Nonthermal Technologies for Nonalcoholic Beverages

CHAPTER 7

Nonthermal Technologies for Nonalcoholic Beverages G.J. Swamy1, K. Muthukumarappan1, A. Sangamithra2, V. Chandrasekar3 and S. Sasikala4 1

Department of Agricultural and Biosystems Engineering, South Dakota State University, Brookings, SD, United States 2Department of Food Technology, Kongu Engineering College, Perundurai, India 3 ICAR-CIPHET, Ludhiana, India 4Department of Food Process Engineering, School of Bioengineering, SRM University, Kattankulathur, India

Chapter Outline 7.1 Introduction 202 7.2 Ultrasound 202 7.2.1 Generation of Power Ultrasound 202 7.2.2 Microbial Inactivation in Nonalcoholic Beverages

7.3 7.4 7.5 7.6 7.7 7.8

204

Ozonation 207 Ozone Generation 208 High-Pressure Processing 210 High-Pressure Processing Equipment 211 Ultraviolet and Pulsed-Light Technology 212 Irradiation 213 7.8.1 Mode of Inactivation of Microbes

7.9 Cold Plasma

216

217

7.9.1 Mode of Action of Cold Plasma 218 7.9.2 Treatment of Nonalcoholic Drinks with Plasma

7.10 Pulsed Electric Field Processing 7.10.1 PEF Equipment Design

220

220

7.11 Dense-Phase Carbon Dioxide Technology 7.12 Conclusion 226 References 227

Trends in Non-alcoholic Beverages. DOI: https://doi.org/10.1016/B978-0-12-816938-4.00007-0 © 2020 Elsevier Inc. All rights reserved.

221

201

218

202 Chapter 7

7.1 Introduction Traditional thermal treatment processes are a keystone of the food industry to provide the required safety profile and addendums to the food’s existing shelf-life period. However, such processes may lead to losses of preferred organoleptic properties and damage to thermolabile nutrients. Nonthermal technology has been researched to satisfy food safety demands. In addition, it prevents adverse impacts on nutritional and sensory aspects of the food products. Novel technologies are of benefit to both food processors and consumers; however, depending on the complexity of the food material and the variety of foods produced, the validation process is a challenge for the food industry. The factors that drive the necessity of the validation process include extension of shelf life, nutritional and sensory aspects, organoleptic properties, consumer acceptance, and impact on the environment.

7.2 Ultrasound Ultrasound is known to have a major influence on the rate of different processes in the food and bioprocessing industry. Most processes can be completed in a few seconds or minutes with high reproducibility using ultrasound, thereby reducing the processing cost, with higher purity of the final product and consuming only a small portion of the energy normally needed for conventional processes. Several ultrasound-assisted processes such as extraction, freezing and thawing, and cutting and drying have been carried out efficiently in the food industry. Food processes executed by the action of ultrasound are supposed to be influenced by cavitation phenomena and mass transfer enhancement. From various researches who deal with the impact of ultrasound on the quality and stability of liquid foods, it is clearly evident that sonication can be successfully implemented to extend the shelf life of nonalcoholic beverages (Swamy et al., 2018). Combining ultrasound with mild temperature (thermosonication) or pressure-temperature (manothermosonication) can create a better effect. Two or more nonthermal techniques may also be combined to produce a synergistic effect; however, in large-scale applications, the process is expensive and tedious to scale-up. Food analysis and food processing are the segments of ultrasonic application. Ultrasound can be classified as illustrated in Fig. 7.1:

7.2.1 Generation of Power Ultrasound Sound is created from electrical energy through the vibration created by ultrasonic transducers. Piezoelectric and magnetostrictive transducers may be employed, although the former are preferred as they are efficient in terms of power consumption. Acoustic cavitation is the factor that drives the processing effects of sonication. In spite of cavitation being a source of erosion in fluid flow through pipes, its harnessed form is used for sonic applications. Cavitation bubbles are formed when sonic waves pass through the liquid, as in

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Ultrasound

Low power (<1 W/cm) High frequency (5–10 MHz)

Provides information about physicochemical properties For example: Composition, structure, texture, physical state, and flowrate

High power (10–1000 W/cm2) Low frequency (20–100 kHz)

Physical or chemical alteration of food properties For example: Generate emulsions, disrupt cells, promote chemical reactions, inhibit enzymes, tenderize meat, and modify crystallization processes

Figure 7.1 Classification of ultrasound in food applications.

the case of fruit juices. Transmission occurs as a sequence of compression and rarefaction cycles disturbing the molecules in the liquid. During the rarefaction cycle, the negative components are too strong between the liquid molecules. This leads to the formation of a cavity. The cavity captures vapor so that during the compression cycle it is not collapsed. It continually grows in size to form a bubble in the successive cycles. The cavitation bubbles may be one of the two types: 1. Stable cavitation: Nonlinear oscillating bubbles that form large bubbles during many cycles of acoustic pressure. 2. Transient cavitation or inertial cavitation: Short-lived bubbles that exist for less than one cycle and collapse vigorously. In stable cavitation, when an unstable size is reached, the bubbles collapse violently to produce localized temperatures of B5000K and pressures of B50 MPa. The pressure changes during the implosions lead to microbial cell disruption. Cavitation via the Venturi effect is another way of implementing sound waves to preserve liquid products. This method involves forcing the juice at high pressure through a small orifice, and is called hydrodynamic cavitation. The constriction may be a throttle valve, orifice plate, or venturi. When the liquid passes through the constriction, the velocity of the liquid and cavities are generated if the throttling causes the pressure around the point of vena contracta to fall below the threshold pressure for cavitation. However, the cavities collapse when the liquid jet expands and the pressure recovers. Systematic design creates cavity collapse conditions similar to acoustic cavitation, enabling different applications at lower energy inputs than sonochemical reactors. A comparative study of bubble behavior by hydrodynamic and acoustic cavitation was carried out. It is based on numerical solutions of the Rayleigh Plesset equation (Moholkar et al., 1999). The variations in cavity size, intensity, pressure, and time for hydrodynamic cavitation have a pronounced impact on

204 Chapter 7 bubble dynamics. Simulations revealed that the collapsing nature of hydrodynamic cavitation creates a large number of pressure pulses with smaller magnitude. One or two pulses are produced under an acoustic cavitation. Moreover, hydrodynamic cavitation controls the operating parameters and the cavitation intensity more effectively compared with the ultrasonic cavitation.

7.2.2 Microbial Inactivation in Nonalcoholic Beverages A series of steps are involved in the microbial inactivation process by ultrasonic cavitation. This may lead to weakening or destruction of the cell wall. The steps are as follows: • • •

Collapse of the cavitation bubbles within or around bacteria causes a change in the pressure gradient. This, in turn, induces mechanical effects leading to bacteria cell wall damage. The bacteria itself creates microstreams that build shear forces. During cavitation, free radicals are formed. The chemicals generated by the free radicals are lethal to the cell wall and lead to its disintegration. In addition, hydrogen peroxide (H2O2), a bactericide is naturally formed during ultrasonication.

The exact mechanism of cell-wall damage during sonication is yet not vivid. Both physical and chemical effects contribute to the destruction of the cell wall. Inactivation mechanisms are dependent on processing factors such as: 1. ultrasound source and reactor geometry; 2. frequency; 3. acoustic energy density. Efficiency of inactivation is also influenced by media properties like: 1. 2. 3. 4.

treatment volume; temperature; viscosity; gas concentration.

Intracellular cavitation is one of the important bactericidal effects of acoustic waves. It affects the structural and functional parts of the cell wall until lysis through micromechanical shocks. Localized heating and free-radical formation during sonication of water lead to thinning of the cell membrane. Such free radicals are present during sonication of the water molecule in fruit juices. The combined processes lead to microbial inactivation. Ultrasound has also been used to assess the safety and quality of nonalcoholic beverages. The results are presented in Table 7.1. From the table, it is implicated that the effect of food properties such as fruit juice type, pulp content, soluble solid content, and viscosity have a pronounced effect on the inactivation rate and processing time to attain the desired log reduction.

