1 Introduction

Foods are derived from either plant or animal origin and contain various nutrients like carbohydrates, proteins, lipids, vitamins, minerals, and other bioactive components. They are prone to spoilage due to different physical, chemical, and microbial agents. Food preservation is defined as processes by which the shelf life of food products can be increased without affecting the product quality in terms of nutrient retention and sensorial attributes [1]. Beverages provide energy, water, and nutrients like vitamins, minerals, proteins, lipids, and carbohydrates. Beverages can be classified into water, unsweetened tea or coffee, milk, sweetened with non-nutritive sweeteners, energy as well as nutrient-rich, and only energy-yielding sweetened beverages [2,3,4]. The demand for health-promoting beverages in the global market is continuously growing due to consumers' continuous health awareness, and they prefer foods of nutritional value that can reduce the risk of diseases [5, 6]. Conventionally, fruit or vegetable-based beverages are processed using thermal processing methods [7, 8]. However, thermal processing can cause severe physical and chemical changes, affecting the organoleptic properties and nutrient bioavailability [9, 10].

Non-thermal processing techniques like ultrasonication, cold plasma technology, supercritical carbon dioxide (SC-CO2), pulsed light, high hydrostatic pressure (HHP), membrane technology, and pulsed magnetic field can be used for processing health-promoting beverages (Fig. 1). These techniques can be used to prevent the aforementioned drawbacks of conventional thermal processing methods. The non-thermal processing methods can result in a preservation effect similar to thermal processing methods while minimizing the deleterious effects on nutrients, color, texture, and sensorial characteristics of food products [11,12,13,14,15]. Thermal processing requires huge energy requirements and also results in products of poor quality; hence, it can be replaced with environmentally friendly non-thermal processing techniques. During non-thermal treatment, the microbes are inactivated for a shorter duration due to the alteration in the membrane structure of bacteria and the unfolding of DNA structure [16,17,18]. It also affects the non-covalent bonds like hydrogen and ionic bonds to denature the protein, gelatinize the starch, and destroy the pathogenic or food spoilage-causing microorganisms [19,20,21,22]. The thermal treatment affects both covalent and non-covalent bonds, resulting in product quality deterioration [23]. In this review article, the principle and effect of different non-thermal processing technologies on the quality of health-promoting beverages are described.

Fig. 1
figure 1

Non-thermal processing technologies for health-promoting beverages

2 Ultrasonication

In ultrasonication, the treatment of food products is carried out at lower temperatures whereas, in thermosonication, food products are subjected to both ultrasound and moderate temperature [24, 25]. Manosonication is the treatment in which food materials are exposed to ultrasound and pressure (100–300 kPa). In manothermosonication, food products are treated with ultrasound in combination with pressure and temperature [26, 27]. The thermophilic microorganisms can be inactivated by manothermosonication because both the temperature and pressure provide a synergistic effect leading to the collapse of created cavities.

2.1 Working principle

Ultrasound is a sound wave with a frequency higher than 20 kHz which is more than normal human hearing frequency. Ultrasound waves oscillate through the medium resulting in the creation of numerous cycles of expansion and compression [28]. The small cavities are formed due to the presence of air and the cavities expand to a definite size followed by collapse. This results in the generation of huge energy and local hot spots while increasing heat and mass transfer rates [29]. The direct heating of the product takes place during ultrasound treatment due to the release of high energy and intense agitation. Ultrasonication can be classified into low (20–100 kHz), medium (100 kHz–1 MHz), and high (1–100 MHz) range frequencies. Low frequency can produce a large shear force, while medium produces radical species and high frequency produces less shear force. The medium-range frequency of ultrasound waves is more suitable for various processes because that can cause the oxidation of lipids and proteins during food processing. It is carried out by immersion of the health-promoting beverages at a suitable frequency in an ultrasonic bath resulting in the desirable changes in the subjected food material [30]. The diagrammatic representation of ultrasonication is provided in Fig. 2.

