Advances in mass transfer and fluid flows in non-thermal food processing industry – a review

Abstract

All around the world, food processing techniques make use of various kinds of treatments to improve the shelf-life of foods. The commonly used thermal treatments are likely to result in deteriorating the sensory as well as nutritional qualities of foods. However, consumers are now demanding for safer and cleaner food without needing to compromise on the quality. Owing to the evolving nature of consumer demands, food technologists and others in the agro-food chain have devised processes to meet these changing demands by considering new non-thermal food processing techniques, which achieve microbiological inactivation in food materials without the application of heat directly. This review provides an appraisal on certain non-thermal food processing technologies with a focus on their operational mechanisms and success in the preservation of numerous kinds of food and offers an outline on the developments in non-thermal food processing techniques used in the food industry to enhance mass transfers. Increase in mass transfer is of industrial interest owing to a reduction in operation time. Use of a faster mass transfer velocity in the process produces multiple benefits, such as an increase in productivity, the preservation of physiological and nutritional value of food components, and a reduction in economic costs. The review demonstrates that techniques such as Pulsed Electric Field, Ultrasonication and Supercritical technology are viable treatments for enhancing mass transfer in the food processing industries.

Graphical Abstract

Introduction

From early on, food processing technologies have focused on guaranteeing the safety of foodstuffs and prolonging their shelf-life. Recently, authors tempt to develop stainable food systems in optimal food availability, retention, and production (Gould 2011; Hendrickx & Knorr 2002; Bellisle 1998; Knorr 1983, 2003). A wide number of diverse changes have been made to food processing technologies since then, especially within the agro-food industry (Roobab et al. 2018; Peña et al. 2019; Troy et al. 2016; Hernández-Hernández et al. 2019). In the agro-food chain, consumers are key. Their demand for fresh and nutritious foods with longer shelf-lives has increased over the years. Owing to the evolving nature of consumer demands, food technologists and others in the agro-food chain have devised processes to meet these changing demands (Hernández-Hernández et al. 2019).

The primary method for treatment of microbiological stabilization and sensory and nutritional property preservation for many years have been largely associated with heat (Knockaert et al. 2012; Zhong et al. 2019). Whilst the key aim of food processing is to reduce pathogenic microorganisms in food and food spoilage by extension, heat adversely affects both sensory characterises and nutrient contents of foods, resulting in a change in the foods physico-chemical attributes which affects both the organoleptic quality and can result in the breakdown of key nutrients within the food. Some of these unwanted and undesirable affects because of heat processing technologies are modifications in the concentration of thermo-sensitive bioactive compounds in food, nutrient content, appearance, texture and sensory characteristics of food. The drive for innovative non-destructive food technologies, therefore, can be attributed to an increased consumer demand for the preservation of nutritional contents and desirable sensory qualities in food (Hernández-Hernández et al. 2019; Valdramidis & Koutsoumanis 2016). These non-destructive technologies are designed to retain the sensory aspect of food whilst ensuring microbial inactivation (Bhattacharjee et al. 2019; Bahrami et al. 2020).

Heat processing eliminates microorganisms and affects food’s physical, sensory, and nutritional properties. Customer demand and this assumption have motivated technology advancement. Furthermore, improvements in medicine, biology, nutrition, nutrigenomics, and food processing have led to various functions that need individual conditioning and preservation procedures to preserve their bioactive components. Non-thermal food preparation is typically recommended for safe, nutritious, and flavorful meals. Pulsed electric field technology, an unique non-thermal food processing procedure that degrades nutrients and tastes less than drying, pasteurization, sterilization, solvent extraction, and heat-sensitive foods like fruit juices and smoothies, has expanded in commercial applications. Lab- and pilot-scale equipment become industrial-scale. Several publications confirm that PEF-treated fruit juices and smoothies are available in various nations (Hernández-Hernández et al. 2019).