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Table 7.1: Impact of ultrasound on nonalcoholic beverage attributes. Juice Watermelon

Process Parameters G

G

G G

G

Temperature (25 C 45 C) Amplitude (24.1 60 μm) Time (2 10 min) Constant frequency 20 kHz Pulse durations—5 s on and 5 s off

Results G

G

G

G

G

G

G

Strawberry

G

G

Acoustic energy densities (AEDs)— 0.33 0.81 W/mL Time—0 10 min

G

G

Raspberry

G

G

Ultrasound frequency (20, 490, and 986 kHz) Time (0, 10, 20, and 30 min)

G

G

G

G

G

G

The retention of ascorbic acid was 94.1%, 92.15%, 91.7%; 98.6%, 90.5%, 75.1%, 92.7%, 96.1%, 73.7% at 24.41, 42.7 and 60 μm for 2, 6, and 10 min processing times respectively. Thermosonication carried out at a higher temperature (45 C), resulted in increased degradation of ascorbic acid. After 10 min, there was a significant degradation in total phenolic content. At the highest amplitude (61 μm) there was reduction in lycopene content. Lycopene retention in processed watermelon juice ranged from 46.35% to 106.68%. The largest increase in L* value was observed at higher processing times and higher amplitude level (10 min, 60 μm). At higher temperatures (35 C and 45 C) and amplitude levels, L* and a* increased significantly. At the highest AED value (0.81 W/mL) and treatment time (10 min), 5% and 15% reduction in anthocyanin and ascorbic acid content was observed. Degradation rate constants for both P3G and AA were linearly related to AED (R2 . 0.91). Sonication at 20 and 490 kHz significantly affected the total antioxidant activity (AOA), total phenolics content (TPC), and total monomeric anthocyanin content (ACY) of red raspberry puree. At 986 kHz had no significant effect on ACY and AOA. Sonication had significant and positive effect on at least one of the measured parameters up to 30 min. Sonication beyond 10 min (and up to 30 min) using 20 kHz had no change or declined AOA and ACY content. At 986 and 20 kHz, TPC increased by 10% and 9.5%, respectively, after 30 min. At 20 kHz, AOA and ACY increased by 17.3% and 12.6% after 10 min.

References Rawson et al. (2011)

Tiwari et al. (2009b)

Golmohamadi et al. (2013)

(Continued)

206 Chapter 7 Table 7.1: (Continued) Juice

Process Parameters

Results G

Pineapple

G G G

Power—40 80% Time—2 6 min Pulse—2 6 s

G

G

Pear

G

G G G

Temperature—25 C, 45 C, and 65 C Time—10 min Frequency—20 kHz Amplitude—70%

G

G

G

G G

Mango

G

G G G

Guava

G G

Time—15, 30, and 60 min Temperature—25 C Frequency—40 kHz Power—130 W

Frequency—35 kHz Time—30 min

G

G

G

G

G

References

Results show that 20 kHz ultrasound treatment, when limited to 10 min, was the most effective for extraction of bioactive compounds in red raspberry Sonication reduced W. anomalus from 6.69 to 5.04 log CFU/mL, while in the sample treated by ultrasound 1 benzoate 1 citrus extract reduced yeast counts by 2.73 log CFU/mL. The effect of this combination was also significant within storage and caused yeast inactivation below the detection limit after 4 days Substantial reduction in residual activities of peroxidase (POD), polyphenol oxidase (PPO), and pectin methyl esterase (PME) in US45 that were 43.2%, 37.83%, and 40.22%, respectively. However, the highest enzyme inactivation was found in US65 which showed residual activities of POD, PME, and PPO as 4.3%, 3.25% and 1.91%, respectively. No significant changes were observed in  Brix, pH, and acidity. Significant increase in the contents of ascorbic acid, total phenols and flavonoids. Ultrasound. A complete inactivation of microbes was found in US65 treatments. In aerobic plate count, the S60 sample recorded the highest reduction of microbial count (26%) when compared to other sonicated samples, S30 (17%) and S15 (8%). A significant increase in extractability of carotenoids (4% 9%) and polyphenols (30% 35%) was observed for juice subjected to ultrasonic treatment for 15 and 30 min. Sonication resulted in higher ascorbic acid content while samples treated with both sonication and carbonation showed the highest ascorbic acid contents. Carbonation enhanced the manifestation of cavitation and subsequently produces juice with higher ascorbic acid content, lower clarity and higher polyphenoloxidase activity. Unfortunately, these treatments do not have strong lethal effects on microorganisms.

Bevilacqua et al. (2015)

Saeeduddin et al. (2015)

Santhirasegaram et al. (2013)

Cheng et al. (2007)

(Continued)

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207

Table 7.1: (Continued) Juice Cantaloupe melon

Process Parameters G

G

Power—100, 300, 500 W Intensity—75, 226, 376 W/cm2

Results G

G

G

G

Cactus pear

G

G

Amplitude—(40% and 60% for 10, 15, 25 min; 80% for 3, 5, 8, 10, 15, and 25 min)

G

G

G

Blackberry

G

G G

G

Amplitude— 40% 100% Time—0 10 min Constant frequency 20 kHz Pulse durations—5 s on and 5 s off

G

G

The experimental condition that favored the decreased peroxidase, polyphenoloxidase, and ascorbate peroxidase activities was 376 W/cm2 for 10 min. The cloud stability of the melon juice was improved due to the ultrasound treatment. The juice remained completely homogeneous during 6 weeks of refrigerated storage after the same processing conditions. Although sonication caused some phenolic degradation, this technology proved to be suitable for cantaloupe melon juice processing due the pulp, color stability, and enhancement. Total plate count and enterobacteria was reduced when juice was sonicated for $ 15 min. Treatments at 80% amplitude level for 5 and 8 min had a significant release of total phenolics content (2077.4 6 68.1 and 2160.7 6 58.2 mg GAE/L, respectively). At 80% amplitude level for 25 min, ascorbic acid content increased from 352.6 6 4.3 to 415.6 6 7.0 mg AA/L. A significant change only in color values and anthocyanin retention was observed. Correlation coefficients (R2) of 0.93, 0.89, 0.99, 0.97, and 0.94 for L, a, b, Lab and DE were predicted by the models. A decrease of 5% was observed at the maximum treatment conditions of 100% amplitude for 10 min.

References Fonteles et al. (2012)

Zafra-Rojas et al. (2013)

Tiwari et al. (2009a)

7.3 Ozonation Ozone is derived from the Greek word “Ozein” which means “smell.” It is the allotropic form of oxygen arranged as an isosceles triangle with an angle of 116.8 degrees between ˚ . Ozone is a two oxygen bonds. The bond distance between the two oxygen atoms is 1.27 A bluish gas that is relatively unstable at normal temperature and pressure. Ozone is denser than air at 0 C and atmospheric pressure. It is partially soluble in water and the solubility varies with temperature. The solubility of ozone in water decreases with increasing

208 Chapter 7 temperature. At 0 C, solubility is 0.640 L ozone/L water, whereas at 60 C it is insoluble in water. The solubility is 13-times more than that of oxygen at 0 C 30 C and it is progressively more soluble in colder water. Ozone has a characteristic pungent odor and oxidizing properties, and is the strongest disinfectant suitable for contact with foods. Ozone is characterized by high electrochemical potential (12.075 V) indicating strong oxidizing properties. The oxidation potential conveys bactericidal and virucidal properties and its ability to diffuse through biological membranes. It is a potent antimicrobial agent against bacteria, fungi, viruses, protozoa, and bacterial and fungal spores (Asokapandian et al., 2018). Ozone inactivates microbes through oxidization, and residual ozone spontaneously decomposes to oxygen, making it an environmentfriendly antimicrobial agent for use in the food industry.