Fig. 2
figure 2

Schematic representation of ultrasonication mechanism [99]

2.2 Application of ultrasound in the processing of health-promoting beverages

Ultrasonication can also be used for degassing carbonated beverages by which microbial load reduction can also be attained. A continuous flow high-intensity ultrasound was used for the inactivation of various enzymes during the processing of milk [25]. The synergistic effect of heating (61–75.5 °C) along with ultrasound resulted in the denaturation of enzymes (alkaline phosphatase, gamma-glutamyltranspeptidase, and lactoperoxidase) and proteins (alpha-lactalbumin and beta-lactoglobulin). There was no change in the casein structure but fat globule size was reduced up to 81.5%. The particles were evenly distributed at ~ 70 °C compared to processing at lower temperatures. Ultrasound treatment improves the homogeneity of the solution due to the reduction in particle size and results in superior product quality.

The synergistic effect of carbonation and ultrasonication on nutrient quality and the microbial load reduction in guava juice was investigated by Cheng et al. [31]. Carbonation facilitates the formation of numerous nuclei for cavitation which in turn removes dissolved oxygen. This treatment resulted in the juice with higher ascorbic acid retention but microbial load reduction was low. Sonication of strawberry juice samples at 40–100% amplitude levels at 20 kHz for 2–10 min and pulse durations of 5 s ON and 5 s OFF was reported [32]. The retention of anthocyanin and ascorbic acid content after 10 min of ultrasound treatment was 96.8 and 89%, respectively. The shelf life of sonicated orange juice (0.3–0.81 W/mL for 2–10 min) stored at 10 °C is 27–33 days while thermal pasteurized juice had 19 days of shelf life [33]. The sonicated orange juice retained higher ascorbic acid compared to thermally pasteurized samples. Anthocyanin retention of blackberry juice during ultrasound treatment at 100% amplitude for 10 min is more than 94% with negligible color change [34]. Sonicated passion fruit juice (20 kHz, 263 W, and 89.25 μm) retained the color, pH, and ascorbic acid content higher than thermal preservation while microbial load remained constant for 10 days upon storage at 4 ℃ [35].

Ultrasound treatment of Gulupa juice at 40 kHz for 30 min improved the shelf life to 20 days with minor color changes and a slight decrease in ascorbic acid level [36]. Extraction of noni juice using ultrasound improved the phenolic, and flavonoid content while the nutritional quality and suspension stability of the juice remained the same [37]. The color, pH, soluble solids, flavonoid, and phenolic content of kaji lemon juice are similar to that of thermally processed samples [38]. Ultrasound treatment of strawberry juice for 12 min retained phenolic, flavonoids, and ascorbic acid content similar to that of the unprocessed sample [39]. Conventional pasteurization of pear juice at 95 °C and ultrasound treatment at 65 °C inactivated the microbial load whereas ultrasound treatment resulted in the superior retention of phenolic compounds [40]. The sonicated barberry juice retained higher anthocyanin and phenolic compounds compared to thermally treated samples [41]. Ultrasonication of mulberry juice at 24 kHz for 30 min retained higher anthocyanin (95%) compared to thermally treated samples [42]. Ultrasound treatment of mango juice at 600 W for 40 min resulted in a complete reduction of microbial load and superior retention of nutrients [3).

Table 3 Effect of supercritical carbon dioxide on processing of health-promoting beverages

5 High hydrostatic pressure

High hydrostatic pressure (HHP) is a non-thermal processing technique wherein food products are subjected to a pressure of 100–1000 MPa at low temperatures to achieve pasteurization, enzyme inactivation, and protein denaturation [95, 96]. The efficiency of this process is dependent on temperature, treatment duration, pressure range, and characteristics of food products [97].

5.1 Working principle

The food product is immersed in a liquid medium and then exposed to high pressure for about 10–20 min in a closed chamber to provide uniform exposure of products to pressure irrespective of their size and shape [88]. Le Chatlier’s principle states that applied force can cause any change in the temperature, pressure, and volume of an equilibrium system leading to the development of a new equilibrium. Adiabatic heating is caused due to the exposure of food products to high pressure that in turn increases the temperature of the liquid medium by 3 °C for a pressure increase of 100 MPa [98].

