2.3. Food storage and transportation

on plants' VPD has been determined as shown in Figure 2(a). Moreover, the figure provides a comparison of ideal VPDs for different growth stages of tomatoes [33]. It can be noted that plants are very sensitive to air conditions and require dynamic humidity and temperature at different growth stages. Similarly, using the concept of VPD, the ideal AC zones can be formulated for various greenhouse products as shown in Figure 2(b). It can be seen that each agricultural product requires typical thermal conditions, which may or may not be achievable

Figure 1. Animals' air-conditioning (AC): (a) optimum ventilation rate for livestock building [26, 30]; and (b) optimum air

Figure 2. Greenhouse AC: (a) influences of greenhouse conditions on plants' vapor pressure deficit (VPD); and (b)

for many AC systems.

100 Refrigeration

temperature and humidity levels.

optimum air temperature and humidity levels.

Post-harvest storage and handling of agricultural products is one of the burning issues of the twenty-first century where we have lots of food but still many people are suffering from food shortage and malnutrition. It is mainly due to food wasting, improper management, and high cost of food storage and transportation. Food storage is usually expensive and complicated due to the involvement of numerous physiochemical and biological processes, for example, respiration, transpiration, fermentation, and so on [7]. Moreover, storage conditions and nature of storage are completely different for different types of food, which may be categorized as follows:


As far as conventional storage practices used for above-mentioned food types are concerned, most popular storage techniques are: (i) drying, (ii) mechanical isolation, (iii) refrigeration, (iv) chemical treatment, (v) vacuum, (vi) ionizing radiation, (vii) silo and storage structures, and so on. On the other hand, it is important to mention here that the AC systems could be extremely required in many cases of food storage and transportation, for example, storage of fresh dates. In addition, AC storage method could be considered on top priority for the food products involved in transpiration, respiration, and/or fermentation (i.e., supply or removal of O2 and CO2) [34]. However, AC is not popular for longtime storage of food products due to the expensive technology of VAC systems and lack of distinctive control of Ta and RH. Therefore, low-cost and technically viable AC technology is the dire need for the food industry. From the discussion point of view, ideal temperature and humidity requirements for the storage of fruits and vegetables are compared on psychrometric chart as shown in Figure 3 [4]. The fundamental knowledge used in Figure 3 is obtained from the guidelines provided by the reference [34]. The shelf life of vegetables and fruits can be increased considerably by storing them at desired conditions of Ta and RH (Figure 3). The AC systems can generate these conditions effectively and can also control level of O2 and CO2 by means of fresh/return air flow and, therefore, can be considered for food storage and transportation. Similarly, the AC use could be crucial for the storage and transportation of dry fruits which may require particular moisture contents. In this regard, water vapor mass transfer between air and food (role of water activity) can be controlled by means of relative humidity, RH.