7.4 Ozone Generation Ozone exists naturally at low concentrations in the lower atmosphere. Natural ozone is found in the stratosphere at levels up to 6 ppm. The natural production of ozone is by either lightning or ultraviolet (UV) radiation. Ozone is a highly reactive and unstable gas and is therefore generated at the point of application for commercially demanded treatments. The half-life of ozone is about 2030 min in distilled water at 20 C. Ozone is generated by the rearrangement of atoms when strong O O bonds are subjected to breaking by significant energy input with the formation of a free-oxygen radical. The generation of ozone for commercial use is achieved by four recognized methods, that is, the electrical or corona discharge method, electrochemical method, UV method, and radiochemical method. Table 7.2 presents the different operating parameters selected for the ozone treatment of a variety of nonalcoholic beverages. The electrical or corona discharge method is often called “silent discharge,” where the molecular oxygen is ionized by applying high-power alternating current. The dried air or oxygen is passed through an electric field produced between two high-voltage electrodes separated by dielectric material, usually glass. Initially the electrical current causes the “split” in the oxygen molecules (O2) to form oxygen atoms (O); later the individual oxygen atom combines with the remaining oxygen molecules to form ozone (O3). During ozone generation, around 80% of the applied energy is converted into heat, which needs to be removed immediately to avoid the decomposition of ozone into oxygen molecules and atoms. Normally, 3% 6% ozone is yielded in the gas mixture discharged from an ozonator, if high-purity oxygen is used as the feed gas, whereas for dry air only 1% 3% ozone is obtained. The advantages of this method are the effective generation of a high concentration of ozone, durability of the corona cell compared to that of a UV lamp, and cost effectiveness compared to a UV ozone generator for a large-scale installation.

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Table 7.2: Ozone treatment of various nonalcoholic beverages. Product

Method of Ozone Generation

Flow Rate

Apple cider and orange juice Apple juice

2.4 L/min Oxygen generator (Golden Buffalo; Orange, Calif., United StatesSA) Corona discharge ozone 0.12 L/min generator

Apple juice Corona discharge ozone generator (Model OL80, Ozone services, Burton, Canada Apple juice Corona discharge ozone generator (Model OL80, Ozone services, Burton, BC, Canada) Apple juice Ozone generator (Model OL80, Ozone services, Canada) Apple juice ozone generator (Ozonetech Co., Ltd, Korea)

0.12 L/min

Apple juice Ozone generators (Opal, Ankara, Turkey

0.4 L/min

Orange juice

Orange juice

Orange juice

Orange juice

0.12 L/min

0.125 L/min

3.0 L/min

Ozone Concentration

Organisms and Other Parameters

References

0.9 g ozone/h

Escherichia coli O157: H7 Salmonella

Williams et al. (2005)

0.48 mgO3 min21/mL

E. coli ATCC 25922 and NCTC 12900 Temp: 20 C 6 1.5 C Time: 0 10 min 0.48 mgO3 E. coli ATCC 25922 min21/mL and NCTC 12900 Time: 18 min pH: 3.0, 3.5, 4.0, 4.5, 5.0 33 40 log/mL Saccharomyces cerevisiae ATCC 9763 Temp: 15 C 18 C, Time: 8 min 1 4.8% w/w of E. coli O157:H7 oxygen Temp: 20 C 6 0.5 C. 2.0 3.0 g/m3

Patil et al. (2010a)

Patil et al. (2010b)

Patil et al. (2011)

Torres et al. (2011) E. coli O157:H7, Sung et al. Salmonella typhimurium, (2014) Listeria monocytogenes Temp: 25 C, Time: 20 s, 40 s or 1 min Alicyclobacillus Torlak acidoterrestris spores (2014)

2.8 and 5.3 mg/L Temp: 4 C and 22 C Time: 10, 20, 30, and 40 min Corona discharge ozone 0 0.25 L/min 1.2 4.8% w/w Time: 2 10 min generator (Model OL80F, Ozone services, Burton, B.C., Canada 0.6 10.0% Temp: 20 C 6 0.5 C, Corona discharge ozone 0.125 L/min w/w of oxygen Time: 0, 2, 4, 6, 8, generator (Model OL80, Ozone services, Burton, and 10 min Canada 75 78 μg/mL E. coli ATCC25922 Corona discharge ozone 0.12 L/min and NCTC 12900 generator (Model OL80, Ozone services, Burton, Canada Corona discharge ozone 0.12 L/min 0.098 mg/min/ L. monocytogenes ATCC generator (Model OL80, mL 7644, L. monocytogenes Ozone services, Burton, NCTC 11994, and L. Canada innocua NCTC 11288 Time: 7 8 min

Tiwari al. (2008a)

Tiwari et al. (2008b) Patil et al. (2009)

Patil et al. (2010c)

(Continued)

210 Chapter 7 Table 7.2: (Continued) Product

Method of Ozone Generation

Flow Rate

Ozone Concentration

Grape Juice

Corona discharge ozone generator (Model OL80, Ozone services, Burton, BC, Canada) Corona discharge ozone generator (Model OL80, Ozone services, Burton, Canada Corona discharge ozone generator (Model OL80, Ozone services, Burton, Canada Corona discharge equipment model UTKO-4 (UNITEK, Mar del Plata, Argentina

0.06 L/min

0 7.8% w/w of Time: 0 10 min oxygen

Tiwari et al. (2009c)

0.0625 L/min 0 7.8% w/w of Time: 0 10 min oxygen

Tiwari et al. (2009d)

0.0625 L/min 0 7.8% w/w of Time: 0 10 min oxygen

Tiwari et al. (2009e)

5 L/min

Loredo et al. (2015)

Tomato juice

Blackberry juice

Peach juice

Organisms and Other Parameters

10 and 18 ppm E. coli ATCC 11229, L. innocua ATCC 33090, and S. cerevisiae KE162, Temp: 20 C 6 1 C).

References

In the electrochemical method of ozone generation, an electrical current is applied between an anode and cathode placed in an electrolytic solution containing water and highly electronegative anions. A mixture of oxygen and ozone is produced at the anode. The merits of this method are the use of a et alet allow-voltage DC current, no preparation of feed gas, compact equipment size, and probable high concentration of ozone generation. Ozone generation using UV light is a photochemical process in which ambient air is passed over a UV lamp emitting UV light of 140 190 nm wavelength. Through photodisassociation, oxygen molecules are split into oxygen atoms, which further combine with other oxygen molecules to form ozone. The disadvantage of this method is that very a low concentration of ozone (0.1% w/w) is produced, which limits the practical application of this method. High-energy irradiation of oxygen by radioactive substances can also produce ozone. Usually isotopes such as 137Cs, 60Co, or 90Sr are used for excitation of circulating air which initiates the dissociation of oxygen molecules to form oxygen atoms, which combine to form ozone. This technique is rarely associated with commercial use due to its complicated application and the danger of radioactive contamination. With the approval of FDA to use ozone as a direct food additive, promising applications on liquidfood processing have emerged (Rajauria and Tiwari, 2017).

7.5 High-Pressure Processing High-pressure processing is a method of food processing where food is subjected to elevated pressures (up to 87,000 pounds per square inch or approximately 600 MPa), with

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or without the addition of heat, to achieve microbial inactivation or to alter the food attributes in order to achieve consumer-desired qualities. The technology is also referred to as high hydrostatic pressure processing and ultrahigh pressure processing in the literature. The history of the use of high pressure to inactivate microorganisms in food dates back to 1899 when Hite demonstrated the application of high pressure in preserving milk and later to preserve fruits and vegetables (Cullen et al., 2012). During pressure treatment, the application of pressure is governed by certain basic principles. The Le Chatelier’s principle states that any phenomenon such as phase change, change in molecular configuration, chemical reaction, and others, that is accompanied by a decrease in volume is enhanced by pressure and vice versa. The isostatic principle states that pressure is transmitted in a uniform and quasiinstantaneous manner throughout the whole sample, thus making the process independent of volume and geometry of the product (Zhang et al., 2011). It has been generally accepted that the isostatic principle is assumed to be true for high-pressure food processing applications. However, deviations are possible for heterogenous, large, and solid samples. Once the desired pressure is reached, it can be maintained for an extended period of time without any further energy input. The microscopic ordering principle states that at constant temperature, an increase in pressure increases the degree of ordering of molecules of a given substance. Thus it is important to consider the possibility of synergistic or antagonistic reactions when processing foods by combined pressure heat treatment. Unlike high-pressure homogenization where the food is exposed to high velocity, turbulence, and shear forces, during high pressure processing (HPP) the food is subjected to isostatic pressure treatment. However, foods such as marshmallows or strawberries that contain large air packets are deformed during pressure treatment due to differences between the compressibility of air and the rest of the food.