5.2 Applications of high hydrostatic pressure for processing of health-promoting beverages

The processing of beverages using HHP can prevent the Maillard reaction and caramelization. The texture, color, flavor, and bioactive compounds of food products can be retained after HHP-based processing [99]. The HHP-based processing induces chemical reactions that can prevent microbial growth and also cause cell death by affecting the membranes [100]. The HHP-based treatment of soy smoothie at a pressure of 650 MPa and 20 °C for 3 min resulted in ascorbic acid retention of 55% and no changes in color and bioactive compounds [101]. It has also improved the antioxidant activity due to the increase in the content of β-carotene and lycopene. The sensory characteristics of treated smoothies (450 MPa) and fresh smoothies were similar. The HHP treatment of cucumber juice at 500 MPa for 5 min improved the sensory characteristics compared to high-temperature short-time treated juices [102]. The treatment of watermelon juice at 50 °C and 30 MPa for 30 min reduced polyphenol oxidase activity to 4% [103]. Mulberry juice exposed to the pressure of 500 MPa for 10 min resulted in the inactivation of aerobic mesophiles from 4 log CFU/ml to an undetectable level followed by the complete elimination of yeast and molds [104]. This has also increased flavonoids, phenolics, antioxidant capacity, resveratrol, and volatile compounds like aldehydes, alcohol, and ketones. The HHP-based treatment of strawberry puree at a pressure of 400–600 MPa resulted in higher retention of anthocyanin, phenolics, and ascorbic acid [105]. Aronia berry puree processed at 400 and 600 MPa for 5 min decreased yeast and mold to 1 log CFU/g and aerobic bacteria to < 2 log CFU/g without altering the phenolic content as well as antioxidant activity [106].

The HHP-based process (30–90 MPa, 10–25 °C for 1–7 cycles) reduced the methanol content in sorghum spirits while the sensorial characteristics were improved due to the formation of aroma compounds like methyl acetate [107]. The HHP-based processing of fruit and vegetable smoothies at 630 MPa and 20 °C for 6 min inactivated the peroxidase, polyphenol oxidase, and pectin methylesterase by 31.4, 9.7%, and 83.9%, respectively [108]. The pH and soluble solid content of smoothies were not affected. The exposure of reconstituted cow milk powder containing E. coli, P. fluorescens, and Enterobacter aerogenes to 500–600 MPa and 25 °C for 3–5 min resulted in the inhibition of these gram-negative bacteria [109].

Milk treated at a pressure of 600 MPa for 3 min resulted in the 5 log reduction of E. coli, Salmonella, and L. monocytogenes. This treatment also enhanced the shelf life to 7 days which is comparable to commercial pasteurized milk. The casein content and particle size of fat molecules were similar between HHP-treated and raw milk [110]. Milk processed using HHP for yogurt production resulted in the improvement of product firmness and controlled syneresis [111]. Multifruit-soymilk smoothies processed at 450–650 MPa for 3 min at 20 °C have not modified the color and bioactive compounds (lycopene, β-carotene, and antioxidants). The stability of these compounds was also maintained during refrigerated storage.

The HHP treatment (200–600 MPa for 5–15 min at < 40 °C) of goat milk resulted in the 7-log reduction of Staphylococcus aureus [112]. The viscosity and soluble solid content remained unaltered after HHP treatment and shelf life was improved to 10 days at refrigerated conditions. The treatment of orange juice at 400–600 MPa and 20 °C for 15 min improved the lightness and redness without altering the content of cyanidin-3-glucoside [113]. Treatment of citrus fruits in HHP retained the color and enhanced the shelf life [114]. Raw milk from Bordaleira, as well as Churra Mondegueira da Serra da Estrela sheep breeds treated using HHP of 121 MPa for 30 min, resulted in better curd yield (> 9%) and retained the microbiota beneficial for cheese preparation [115]. Shiikuwasha juice processed at a pressure of 600 MPa for 150 s resulted in > 5 log reduction of E. coli and provided shelf life stability for 28 days without affecting the color, aroma, phenolics, and flavonoids [116]. Carrot orange juice blend treated using HHP of 200–400 MPa for 300 s resulted in the extension of shelf life up to 28 days without altering the phenolic and carotenoid content [117].

