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Basic physics and chemistry of controlled hydrodynamic cavitation

The basic physics of cavitation in liquid media is rather simple. Whenever the local hydrodynamic pressure falls below the liquid’s vapor pressure at a given temperature, vaporization occurs along with a myriad of bubbles on the micro- to nano-scale (Carpenter et al., 2017), whereas in extreme cavitation regimes even vacuum, or plasma-filled, bubbles can arise (Baurov, Albanese, & Meneguzzo, 2014; Baurov, Meneguzzo, Baurov, & Baurov, 2012).
While uncontrollably arising in hydrothermal and propulsion machinery such as pumps, turbines and ship propellers, to which it can cause irreversible erosion damage (Dular, 2016), cavitation can be controlled and harnessed. Actually, the pressure fall giving rise to controlled cavitation can be produced by different mechanisms, such as ultrasound irradiation, creating compression/rarefaction waves in a liquid at rest (Colmenares & Chatel, 2017), giving rise to the so called acoustic cavitation (AC), or mechanical methods, such as Hydrodynamic Cavitation (HC), inducing liquid acceleration and pressure drop according to Bernoulli’s equation (Gogate & Pandit, 2011). The latter include several different devices and respective methods, such as rotor-stator arrangements, where mechanical parts move in a liquid volume (Badve, Alpar, Pandit, Gogate, & Csoka, 2015), combination of centrifugal pumps with mechanical constrictions and nozzles, the latter either orifice plates (Gogate & Kabadi, 2009; Rudolf et al., 2017), Venturi tubes (Šarc, Stepišnik-Perdih, Petkovšek, & Dular, 2017; Zamoum & Kessal, 2015), or combination of both, such as orifice plates with Venturi-shaped holes (X. Li et al., 2017), and vortex diodes (Askarian, Vatani, & Edalat, 2017; Bhandari, Sorokhaibam, & Ranade, 2016; Suryawanshi, Bhandari, Sorokhaibam, Ruparelia, & Ranade, 2017). Cavitation can be produced also by means of localized heating and vaporization using pulsed laser irradiation (optical cavitation) (Ozonek, 2012; Verhaagen & Fernández Rivas, 2016). In the treatment of viscous food liquids, especially with solid particles, Venturi tube reactors are often a good choice, due to the minimization of the obstruction risk, their simplicity and robustness, as well as their proven superiority over orifice plates in terms of spoilage microorganisms lethality (Albanese, Ciriminna, Meneguzzo, & Pagliaro, 2015).
When the generated vapor cavities meet a zone with higher pressure, either being invested by a compression wave in AC, or decelerating downstream the nozzle in HC, they undergo fast collapse (implosion). The same occurs with optical cavitation when bubbles meet colder liquid zones.
Physical phenomena associated with the collapse of cavitation bubbles can be quite extreme: temperature and pressure inside a collapsing bubble increase dramatically up to 5,000-10,000 K and 300 atm, respectively, due to the work done by the liquid to the shrinking bubble, producing very strong shear forces, micro-jets and pressure shockwaves. Shortly, cavitation processes concentrate the energy of the bulk liquid medium into a myriad of microscopic “hot spots” endowed with extremely high energy density (Pawar, Mahulkar, Pandit, Roy, & Moholkar, 2017; Yasui, Tuziuti, Sivakumar, & Iida, 2004).
Due to the well-established superiority of HC over both optical and acoustic cavitation, in terms of complexity and operating costs (Habashi, Mehrdadi, Mennerich, Alighardashi, & Torabian, 2016), energy efficiency (2 to 10 times) and scalability (Gogate et al., 2001; Langone et al., 2015; Save, Pandit, & Joshi, 1997), cavitational yield (around 10 times) (Gogate et al., 2001; Gogate & Pandit, 2005), in the following only HC will be considered for industrial-scale applications.
In HC devices, physics can be numerically described by means of the Rayleigh-Plesset equation of bubble dynamics along with other diffusion, balance and continuity equations (Capocelli, Musmarra, & Prisciandaro, 2014; Moholkar & Pandit, 2001; Zamoum & Kessal, 2015). However, for the purposes of this Chapter, different HC regimes will be practically identified based on the values assumed by a single dimensionless parameter, i.e. the cavitation number (σ) derived from Bernoulli’s equation. It represents the ratio between the pressure drop needed to achieve vaporization and the specific kinetic energy at the cavitation inception section (Šarc et al., 2017; Yan & Thorpe, 1990), shown in its simplest form in Eq. (1).