New non-thermal food processing techniques, which achieve microbiological inactivation in food materials without the application of heat directly (Troy et al. 2016; Hernández-Hernández et al. 2019; Bhattacharjee et al. 2019), are emerging and novel alternatives to the conventional thermal processing techniques (Hernández-Hernández et al. 2019; Chemat, Rombaut, Sicaire, et al. 2017). These newer methods, yet to replace their conventional counterparts, include pulse electric fields (PEF), non-thermal plasma / cold plasma (NTP), pulsed light, ultrasound technology (Rahaman et al. 2016; Dong et al. 2021), ozone treatment (Guzel-Seydim et al. 2004; Komanapalli & Lau 1996; O’Donnell et al. 2012), and high-pressure processing (HPP) (Zhong et al. 2019). Ionizing radiation, ultrasound, pulsed light, ultraviolet radiation, HPP, and PEF technologies are classified as physical processes whereas cold plasma and ozone technologies are classified as chemical processes (Guzel-Seydim et al. 2004; Komanapalli & Lau 1996; O’Donnell et al. 2012; Rahaman et al. 2016; Dong et al. 2021).

As mentioned earlier, non-thermal food processing technologies involve ultrasound technology, cold plasma (non-thermal plasma), ozone treatment, high-pressure processing (HPP), ionizing irradiation (IOR), ultraviolet radiation (UV), pulsed light (PL) and pulsed electric field (PEF) (Chacha et al. 2021). Non-thermal techniques may increase food quality and yields alone or with other strategies. Maximizing energy and mass transfer, mixing components, conserving food properties, and decreasing heat and concentration gradients improve filtration, freezing, separation, drying, emulsion, thawing, brining, oxidation, homogenization, meat tenderization, sterilization, and extraction. Ultrasounds increase drying kinetics, saving energy and time. Hydrophilic nutrients and chemicals are better at mass and energy transfer, mixing, food characteristics, and decreasing temperature and concentration gradients, therefore, they are less likely to be lost if the product is not immersed. Ultrasounds before drying typically increase drying kinetics, reducing drying time. In addition, ultrasonic technology inhibits browning enzymes by rupturing cell membranes, which has garnered attention. Chiozzi et al. 2022 compared thermal (pasteurization, sterilization, and aseptic packing) and non-thermal (ultrasounds, UV radiation, ozonation, and high hydrostatic pressure) food preparation procedures (Chiozzi et al. 2022; Al-Sharify et al. 2020). They investigated ultrasounds application in Fruits and Vegetables (including strawberry, papaya, pineapple, pomegranate, guava, and melon in addition to pre-treatment for sweet potatoes prior to frying), application in Meat and Fish Products (including meat from pork, beef, chicken, and rabbits), applications in Cereal Product (flour dough and bakery products such as bread, crackers, biscuits, wafers, and batters (pancakes, donuts)), application in Dairy Products and Emulsified Products (Chiozzi et al. 2022).

Food processing using non-thermal technologies is well established in scientific literature and subject to increasing research by scientists. Moreover, a broad range of food products already utilize these methods. Continuous synthesis of the literature is needed as it serves to benefit food processors and potentially several others in the supply chain of agro foods. Additionally, it serves to enhance the current knowledge. Therefore, this review aims to offer an appraisal on selective non-thermal food processing technologies with a focus on their operational mechanisms and success in the preservation of numerous types of foods, and to provide an outline on the state-of-the-art applications of non-thermal food processing techniques used in the food industry to improve the mass transfer.

Mass transfer in the food industry

Mass transfer is the movement of a substance between two phases of varying concentrations till a chemical equilibrium is reached (Welti-Chanes et al. 2005). Mass transfer is utilized widely in the food industry across several processes. For example, mass transfer is used in introducing desired substances into food (salting, curing, osmotic dehydration), in extracting desired substances from food (antioxidants, colorants, sugar, fruit juices, etc.) and in removing water from foods (drying) (Chiozzi et al. 2022; Al-Sharify et al. 2020; Welti-Chanes et al. 2005; Onyeaka et al. 2023; Nobel 1999).

