco' and 8.5 ± 0.1 h with micro-perforated Xtend® liners. As a result, more energy was consumed in pre-cooling fruit packed in liners than with no-liners. However a higher stack cooling uniformity (81.6 ± 1.7 and 78.7 ± 1.5 %) was obtained for fruit packed with non-perforated 'Decco' and micro-perforated Xtend® liners, respectively, compared to fruit packed with no-lines (64.2 ± 0.2 %).The effect of non-perforated ('Decco' and 'Zoe'), micro-perforated (Xtend®), macro-perforated 2 and 4 mm HDPE liners on fruit quality during storage at 5 o C and 90 ± 5 % relative humidity (RH) for 12 weeks and subsequently 5 days at 20 o C, was evaluated. At the end of 12 weeks of cold storage, the no-liner fruit lost 15.6 ± 0.3 % of its initial weight. Non-perforated ('Decco' and 'Zoe') liners minimized weight loss by 95.0 % compared to Xtend® micro-perforated (73.2 %), 2 mm macro-perforated HDPE (84.3 %) and 4 mm macro-perforated HDPE (62.5 %) liners, respectively. Fruit packed in perforated and non-perforated liners maintained a lower respiration rate and retained better peel colour than fruit with no-liners. Micro- and macro-perforation of liners increased diffusion of moisture lost from the fruit across film to the room atmosphere. This minimized moisture condensation inside the liners leading to a reduced fruit decay, with acceptable shrivel severity. The type of liner and perforation quality (size and number) did not have a significant impact on total soluble solids (TSS), titratable acidity (TA), juice colour, total phenolic concentration and antioxidant activity. Overall, the use of perforated liners reduced RTA, energy consumption and moisture condensation associated with non-perforated liners, and yet retained fruit texture, colour, weight and chemical quality attributes during and after prolonged cold storage.

[发布机构] Stellenbosch University