Application of Room Cooling and Thermal Insulation Materials to Maintain Quality of Okra during Storage and Transportation

Abstract

A combination of room cooling and the use of thermal insulation materials to maintain okra quality under simulated storage and transportation was evaluated. Okra pods were packed in plastic baskets and either cooled at 18 °C or not cooled in a room for 2 h. After either room cooling or no cooling, the okra pods were covered with three different materials: (1) perforated linear low-density polyethylene (P-LLDPE), (2) two layers of heat-reflective sheet with thin nonwoven (HRS+TNNW), and (3) metalized foam sheet (MFS). Typical handling (TP) without cooling and covering with P-LLDPE was used as the control. The six treatments were conducted during simulated storage (18 °C for 48 h) and transportation (30 °C for 15 h). Results showed that MFS gave the best insulation properties (Qx and R-values), followed by HRS and TNNW. After room cooling, both HRS+TNNW and MFS materials delayed the time for pulp temperature to reach 18 °C (10 h), compared to P-LLDPE (2 h). TP presented the highest mass loss (17.8%) throughout simulated conditions, followed by cooling plus P-LLDPE (15.2%) and either of the thermal insulation materials with or without room cooling (3.6% to 5.2%), respectively. TP, cooling plus P-LLDPE, and no cooling plus MFS (44% to 56%) showed the highest percentage of decay, while cooling combined with both HRS+TNNW and MFS gave the lowest decay incidence (11–21%). Findings demonstrated that room cooling combined with HRS+TNNW had the highest efficiency for preserving cool temperature and reducing decay, compared to TP and room cooling plus MFS.

Performance of Thermal Insulation Covering Materials to Reduce Postharvest Losses in Okra

“…The use of thermal insulation covers containing aluminum sheet (HRS + TNNW, HRS + TKNW and MFS) over 7 h resulted in greater heat accumulation inside the cover, caused by the high respiration of okra compared with no cover and P-LLDPE treatments (Figures 5-7). Similarly, our previous study showed that thermal insulation materials (HRS + TNNW and MFS) tended to build up pulp temperature of okra under simulated transportation at 30 • C for 15 h [16]. This result was consistent with Bycroft et al [42] who recommended that long-term covering of asparagus should be reconsidered due to higher heat accumulation compared to no cover.…”

“…Equipment settings and thermal heat energy measurements were performed following the procedure of Harvey [25] and our previous research [16]. Briefly, rate of thermal heat energy (Q x ) was determined as the rate at which heat energy passed through the material by using two expanded polystyrene (EPS) boxes with a hole (10 × 10 cm 2 ) between two chambers.…”

“…The rate of okra respiration was measured in a closed system, as shown in Figure 3. The details of the test set up were described elsewhere in our previous study [16]. Briefly, the okra pods (150 g) were packed in a plastic food container (8400 mL) under three storage temperature conditions (10, 20, 30 • C) with a range of 70-90% RH with three replicates in each condition.…”

“…Furthermore, the difference in postharvest loss between no room cooling and room cooling observed in HRS + TNNW and MFS treatments were 11% and 25%, respectively. This indicated that room cooling plays an important role in maintaining the okra quality as a pretreatment before covering with thermal insulation material [16].…”

“…In India, room cooling at 15 • C was applied to exported okra before storage at 8 • C [15]. Recently, room cooling at 0 • C for 2 h was applied in combined with usage of thermal insulation covering materials, to reduce decay incidence and mass loss of okra in Thailand [16].…”