Factors influencing the rate of mass transfer vary from the strength of the concentration gradient to the resistance faced by the particles of the substance in transfer between the phases. For food material composed of cells, mass transfer is mainly dependent on diffusion through the cell membrane. Compared to its adjacent aqueous solution, the mean diffusion coefficient of a solute in cell membrane is estimated to be much lesser (Onyeaka et al. 2023). Previously, maintaining food demands quality t typical food preservation techniques subject foods to high temperature, which affects its texture, organoleptic qualities, and temperature-sensitive nutritional components (Jadhav, Annapure, et al. 2021).

Food specialists investigated non-thermal alternatives processing exposes food to ambient temperature for a minute or less, preserving its nutritional value, texture, and mouthfeel. Due to consumer demand for fresh foods with longer shelf life and better taste, non-thermal food treatment has been studied extensively. Non-thermal food processing and preservation processes, which use less power and provide healthier food, may replace thermal methods. Non-thermal methods preserve food better than thermal technologies since they don’t produce product qualities or byproducts. When using cold plasma it apparently eliminates microbes at room temperature. As ambient temperature is being used, heat-sensitive foods are protected (Jadhav, Annapure, et al. 2021). Recent studies investigate mass transfer and have examined supercritical fluids employed in supercritical technologies and may substitute organic solvents in many procedures. Supercritical fluids are fluids heated above their critical temperature and pressure. A supercritical fluid is gaseous and liquid-like. Its diffusion coefficient and viscosity are just like gases and liquids. Supercritical fluid, which has enhanced properties like liquid, may be used as a solvent to extract bioactives from various sources, including animals and plants. Fluids change with temperature and pressure. Carbon dioxide is a desirable supercritical fluid in the food processing sector since it may become supercritical at 31.1 °C and 7.4 MPa. Supercritical fluids are used in the food sector for extraction, microbial inactivation, improving mass transfer during synthesis, etc. Among other applications, supercritical extraction is widespread. According to earlier studies, high-pressure carbon dioxide at 1 MPa pressure for 26 h decreased the microbial load of ground beef. A careful review of the literature suggests that supercritical technology might be used in the food processing sector to extract food components and preserve and enhance their physiological qualities for use in functional and nutraceutical formulations (Jadhav, Annapure, et al. 2021). Many authors used thermal processing to enhance food’s flavor, texture, applicability, and shelf life. Most food thermal processing methods use heat and mass transfer to achieve these aims and manufacture flavour components from chemical processes. Heat and mass transmission must account for the whole effects of processing on food matrix with intricate physics. Nevertheless, many studies overlook capillarity, shrinkage, and expansion during heat and mass transmission, which leads to model errors. To properly comprehend the relationship between structure and property, including as many of the above factors as possible, especially those that may affect transfer processes, is important. Mass and heat transport frequently cause food deformation during thermal processing. Therefore, mass and heat transfer will be significantly affected. Moreover, shrinkage and processing factors match nicely (temperature, air flow rate, or time) (Li et al. 2022).

In the design of food processing equipment and processes, and the control of food storage and packaging, the mass transfer coefficient of the interface is crucial. The qualities of the food processing equipment used strongly affects transfer coefficients. As such, the mass transfer coefficient is highly significant in the design of drying, separation, and storage processes (Li et al. 2022).

The following correlation can be used to define the surface mass transfer coefficient:

$$J= {h}_{M}A({X}_{A}-{X}_{AS})$$

(1)

where

$J$ = rate of mass transfer (kg/s)h_M = surface mass transfer coefficient at the material-air interface (kg/m² s)

A = effective surface area (m²)

X_AS = air humidity at the solid interface (kg/kg)

X_A = air humidity at the bulk air interface (kg/kg)

Calculations using empirical equations with the dimensional numbers below can be performed to determine the mass transfer coefficient. Alternatively, it can be experimentally determined.