where P0 (Nm-2) is the average pressure downstream of a cavitation reactor, such as a Venturi tube or an orifice plate, where cavitation bubbles collapse, Pv (Nm-2) is the liquid vapor pressure (a function of the average temperature for any given liquid),  (kgm-3) is the liquid density, and u (ms-1) is the flow velocity through the nozzle of the cavitation reactor.
A thorough discussion of the issues raised by the use of the cavitation number as per Eq. (1) was recently advanced (Šarc et al., 2017). It was shown that, changing the very definition of the different parameters included in the expression for σ, could lead to differences in the respective resulting values as large as two orders of magnitude. In particular, pressure P0 and velocity u should always be measured downstream of the cavitation constriction and through it, respectively. Indeed, independent scholars have shown that the control of the downstream pressure allows to obtain and describe the most relevant and desired HC’s features (Soyama & Hoshino, 2016).
Three intervals in the range of values assumed by the cavitation number were identified, corresponding to distinct controlled cavitation regimes through a nozzle nested into a hydraulic circuit, which can at least provide a practical guidance (Bagal & Gogate, 2014; Gogate, 2002). At low cavitation numbers, i.e. 0<σ<0.1, cavitation can be chocked, resulting in an almost stationary bubble cloud from merging of individual bubbles, and no, or very weak and rare, collapsing events, in a regime also called “supercavitation”. In the range 0.1<σ<1, cavitation is developed, with fairly strong and frequent collapses. Finally, for σ>1, cavitation becomes more and more residual, depending on the nature and concentration of impurities and dissolved gases, and virtually absent for σ>4, with rare but very strong collapses.
However, subtle and significant effects, modulating the cavitation inception, extent and intensity, arise from reactor’s geometry (Carpenter et al., 2017; Šarc et al., 2017), upstream flow rate, in turn connected with the inlet pressure, i.e. with the geometry and mechanical power of the impellers (Carpenter et al., 2017; Pawar et al., 2017), medium temperature (Dular, 2016), as well from gas and solid particles content (Patil & Pandit, 2007).
The formation of powerful oxidants such as hydroxyl radicals (·OH, oxidation potential 2.80 eV), as a result of water splitting, whenever the internal temperatures of the collapsing bubbles grow over 2,500 K, was first predicted in the early 2000’s (Yasui et al., 2004). Later, a complete set of reactions explaining the pathway to ·OH generation was built, based on theoretical and experimental arguments (Batoeva, Aseev, Sizykh, & Vol’nov, 2011; Rajoriya, Bargole, & Saharan, 2017; Rajoriya, Carpenter, Saharan, & Pandit, 2016; Soyama & Hoshino, 2016).
Oxidation processes are harmful for the quality of processed food liquids (Ngadi, Latheef, & Kassama, 2012). However, within the range of HC regimes used in the field of food applications, oxidation processes have been shown to play quite a marginal role in comparison to straightforward mechanical effects (shear forces, jets and pressure shockwaves) generated by the collapse of cavitation bubbles (Yusaf & Al-Juboori, 2014). Indeed, only the use of specific additives, such as hydrogen peroxide, ozone and Fenton reagents, or UV irradiation, allows achieving the needed extent of organics oxidation in applications such as water disinfection and remediation (Carpenter et al., 2017; Čehovin et al., 2017; Ciriminna, Albanese, Meneguzzo, & Pagliaro, 2016; Rajoriya et al., 2016). Actually, no oxidation whatsoever was observed by the authors either in wort or in final beer produced by means of HC-assisted brewing processes (Albanese, Ciriminna, Meneguzzo, & Pagliaro, 2017).

Main applications of controlled hydrodynamic cavitation

Hydrodynamic cavitation (HC) has found increasingly numerous and remarkable applications, often in synergy with conventional techniques.
Few comprehensive reviews are available, focusing on specific technical fields, such as wastewater remediation (Ciriminna, Albanese, Meneguzzo, & Pagliaro, 2017; Dindar, 2016), preparation of nanoemulsions, biodiesel synthesis, water disinfection, and nanoparticle synthesis (Carpenter et al., 2017), ethanol production (Ramirez-Cadavid, Kozyuk, Lyle, & Michel, 2015), delignification of ligno-cellulosic biomass for the transformation industry (Iskalieva et al., 2012), as well as for the enhancement of biogas generation (Dahadha, Amin, Bazyar Lakeh, & Elbeshbishy, 2017), and enzymatic digestibility (Terán Hilares et al., 2017).