7.6 High-Pressure Processing Equipment Fluid foods such as juices can be processed in batch or semicontinuous modes. The equipment typically consists of (Balasubramaniam et al. 2016): 1. 2. 3. 4. 5. 6.

pressure vessel top and bottom end closures yoke (structure for restraining end closures) high-pressure pump and intensifier for generating target pressures process control and instrumentation handling system for loading and removing the product

In the batch mode, the liquid product is prepackaged, preconditioned, and pressure treated. A typical batch process cycle consists of loading the vessel with the prepackaged, preconditioned product, and filling the remainder of the vessel with water, which acts as the

212 Chapter 7 pressure-transmitting fluid. The vessel is closed and the desired process pressure is achieved through the introduction of pressure-transmitting fluid in the vessel. After holding the product for the desired time at the target pressure and temperature, the vessel is decompressed by releasing the pressure transmitting fluid. Because the pressure is transmitted uniformly (in all directions simultaneously), the food retains its shape. In addition, because of minimal thermal effects, the sensory characteristics of the food are retained without compromising its microbial safety. Semicontinuous pressure equipment employs two or more pressure vessels with freefloating pistons arranged to compress the liquid foods. A low-pressure transfer pump is used to fill the pressure vessel with the liquid food. After filling, the pressure vessel inlet valve is closed, and the pressure-transmitting fluid (usually water) is introduced to compress the liquid food. After the appropriate holding time, releasing the pressure on the pressure-transmitting fluid decompresses the system. The treated liquid food can then be filled aseptically into sterile containers. Three batch vessels in a semicontinuous system can be connected such that while one vessel discharges the product, the second is being compressed, and the third is being loaded. In this way continuous output is obtained. Juice and beverage companies using HPP are almost exclusively smaller companies processing bottled premium juices and smoothies for regional markets. Continuous high-pressure equipment for liquid foods processing is not readily available. Use of batch or semicontinuous equipment constrains the throughput needs of some of the commodity-type beverages and limits the widespread technology implementation for processing such liquid foods.

7.7 Ultraviolet and Pulsed-Light Technology UV light is the part of the electromagnetic spectrum with wavelengths between 100 and 400 nm. The application of UV light for treatment of liquids on a municipal scale began in Marseille, France, in 1906, for disinfection of drinking water. UV light has broad antimicrobial action, providing effective inactivation of viruses, vegetative bacteria, bacterial spores, yeasts, conidia, and parasites (Cullen et al., 2012). UV can be utilized similarly in the disinfection of surfaces, foods, and other liquids. The application of UV light can also improve the toxicological safety of foods through its ability to reduce levels of toxins such as patulin and mycotoxin. UV-light treatment of foods is a nonthermal method for microbial inactivation that is free of chemicals and waste effluents, which makes it ecologically friendly. It does not produce by-products. Even though the term “irradiation” is frequently used for this treatment, UV light is a nonionizing radiation and it must not be associated with gamma irradiation. It is safe to use, although precautions must be taken to avoid human exposure to UV light and to evacuate ozone generated by vacuum and far-UV wavelengths. UV light present in the

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range of 200 280 nm wavelength of the light spectrum has a germicidal effect on microorganisms such as bacteria, yeast, mold, and viruses (Knorr et al., 2011). UV-light treatment of liquid foods can be performed by use of continuous or pulsed UV sources. Continuous UV treatments are performed by mercury lamps that continuously emit UV photons and are called continuous-wave UV (CW UV) lamps in both monochromatic and polychromatic modes (Guerrero-Beltre´n and Barbosa-Ca´novas, 2004). Mercury-based UV lamps have been in use for over 100 years. Pulsed-light (PL) treatment is a more modern technology, in which shorttime pulses of a high-power polychromatic flash, rich in UV-C emitted by a xenon lamp, are rapidly and repeatedly released on the sample surface. Its main advantage over CW UV light is that processing time can be dramatically reduced and PL sources do not need to be warmed up, while its main disadvantage is the possibility of sample heating. Due to the low penetration capacity of UV light into low UV transmittance (UVT) or almost-opaque substances such as liquid foods, it was initially intended to be used only for disinfection of food surfaces or packaging. Its use in fluid foods was originally limited to highly transparent liquids; however, development of new reactors with optimized hydraulics and thin-film design now allows delivery and exposure of target microorganisms to UV light in low-UVT fluids. An absolute prerequisite for UV-based microbial inactivation is the effective exposure of the UV photons to the target microorganisms (Koutchma, 2008). In solid foods, microorganisms located below the food surface are shielded from photon contact because the food surface will absorb photons intended for the microorganisms. In fluid foods, microorganisms located far from the UV source may be protected from photon contact by the highly absorbing fluid layer present between them and the UV source (Forney and Moraru, 2009). The level of this protection is a function of the fluid UVT and the thickness of the layer. However, in contrast with solid foods, UV reactors for fluid treatment can relocate microorganisms, via hydraulic and reactor design, to a place where the fluid layer is not thick enough to absorb all the UV photons and consequently enables inactivation. In this regard, UV light is more suitable for fluids than for solid-food treatment. Table 7.3 shows how UV can be applied for various nonalcoholic beverages.

7.8 Irradiation Among the various technologies proposed for the processing of liquids is irradiation, particularly the use of ionizing radiation. Irradiation is a food-processing treatment endorsed by a variety of professional and governmental organizations. Dose ranges may be characterized as low (,3 kGy), medium ( . 3 and ,10 kGy), or high ( . 10 kGy) (Molins, 2001). The irradiation treatment is based on the energy absorbed. For most juices and liquid products, the controlling factors are the packaging size and shape, and orientation also becomes significant (Urbain, 2012). The three types of ionizing radiation used for commercial food processing are gamma rays, e-beam, and X-rays. All these technologies are of sufficient energy to ionize molecules in the food target, leading to the generation of radicals, breakage of DNA, and other radiochemical effects. As with other food-processing

214 Chapter 7 Table 7.3: HPP treatment of various nonalcoholic beverages. Product

Independent Variable

Orange juice milk beverage

Pressure (100, 200, 300, and 400 MPa). Treatment times (120, 300, 420, and 540 s).

Milk and soysmoothies

Green asparagus juice

Carrot juice

Milk

Result

Ascorbic acid retention in the orange juice milk beverage was higher than 91% in all cases after HPP. There was a significant increase (P , .05) in phenolic compounds at 100 MPa/420 s; however, at 400 MPa/540 s a nonsignificant decrease was observed. Total carotenoid content was significantly higher in all samples treated by HPP when treatment time was 420 and 540 s. A 5-log reduction of Lactobacillus plantarum CECT 220 was obtained in the orange juice milk beverage after HPP (200 MPa, 300 s). Untreated, pasteurized Milk and soy-smoothies showed a total reduction (80 C/3 min) and HPP in microorganisms after pasteurization and HPP at the pressure conditions applied. HPP maintained (450 650 MPa for microbial stability until the end of the storage 3 min at 20 C). period (45 days at 4 C). Based on the data, 450 MPa are sufficient to obtain safe smoothies whose organoleptic properties are equally acceptable to consumers as freshly made smoothies. Pressure (200, 400, and HPP at 400 and 600 MPa for both treatment 600 MPa) and treatment times decreased the total mesophilic bacteria to undetectable levels as the thermal treatment did, times (10 and 20 min). thus ensuring the safety of asparagus juice. All HPP treatments retained significantly more ascorbic acid, rutin and total phenolic contents, and higher total antioxidant activity than thermal treatment. The main volatile compounds in asparagus juice were aldehydes, alcohols, and ketones. HPP treatments maintained significantly higher concentrations of aldehydes, alcohols, and ketones than thermal treatment. Pressure 550 MPa for After HPP and HTST, the total plate count (TPC) 6 min was found to significantly decrease by 4.30 and High-temperature short- 4.88 log10 CFU/mL, respectively, and yeasts and time (HTST) processing molds (Y&M) were completely inactive. During 20 at 110 C for 8.6 s days of storage at 4 C, both HPP and HTSTtreated juices were microbiologically safe (i.e., TPC , 2.4 log10 CFU/mL, and Y&M were not detected), and their antioxidant capacities decreased linearly due to a decrease in carotenoid and polyphenol contents. 450 MPa for 900 s Optimized PSU broth significantly increased the recovery of L. monocytogenes following high 600 MPa for 90 s pressure processing (HPP), and was 63 times more likely to recover L. monocytogenes following HPP, compared to listeria enrichment broth (LEB), buffered LEB (BLEB) and modified BLEB (MBLEB)