$$\mathrm{Mass\, transfer\, factor }\,{j}_{M}=\left(\frac{{h}_{M}}{\mu \rho }\right){Sc}^{2/3}$$

(2)

$$\mathrm{Reynolds\, number }\,Re=\mu \rho d/\eta$$

(3)

$$\mathrm{Schmidt\, number }\,Sc=\eta /\rho d$$

(4)

whereu = air velocity (m/s)ρ = air density (kg/m³)d = particle diameter (m)η = dynamic viscosity of air (kg/ms)

The Re number depends on the particle diameter d as well as the actual air velocity u. For particles that are non-spherical, d is described as:

$$d= 6{V}_{p}/{A}_{p}$$

(5)

where

V_p = particle volume

A_p = particle surface areak_C, the mass transfer coefficient often utilised in research works is associated to h_M by the following correlation:

$${k}_{C} = {h}_{M} /\uprho$$

where ρ is the fluid density. At ambient temperature and atmospheric pressure, the dry air density for air/water systems is about 1 kg/m³. Thus, the magnitude of k_C (m/s) and h_M (kg/m²s) is same (Perry & Green 1997; Saravacos 1997).

Increase in mass transfer is of industrial interest owing to a reduction in operation time. Use of a faster mass transfer velocity in the process produces multiple benefits, such as an increase in productivity, the preservation of physiological and nutritional value of food components, and a reduction in economic costs. Food materials, across many cases, are pre-treated by heat, enzymes, or mechanical grinding to influence and increase the transfer rate. These methods deteriorate the cytoplasmic membrane and increase its permeability, resulting in the loss of the diffusion barrier (Toepfl et al. 2006). However, significant expenditures of thermal and mechanical energies are required for these methods. They can also potentially be destructive to valuable food compounds. Non-thermal food processing techniques can replace these conventional methods in the treatment of food material (Li et al. 2022).

Vegetables and fruits are crucial sources of compounds such as antioxidants, natural colors, fibre, vitamins, and minerals. These nutraceutical compounds are necessities to the human diet and beneficial to the human body (Omolola et al. 2017; Ramya & Jain 2017). Because of their high moisture content, however, biochemical and microbiological changes are common in vegetables and fruits as exhibited by the shortened shelf lives. Dehydration can be used to reduce moisture levels in these foods to low or intermediate levels, and in turn prolong their shelf lives (Chitrakar et al. 2019; Qiu et al. 2019). Using a higher temperature in the dehydration process, reduces the process time but also leads to undesirable changes as in changes to quality parameters, morphometric changes, depletion of thermo-sensitive nutrients, and changes to sensory characteristics (from enzymatic or chemical reactions) (Santillana Farakos et al. 2013). In contrast, osmotic dehydration allows for moisture reduction to intermediate levels whilst improving the taste and appearance of fruits and vegetables by inhibiting enzymatic browning. Osmotic dehydration involves both, the removal of water and the incorporation of solutes (Omolola et al. 2017; Ramya & Jain 2017; Sabarez et al. 2018).

Figure 1 presents a schematic diagram of the osmotic dehydration procedure that usually occurs in vegetables and fruits.

Fig. 1

Mass transfer in osmotic dehydration procedure of vegetables or fruits (González-Pérez et al. 2021)

However, mass transfer is slow in osmotic dehydration. Also, there may be loss of food components such as organic acids, minerals, or vitamins (Kuo et al. 2018; Yadav & Singh 2014). Various rate controlling parameters affect the mass transfer rate. Some examples of rate controlling parameters include the process conditions (temperature, agitation, time), the food matrix (physiochemical characteristics), and the osmotic agent in use (concentration and component make up) (Cichowska et al. 2019; Fernandes et al. 2017; González-Pérez et al. 2019; Monnerat et al. 2010; Nowacka, Wiktor, et al. 2019; Nowacka, Laghi, et al. 2019).