Among further specific applications, prevention and removal of fouling and scaling (Heath, Širok, Hocevar, & Pecnik, 2013), increase of laundry efficiency (Stepišnik Perdih, Širok, & Dular, 2017), removal of harmful microorganisms from microalgae cultivation ponds (Kim et al., 2017), as well as removal of harmful cyanobacteria responsible for algal blooms in ponds, reservoirs, and lakes (Medina, Griggs, & Thomas, 2016), flotation using HC-generated nanobubbles, aimed at recycling fine particles of minerals (Calgaroto, Azevedo, & Rubio, 2015), or at recovery of combustible material (Xiong & Peng, 2015), as well as the potentially game-changing demonstration of HC capability to remove viruses from water (Kosel et al., 2017).
In the field of food liquids manufacturing, a particularly useful capacity of HC processes consists in liquid degassing, especially for the removal of volatile compounds (Arias & de las Heras, 2017; Gogate & Pandit, 2011). Degassing effectivity, as well as energy efficiency, were found to be similar to ordinary thermal boiling; however, since HC degassing can occur at moderate temperatures, thermosensitive compounds in liquid foods can be preserved from excessive degradation.
In all the above-mentioned applications, common to the different, respective devices and methods are the relative easiness in structural design and operational management. On the other hand, all such applications share a strong dependency of results – efficacy, efficiency, yield, and, sometimes, scalability – on the geometric details of the cavitation reactor, and the operating parameters such as inlet pressure, flow velocity, and downstream pressure (Carpenter et al., 2017; Šarc et al., 2017), with evidence arising that crossing from one cavitation regime to another (e.g., supercavitation) could be required for specific applications (Šarc, Oder, & Dular, 2016).
Further, when strong oxidation activity is needed, results show a considerable dependence on additives, in terms of the respective nature and doses, the latter usually exhibiting sharply non-linear relationships with the desired results due to the radicals scavenging action of unreacted additives at sufficiently high doses (Čehovin et al., 2017; Kumar, Sonawane, & Pandit, 2017; Thanekar & Gogate, 2018). However, a common trait of applications requiring strong oxidation activity is the large saving of additives allowed by HC processes (Ciriminna, Albanese, Meneguzzo, et al., 2017; Thanekar & Gogate, 2018).

HC-assisted processing of beverages

Hydrodynamic cavitation (HC) can benefit the processing of edible beverages in several ways, mainly from the simultaneous occurrence of processes otherwise requiring different devices and methods, such as homogenization, pasteurization or sterilization, therefore increasing the stability and extending the shelf life of food products, mechanical stirring, and creation of stable or ultra-stable emulsions (Carpenter et al., 2017).
Further advantages from HC processes in liquid foods arise from volumetric heating, occurring mostly in the cavitation active volume, where the fluid undergoes the greatest frictional losses, with consequent suppression of thermal gradients, in turn preventing caramelization hazards as well as mineral scale fouling on the inner pipes walls (Albanese et al., 2015; Heath et al., 2013). The same volumetric heating reduces thermal dissipation through pipe sidewalls, section changes, curves and other discontinuities in the hydraulic piping, leading to energy savings, increasing with the operating temperature (Baurov et al., 2014).
In the earliest, fundamental experimental studies with HC processes in real-scale liquid volumes, published in 1994 and 1997, microbial cell disruption in water was demonstrated for different types of yeast cells, yielding better results than other established techniques (Save, Pandit, & Joshi, 1994; Save et al., 1997). A year later, for the first time, the specific HC role processes in microbial cell disruption was rigorously identified, thus opening the way to HC applications in the food processing sector (Shirgaonkar, Lothe, & Pandit, 1998).
Two seminal papers were published about a decade later, showing the ability and comparative convenience of a shockwave power reactor (comprising a stationary outer cylinder and a rotating inner cylinder) to inactivate spoilage and harmful microorganisms in real liquid foods, such as apple juice, tomato juice and skimmed milk.