Sea buckthorn juice treated at 500 MPa for 5 min retained aroma and flavor similar to fresh juice while the carotenoid and phenol content is comparatively higher than the thermally processed sample [118]. Microorganisms in HHP-treated aronia juice (200–600 MPa for 10 min) after storage for 80 days at 4 °C were below the detection limit and about 8–12% loss in phenolic content was observed [119]. The HHP treatment of apple juice (300 MPa for 10 min) resulted in a 3.7 log reduction of A. acidoterrestris without significantly affecting the pH and color of the juice [120].

The exposure of beetroot juice to HHP treatment at 500 MPa for 10 min resulted in the degradation of betacyanin (12.2%) and betaxanthin (8.9%) while the lactic acid bacteria was reduced up to 4.5 log [121]. Treatment of tomato juice in HHP at a pressure of 500 MPa for 5 min resulted in the superior retention of lycopene content and volatile compounds compared to the thermal pasteurization process. Treatment of kiwi juice in HHP at a pressure of 500 MPa for 10 min resulted in a 2-log reduction of aerobic mesophiles and enhanced the shelf life to 42 days [122]. The exposure of kiwi juice at 200 MPa for 3 cycles in HHP resulted in the extension of shelf life up to 48 days and 7 days in cold storage conditions and room temperature, respectively [123]. The HHP treatment of peanut sprout juice at a pressure of 600 MPa for 5 min retained aroma, color, and pH while the shelf life was extended up to 90 days [124].

The HHP treatment (250 MPa for 4 min) of grape juice resulted in the inhibition of B. cinerea without altering the sensory properties [125]. The HHP treatment of orange juice at a pressure of 600 MPa for 10 min resulted in the reduction of A. acidoterrestris spores to 3.5 log with the extension of shelf life up to 60 days [126]. About 22% of pectin methyl esterase was inactivated while a high reduction of molds (1.85–3.72 log) and yeast (3.19 log) in raspberry juice was attained at HHP treatment of 600 MPa for 10 min [127]. The shelf life of tender coconut water increased up to 120 days after HHP treatment at a pressure of 593 MPa for 3 min without any changes in aroma, pH, color, and taste [128]. Cloudy hawthorn berry juice treated at 300–600 MPa for 30 min at 65 °C inhibited the aerobic mesophiles, lactic acid bacteria, yeast, and mold which in turn improved the shelf life to > 150 days [129]. It has not affected the pH, or titratable acidity but enhanced the sugar content and aroma compounds leading to better flavor and taste. The various reports on the processing of health-promoting beverages using HHP are discussed in Table 4.

Table 4 Effect of high hydrostatic pressure on processing of health-promoting beverages

6 Pulsed light treatment

The pulsed light treatment is one of the non-thermal processing technologies which is recently been used for processing food products to enhance the shelf life of foods by inactivation of food spoilage and food-born pathogenic microorganisms [129,130,131]. This is due to the inactivation of double-bonded carbon atoms in proteins and nucleic acids leading to the disruption of structure, transcription, and translation processes [132]. The high energy intensity of pulsed light flashes also contributes significantly to microbial inactivation. The effect of microbial inactivation by pulsed light is higher in clear liquids compared to opaque liquids because of the decrease in light intensity due to the absorption and scattering of the light [96].

6.1 Working principle

Pulsed light technology emits high-power pulses either in single or continuous modes of wavelength ranging between 170 and 1000 nm with a gradual increase in energy by using inert gas flash lamps like xenon [133]. The electromagnetic radiation is stored in the capacitor and light flashes can be emitted using inert gas flash lamps to inactivate microorganisms [134, 135]. The process efficiency depends on treatment duration, nature of the food product, packaging material, nature, and number of microorganisms present in the sample [11, 136, 137].