Typically, the temperature used in the osmotic dewatering is the parameter altered to reduce the operating times of the process as a rise in the temperature, rises the permeability of the cell membrane, ergo accelerating mass transfer (Akharume et al. 2019; Assis et al. 2016). However, higher process temperatures adversely affect product quality and seen by changes to flavour, texture, color, etc. (Sabarez et al. 2018; Barbosade Lima et al. 2016). Non-thermal methods like osmo-sonification, ultrasound, electrical pulses, vacuum pulses, along with high hydrostatic pressure have been developed to enhance the mass transfer whilst eliminating adverse affects on quality (Dash et al. 2019; de Mello et al. 2019; Martín-Belloso et al. 2018; Nowacka et al. 2018; Osae et al. 2019).

Combining osmotic dehydration with non-thermal methods enables effective reduction of fruit and vegetable processing time. This combined method increases the rate of mass transfer and allows for changes to membrane permeability without affecting product quality (Deng et al. 2019; Dermesonlouoglou et al. 2016; Onwude et al. 2017).

Pulsed electric field

Pulsed Electric Field (PEF) treatment is the application of low to moderate intensity electric fields by direct current voltage pulses to materials placed in between two electrodes for very brief periods of time. Between the microseconds to milliseconds an electric field is generated due to the voltage pulses, the strength of which is determined by the distance between plates and the voltage applied. Typically, low intensity fields are of strengths < 0.1 kV cm⁻¹, moderate intensity fields are between 0.1 to 1 kV cm⁻¹, and high intensity fields are above 1 kV cm⁻¹ although no formal definition exists (Asavasanti et al. 2010).

The mass transfer is improved due to the permeabilization of eukaryote cells. Shorter processing periods vary between 100 to 10,000 μs for electric fields in the range of 1 to 10 kV cm⁻¹ (Nowacka et al. 2018). Permeabilization, or cell membrane puncturing enables access through the cell membrane and fluid movement, thereby enhancing mass transfer (Novak & Ribera 2003; Molgaard et al. 2016; Burry 2009).

The limitations of non-thermal processing techniques particularly addressed over the past several decades. Non-thermal techniques classified as value-added technologies have gained prominence as viable alternatives to standard food processing. The direct influence is represented by the reduction of energy effect during storage and the effective reduction of water and energy usage during processing. In contrast, the Influences of non-thermal treatment are projected to lower organic waste and boost the worth of biomass resources (Chemat, Rombaut, Meullemiestre, et al. 2017; Pereira & Vicente 2010). However, food losses, inefficient by-product/processing impurities consumption, and unessential quality degradation within the supply chain are all significant inefficiencies within the food manufacturing industry, the indirect impact of non-thermal processing on food processing sustainability may be even more significant than direct impacts (Pereira & Vicente 2010).

Figure 2 presents the results of one recent experimental investigation that looked at the colour of extraction media after four separate extraction times. Red beetroots were utilised in the study where one sample was untreated (0 kV cm⁻¹) and then samples were treated by pulsed electric fields at varying intensities (1, 3, 5 and 7 kV cm⁻¹). The results revealed that at 7 kV cm⁻¹, the application of five pulses led to an increase of about four times in the overall quantity of betalain obtained through red beetroot (López et al. 2009; Puértolas et al. 2012).

Fig. 2

Effects of different intensities of pulsed electric fields on red beetroots samples (Puértolas et al. 2012)

Electroporation, or Electro-permeabilization, is the phenomenon in which applying external electric field pulses for micro-millisecond durations results in increases to cell membrane permeability (Tsong 1991). In recent times, electroporation is being suggested as an alternate technique to thermal processing for inactivating microorganisms as it performs effectively with lower temperature requirements. It is also routinely utilized to access and introduce molecules into cell cytoplasm in molecular biology (Teissie et al. 2002).

