Assessing weight loss control strategies in pomegranate (Punica granatum L.) fruit: plastic packaging and surface waxing

Abstract

Pomegranate fruit is highly prone to moisture loss due to the plentiful micro-pores and slits in the skin, despite having a thick rind. Water loss results in a huge financial loss to the industry through direct loss of marketable fresh weight and the associated diminished commercial value of affected fruit. Plastic packaging and surface coating are broad rivals as water loss control technologies and have attracted increased attention in the fruit industry in the last decade. In this present study, weight loss control techniques including conventional plastic packaging (liner packaging and shrink wrapping) and environmentally sustainable surface coating/waxing technologies were investigated on ‘Wonderful’ pomegranates harvested at commercial maturity with total soluble solids (TSS) of about 16.75 °Brix. Secondly, the different methods of waxing application including dipping, brushing and spraying were investigated. Furthermore, fruits were half dipped in wax by dipping only the top or bottom half of the fruit and this was to assess weight loss variation within individual fruit. Batch 1 fruits were stored at 7 °C and 90% RH for 42 d and thereafter transferred to shelf conditions of 23 °C and 58% RH for 8 d, simulating the maximum sea freight duration from South Africa to Europe across the Atlantic Ocean, followed by open-shelf marketing before consumption. Batch 2 fruits were immediately stored under shelf conditions for 16 d, to simulate prolonged shelf conditions of fruit without a cold storage regime. The fruit weight loss, decay incidence, respiration rate, external total colour difference (TCD), total soluble solids and titratable acidity were investigated and scanning electron microscopy (SEM) was carried out on waxed fruit. The weight loss was highest in control fruit (7.7%), followed by bottom-dip waxed (6.0%), top-dip waxed (5.8%), wax sprayed (4.8%), wax brushed (4.6%), wax dipped (4.0%), and liner packaged (2.1%) and least in shrink wrapped (0.8%) fruit, by the end of the 42 d of cold storage. Dipping was the best wax application method in controlling pomegranate fruit weight loss as compared to half waxing (top and bottom dipped), brushing and spraying application methods. Furthermore, shrink wrapping, liner packaging and wax dipping best maintained a lower TCD and thus better-preserved fruit appearance compared to the rest of the treatments.