Equilibrium in Pressurized Systems (Sub and Supercritical)

FORTUNATTI MONTOYA, MARIANA; SANCHEZ, FRANCISCO; PEREDA, SELVA

Thermodynamics of Phase Equilibria in Food Engineering

Elsevier

Lugar: Londres; Año: 2018; p. 385 - 412

High-pressure processing (HPP) has emerged as a novel, additive-free, nonthermalpreservation technology driven by the interest of consumers inhealthier foods that ensures both food safety and flavor [1]. Moreover,nowadays there is a growing tendency to design and develop high qualityproducts by means of sustainable processes, also called ?green technologies?.These are based on principles such as a more efficient use ofenergy, the replacement of traditional organic solvents by less contaminantalternatives, and the use of renewable raw materials. These changes are promotednot only by environmental concerns and governmental regulationsbut also by a higher commitment of the consumers, who are graduallymodifying their habits and preferences toward more natural products.An overview about the effect of high pressure treatment on differentaspects that may influence nutrients final quality can be found in the literature[2]. In addition to the current commercial applications for foodsafety and shelf-life extension, they highlighted several opportunities ofhigh-pressure treatments to manipulate the functionality, extractability,allergenicity, and bioavailability of micronutrients in a variety of foods.Despite the high price of the HPP units, the number of equipmentglobally installed for commercial applications has rapidly grown in the last10 years [1]. This trend in food pasteurization illuminates the commercialdevelopment of other high-pressure applications in the food industry. Forinstance, supercritical technologies, which have catalyzed a great deal ofresearch works to isolate natural products, carry out chemical reactions,formulate excipients, to mention the most plentiful. Even though nowadayshundreds of novel supercritical applications are patented yearly [3,4],the high-initial capital investment limits the applications to high-valueproducts [5]. Nevertheless, it is worth noting that in some cases, HPP isthe only way to meet product specifications [6].In this context, high pressure and supercritical fluid (SCF) technologiesappear as an attractive alternative to traditional processes. The mostcommonly used near critical and SCFs, namely, carbon dioxide, ethane,propane, dimethyl ether, are considered ?green solvents? because they areenvironmentally friendly substances (non-toxic), and, as gases at ambientconditions, they do not leave residue in the final products after depressurization.These SCFs are compatible with food and pharmaceuticalproducts due to their very low toxicity; they are non-expensive andusually non-reactive. By far, the most widely used is carbon dioxide(CO2) [7]; even in cases when it might not be a good solvent, developerschoose to enhance its solvent capacity by adding cosolvents such asethanol. The additive may enhance processing yields under milder conditions;however, the product will require further purification steps toremove the cosolvent, hindering some of the benefits of simply usingcompressed gas as solvents. An alternative to enhance CO2 solventproperties is the design of mixed gas solvents, improving the solventcapacity of CO2 without losing the non-flammability and other favorablecharacteristics [8].In the case of natural products processing, SCFs technologies providemany promising opportunities, such as the use of SCF solvents as precipitationand separation agents, or even as reaction media. There is an extensiveliterature concerning the potential applications of high pressure andsupercritical technologies in the field of food industries [6,911].Particularly, King [9] shows a timeline of the variety of fields where SCFstechnology has had impact. He discusses the development of each fieldand provides an extensive list of applications and food-related productsfor each case. In addition, even though it might not be directly related tofood production, it is worth noting that SCF also had many applicationsin material science, both formulation and impregnation, which is a promisingfield for smart food packaging design. In general, academic studiesreport results on each of these technologies with a given specific aim;however, future industrial development of this field may also involve integrationof more than one HPP step before pressure relief.