**1. Introduction**

Production and consumption of pomegranate (*Punica granatum* L.) fruit is on the increase worldwide. The fruit has an edible portion of about 55–60% [1] and can be eaten fresh or processed into juice, wine, and jam [2–4]. Freshly harvested fruit is kept under cold storage awaiting export to distant markets. Fruit from South Africa takes about 42 d to reach Europe as the major export market destination and therefore a need to maintain good postharvest quality during prolonged storage and export conditions. Storing pomegranate (cv. Wonderful) for 3 months at 5 ◦C and above 92% relative humidity (RH) minimises physiological disorders and maintains internal and external quality attributes [5]. Chilling injury increases with storage duration and temperatures lower than 5 ◦C [6].

In postharvest fruit handling, weight loss and fruit decay are common physiological disorders, among others such as chilling injury and scalding, contributing to quantitative and qualitative loss [6,7]. Pomegranates are highly prone to moisture loss owing to the relatively high water permeability across the skin through minute openings, despite having a thick rind [6,8,9]. Fruit moisture loss if not well controlled results into shrinkage; shrivel; and quantitative loss in weight, taste, and overall acceptability of the fruit, and hence market loss [10].

Internal packaging techniques have been used in the fresh fruit industry to minimise moisture loss. Internal packaging refers to additional packaging materials applied

**Citation:** Lufu, R.; Ambaw, A.; Opara, U.L. The Influence of Internal Packaging (Liners) on Moisture Dynamics and Physical and Physiological Quality of Pomegranate Fruit during Cold Storage. *Foods* **2021**, *10*, 1388. https://doi.org/10.3390/ foods10061388

Academic Editors: Eleni Tsantili and Jinhe Bai

Received: 6 May 2021 Accepted: 10 June 2021 Published: 16 June 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

around the fruit within the external package. Surface coating and waxing has been applied on apples, oranges, plums, and pomegranate to minimise moisture loss [8,11–15]. For pomegranates, heat shrinkable wraps on individual fruit in cartons have also been applied [8,16,17]. On the other hand, shrink wrapping, surface coating, or waxing can lead to anaerobic respiration by creating an oxygen deficit and yet promoting a high CO2 atmosphere around the fruit. This results in the production of off flavors and a change in taste [18,19]. Plastic liners are a commonly applied internal packaging to minimise moisture loss for pomegranate fruit packaged in ventilated cartons [20–22]. Previous research has reported their ability to modify gaseous atmosphere around the fruit, preserving physical and physio-chemical quality [16,22]. However, non-perforated liners negatively affect the fruit cooling rate and increase energy usage during forced air-cooling operations [23,24]. The authors investigated the effect of individual carton design, stack orientation, and presence of internal packaging liners. The internal liner was identified as the most significant factor influencing the produce cooling rate, increasing the seven-eighth cooling time by more than twofold and the corresponding energy usages by up to threefold compared to stacks with no liners. In addition, non-perforated liners promote moisture condensation and consequential fruit decay. Mphahlele et al. [20] reported a higher decay incidence of 33.9% in fruit packed inside plastic liners compared to 29.2 and 16.7% for fruit packed in shrink-wraps and open cartons, respectively, by the end of three months of storage at 7 ◦C and 90% RH.

The use of perforations is identified as a solution to minimise moisture condensation on fruit surfaces and liner walls, thus minimising the consequential fruit decay as a result of the improved vapor transmission capabilities of the perforated liners [25,26]. However, there is still very limited literature on the effect of liner on the keeping quality of pomegranates. Specifically, perforated liners have not been properly studied and yet have the potential to reduce quality losses during prolonged fruit storage. Therefore, the role of liner perforation in counterbalancing between minimising excessive moisture loss and fruit decay will be demonstrated during prolonged storage. The present study focused on relating the ability of plastic liners (non-perforated, micro-perforated, and macroperforated) as internal packaging to modify both gaseous and moisture atmosphere around the fruit, to moisture dynamics and physical and physiological quality of pomegranate fruit (cv. Wonderful) during storage.
