**3. Results and Discussion**

*3.1. Liner Properties*

3.1.1. Gas Composition Inside Liners

There was a decrease in O2 and an increase in CO2 composition within non-perforated 'Decco' and 'Zoe' liners and to a slight extent inside micro-perforated Xtend® liners (Figure 1). Non-perorated liners provide the barrier that restricts movement of gases across packaging walls. However, there was no change in gas composition of the atmosphere inside the 2 mm macro-perforated and 4 mm macro-perforated HDPE liners. For fruit packed in non-perforated 'Decco' and 'Zoe' liners, O2 composition inside the liners decreased from 21.4 to 15.9 and 15.6%, respectively, while CO2 composition increased from 0.0 to 2.2 and 2.4%, respectively, after 5 d of cold storage. At 28 d of cold storage, CO2 composition further increased to 3.1% and 4.0%, inside non-perforated 'Decco' and 'Zoe' liners, respectively. After 28 d, gas composition inside non-perforated liners remained more stable. Mphahlele et al. [20] observed a more stable O2 concentration inside polyliners after a month of storing pomegranate (cv. Wonderful) at 7 ◦C. However, a steadier decrease in O2 and increase in CO2 concentrations inside different modified atmosphere packaging (MAP) liners was observed for other pomegranate cultivars ('Hicaznar' and 'Hicrannar') stored at 6 ◦C [21,22]. Quite similar to the current findings, Selcuk and Erkan [22] reported an increase in CO2 from 0.0 to 3.9 and 2.5% for pomegranate packed in MAP1 and MAP2 liners, respectively, after 20 d of storage at 6 ◦C.

**Figure 1.** Gas composition inside plastic liners packed with pomegranate fruit (cv. Wonderful) stored at 5 ◦C and 90% relative humidity (RH). HDPE: high density polyethylene.

#### 3.1.2. Water Vapor Transmission Rate (WVTR)

The rate at which a plastic liner is able to allow moisture across its walls is important in controlling humidity within the bag and around the fruit, and hence reducing condensation and associated risks of fruit decay during prolonged storage [31,32]. Water vapor transmission rate is dependent on liner permeability and prevailing storage temperatures and humidity differences inside and outside the plastic bags [27,33–35]. Generally, for all treatments WVTR decreased with time and then became more stable after about 15 d. Water vapor transmission rate was higher at 20 ◦C and 65 ± 5% RH than at 5 ◦C and 95% RH (Figures 2 and 3). The micro-perforated Xtend® liner exceptionally had a higher WVTR of 72.2 7 and 78.7 g m−<sup>2</sup> d−<sup>1</sup> at 5 ◦C and 20 ◦C, respectively. There was no difference

in WVTR across all non-perforated films, irrespective of the type of plastic material and temperature of storage.

**Figure 2.** Water vapor transmission rate (WVTR) across plastic liner films under a controlled environment of 5 ◦C and 90% relative humidity (RH). The non-perforated film section of the 2 mm HDPE (\*) and 4 mm HDPE (\*\*) liners were used. HDPE: high density polyethylene.

**Figure 3.** Water vapor transmission rate across plastic liner walls under a controlled environment of 20 ◦C and 65% relative humidity (RH). The non-perforated film section of the 2 mm HDPE (\*) and 4 mm HDPE (\*\*) liners were used. HDPE: high density polyethylene.

Perforations improved the WVTR of the HDPE films. The presence of one 4 mm diameter perforation improved ventilation area of the HDPE film by 2.56% compared to 0.64% by one 2 mm diameter perforation. At 20 ◦C, the HDPE film with one 4 mm diameter perforation had 66.6% and 44.6% faster WVTR compared to micro-perforated Xtend® film and HDPE film with one 2 mm diameter perforation, respectively (Figure 4). Therefore, the size of perforation plays a significant role in moisture transmission and controlling condensation within bags. Dirim et al. [33] reported a good relationship between film perforation area and WVTR at different temperature and RH conditions. Similar to our results, Opara et al. [27] observed increased WVTR with increased temperature, across biodegradable and synthetic polyfilms. The authors reported that increasing the number of perforations increased WVTR more than increasing storage temperature. Studies on water permeability across polypropyrene films showed increasing WVTR with increasing perforation diameter [34].

**Figure 4.** Effect of perforation on water vapor transmission rate (WVTR) under a controlled environment of 20 ◦C and 90% relative humidity (RH). HDPE: high density polyethylene.

3.1.3. Moisture Condensation Dynamics One-Day Condensation Characteristics

The barrier effect of the liners permits them to retain a high RH around the fruit [36], resulting in moisture condensation. Generally, the rate of one-day condensate buildup was higher in non-perforated liner treatments than in perforated liner treatments (Table 1). Perforations improve vapor transmission capability of the liners, minimising vapor condensation inside MAP liners [25]. One-day condensate build-up was high in 2 mm macro-perforated HDPE liners, probably because of low perforation area (0.022%). However, one-day condensate build-up was lowest in micro-perforated Xtend® liners and in 4 mm macro-perforated HDPE liners because of their high moisture permeability. Similarly, a higher one-day condensation severity score was observed in non-perforated liners than in perforated liners. One-day condensation severity was such that non-perforated

'Decco' > non-perforated 'Zoe' > 2 mm macro-perforated HDPE > 4 mm macro-perforated HDPE > micro-perforated Xtend® liners (Table 2). A difference in the general characteristics (size and distribution) of condensate droplets formed within the different liner bags was observed (Table 2).

**Table 1.** Rate of moisture condensation and corresponding weight loss for 12 pomegranate fruit inside plastic liner bags, at 5 ◦C and 90% relative humidity (RH). HDPE: high density polyethylene.


**Table 2.** Condensate characterisation inside plastic liner bags for pomegranate fruit stored at 5 ◦C and 90% relative humidity (RH). HDPE: high density polyethylene.


<sup>1</sup> Condensation was scored using 0–10 score scale (where 0 = none; 1–2 = trace; 3–4 = slight; 5–6 = moderate; 7–8 = severe; 9–10 = extremely severe).