In the first study, the above-mentioned beverages were inoculated with vegetative cells of yeast, bacteria, yeast ascospores, and heat-resistant bacterial spores. The process parameters enabling the respective inactivation up to the pasteurization or sterilization level, while dependent on the specific beverage composition and inoculated microorganism, resulted in lower process temperatures, therefore lesser nutritional and sensorial degradation, and higher energy efficiency in comparison with conventional techniques (Milly, Toledo, Harrison, & Armstead, 2007).
The second study focused on apple juice, inoculated with the yeast strain Saccharomyces Cerevisiae, i.e. the major spoilage microorganisms in high-acid fluid foods such as fruit juices, and salad dressings. Pasteurization by means of HC processes was achieved at much lower temperatures (65.6 to 76.7°C) compared with the conventional thermal technique (88°C for 15 s), further resulting in non-recoverable viable cells, as well as showing a remarkably higher energy efficiency that, once brought to the industrial scale, was estimated in the range 55% to 88% (Milly, Toledo, Kerr, & Armstead, 2008). In 2011, a comprehensive review was published, including the above-mentioned and other studies, up to 2010 (Gogate, 2011).
Few years later, HC and conventional thermal treatment were compared for the inactivation of Saccharomyces Cerevisiae in a water-sugar solution, using both an orifice plate and a Venturi tube as cavitation reactors (Albanese et al., 2015). Results confirmed and extended previous findings from the above-mentioned studies, in particular the synergy between cavitation and temperature was fully exploited, leading to a decrease up to nearly 10°C of the pasteurization temperature with non-recoverable yeast cells, as well as to energy saving exceeding 20%, compared with conventional thermal processes. A particularly useful guidance was provided by the evidence that the Venturi tube setup outperformed the orifice plate setup in terms of yeast lethality, confirming previous experimental and theoretical studies (Arrojo, Benito, & Tarifa, 2008). The figure below shows the yeast lethality curves for all tests performed with the Venturi tube reactor, under different operational regimes (temperature, downstream pressure), as well as for the conventional thermal treatment, which was used as a benchmark: the 90% lethality threshold was achieved in the HC tests in correspondence of temperature differences in the range 6.3°C to 9.5°C.
Lastly, an original model simulating the yeast lethality rate as a function of temperature and cavitation number was advanced, allowing predictions at least in the range of the explored values of the cavitation number, which fell in the developed cavitation regime.

Yeast lethality curves for tests with a Venturi tube reactor, under different cavitation regimes. The dashed portion of the brown curve highlights the extrapolation beyond the maximum temperature achieved in the VENTURI test #2; the thick black curve represents the yeast lethality in the absence of any cavitation process. Adapted from (Albanese et al., 2015).

More recently, a further unexpected development occurred, namely the demonstration of the superior capability of the until then neglected supercavitation regime in the eradication of certain waterborne bacteria, such as Legionella pneumophila (Dular et al., 2016; Šarc et al., 2016). Therefore, the sudden, extreme pressure drop in the bulk medium, induced by supercavitation, added to the already proven mechanical effects arising from micro-jets, pressure shockwaves, and shear forces, as major agents for the rupture of cellular walls and bacteria inactivation. It is now well established that, in the field of HC-assisted disinfection of water and other liquids, including liquid foods, in the absence of additives, chemicals (i.e., HC-generated free radicals), and heat spikes (local hot spots at the collapse of the cavitation bubbles) play a secondary supporting role (Arrojo et al., 2008; Gogate, 2007). Quite luckily, as mentioned in Section 2, in the absence of oxidizing additives, whose possible unreacted residues could contaminate edible beverages, HC alone has also revealed unable to cause detectable oxidation in liquid media.
Until recently, practically all the research about HC applications to liquid foods and vegetable beverages focused on microbial disinfection, i.e. pasteurization and sterilization, bringing with it the side effect of improved nutritional and organoleptic quality, due to lower operating temperatures. However, perspectives have grown to exploit HC processes in further segments of liquid food processing, such as boosting the extraction of antioxidant bioactive compounds (e.g., phenols, flavonoids, carotenoids) (Carpenter et al., 2017). Such perspective arose as well from evidence coming from different non-thermal technologies applied to the production of fruit and vegetable beverages, such as high-intensity pulsed electric fields, high hydrostatic pressure, ultraviolet, and especially ultrasound (i.e., AC), considering the proven superiority of HC in efficiency, yield, and scalability. In a recent comprehensive review, it was shown that, by means of the above-mentioned non-thermal processes, vegetable beverages of good sensorial qualities could be produced, while also preserving and even enhancing bioactive compounds, such as vitamins and polyphenolic compounds, and favoring their bioaccessibility, bioavailability, and health effects, compared with traditional thermal treatments, although conditioned on a particularly fine tuning of the respective operational parameters (Domínguez Avila, Wall Medrano, Ruiz Pardo, Montalvo González, & González Aguilar, 2017).