References Barba et al. (2012)

Andre´s et al. (2016)

Chen et al. (2015)

Zhang et al. (2016)

(Bull et al. (2005)

(Continued)

Nonthermal Technologies for Nonalcoholic Beverages

215

Table 7.3: (Continued) Product

Independent Variable

Result

References

broths (P , .05; Odds Ratio 5 63.09, C.I. 23.70 167.96). HPP-injured L. monocytogenes could be recovered using both LEB and optimized Penn State University (oPSU) broths after storage of milk at 4 C, 15 C, and 30 C, with recovery being maximal after 24 72 h of storage; however, recovery yield dropped to 0% after prolonged storage of milk at 4 C and 30 C. In contrast, storage of milk at 15 C yielded the most rapid rate of recovery and the highest recovery yield (100%), which remained high throughout the 14 days of storage at 15 C. Cranberry juice

Blueberry juice

HPP for 5 min (450 MPa) and ultrasonic treatment for 5 min (600 and 1200 W/L), followed by HPP for 5 min (450 MPa). Pressure (200, 400, and 600 MPa) and treatment times (5, 9, and 15 min)

Both nonthermal treatments preserved the FOS content maintaining the prebiotic property of the juice. The retention of organic acids was high ( . 90%) and an increase in anthocyanin content (up to 24%) was observed when ultrasound was followed by HPP. The changes in instrumental color, soluble solids content, and pH were negligible. HPP treatments resulted in more than 92% vitamin C retention at all treatment intensities. On the other hand, total phenolic content in the juice was increased, mainly after HPP at 200 MPa for all treatment times. The total and monomeric anthocyanin were similar or higher than the value estimated for the fresh juice being maximal at 400 MPa/15 min (16% increase). Antioxidant capacity values were not statistically different for treatments at 200 MPa for 5 15 min in comparison with fresh juice; however, for 400 MPa/15 min and 600 MPa for all times (8% 16% reduction) is was statistically different

Gomes et al. (2017)

Barba et al. (2013)

technologies, temperature control during irradiation is an essential element of proper implementation. Acceleration electron beams (e-beams) are produced by linear or cyclotron accelerators. In commercial food irradiators, energies of up to 10 MeV are used. The processing dose is delivered as a pulse of electrons and the full dose is delivered quickly, taking typically .5 s. Short exposure times generally prevent any significant rise in temperature during processing. E-beam penetrability is lower than that of gamma rays or X-rays. Single bags, relatively thin packages ( . 4 inches), and very low-bulk-density items have been irradiated successfully with e-beam systems (Farkas, 1998). Packaging and product configuration must be carefully considered to avoid unacceptably uneven treatment.

216 Chapter 7 X-rays are high-energy photons generated when an e-beam is directed at a metal plate (Diehl, 2002). Alloys of high-density metals, such as tungsten or tantalum, provide the most efficient conversion rates. Electrons are absorbed by the metal atoms, stimulating the release of the X-rays. Depending on the specific alloy used in the metal target plate, the efficiency of this conversion is relatively low, typically 5% 10%, with the balance lost as waste heat. Cooling subsystems in the metal plate are necessary for operation of X-ray irradiators. As photons, X-rays have greater penetration than e-beams, which makes them suitable for irradiating large or bulky food items, up to and including pallet- or crate-sized packages (Thayer, 1990). The speed of processing is comparable to that of e-beam. Gamma rays do not require significant inputs of electricity to create, as is the case with ebeam or X-ray systems (Thakur and Singh, 1994). Gamma rays are high-energy photons produced by the radioactive isotopes cobalt-60 and, less commonly, cesium-137. Gamma rays have penetrability similar to X-rays, which makes these systems comparably suitable for irradiating large or bulky food items. The time required for processing is dependent on the dose desired and the strength of the source. Speed of processing is slower than X-ray or e-beam. Shielding for all three types of irradiators is comparable. The radioactive material used in gamma irradiators is continuously producing radiation and must, therefore, be shielded for worker access all the time. Although e-beam and X-ray systems do not produce any ionizing radiation when the systems are powered down, while in operation they require control systems and shielding similar to that of gamma systems (Wilkinson, 1997). This is typically concrete, steel, lead, or a combination of these.

7.8.1 Mode of Inactivation of Microbes High-energy photons (gamma rays or X-rays) energize electrons within the atoms of the food. These electrons may leave the atom completely (ionization) or raise the energy of the electrons to a higher level (excitation) (Byun et al., 2002). These processes yield free radicals, that is, atoms with unpaired electrons on their outer shell. e-Beams interact with atoms to create these free radicals directly. Free radicals are very reactive, because their unpaired electrons pair up with outer shell electrons of the atoms in cells. In most foods, water makes up the bulk of mass. As a result, the majority of the absorbed energy from irradiation goes into the creation of hydrogen and hydroxyl radicals from water molecules. Interaction of free radicals with organic molecules of the food is the main mode of action of irradiation. Under conditions of limited free water, such as in dried or frozen products, fewer radicals are produced per unit of energy applied. Also, as the radicals have reduced mobility in dry or frozen products, higher doses become necessary for microbial control in

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these commodities. This can have significance for juice concentrates with a reduced water activity and high-osmotic potential, particularly if these concentrates are frozen as part of production and/or distribution. Biochemical changes in selected gamma-irradiation induced mutants of Lactobacillus bulgaricus and Lactobacillus casei were examined (Singh and Ranganathan, 1977). Cultures were tested after 24 h of incubation at 37 C for titratable and volatile acidities and proteolytic activity. The gamma-irradiation induced mutants exhibited 50% 95% greater proteolytic activity than the unirradiated parent cultures. Some of the mutants produced greater titratable and volatile acidities in milk compared to parent cultures. Two mutant cultures, Lb/G-1 from L. bulgaricus 59 and Lc/G-1 from L. casei RTS released significantly greater amounts of soluble nitrogen and amino nitrogen in whole casein and selected fractions than did parent cultures. Combining the mutant cultures with Streptococcus lactis C10 or Streptococcus cremoris C1 resulted in greater acid-producing ability than that of the parent cultures mixed with the streptococci. Apple juice was γ-irradiated at 5 C at doses ranging from 0 to 8.9 kGy and then stored at 5 C for 15 days (Fan and Thayer, 2002). Ionizing radiation reduced the browning of apple juice and increased antioxidant activity measured by the ferric-reducing antioxidant power (FRAP) assay. The magnitude of changes increased with radiation dose. The level of malondialdehyde (MDA) measured using the thiobarbituric acid reactive substrates assay increased at radiation doses above 2.67 kGy. The browning of irradiated juices increased during storage at 5 C, but the irradiated juices were still lighter than controls at the end of storage. Differences in FRAP values disappeared during early periods of storage while higher MDA levels were observed in irradiated samples during most of the storage period.

