Determination of moisture loss of pomegranate cultivars under cold and shelf storage conditions and control strategies

Abstract

Pomegranates are prone to moisture loss, despite having a thick rind. This study aimed to characterise the moisture loss in the three most exported pomegranate cultivars (‘Acco’, ‘Herskawitz’ and ‘Wonderful’) of South Africa during cold and shelf storage. The contribution and susceptibility of the different parts of the fruit to moisture loss were measured and characterized. Furthermore, water loss control strategies (liner packaging, shrink wrapping and surface waxing) were investigated. Sample pomegranates were stored for 42 d at 7 °C and 90% relative humidity (RH) and thereafter transferred to shelf conditions of 23 °C and 58% RH. Another group of pomegranates were directly stored at 23 °C and 58% RH for 16 d to simulate prolonged shelf conditions. The fruits were examined for the moisture loss, transpiration rate (TR), respiration rate (RR), fraction of peels and arils, moisture content of the fractions, peel thickness and chemical attributes of the fruit juice. Moisture loss in pomegranates significantly varies among cultivars, especially during shelf storage as compared to cold storage and is significantly influenced by the size, RR, peel and aril fraction, moisture content, and peel thickness. Medium-sized fruit (‘Herskawitz’ and ‘Wonderful’) had a significantly higher moisture loss of 0.32 ± 0.01 g cm⁻² (TR = 0.16 mg kg⁻¹ s⁻¹) than the small-sized fruit (‘Acco’) which had a moisture loss of 0.25 ± 0.01 g cm⁻² (TR = 0.14 mg kg⁻¹ s⁻¹) at a vapour pressure deficit (VPD) of 1.176 kPa during the prolonged 16 d of shelf storage. The maximum moisture loss (24.2%) observed under the tested conditions was almost entirely from the peel portion of the fruit. Liner packing (2.1%), shrink wrapping (0.8%) and surface waxing (4.0%) significantly (P < 0.0001) minimised the moisture loss of the un-treated (7.7%) fruit during cold storage. In addition, waxing, liner packaging and shrink wrapping greatly increased the critical time C_t (time to reach a moisture loss of 5%) of un-treated ‘Wonderful’ fruit under cold storage from 26.1 d to 52.9, 98.0 and 251.6 d, respectively.