In this respect, a decisive step forward was represented by few recently published studies, showing HC ability to boost the extraction of important bioactive compounds and, consequently, the antioxidant activity, of specific food raw materials potentially usable for the production of vegetable beverages. Underlying those findings was the prevalence of phenolic compounds in plants in the bound form with carbohydrates, lignin, pectin and proteins, along with the HC destructuring (i.e., breaking down of complex large molecular weight molecules) and separation actions.
HC-based hydrothermodynamic processes, also causing heating and mechanical turbulence, performed in a nearly air-free, pressurized (pressure left free to increase up to 3 atm due to liquid thermal expansion), innovative device comprising a Venturi tube and suitably designed converging streams, were proven able to retain a large fraction of the most valuable flavonoids in frozen blueberries, i.e. anthocyanins, within 48 hours storage of the produced puree after processing (Satanina, Kalt, Astatkie, Havard, & Martynenko, 2014). Besides the higher extraction rate, the preservation of anthocyanins exceeded by far the levels achieved in conventional thermal processing technology, despite the same pasteurization temperature (95°C), as well as the levels observed in commercially available products. Such puree can be considered as a high-quality and uniform starting material for a range of processed blueberry products, such as juices.
The release of bound phenolics and the increase of oxidant activity of naturally fermented sorghum flour (a starchy material) and apple pomace (a fibrous material) was proven, using a rotor-stator cavitation reactor, revealing strong dependence on cavitation regimes, i.e. inlet pressure and operating temperature, as well as on the specific raw food material and the respective concentration in water (Lohani, Muthukumarappan, & Meletharayil, 2016). For sorghum flour, the density of the sample (flour to water ratio) prevailed over the inlet pressure, favoring the use of lower concentrations, while for apple pomace the opposite held true. Different structures of the cavitation reactor, therefore of cavitation regimes, revealed optimal for the considered raw materials, as well as lower operating temperatures for sorghum flour (35°C), compared with apple pomace (45°C), produced better results. It should be noted that the moderate optimal temperatures prevent the degradation of thermosensitive nutritional compounds as well as organoleptic qualities.
In the optimal conditions, HC processes increased the total phenolic content by 39.5% in sorghum flour and 42% in apple pomace, while the antioxidant activity increased by 38.6% and as much as 97%, respectively. A control test carried out under the optimal conditions but without cavitation proved that HC was instrumental to produce the above-mentioned results. Scanning electron microscope analysis of cavitated sorghum flour revealed that HC damaged the plant cell structure and increased porosity, as well as starch granules were downsized and the respective surface area increased largely, therefore releasing more phenolics, previously bound with the protein–carbohydrate matrix. For apple pomace, the compact and nonporous structure was deeply changed by HC processes, leading to the disruption of the fibrous structure and the release of more phenolics from the bound matrix.
Very recently, preliminary evidence arose about the capability of HC-assisted brewing processes to extract valuable polyphenols (mainly flavonoids) from raw unmalted grains harvested from old typical wheat varieties, while preserving the respective functionality and antioxidant activity (Albanese, Ciriminna, Meneguzzo, & Pagliaro, 2018). Such capability can be useful not only for alcoholic beer making, but for the production of any cereal-based vegetable beverages.
A recent review focused on the negative pressure cavitation application to the extraction of bioactive compounds, among which flavonoids, isoflavonoids and polyphenols, from several food raw materials (Roohinejad et al., 2016). In this method, cavitation is generated by negative pressure created by a vacuum pump, aimed at corroding the surface of solid particles, as well as enhancing turbulence, collision and mass transfer between the extracting solvent and solid matrix. As a result, secondary metabolites can be effectively and quickly released into the extraction solvent. Unfortunately, all studies included in that review, and published so far, used solvents other than water, such as ethanol (Wu, Ju, Deng, & Xi, 2017), since the aim was to isolate bioactive compounds for industrial use, while in the direct processing of a raw liquid food the use of other solvents is not advisable. Nevertheless, certain extracted bioactive compounds could be used for fortification of vegetable beverages, as well as negative pressure cavitation, although slightly more complex than other HC technologies, could be potentially used in the direct processing of liquid foods, if its scalability will be proven. Results show that negative pressure cavitation exhibits greater energy efficiency and yield compared with both traditional and newer methods and allows achieving higher extraction efficiency and better antioxidant activity. Again, a qualifying feature was the high efficiency at room temperature, which reduces or prevents the degradation of thermosensitive compounds.