7.9 Cold Plasma Plasma is often referred to as the fourth state of matter, according to a scheme expressing an increase in the energy level from solid to liquid to gas, and ultimately to an ionized state of the gas plasma, which exhibits unique properties. Thus any source of energy which can ionize a gas can be employed for the generation of plasma. Plasma is comprised of several excited atomic, molecular, ionic, and radical species, coexisting with numerous reactive species, including electrons, positive and negative ions, free radicals, gas atoms, molecules in the ground or excited state, and quanta of electromagnetic radiation (UV photons and visible light). The free electric charges—electrons and ions—make plasma electrically conductive, internally interactive, and strongly responsive to electromagnetic fields. Most active chemical species of plasma are often characterized by very efficient antimicrobial action.

218 Chapter 7 Plasmas can be subdivided into equilibrium (thermal) and nonequilibrium (low temperature) plasma. If a gas is heated to sufficiently high temperature typically in the order of 20,000K for achieving the ionization of the gas, such plasma would be referred to as “thermal plasma” (Misra et al., 2011). In thermal plasma, all the constituent chemical species, electrons, and ions exist in thermodynamic temperature equilibrium. The low temperature plasma can be further branched into quasiequilibrium plasma (typically 100 C 150 C) and nonequilibrium plasma (,60 C) (Pankaj and Keener, 2017). In the former type, a local thermodynamic equilibrium among the species exists, whereas in the latter, cooling of ions and uncharged molecules is more effective than energy transfer from electrons, and the gas remains at low temperature; for this reason nonequilibrium plasma is also called NTP or cold plasma. Nonequilibrium plasmas are typically obtained by means of electrical discharges in gases. Cold plasma is obtained at atmospheric or reduced pressures (vacuum) and requires less power input. Cold plasma can be generated by an electric discharge in a gas at lower pressure or by using microwaves. Typical illustrations for plasma generation at atmospheric pressure include corona discharge, dielectric barrier discharge (DBD), radio-frequency plasma, and the gliding-arc discharge. In contrast, thermal plasmas are generated at higher pressures and require high-power inputs (Thirumdas et al., 2015).

7.9.1 Mode of Action of Cold Plasma There are two major differences between the application of plasma on solid/dry media and liquid media, namely (1) the penetration depths or contact surface between plasma and food, and (2) the chemistry/physics initiated by reactive oxygen species (Conrads and Schmidt, 2000). Liquid foods behave very contrary to this, because every volume element comes into contact with the plasma applied (or at least with subsequent reaction products) so that penetration depth is not that important. Thus if plasma is applied in order to decontaminate a liquid, not only will the microorganisms be harmed, but also all the other surrounding components. Therefore optimization with regard to a good antimicrobial efficacy and retention of other food constituents at the same time represents a key challenge.

7.9.2 Treatment of Nonalcoholic Drinks with Plasma Cold plasma’s ability to inactivate Citrobacter freundii in apple juice was investigated (Surowsky et al., 2014). C. freundii loads in apple juice were reduced by about 5 log cycles after a plasma exposure of 480 s using argon and 0.1% oxygen together with a subsequent storage time of 24 h. The results indicate that a direct contact between bacterial cells and plasma is not necessary for achieving successful inactivation. The plasma-generated

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compounds in the liquid, such as H2O2 and most likely hydroperoxyl radicals are particularly responsible for microbial inactivation. The bactericidal effect of DBD-ACP on Escherichia coli in apple juice was studied (Liao et al., 2018). Under a 30 50 W input power, less than 40 s treatment time was required for DBD-ACP to result in 3.98 4.34 log CFU/mL reduction of E. coli in apple juice. During the treatment, the cell membrane of E. coli was damaged severely by active species produced by plasma, such as H2O2, ozone, and nitrate. In addition, the ACP exposure had a slight effect on the  Brix, pH, titratable acidity (TA), color values, total phenolic content, and antioxidant capacity of apple juice. However, higher level of DBD-ACP treatment, 50 W for more than 10 s in this case, resulted in significant change of the pH, TA, color, and total phenolic content of apple juice. Chocolate-milk drinks can also be manufactured using cold-plasma technology. A study evaluated the effect of the process time (5, 10, and 15 min) and flow rate (10, 20, and 30 mL/min) of cold-plasma technology on physiochemical characteristics (pH), bioactive compounds (N,N’-Diphenyl-p-phenylenediamine (DPPD), total phenolic compounds, ACEinhibitory activity values), fatty acid composition, and volatile compound profiles of chocolate-milk drinks (Coutinho et al., 2019). The mild (lower flow rate and process time) and more severe (higher flow rate and process time) conditions led to a reduction of the bioactive compounds (total phenolic compounds and ACE-inhibitory activity), changes in fatty acid composition (increased saturated fatty acid and decreased monounsaturated fatty acid and polyunsaturated fatty acid), less-favorable health indices (higher atherogenic, thrombogenic and hypercholesterolemic saturated fatty acids, and lower content of desired fatty acids) and a lower number of volatile compounds. In contrast, in intermediate coldplasma conditions, an adequate concentration of bioactive compounds, fatty acid composition, and health indices, and increased number of volatile compounds (ketones, esters, and lactones) were observed. Overall, cold-plasma technology has proven to be an interesting alternative to chocolate-milk drinks, being of paramount importance in the study of the coldplasma process parameters. Another study evaluated the microbial and physicochemical characteristics of milk that was treated with encapsulated DBD plasma (Kim et al., 2015). Encapsulated DBD plasma was generated in a plastic container (250 W, 15 kHz, ambient air) and DBD plasma treatment was applied to milk samples for periods of 5 and 10 min. The total aerobic bacterial count in the untreated control sample was 0.98 log CFU/mL. Following plasma treatment, no viable cells were detected in the milk samples. When milk samples were inoculated with E. coli, Listeria monocytogenes, and Salmonella typhimurium, plasma treatment for 10 min resulted in a reduction in bacterial counts by approximately 2.40 log CFU/mL. The pH of the sample milk was found to decrease after the 10 min plasma treatment. The results of this study indicate that encapsulated DBD plasma treatment for less than 10 min improved the microbial quality of milk with only slight changes in the physicochemical quality of milk.

220 Chapter 7

7.10 Pulsed Electric Field Processing Pulsed electric field processing (PEF) involves the application of short pulses (μs) of high voltage (kV/cm) to foods placed between two electrodes. Application of PEF is restricted to food products that can withstand high electric fields, have low electrical conductivity, and do not contain or form bubbles. The particle size of the food may also be a limitation. Processing factors such as electric field strength, treatment time, and pulse shape, width, frequency, polarity, and temperature, as well as the treatment in batch or continuous flow mode have been reported to have influential effects on the efficiency of PEF technology for processing fluid foods. Electric field strength and total treatment time are the most studied PEF treatment parameters.

7.10.1 PEF Equipment Design In general, PEF treatment systems are composed of PEF treatment chambers, a pulse generator, a fluid-handling system, and monitoring systems. The treatment chamber is used to house electrodes and deliver a high voltage to the food material. It is generally composed of two electrodes held in position by insulating material, thus forming an enclosure containing the food material. Therefore the proper design of the treatment chamber is an essential component for the efficiency of the PEF technology. Optimization of the treatment chamber design is of great importance to properly apply the electrical field, but also to avoid unexpected phenomena during the treatment such as heat accumulation, electric-field perturbations, deposition of particles, gas-bubble formation, and arching. With regards to PEF treatment-chamber configuration, parallel, coaxial, and colinear configurations are used for processing foods by PEF. The parallel-plate chambers are generally separated by a gap that is considerably smaller than the electrode’s surface. Treatment chambers with parallel plate-electrodes provide a uniform electrical-field distribution along the gap axes and electrode surfaces, but create a field enhancement problem at the edge of the electrodes. On the other hand, coaxial and cofield chambers are widely used due to their simplicity in structure. Electrical current flows perpendicularly to food flow in coaxial PEF treatment chambers and in parallel to food flow in cofield flow PEF treatment chambers. The cofield chamber configuration has advantageous fluid dynamics, highly desirable for food processing and convenient for cleaning in place. Treatment chamber design has evolved from static to continuous treatment chambers. Static chambers are mainly suitable for laboratory use in order to evaluate the influence of any relevant parameter critical to the process efficiency, while for large-scale operations continuous chambers seem to perform much better. The main limitation of parallel chambers is the batch nature of the process. However, while cofield and coaxial chambers allow continuous treatment, the electric fields are not as homogenous as in the case of parallel chambers. Chamber electrodes, as well as insulating components, must be made of