Electroporation in the food industry for microbial activation and mass transfer increase is irreversible whereas in traditional biotechnical application reversible electroporation is used. Reversible electroporation preserves cell viability by external electric fields application near the critical value. This way the cell membrane is allowed to recover its functionality and structure. Exceeding the critical, as is done in irreversible electroporation, disintegrates the membrane resulting in the loss of cell viability. Experiments on liposomes, which are representative of model systems, and eukaryote cells, individually, have been used to explain electro-permeabilization by some theories. However, cells of food materials make up tissues with inhomogeneous and complex structures having spatially dependent properties. As such, the local electric field distribution represents an intricate function of the electrical characteristics of the material structure, the changes during the PEF treatment, porosity, and constituents (Vorobiev & Lebovka 2006). Whilst a fundamental understanding is crucial in setting the critical process parameters for improves mass transfer with PEF treatment, available information about membrane permeabilization is limited.

From the extraction of sugar and rapeseed oil from sugar beets to the dehydration of red bell peppers and coconuts, the cell disintegration index has proven to be highly beneficial in setting conditions for PEF treatment that are optimized to increase mass transfer (Ade-Omowaye et al. 20002003; Eshtiaghi & Knorr 2002; Guderjan et al. 2007). Whilst most studies on PEF treatments have been done at room temperature, PEF-induced damage in plant tissues has been demonstrated to be influenced by temperature. Applying electric fields stronger than the critical value increases cell membrane electroporation. In turn, this increases the mass transfer rate. The transfer rate is dependent of electric field intensity and process times. Increases in field strength beyond the threshold value results in maximum permeabilization and does not increase mass transfer any further (Knorr & Angersbach 1998; Praporscic et al. 2004; Hasan 2022; Mhawesh et al. 2022).

From the above, the capacity for PEF as a viable treatment to improve mass transfer can be seen. Due to advantages such as the short processing times and low energy consumption required for permeabilization of eukaryote cells, PEF treatment should be implemented across the food industrial level immediately. Then to summarize, PEF treatment increases the period for which quality of rehydrated and thawed foods is maintained, decreases the time required for drying and freezing food, and improves the pre-drying diffusion coefficient for water. PEF is used in enhancing the chemical and physical properties of certain polysaccharides and food components (Hasan 2022; Dong et al. 2020; Zhu 2018), the modification of potato starch (Chen et al. 2020), alongside being used in modification of properties of oat flour (Duque et al. 2020). Lastly, because of its high intensity and subsequent enhancement of heat transfer, PEF can be utilised in esterification (Lin et al. 2012) and it increases the rate of reaction and the mass transfer in chelation (Zhang et al. 2017). Advancements in instrumentation dealing with high strength PEF are needed for industrial use due to the numerous benefits of PEF as a non-thermal treatment method (Chemat & Zill-E-Huma 2011).

Ultrasonication

Ultrasonication is a well-established food processing technique across many sectors and is emergent in the food sector. As a non-thermal technology, ultrasonication relies on ultrasound. Ultrasound consists of any sound wave with a frequency higher than 20,000 kHz which is typically the upper limit of normal human hearing (Mason & Cintas 2007). As the ultrasonic waves pass through a medium, they oscillate. The resulting oscillation generates a series of compressions and expansions in the medium. In the presence of air, small cavities are formed. These cavities collapse after reaching a desired size, producing hot spots locally and releasing large amounts of energy. In turn, mass and heat transfer rates are increased (Bhangu & Ashokkumar 2016). Chemical synthesis involving organic compounds is sped up by ultrasonication due to the increased yield produced by the enhanced mass and heat transfer. Shear forces produced in the medium by ultrasonication depends on the frequency as low frequencies produce larger forces and high frequencies produce smaller forces. Matching the frequency to that of the medium, as various sonochemical-assisted processes are optimized, results in the formation of radical species which can lead to oxidative changes to proteins and lipids amongst other undesirable affects (Delmas et al. 2015).

