Revisiting Non-Thermal Food Processing and Preservation Methods-Action Mechanisms, Pros and Cons: A Technological Update (2016-2021)

Abstract

The push for non-thermal food processing methods has emerged due to the challenges associated with thermal food processing methods, for instance, high operational costs and alteration of food nutrient components. Non-thermal food processing involves methods where the food materials receive microbiological inactivation without or with little direct application of heat. Besides being well established in scientific literature, research into non-thermal food processing technologies are constantly on the rise as applied to a wide range of food products. Due to such remarkable progress by scientists and researchers, there is need for continuous synthesis of relevant scientific literature for the benefit of all actors in the agro-food value chain, most importantly the food processors, and to supplement existing information. This review, therefore, aimed to provide a technological update on some selected non-thermal food processing methods specifically focused on their operational mechanisms, their effectiveness in preserving various kinds of foods, as revealed by their pros (merits) and cons (demerits). Specifically, pulsed electric field, pulsed light, ultraviolet radiation, high-pressure processing, non-thermal (cold) plasma, ozone treatment, ionizing radiation, and ultrasound were considered. What defines these techniques, their ability to exhibit limited changes in the sensory attributes of food, retain the food nutrient contents, ensure food safety, extend shelf-life, and being eco-friendly were highlighted. Rationalizing the process mechanisms about these specific non-thermal technologies alongside consumer education can help raise awareness prior to any design considerations, improvement of cost-effectiveness, and scaling-up their capacity for industrial-level applications.

Keywords: agro-food industry; food preservation; food processors; non-thermal food processing; product development.

Figure 1

Schematic representation of non-thermal food processing technologies synthesized (which include: pulsed electric field (PEF), pulsed light (PL), ultraviolet radiation (UV), ionizing irradiation (IOR), high-pressure processing (HPP), ozone treatment, cold plasma (non-thermal plasma), and ultrasound technology) with the overview strategy (which include: mechanisms/principles of action, and the associated merits, and restrictions).

Figure 2

Schematic flow of PEF operation pathway (Source: Mohamed and Eissa [18]; permission to use not required).

Figure 3

The food system under high hydrostatic pressure showing how the latter gets applied from all sides to the food material (Source: Khan et al. [36]; permission to use given by Elsevier Science).

Figure 4

Schematic diagram showing the cavitation and sponge effect of ultrasound technology (Source: Astráin-Redín et al. [66]; permission to use not required).

Figure 5

Schematic diagram of a pulsed light (PL) chamber (Source: Mahendran et al. [73]. Permission to use given by Elsevier Science).

Figure 6

Schematic diagram for set-up of ozone generator highlighting corona discharge instrument: Key: A = Oxygen cylinder; B = Flow rate controller; C = Bubble type flow meter; D = Ozone generator; E = Transformer; F and G = Excess ozone traps (4% KI); H = Rotating vessel (90 rpm); V = Valve; X = High tension electrode (Source: Okpala, [103]; Permission to use not required).

Figure 7

Schematic depiction of three typical electrical discharges for generating the non-thermal plasma with typical sizes indicated and discharge appearance (Source: Scholtz et al. [128]; permission to use given by Elsevier Science).