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food-grade, chemically inert materials in order to prevent food contamination. In addition, PEF treatment chamber materials should be washable and autoclavable. With regards to continuous PEF treatments, two different fluid handling systems can be used to allow the treatment of liquid foods. On the one hand, the fluid can be repeatedly pumped though the system, as many times as needed, to apply the desired treatment time in a stepwise circulation mode. On the other hand, a recirculation mode is also possible. In the latter case, liquid is pumped to the feeding container without interruption until the whole treatment is applied. Pulse generators convert low voltage into high voltage and provide the latter to PEF chambers. Generation of PEF requires a fast discharge of electrical energy within a short period of time. Square, exponential decay, or oscillatory pulses are generally used for PEF treatment of fluid foods. Because discharge time is extremely short, heating of the foods is minimized. Temperature and pulse-monitoring systems are the main equipment used to supervise PEF processing. Temperature is monitored with thermocouples, while pulses are monitored with high-voltage probes, current monitors, and oscilloscopes.

7.11 Dense-Phase Carbon Dioxide Technology The need for a food preservation method that is safe, inexpensive, and that preserves heatsensitive compounds resulted in the use of pressurized CO2 as a food preservation method. CO2 is used because of its safety, low cost, and high purity. Dense-phase carbon dioxide (DPCD) treatment has attracted great interest in the nonthermal treatment of liquid foods or liquid model solutions. DPCD has been shown to inactivate microorganisms as well as conventional heat pasteurization without the loss of nutrients or quality changes that may occur due to thermal effects. In the DPCD process, food is contacted with pressurized subcritical or supercritical CO2 for a period of time in a batch, semibatch, or continuous manner. The CO2 pressures can range from 7.0 to 40.0 MPa. These levels are much lower than those of ultrahigh pressure processes, for example, making the management and control of pressure during the process easier. Process temperatures can range from 20 C to 60 C and, therefore, the temperature levels that may cause thermal damage to foods are avoided. The temperature increase induced by the pressure build-up is negligible. The treatment times can range from about 3 to 9 min for continuous, or from 120 to 140 min for semicontinuous or batch DPCD processes. Several batch, semicontinuous, and continuous systems have been developed for DPCD applications. In a batch system, CO2 and the solution to be treated are stationary in a container during treatment. A semicontinuous system allows a continuous flow of CO2 through the chamber; however, the liquid remains stationary. A continuous system allows flow of both CO2 and the liquid food through the system. Pressure and temperature are the main control parameters for DPCD. They significantly affect microbial inactivation and they influence the CO2 physical state (i.e., liquid, gas, or supercritical) and its properties

222 Chapter 7 such as viscosity and diffusivity. These parameters, coupled with the composition of the medium, influence CO2 solubility in the liquid food. The different steps in this simplified inactivation mechanism can be listed as follows. Most of these steps will not occur singly or consecutively, but take place simultaneously in a complex and interrelated manner (Tables 7.4 and 7.5). Table 7.4: UV treatment of various nonalcoholic beverages. Product

Process Parameters

Tiger nut Mercury lamp with 9 W milk beverage output Maximum peak radiation at 253.7 nm Maximum temperature 27 C Estimated fluence rate at the position chosen was 2.35 mW/cm2

Apple juice

Time—120 min High-pressure mercury lamp of 400 W that emits in a range between 250 and 740 nm with a resulting incident energy of 3.88 3 1027 E/min.

Pineapple juice

Wavelength 254 nm (53.42 mJ/cm2, 4.918 s). Thermal pasteurization at 800 C for 10 min.

Product Quality

References

Color changes measured as total color difference and browning index were imperceptible even when the liquid was treated at high UV-C doses. Likewise, the fat content and its oxidation level remained unaffected. By contrast, the antioxidant capacity of treated samples decreased with increasing doses of UV-C. In particular, the peroxidase activity decreased up to 85% at the highest UV-C dose applied. Notably, UV-C effectively inactivated up to 3-log10 cycles of spoilage-related microorganisms (yeasts and molds, mesophilic flora, and psychrotrophic bacteria). Polyphenol oxidase was inactivated in 100 min, while peroxidase was completely destroyed in only 15 min in all the four varieties. The content of vitamin C in juices from Golden, Starking, and Fuji slightly changed during the experiment, decreasing a 4.0% in Fuji juice, 5.7% in Golden one, and 5.6% in Starking one. Meanwhile, in the juice from King David the loss was 70.0%. There were significant changes in the total soluble solids, pH, titratable acidity (TA), and turbidity of UV-irradiated juice during storage, whereas the same quality attributes of thermally pasteurized juice remained stable throughout the storage time. There were no significant changes in total phenolics for both treatments throughout the storage period. UV-irradiated pineapple juice preserved better quality attributes (total soluble solids (TSS), pH, TA, ascorbic acid, turbidity, total phenolic, L [lightness], hue angle, and chroma) than the thermal pasteurized juice during the storage time.

Corrales et al. (2012)

Falguera et al. (2011)

(Chia et al. (2012)

(Continued)

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Table 7.4: (Continued) Product

Process Parameters

Pomegranate juice

Control (untreated); heat treated (90 C, 2 min). 9 Germicidal UV lamps (254 nm; 28 W UV-C output). The dosages applied were 12.47 J/mL, 37.41 J/mL, and 62.35 J/mL after 1, 3, and 5 passes.

Orange juice

Grape juice Apple juice

Product Quality

After UV-C treatment, total monomeric anthocyanin content of pomegranate juice did not change significantly and the decrease in individual anthocyanin pigments was between 8.1% and 16.3%. However, anthocyanin content of PJ was significantly affected by heat treatment (P , .05) and 15.4% and 28.3% of individual anthocyanin pigments were lost after this process. Also, differences between the control and UV-C treated PJ samples were small in terms of polymeric color values (P . .05) while polymeric colors of PJ were significantly affected by heat treatment (P , .05). Low-pressure UV lamp with a The decimal reduction doses required for length of 40 cm and 30 W the reconstituted orange juices (OJ; total power, emitting 6 W of 10.5 Brix) were 87 6 7 and 119 6 17 mJ/ cm2 for the standard aerobic plate count germicidal UV (254 nm). (APC) and yeast and molds, respectively. The shelf life of freshly squeezed OJ was extended to 5 days with a limited exposure of UV (73.8 mJ/cm2). The degradation of vitamin C was 17% under high UV exposure of 100 mJ/cm2, which was similar to that usually found in thermal sterilization. The energy required for UV treatment of OJ (2.0 kW h/m3) was much smaller than that required in thermal treatment (82 kW h/m3). UV light intensity (1.31, 0.71, The best reduction (5.5-log) was achieved in grape juice when the UV intensity was and 0.38 mW/cm2). 1.31 mW/cm2. The maximum inactivation Exposure time (0, 3, 5, 7, 10, was approximately 2-log CFU/mL in apple 12, and 15 min). juice under the same conditions. The results Constant depth (0.15 cm) showed that first-order kinetics were not suitable for the estimation of spore inactivation in grape juice treated with UVlight. Since tailing was observed in the survival curves, the log-linear plus tail and Weibull models were compared. The results showed that the log-linear plus tail model was satisfactorily fitted to estimate the reductions.

References (Pala & Toklucu, 2011)

Tran and Farid (2004)

Baysal et al. (2013)

(Continued)

224 Chapter 7 Table 7.4: (Continued) Product

Process Parameters

Starfruit juice Time 0, 30, and 60 min Room temperature (25 C 6 1 C)

Mango nectar

Flow rates (0.073 0.451 L/min) UV light doses (75 450 kJ/m2)

Product Quality

References

Microbial studies showed reduction in APC, yeasts, and mold counts by 2-log cycle on UV treatments. On exposure, the TA significantly decreased, while the decrease in  Brix and pH were not significant. With regard to colorimetric parameters, L* value increased significantly with a subsequent decrease in a* and b* values corresponding to UV treatment time. The first-order kinetics modeling found that DUV-values in mango nectar ranged from 27.9 to 10.9 min (R2 . 0.950) and 26.0 to 11.8 min (R2 . 0.962) for total microbial count and yeast count, respectively. The maximum log reduction (CFU/mL) was 2.71 and 2.94 for total microbial count and yeast count, respectively, after 30 min of UV treatment at 0.451 L/min.