The frequency range utilized in food processes such as in intensified synthesis, debittering, cooking, emulsification, and extraction of bioactives is 20 kHz-100 kHz. On designer lipid synthesis using sonification, Jadhav, Gogate, et al. (2021) reported a 92% maximum yield in 6 h of the reaction. Ultrasonication as an alternative to intensify yield is excellent as it increases the rate of mass transfer. Compared to conventional synthesis, ultrasonication-assisted synthesis is rapid and benefits from high-energy spot generation (Jadhav & Annapure 2021). Ultrasound, by assisting the interfacial transfer of molecules, enhances the extraction of bioactives whilst improving the chemical and physical properties of the extracted bioactives from animal and plant sources. This was reported recently by Sun et al. (2020), who found superior properties for protein extracted from ultrasonication in terms of structure, emulsification power and size of particle.

Ultrasonic-assisted filtration is utilized within the dairy and beverage industry. For example, due to its effectiveness, the process of membrane filtration is utilised in the cheese making industry to completely separate milk protein from other milk solids (Saxena et al. 2009). For procedures involving drying, thawing as well as freezing of food products, ultrasonication is also highly useful (Chow et al. 2005; Miles et al. 1999; Cheng et al. 2014). After reviewing ultrasound technology for food fermentation application, Ojha et al. (2017) showed that a better process and production rate could be obtained using a low frequency between 20–50 kHz due to enhancements to both mass transfer and cell permeability (Prestes et al. 2023).

Ultrasound has proven its viability as a potential alternative across critical areas of the food sector. These areas include food preservation, extraction, and intensified synthesis alongside the advancement of chemical and physical characteristics of foods. Due to a lack of consumer awareness and limited technical information, ultrasonication has faced poor commercialization prospects within the food industry. As such, an understanding of the effects of ultrasonication of bulk food is important before industrial wide implementation (Jadhav, Annapure, et al. 2021; Prestes et al. 2023).

Supercritical technology

Supercritical technology is based on the use of supercritical fluids. These are fluids that attain a supercritical state due to heating beyond the critical temperature and pressure and show a mix of properties of liquids and gases. These fluids show viscosity and diffusivity like gasses and density like liquids (Mason & Cintas 2007). They are considered good organic solvent replacements in various processes as such (Temelli et al. 2012). For example, in bioactives extraction from animal and plant sources, supercritical fluids can be used as solvents to increase mass transfer rate. Another added benefit is that their properties can be tuned by varying the temperatures as well as pressures. Amongst several other fluids, carbon dioxide as a supercritical fluid is excellent for use in the food processing industry due to its modest pressure and temperature requirements (7.4 MPa and 31.1 °C, respectively) to attain its supercritical state. Whilst primarily employed in extraction processes, supercritical fluids have also found use in synthesis mass transfer enhancement, microbial inactivation, etc.

For the purpose of extraction, supercritical carbon dioxide is used as it easily separated from the final product and is non-toxic (Brunner 2005; Deotale et al. 2021). The quality of material extracted is much higher as natural bioactives are susceptible to effects of temperature and oxygen. Using supercritical carbon dioxide, allows the use of low temperatures and ensures there is no contamination by oxygen. The extracted material can be used in various nutraceutical formulations as a functional ingredient (Deotale et al. 2021).

