**6. Industrial Implementation**

As previously mentioned, many papers in the literature have confirmed the e fficacy of HS-RT to extend, in terms of food safety and quality, the shelf-life of not only fruit juices, but also a wide variety of food products. Despite this, HS-RT has not ye<sup>t</sup> been introduced in the industry, probably due to the lack of equipment specially designed for it.

Figure 1 presents a simplified description of how hyperbaric storage could be implemented in a juice factory. Once the juice has been obtained, it would be pumped in tanks and pressurized. Then, the pressurized tanks would be sealed with a valve to avoid pressure release and moved to a warehouse. Here, the pressurized juice would be stored at room temperature until distribution. Depending on the customer demands, distribution could be performed either under pressure or the tanks could be decompressed prior to transport.

**Figure 1.** Ideal implementation of hyperbaric storage in a fruit juice factory.

It is clear from Figure 1 that the main components needed in a HS-RT installation are simple: a hydraulic pump and a set of pressure tanks. As pressures employed in HS-RT are quite moderate, the hydraulic pump should not be a problem, but the pressure tanks could present one as currently, tanks do not exist that have been specifically designed for food storage under pressure. Obviously, the feasibility of the logistics managemen<sup>t</sup> at an industrial scale will depend on the size and weight of these tanks. They must be moved from the pressurization point to the warehouse and then transported to their final destination. Too large or too heavy tanks would make these displacements unviable.

The tank size and weight depend on several factors such as the tank material, the tank shape, the amount of product to store, and the storage pressure (the higher the storage pressure, the thicker the tank wall). Taking into account that typical forklifts can easily move loads up to 3000 kg, Bermejo-Prada, Colmant, Otero, and Guignon [58] deemed pressure tanks larger than 2 m and heavier than 2000 kg (mass of the vessel filled with product) would be di fficult to handle inside an industrial facility. They considered cylindrical stainless steel (15-5 PH) tanks, with a fixed diameter/length ratio (0.66), and calculated a domain of viable designs for variable product masses and storage pressures. For a storage pressure of 25 MPa, the largest viable tank should have a length of 1.6 m, a diameter of 1.1 m, and could store 1040 kg of strawberry juice. This volume is much larger than the standard juice batches sold in the industry that usually do not exceed 200 kg. For this mass of juice, the maximal storage pressure for which the tank design would be viable would be 157 MPa. This pressure level is considerably larger than those needed for fruit juice preservation, which are usually between 50 and 100 MPa. Therefore, the construction and handling of pressure tanks appropriate for hyperbaric storage is perfectly viable.

However, logistics managemen<sup>t</sup> is not the only consideration needed to assess the feasibility of its industrial implementation. The cost of hyperbaric storage is also an important factor to take into account. When calculating the storage cost, the amortization cost of the initial investment, the maintenance cost, and the electricity consumption throughout the storage period must be considered. Taking all of these factors into account, Bermejo-Prada, Colmant, Otero, and Guignon [58] estimated that, today, the HS-RT cost would be considerably higher than that of conventional refrigeration. Even though the electrical consumption in HS-RT is almost negligible, the initial cost of the HS-RT equipment is high and this is, without any doubt, the limiting factor for the implementation of this technology in the food industry. However, it is important to note that the high price of high-pressure equipment has not been an impediment for the successful industrial implantation of conventional high-pressure processing, and thanks to the increasing demand, a decreasing trend in the cost of high-pressure equipment has been observed from 1996 to now. In contrast, the growing tendency of electricity prices could increase the refrigeration cost in the following years and contribute to making this technology less competitive from an economic point of view.

#### **7. Environmental Impact of Hyperbaric Storage**

The environmental impact of hyperbaric storage can be roughly estimated by calculating its carbon footprint (CF), that is, the overall emissions of carbon dioxide (CO2) and other greenhouse gases associated with it. To do so, the equivalent CO2 emissions associated with both the production of the high-pressure vessel material (direct emissions) and the energy consumption during operation (indirect emissions) must be considered. In this way, Bermejo-Prada, Colmant, Otero, and Guignon [58] estimated that the total CF associated with the storage of 1 kg of strawberry juice at 25 MPa for 15 days was 0.0042 kg CO2·kg−<sup>1</sup> juice. They showed that the HS-RT emissions associated with the vessel material corresponded to almost 100% of the emissions while those derived from the electricity consumption during storage were almost negligible (Figure 2). In contrast, in conventional refrigeration, the total CF was 0.1085 kg CO2·kg−<sup>1</sup> juice, that is, 26 times higher than that of HS-RT and the consumed electricity and refrigerant leakage amounted to almost 95% of the CO2 total emissions.

Cold facilities are huge consumers of energy and represent about 50% of the total energy consumption in the food industry [5]. Moreover, refrigerants are an important source of GHG emissions and some of them also split and release ozone destructive chlorine atoms. Therefore, HS-RT could represent an important breakthrough for food preservation in terms of refrigerant elimination, energy saving, and environmental protection. Thus, the above results prove that both the needlessness of refrigeration facilities and the extremely low energy requirements (only during compression of the product) represent a real environmental benefit as they contribute to greatly diminish the HS-RT carbon footprint. This is especially important today when global energy savings are demanded in the food industry to fight against climate change.

**Figure 2.** Contribution of different sources to CO2 emissions in conventional refrigeration and hyperbaric storage at room temperature.