Bhat et al. (2011)

GuerreroBeltre´n and BarbosaCa´novas (2006)

Table 7.5: Influence of pulsed electric field on beverages. Product

Process Parameters

Product Quality

References

Orange juice milk beverage

Gap distance of 2.93 3 1023 Temperature—35 C and 55 C Flow rate 6 3 1022 L/min Treatment time— 0 180 3 1026 s Electric field—35 3 105 and 40 3 105 V/m

Sampedro et al. (2007)

Fruit juice (orange, kiwi, pineapple) soymilk beverage

High-intensity pulsed electric fields (HIPEF) treatment (35 kV/cm, 4 μs bipolar pulses at 200 Hz for 800 or 1400 μs)

The inactivation curve had different slopes, one up to application of 200 285 3 103 J/L, a second stage up to application of 813 891 3 103 J/L in which the inactivation did not increase significantly, and a third stage up to application of 1069 1170 3 103 J/L. When the process temperature was raised to 55 C the inactivation increased by 0.5 cycles, achieving an energy saving of up to 60%. No increase in inactivation was achieved when the pulse width was increased from 2.5 3 1026 to 4 3 1026 s. HIPEF processing for 800 μs ensured the microbial stability of the beverage during 31 days; however, longer microbial shelf life (56 days) was achieved by increasing the treatment time to 1400 μs or by applying a thermal treatment. Peroxidase and

Moralesde La ˜a et al. Pen (2010)

(Continued)

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Table 7.5: (Continued) Product

Process Parameters

Product Quality

References

lipoxygenase of HIPEF treated beverages were inactivated by 17.5% 29% and 34% 39%, respectively, whereas thermal treatment achieved 100% and 51%. Milk

3
7 μs pulse duration time 250 Hz pulse repetition rate 1 mL/s flow rate 460 μs total treatment time 3
5 kV/mm electric field strength

Tropical fruit smoothie based on pineapple, banana, and coconut milk

Heat treatment—25 C to either 45 C or 55 C over 60 s and subsequently cooled to 10 C Electric field strength—24 and 34 kV/cm Specific energy inputs of 350, 500, and 650 kJ/L

Tomato juice

Electric field strengths— 20 35 kV/cm for up to 2000 μs using bipolar 1-μs pulses at 250 Hz

There was a significant decrease in S. aureus cells caused by the two-fluid handling systems (probability P , .05). The difference in the inactivation due to the PEF treatment with the fluid handling systems was not significant (P . .05). After the PEF treatment, there was no significant injury of the PEF-treated cells (P . .05). Relative to the control samples, there was a significant reduction in the number of the PEFtreated cells at 4 C for 2 weeks (P , .05). By increasing the temperature from 45 C to 55 C, a higher reduction in E. coli numbers (1 compared with 1.7 log10 colony forming units per milliliter, P , .05) was achieved. Similarly, as the field strength was increased during stand-alone PEF treatment from 24 to 34 kV/cm, a greater number of E. coli cells were inactivated (2.8 compared with 4.2 log10 CFU/mL, P , .05). An increase in heating temperature from 45 C to 55 C during a combined heat/PEF hurdle approach induced a higher inactivation (5.1 compared with 6.9 log10 CFU/mL, respectively (P , .05), with the latter value comparable to the bacterial reduction of 6.3 log10 CFU/mL (P $ .05) achieved by thermal pasteurization (72 C, 15 s). Fresh tomato juice had a lycopene content of 77 mg/L. Lycopene concentration was enhanced significantly after HIPEF processing from 3.8% to 37.7% compared to the untreated juice. Electric field strength and treatment time had a significant

Evrendilek et al. (2004)

Walkling Ribeiro et al. (2008)

OdriozolaSerrano et al. (2008)

(Continued)

226 Chapter 7 Table 7.5: (Continued) Product

Process Parameters

Product Quality

References

effect on tomato juice lycopene content. HIPEF-treated tomato juice processed at 20 kV/cm had the highest antioxidant capacity, followed by that treated at 35 kV/cm. Carrot juice

• • • • • • • •

Pulse width (1 7 μs) Pulse frequency (50 250 Hz)

The total treatment time and the electric field strength were set at 1000 μs and 35 kV/cm, respectively, at a temperature below 35 C. The results showed that HIPEF-treated carrot juice at 35 kV/cm for 1000 μs applying 6 μs pulse width at 200 Hz in bipolar mode led to 73.0% inactivation of POD. The color coordinates did not change significantly.

Quita˜oTeixeira et al. (2008)

Solubilization of pressurized CO2 in the external liquid phase. Cell membrane modification. Intracellular pH decrease. Key enzyme inactivation/cellular metabolism inhibition due to internal pH lowering. Direct inhibitory effect of molecular CO2 and HCO32 on metabolism. Disordering of the intracellular electrolyte balance. Extraction of vital constituents from cells and cell membranes. Physical disruption of cell membrane.

In Table 7.6 a literature review on the microbial inactivation in some nonalcoholic beverages is provided.

7.12 Conclusion From various research which deal with the impact of nonthermal technologies on the quality and stability of nonalcoholic beverages, it is clearly evident that these technologies can be successfully implemented to extend the shelf life of these beverages. Moreover, combining it with temperature or pressure for a better effect can be produced. Two or more nonthermal techniques may also be combined to produce a synergistic effect; however, in large-scale applications, the process is expensive and tedious to scale-up.

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Table 7.6: Microbial inactivation in liquid foods by dense-phase CO2. Product

Process Parameters 

Coconut water

DPCD-treated (34.5 MPa, 25 C, 13% CO2, 6 min) Heat-pasteurized (74 C, 15 s) and untreated beverage

Grape juice

Temperature (25 C and 35 C) CO2 concentration (0, 85, and 170 g/kg) Pressure (6.9, 27.6, and 48.3 MPa)

Hami melon juice

DP-CO2 (55 C, 60 min, and 35 MPa) Thermal pasteurization—90 C for 60 s

Diluted apple cider

CO2/product ratio (0, 70, and 140 g/kg) Temperature (25 C, 35 C, and 45 C), Pressure (6.9, 27.6, and 48.3 MPa)

Apple juice

DPCD-treated (15 MPa, 35 C, 15 min; 25 MPa, 35 C, 15 min) Heat-pasteurized (75 C, 15 s) and untreated apple juice

Results

References

DPCD increased TA, but did not change pH (4.20) and  Brix (6.0). Total aerobic bacteria of DPCD and heat-treated samples decreased The dense-phase CO2 process resulted in more than a 6 log reduction in yeast population. CO2 in the supercritical state was more effective in inactivating yeast than in the subcritical state. The process did not cause detectable flavor degradation. There were significant differences between treatments in microbial count, vitamin C, β-carotene, and volatile compound concentrations. Escherichia coli was very sensitive to dense CO2 treatment, with a more than 6-log reduction in treatments containing 70 and 140 g/kg CO2, irrespective of temperature and pressure. The CO2/product ratio was the most important factor affecting inactivation rate of E. coli. The DPCD processing carried out at 15 MPa resulted as effective as 25 MPa in reducing microbial cells. Trolox equivalent of DPCD treated at 25 MPa (0.41 mm) resulted significantly (P , .05) lower than DPCD treated at 15 MPa (0.48 mm). Head space analysis of volatile compounds indicated the lowest decrease in apple aroma compounds (59% esters and 59% aldehydes) in DPCD treated at 15 MPa.

Damar et al. (2009) Gunes et al. (2005)

Chen et al. (2009) (Gunes et al. (2006)

Porto et al. (2010)

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