6.2 Application of pulsed light in the processing of health-promoting beverages

The E. coli in apple and orange juices treated with a pulsed light dose of 4 J/cm2 was reduced by 2.9 and 4 logs, respectively [138]. Pulsed light treatment of whey protein isolate at 4–16 J/cm2 improved the formation of carbonyl and free sulfhydryl groups that in turn induced dissociation and partial unfolding of proteins [139]. These changes enhanced the different functional properties like foaming and solution stability. The lactic acid fermented mulberry juice exposed to 2–8 s at a pulse range of 14 J/cm2 resulted in the reduction of microbial load to 1 log CFU/ml [140]. There were no significant changes in the pH, titratable acidity, and soluble solids between pulsed light-treated juice and fresh juice. A slight increase in the phenolic content was observed in the mulberry juice after pulsed light treatment. A decrease in anthocyanin concentration was observed which can be attributed to the adverse photochemical reactions. A slight decrease in the lightness of juice was observed after pulsed light treatment because of the changes in the pigment concentration. The concentration of volatile compounds and odor activity values were enhanced during pulsed light treatment.

The reduction of E. coli in tender coconut water, orange, and pineapple juice using pulsed light treatment (95.2 J/cm2) for 15 s was 4, 4.5, and 5.33 log, respectively [141]. The pulsed light treatment of apricot juice at two different intensities (7 and 14 kV/cm) for 500 µs has not significantly affected the pH, °Brix, and color compared to unprocessed samples. The pulsed light treatment resulted in increased content of phenolic compounds, flavonoids, and antioxidant activity [142]. Apple juice was exposed to pulsed light of different cycles like 4, 6, and 8 with a total number of pulses in the range of 200–400 pulses [143]. The changes in bioactive compounds, ascorbic acid, and polyphenol content were not observed in pulsed light-treated juice even after 72 h of refrigeration. Pulsed light treatment of pineapple juice at 13 kV/cm resulted in higher microbial load reduction compared to treatment at 9 and 11 kV/cm [144]. The total phenolics, flavonoids, ascorbic acid, and β-carotene content was not affected. The pulsed light treatment (31.2 kV/cm, 20 pulse widths at 100 Hz frequency) retained higher antioxidant activity and sensorial properties of ready-to-serve beverage containing tender coconut water and nannari extract in comparison to conventional pasteurization (96 °C for 360 s) [145]. Raspberry juice exposed to pulsed light treatment at 200 Hz retained higher phenolic content (426.4–567.2 mg GAE/100 g) and around 19% of pectin methyl esterase enzyme was inactivated [127]. Complete inactivation of peroxidase and polyphenol oxidase in amla juice was attained when exposed to pulsed light at 3.32 kV/cm for 3 min [146]. The exposure of mixed fruit beverage containing amla, pineapple, and coconut water to pulsed light at 3.3 kV/cm for 3 min resulted in 5 log reduction of aerobic mesophiles, yeast, and mold counts while the oxidative enzymes were completely inactivated [147]. The pulsed light treatment of bael fruit juice at 3.3 kV/cm for 4.5 min inactivated the oxidative enzymes like polyphenol oxidase, and peroxidase (73.5–90%) better than the thermal process [148]. The 5 log reduction of Listeria monocytogenes and E. coli in sweet lime juice was attained after pulsed light treatment at 3.3 kV/cm for 4.5 min without any changes in pH, color, or taste of the juice [149]. The continuous flow pulsed light treatment of coconut water, pineapple, and orange juice for 43, 44, and 45 s resulted in 5-log reduction of aerobic mesophiles, yeast, and mold without altering their physicochemical properties [150]. Processing tender coconut water with pulsed light at 2.5 kV for 2.5 min resulted in a 5 log reduction of B. cereus and L. monocytogenes [151]. Pomegranate juice treatment with pulsed light at 2.7 kV/cm for 90 s resulted in a 5-log reduction of aerobic mesophiles, yeast & molds and retained a higher amount of phenolics (97%), antioxidants (94%), and ascorbic acid (83%) [152]. Pineapple juice treated with pulsed light at 2.4 kV/cm for 3.5 s resulted in the reduction of aerobic mesophiles, yeast, and molds without affecting the sensory attributes [153]. The treatment of mulberry juice using combined pulsed light (1.2 kV/cm for 3.5 s) and ultrasonication treatment (15 min at a frequency of 28 kHz) retained phenolic and antioxidant activities at higher levels compared with the thermal process [154]. Exposure of verjuice to pulsed light at 6.12 J/cm2 for 3.5 s resulted in a 5.1 log reduction of S. cerevisiae and the shelf life of the juice extended up to 6 weeks without any changes in fresh-like characteristics (color, aroma, taste) and sensory attributes [155]. The pulsed light treatment of grape juice at 66 J/cm2 for 3.5 s resulted in a 2.6 log reduction of E. coli [156]. The shelf life of pulsed light-treated (2.9 kJ/cm2 for 3.5 s) pomegranate juice extended up to 41 days with higher retention of phenolics and antioxidant activity compared to thermal-treated samples [157]. The various reports on the processing of health-promoting beverages using pulsed light are discussed in Table 5.