Utilising supercritical carbon dioxide in extraction for many purposes and has been popular in the food processing industry for several years (Pinto et al. 2020; Gallego et al. 2019; Torres-Ossandón et al. 2018; Priyanka 2020; Ferrentino et al. 2020; Rebolleda et al. 2012; De Oliveira et al. 2014; Salea et al. 2017; Al-Otoom et al. 2014; Molino et al. 2020; Pavlić et al. 2020; Santos et al. 2020; Priyanka 2018; Fornari et al. 2012; Spilimbergo & Bertucco 2003; Koubaa et al. 2018; Silva et al. 2020; Rushdi et al. 2020; Onyeaka, Miri, et al. 2021; Agbugba et al. 2022; Obileke et al. 2022; Onyeaka et al. 2022; Zaid et al. 2022). It is used in the extraction of bioactives, usable as components in nutraceutical formulations, such as quercetin, anthocyanins, astaxanthin, lycopene, and carotenoids (Pinto et al. 2020; Gallego et al. 2019; Torres-Ossandón et al. 2018), extraction of essential oils (Priyanka 2020; Ferrentino et al. 2020), extraction of green coffee oil and corn germ oil (Rebolleda et al. 2012; De Oliveira et al. 2014), oil from ginger (Salea et al. 2017), oil from olives (Al-Otoom et al. 2014), extraction of fruit seed oil (Molino et al. 2020; Pavlić et al. 2020; Santos et al. 2020; Priyanka 2018; Fornari et al. 2012) and nutraceutical and functional ingredient extraction from microalgae (Molino et al. 2020). Moreover, supercritical technology can be used in microbial load reduction in food. By reducing the pH of bacterial cells, supercritical fluid treatment leads to cell rupture and subsequent bacterial enzyme inactivation. These enzymes are responsible for anabolism and catabolism. As a result, the bacterial cells perish, and the microbial load is reduced (Spilimbergo & Bertucco 2003). The original and organoleptic characteristics of food are retained (Koubaa et al. 2018) whilst using supercritical technology treatment as the operating temperature is low. For example, it is widely used in the preservation of fruits and vegetables and their juices (Silva et al. 2020). Lastly, supercritical fluids are also used for ground meat preservation. More recent studies on food processing using supercritical technology increased dramatically with the wide spread of COVID-19 virus worldwide (Aditya & Kim 2022; Al-Mashhadani et al. 2020; Ekwebelem et al. 2021; Greene et al. 2022; Hamad et al. 2020; Onyeaka, Al-Sharify, et al. 2021; Onyeaka, Anumudu, et al. 2021; Rushdi et al. 2020; Shakor 2022; Sun et al. 2022; Uwishema, Adekunbi, et al. 2022; Uwishema et al. 2021; Uwishema, Chalhoub, et al. 2022; Uwishema, Chalhoub, Zahabioun, et al. 2022; Uwishema, Taylor, et al. 2022; Al-Sharify et al. 2022; Braga et al. 2023), including the use of three-dimension printing of meat following supercritical fluid extraction controlled remotely through the use of IoT system (Aditya & Kim 2022). Recent study focused on supercritical fluid, non-thermal processing, and food science innovations. eliminating germs and mycotoxins in fruit juices while keeping taste and nutrition with healthier options using s upercritical Technology handling Cereal Byproducts. The potential of supercritical technology to valorize maize milling byproducts by evaluating trademarks, techniques, economic feasibility, and future usage (Braga et al. 2023; Barros et al. 2023; Lopes et al. 2023; Santana & Meireles 2023). Reviewing the literature on supercritical technology critically showed the bright potential for supercritical technology in food processing with its usefulness in the enhancement and preservation of physical qualities of food constituents for use as practical ingredients in nutraceutical and functional formulas, alongside its extensive use in extraction (Santana & Meireles 2023).

Conclusions

Non-thermal food processing treatments are being employed more frequently in the food industry because of its advantages with regards to shorter exposure time and lower temperature of treatment which preserves food quality while eliminating possible pathogenic and spoilage organisms in food. Furthermore, there are practically minimal or no chances of heat damage to the food product, ensuring the maintenance of the nutritional and organoleptic quality of the food. This review studied certain selected non-thermal food processing technologies by paying focus on their operational mechanisms and success in the preservation of different types of foods. Also, the review provides an outline on the state-of-the-art uses of non-thermal food processing techniques used in the food industry to improve mass transfer. Increase in mass transfer is of industrial interest owing to a reduction in operation time. Use of a faster mass transfer velocity in the process produces multiple benefits, such as an increase in productivity, the preservation of physiological and nutritional value of food components, and a reduction in economic costs. The review demonstrates that techniques such as Pulsed Electric Field, Ultrasonication and Supercritical technology are viable treatments for enhancing mass transfers in food processing. Due to limitations in understanding the effects of these different non-thermal treatments, it is recommended that further research work is carried out on these techniques before their industrial wide implementation takes place.