In the context of beer-brewing experiments, HC processes proved able, under specific operating regimes, to boost the extraction and retaining of certain hops’ valuable bioactive compounds in the beer wort, such as xanthohumol, desmethylxanthohumol and 6-geranylnaringenin, far exceeding the extraction rate observed in the traditional boiling processes (Ciriminna, Albanese, Di Stefano, et al., 2017). Besides the broad-spectrum contribution to significant chemopreventive actions with regards to certain diseases, such as cardiovascular, neurodegenerative, diabetes, liver diseases and some cancer types (Costa et al., 2013; Liu et al., 2015; Weiskirchen, Mahli, Weiskirchen, & Hellerbrand, 2015), those powerful phytoestrogens and antioxidant compounds improve the shelf-life of final products (beer) by means of the respective antimicrobial activity (Karabín, Hudcová, Jelínek, & Dostálek, 2016).
The intrinsic HC grinding capability with respect to solid particles adds to microbial disinfection (pasteurization), homogenization, and increased extraction of valuable bioactive compounds, towards the chance for using HC processes throughout the entire production cycle of vegetable beverages. Indeed, in applications to corn slurry for bioethanol production, a remarkable fraction of the macroscopic solid particles were downsized by nearly two orders of magnitude, i.e. from 1000 m to around 10 m (Ramirez-Cadavid, Kozyuk, & Michel, 2014).
Following their previous study (Satanina et al., 2014), during 2015-2017, a series of investigations were performed and published by scholars and industrial specialists in Canada, aimed at setting-up and optimizing the novel HC-based technology, and the respective methods, to produce blueberry and cranberry purees and juices as a single-unit operation, simultaneously performing crushing, homogenization and pasteurization.
The developed device and methods were applied again to the processing of blueberry, finding that solid particles were fine-crushed, including seeds, down to sizes much smaller than by means of conventional techniques. As well, superior retaining of anthocyanins up to few months was proven, with increase in the respective antioxidant activity. Product’s shelf life was remarkably improved, as well as energy consumption, capital and operational costs were assessed as lower by a large fraction compared to both traditional and more advanced techniques (Martynenko, Astatkie, & Satanina, 2015).
Later, the effects of combined HC and the related heating on the degradation of anthocyanins in processed blueberries, extendible to other raw food materials, were further investigated, finding that the increased extraction of oxidizing enzymes from the HC-assisted fine crushing of solid particles, such as polyphenol oxidase and peroxidase, was compensated by the respective early inactivation at lower temperatures (around 80°C) than in conventional thermal treatments, leading to lower susceptibility of those polyphenols to temperatures (Martynenko & Chen, 2016). As a consequence, processed blueberry puree showed a much longer shelf life, in comparison to commercially available products, due to the retention of anthocyanins (more than 1.5 years for the retention of 50% of anthocyanins), as well as superior healthy properties.
The application of HC-based hydrothermal processing was further extended to cranberries, a raw food material endowed with plenty of powerful bioactive compounds (Chen & Martynenko, 2017). Results similar to the previous studies were found for anthocyanins, but the analysis extended to the total phenolic content and proanthocyanidin content, as well as to chemical-physical properties such as color, pH and soluble solid content, the latter two found remarkably stable during 285 days of storage. The addition of natural sweeteners (sugars) was found to hinder the degradation of bioactive compounds during HC processing, counterbalanced by a detrimental effect on storage stability. Moreover, anthocyanins were found to be more susceptive to storage temperature, suggesting refrigerated storage. Since the color of processed cranberries was strongly correlated with anthocyanin content, that parameter could be used as a non-destructive indicator of anthocyanin content of cranberry puree.
As a result of the above-described studies by Canadian authors, the proven benefits to the degradation of important bioactive compounds, and to the storage stability, as well as the chance to design and operate single units, demonstrated the potential of devices based on HC processes in manufacturing natural whole foods with high nutraceutical contents (F. Li, Chen, Zhang, & Fu, 2017).

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