Table 5 Effect of Pulsed light treatment on processing of health-promoting beverages

7 Membrane technology

The application of membrane technologies is suitable for the processing of health-promoting beverages due to several advantages like lesser energy consumption, mild processing conditions, and superior product quality compared to conventional thermal processes.

7.1 Working principle

The pressure-driven membrane operations such as microfiltration and ultrafiltration are used for the clarification and concentration of beverages [158]. These processes involve a semipermeable barrier (membrane) for selective separation of compounds from feed solution and pressure gradient acts as the driving force for mass transfer through the membrane. The feed solution is separated into permeate (molecules permeated through the membrane) and retentate (molecules rejected by the membrane). The degree of rejection depends on the pore size, charge, and surface properties of the membrane [159,160,161]. The performance of the pressure-driven membrane process is assessed by permeate flux and degree of separation [162].

7.2 Application of membrane technology in the processing of health-promoting beverages

The pore size of microfiltration and ultrafiltration membranes is 0.1–10 µm and 0.001 to < 0.1 µm, respectively [163]. These membranes can reject the molecules larger than the pore size without causing physicochemical changes in the feed solution. The pathogenic microorganisms can be removed from the beverages by proper selection of membranes of suitable pore size. Ultrafiltration can be used to remove macromolecules like proteins and polysaccharides that in turn cause turbidity in health-promoting beverages. This can also be used for removing all microorganisms. Thereby ultrafiltration can be simultaneously used for clarification and cold sterilization of beverages. The processing of apple juice at the pilot scale level by ultrafiltration membranes composed of ceramic and organic polymer resulted in a 9 and 5-log reduction of bacteria, respectively [164]. The application of an ultrafiltration membrane of 0.03 µm pore size for the processing of white birch sap reduced the microbes from 1.6 × 104 to 2.0 × 102 CFU/mL. The combination of ultraviolet with ultrafiltration resulted in the complete elimination of microorganisms during 40 days of storage at 4 or 25 °C [165]. Banana juice processed using ultrafiltration enhanced the shelf life to 30 days with superior product quality [166]. The quality of bottle gourd juice processed by ultrafiltration was not adversely affected even after 8 weeks of storage [167]. The processing of jamun juice using polysulfone hollow fiber of 50 kDa pore size eliminated the microorganisms [168]. A flat membrane module composed of polyethersulfone (pore size < 0.01 µm) also reduced the microbial load to an undetectable level in coconut water [169].

