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

Lufu, Robert (2017-03)

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

Thesis

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.

AFRIKAANSE OPSOMMING: Plastiek voerings (“liners”) word algemeen gebruik in die verpakking van granate. Voerings skep `n gemodifiseerde atmosfeer rondom vrugte (MAP), wat vogverlies verminder. Voerings is uiteraard `n beskermingslaag, en beïnvloed dus die verkoelingseienskappe deur weerstand teen lugvloei (RTA) te verhoog, verkoeling te vertraag en kondensasie te bevorder, wat lei tot vrug bederf. Tydens hierdie navorsing is die impak van voerings op die verkoelingseienskappe en die na-oes kwaliteit van granate tydens koelstoring en die daaropvolgende raklewe geëvalueer. Die rol en impak van perforasie in die voerings is beklemtoon. Die effek op RTA van nie-geperforeerde ‘Decco’, mikro-geperforeerde Xtend®, makro-geperforeerde ‘Decco’ voerings (2 mm × 70 en 4 mm × 18) en makro- geperforeerde hoë druk HDPE voerings (2 mm × 54 en 4 mm × 36), is in 'n windtonnel bestudeer Oor die algemeen het vrugte wat met nie-geperforeerde ‘Decco’ en mikro-geperforeerde Xtend® voerings in stapels gepak is, die RTA van voeringlose gepakte vrugte met 175.7 en 238.4%, onderskeidelik vermeerder. Maar, met behulp van makro-geperforeerde 2 en 4 mm 'Decco' voerings, het die RTA van die voeringlose gepakte vrugte met slegs 69.2 en 113.6%, onderskeidelik toegeneem Die impak van nie-geperforeerde ‘Decco’ en mikro-geperforeerde Xtend® voerings op verkoelingseienskappe is tydens geforseerde lugverkoeling (FAC) getoets Die 7/8 verkoelingstyd van vrugte wat voeringloos in stapels gepak is, was 3.5 ± 0.2 h in vergelyking met 8.1 ± 0.1 h in nie-geperforeerde ‘Decco’, en 8.5 ± 0.1 h met mikro-geperforeerde Xtend® voerings. Die gevolg was meer energie verbruik tydens die voor-verkoeling van vrugte verpak in voerings, teenoor voeringlose verpakking. `n Hoër stapel verkoelings-eenvormigheid van onderskeidelik 81.6 ± 1.7 en 78.7 ± 1.5 % is verkry vir vrugte wat met nie-geperforeerde ‘Decco’ en mikro-geperforeerde Xtend® voerings voorsien is. Dit is in vergelyking met voeringlose verpakkings (64.2 ± 0.2 %). Die effek van nie-geperforeerde (‘Decco’en ‘Zoe’), mikro-geperforeerde (Xtend®), en makro-geperforeerde 2 en 4 mm HDPE voerings op vrugkwaliteit tydens stoor by 5 o C en 90 ± 5% RH vir 12 weke en daaropvolgend 5 dae by 20 ° C, is geëvalueer. Na 12 weke van die koue- stoor het voeringlose vrugte 15.6 ± 0.3% van die aanvanklike gewig verloor. Nie-geperforeerde (‘Decco’ en ‘Zoe’) voerings het gewigsverlies tot 95.0% beperk in vergelyking met Xtend® mikro-geperforeerde (73.2%), 2 mm makro-geperforeerde HDPE (84.3%) en 4 mm makro-geperforeerde HDPE (62.5 %) voerings, onderskeidelik. Daarbenewens het vrugte verpak in geperforeerde en nie-geperforeerde voerings ‘n laer respirasietempo gehandhaaf, en beter skil kleur behou as vrugte sonder voering. Mikro- en makro-perforasie van voerings het die diffusie van vrugte se vogverlies oor die voering na die kameratmosfeer verminder. Dus is vog kondensasie verminder binne verpakking, wat gelei het tot verlaagde vrugte verval binne gevoerde sakke, met ’ n aanvaarbare verkrimpingskoers. Voering tipe en perforasie kwaliteit (grootte en aantal) het nie `n beduidende impak op totale oplosbare stowwe (TSS), titreerbare suur (TA), sap kleur, totale fenoliese konsentrasie en antioksidant aktiwiteit gehad nie. In die geheel het die gebruik van geperforeerde voerings weerstand teen lugvloei, energieverbruik en vog kondensasie wat verband hou met nie-geperforeerde voerings verminder, terwyl dit nog steeds vrugtekstuur, kleur, gewig en chemiese kwaliteit eienskappe tydens en na 'n lang koue stoor behou het.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/101392
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