Microfiltration can be used as a pretreatment prior to ultrafiltration in order to avoid the fouling problem of the membrane by removing the microorganisms and particles of larger size. Coconut water containing 140 CFU/mL of aerobic mesophiles was processed sequentially using 0.8 µm and 0.45 µm of cellulose nitrate membrane. The growth of microbes was not observed even after 180 days of storage and a slight increase in total soluble solids was observed due to the hydrolysis of carbohydrates [170]. The membrane of 0.3 µm pore size resulted in the reduction of microorganisms in pineapple juice to the desired level [171]. The processing of watermelon juice using an ultrafiltration membrane of polyethersulfone (50 kDa molecular weight cut off) resulted in the reduction of soluble solids (2.8%) and ascorbic acid (11.2%) [172]. Dragon fruit juice treated using ultrafiltration membrane of polyethersulfone of different pore sizes (5, 10, and 20 kDa molecular weight cut off) resulted in the retention of betacyanin (30.6%) at a higher level compared to phenolic compounds (11.3%) level [173]. Processing of broccoli juice in an ultrafiltration membrane of polyethersulfone with 5, 10, and 50 kDa molecular weight cut off decreased the phenolic content by 2.7, 9.6, and 5.5%, respectively [174]. Orange juice processed in ultrafiltration membranes composed of polyethersulfone retained better clarity compared to polysulfone membranes [175]. Lemon juice treated with cellulose acetate membrane (100 kDa) retained higher antioxidant activity with a significant amount of eriocitrin and hesperidin [176]. The treatment of cashew apple juice in an ultrafiltration membrane improved the shelf life by 12 weeks [177]. Cloudy apple juice processed in an ultrafiltration membrane of polyethersulfone (10 kDa molecular weight cut off) enhanced the shelf life to 4 weeks without any changes in the quality [178]. The processing of sugarcane juice by ultrafiltration (polysulfone membrane of 30 kDa) extended the shelf life up to 4 weeks by inactivating the bacteria (Streptomyces, Staphylococcus, Lactobacillus) [179]. Apple beetroot and apple juice processed in the ceramic membrane (15 kDa) retained 68 and 71% of soluble solids, respectively [180]. Mulberry juice treated in an ultrafiltration membrane (100 kDa) retained better color and phenolic compounds [181]. Ultrafiltration of watermelon juice in 1 kDa membrane improved the enrichment efficiency which in turn increased the concentration and purity of lycopene [182]. The various reports on the processing of health-promoting beverages using membrane technology are discussed in Table 6.

Table 6 Effect of membrane technology on processing of health-promoting beverages

8 Pulsed magnetic field

The pulsed magnetic field is one of the emerging non-thermal techniques in recent years for enzyme and microbial inactivation in health-promoting beverages. The major parameters that affect the pulsed magnetic field process are magnetic field intensity and number of pulses.

8.1 Working principle

The electric current flow in a coiled wire or solenoid leads to the generation of magnetic current across the coil. The pulsed magnetic field is generated by the generator in the form of short energy pulses which are stored in the capacitor bank. Superconducting coils can be used to generate magnetic field intensities in the range of 5–50 T. Microorganisms and enzymes contain charged particles that undergo drifting under the influence of Lorentz force in the magnetic field. This results in the formation of induced currents followed by the inactivation of microbes and enzymes. Magnetoporation induced by a pulsed magnetic field leads to microbial death due to the loss of cytosol and nucleic acid together with the increase in intracellular Ca2+ content. The pulsed magnetic field affects the enzyme activity by the unfolding of tertiary structure. The microorganisms respond to the domain of a pulsed magnetic field by stimulation which is known as the “window effect” [183].

8.2 Application of pulsed magnetic field in the processing of health-promoting beverages

The pulsed magnetic field processing of orange juice at 7 T and 20 pulses resulted in the 0.61 log reduction of aerobic mesophiles [184]. The pulsed magnetic field range used in this study was not effective in microbial inactivation indicating the possible window effect. Pulsed magnetic field treatment of 8 T with a pulse number of 60 in cucumber juice resulted in a 1.36 log reduction of E. coli [185]. The increase in intensity to three times reduced the bacteria to an undetectable level even after 4 days of storage at 4 °C. The inactivation of bacteria in vegetable juices (cucumber, carrot, spinach, and bitter gourd) was further facilitated by the combination of a pulsed magnetic field (3 times 8 T with 60 pulses) with Litseacubeba essential oil at a concentration of 1.5 mg/ml [186]. The addition of essential oil slightly masked the natural flavor of the juice but the sensorial attributes were not significantly affected. The cell membrane rupture and the inhibition of intracellular enzymes are the major mechanisms responsible for cell death. The higher bacterial load reduction (99.9%) in bovine colostrum was attained during pulsed magnetic field treatment of 2.53 T with a pulse number of 20 with minimal loss of IgG and sensorial characteristics [187]. Maximum inactivation of E. coli, mold, and yeast in milk was attained at 16.02 T with a pulse number of 6–8 [188]. The pulsed magnetic field processing of apple juice at 6 T with 15 pulses inactivated various oxidative enzymes such as polyphenol oxidase, peroxidase, and pectin methyl esterase [189]. The various reports on the processing of health-promoting beverages using a pulsed magnetic field are discussed in Table 7.

Table 7 Effect of pulsed magnetic field on the processing of health-promoting beverages

9 Current challenges and future prospective

At present, most of the studies are performed on a laboratory scale and very few pilot-scale studies are reported. Hence more scale-up studies have to be performed and economic feasibility studies have to be undertaken to ensure sustainable utilization and implementation. Additionally, more studies focused on the combined or sequential approach of various non-thermal processing methods have to be applied to food products for microbial decontamination, and inactivation of oxidative enzymes. Ultrasonication can be applied for food preservation in combination with other methods to further improve enzyme inactivation and microbial load reduction. The synergistic effect of the ratio of beverage and CO2 in the SC-CO2 process can be studied to improve the process reliability to meet the global demand. In HHP treatment, heat generation leads to process instability and non-uniformity. The other challenges include a lack of data on the synergistic effect between pressure and packaging materials. Dielectric barrier discharge is a type of cold plasma that can be efficiently used for in-pack sterilization of beverages. Further optimization studies of processing variables in pulsed light treatment are needed to obtain products of superior quality. Studies should also focus on the structural integrity, bioavailability, and flow behavior of processed beverages [190]. Ultrafiltration membranes of tiny pore size can result in fouling and poor permeability of nutrients with smaller molecular weight. The proper selection of ultrafiltration membrane of suitable pore size should be selected for the removal of viruses and improved process efficiency. Microfiltration can be used as a pretreatment to remove larger microorganisms to minimize the fouling problem. The application of coagulation agents is also effective in controlling the fouling of membranes [191]. Studies on pulsed magnetic field for microbial load reduction and enzyme inactivation in beverages are very limited. Thus, more studies are required to understand the effect of pulsed magnetic field on the nutritional quality and sensorial attributes of food products [183].

In the future, novel processing techniques can be developed by combining different non-thermal processes to improve product quality and process efficiency. There is also scope for process equipment design and process economics for non-thermal processes to make them more accessible and cost-effective. There is an urgent need for the establishment of streamlined regulatory bodies concerning the utilization of these technologies to make the approval process faster and less expensive. Customized equipment can be developed to process health-promoting beverages to meet consumer demands. Algorithms, artificial intelligence, and data analytics can be incorporated with these advanced techniques for the real-time monitoring and control of the process. For the widespread adoption of non-thermal processing in the beverage industry, it is pivotal to overcome the current challenges as well as to work with future opportunities in this field.

10 Conclusion

Non-thermal food processing techniques are a promising alternative for food processors and provide a glimpse of future innovations in food technology. Conventional thermal treatments are commonly used for the pasteurization of liquid food products but they can affect the product quality in terms of nutrient retention and changes in sensorial attributes. The application of novel green technologies like non-thermal processing methods is environmentally friendly, rapid, and effective in microbial inactivation without affecting product quality. The action mechanisms of various non-thermal food processing techniques driven by different energy sources have been explored in the present review paper. The non-thermal processing methods come under a sustainable approach for microbial inactivation that in turn can improve the shelf life of food products. The non-thermal processes can be combined with preservatives to attain complete sterilization of food products. The low-temperature storage and distribution of non-thermal food products are essential for maintaining their sensorial properties. The HHP treatment can be applied to packaged food products and it has minimal effect on nutrients and sensorial attributes. The pulsed electric field is suitable for processing only liquid food products and reduces the degradation of heat-labile compounds. Ultrasound and membrane technology are economically feasible and also meet the requirements for scale-up. The HHP and SC-CO2 are suitable for both microbial and enzyme inactivation in the temperature range of 35–55 °C. In conclusion, this literature can provide a paramount reference to help the food processors planning to execute these non-thermal techniques for processing several food products.