The influence of pulsed electric fields (PEF) pre-treatment of sweet cherry (Prunus Avium) fruits of “Duroni Nero” variety both on the extraction yield and antioxidant properties of juice obtained by pressing, and on the subsequent extraction with solvent of bioactive compounds from cherry by-products (press-cake) was investigated. PEF pre-treatments were performed at constant specific energy input (WT = 10 kJ/kg) and different electric field strength (E= 0.5-3 kV/cm) before applying a pressure of 1.64 bar for 5 min. PEF-assisted pressing (E = 1 kV/cm) led to a significant increase of juice yield (+40%), anthocyanins (+80%), and antioxidant power (+27%) with respect to untreated samples. However, PEF treatment intensity higher than 1 kV/cm did not significantly improved the quantitative and qualitative characteristics of juice. Compared to the untreated samples, the extracts from electroporated press-cakes achieved after PEF-assisted pressing of cherry fruits at 0.5 kV/cm showed the highest increases in anthocyanins (+38%) and antioxidant activity (+21%). No evidence of selective release or degradation of individual anthocyanins in juice and press cake extracts due to PEF application was observed. Overall, the results of this investigation demonstrated the potential of PEF as a mild technology to improve the efficiency of industrial processing of cherry fruits.

In this work, immature green tomatoes were exposed to different doses of either PL or UV-C irradiation (1-8J/cm2) and then stored at 20±2°C for up to 21days. The effects of light treatments on the physical-chemical properties and antioxidant compounds of tomato fruits, were evaluated during storage and compared with those of untreated samples. Results indicated that, at the energy doses investigated, pH and °Brix of all samples were not affected by light treatments and storage period. The skin colour of untreated and treated fruits turned from green to red during storage and no appreciable influence of the light treatments was detected. However, the content of lycopene, total carotenoid, phenolic compounds and antioxidant activity of light treated samples increased during storage up to, respectively, 6.2, 2.5, 1.3, and 1.5-fold, when compared with the untreated samples. These results demonstrated that PL and UV-C irradiation have the potential to enhance the accumulation of health-beneficial food compounds in tomatoes without significant changes of the physical properties of the product during storage.

The exposure to UV-C and Pulsed Light (PL) light causes stress in plant tissues, which stimulates the biosynthesis of defensive secondary metabolites with antimicrobial and antioxidant activity. For this reason, recent studies have examined the capability of UV-C and PL as effective methods to prolong the fresh status as well as preserve or even improve the content and activity of antioxidant compounds of fresh produce through post-harvest handling and processing. In this work, the effect of PL and UV-C treatments on quality and antioxidant properties of tomatoes and Annurca apples intended for fresh consumption was investigated. Fruits harvested at the green stage were exposed to both light treatments at energy dosages of 2 and 4 J/cm2. Treated and untreated samples were allowed to ripen under day/night cycles illumination conditions at room temperature for up to 21 days for tomatoes and 28 days for apples. The effects of light treatments on the colour, pH, titratable acidity and °Brix as well as on the levels of lycopene, total carotenoids, total phenolic compounds and antioxidant activity, were evaluated through storage and compared with those of untreated samples. Results indicate that pH, titratable acidity and °Brix of all fruit samples were not significantly affected by light treatments and remained almost the same throughout storage. The skin colour of untreated and exposed fruits changed during storage period, with no appreciable influence of the light treatments. However, the exposure of apples and tomatoes to light treatments enhanced the antioxidant properties of these fruits during storage. These results suggest that post-harvest PL and UV-C irradiation can be utilized to the health value of tomatoes and Annurca apples by increasing the level of certain bioactive compounds without inducing significant changes to their physical properties during storage.

In this work, a Multiphysics model based on the Finite Element Method (FEM), was used to study the effect of different electrical parameters as well as chemical composition of the treatment medium on the metal release from the stainless steel (type AISI 316L) electrodes of a PEF chamber. A total of 15 processing conditions obtained by coupling different field strength (12-31 kV/cm) and total specific energy input (20-100 kJ/kg) were simulated with two model liquid food solutions with the same pH (7) and electrical conductivity (2 mS/cm at 25 degrees C) but different halides concentration.The results showed that the concentration of metallic elements (Fe, Cr and Ni) increased with decreasing the field strength applied or increasing the total specific energy input. These results were attributed to the predominant effect of the pulse frequency, rather than the applied voltage, on the average Faradaic current density values which, in turn, determine the extent of the metal release. Moreover, it was shown that the presence of halides in the composition of the processed product, may lower the breakdown potential and increase the Faradaic current density value which lead to an intense localized metal release from the electrode's surface. (C) 2015 Elsevier Ltd. All rights reserved.

A laboratory scale continuous flow unit was set up and used to study the effect of pulsed electric fields (PEF) pre-treatments on microbial inactivation by high pressure carbon dioxide (HPCD) processing with the aim of investigating the synergistic effect of the combined treatment. McIlvaine buffer solution inoculated with Escherichia coli cells ATCC26 was pre-treated with PEF (25°C) at different field strength (E=6–12kV/cm) and energy input (WT=10–40J/mL) and then processed with HPCD (25°C) at pressures of 8.0, 14.0 and 20.0MPa and holding times of 4, 7 and 11min.Results showed that treating the microbial suspension only with PEF, the inactivation level slightly increased with increasing the field strength and energy input with no significant effect of the pressure applied. The maximum inactivation level obtained was 2.25 Log-cycles at 12kV/cm and 40J/mL. When the bacterial cells were treated only with HPCD, the inactivation level was almost independent on the pressure of CO2, and gradually increased with increasing the holding time up to a maximum value of 2.41 Log-cycles. The combination of PEF and HPCD treatment resulted in a marked increase of the microbial inactivation with increasing the field strength, energy input, holding time and operative pressure. A clear synergistic effect was evident when holding time was longer than 4min, regardless the intensity of the PEF treatment applied.Industrial relevanceConsumers demand for fresh and natural products forces food manufacturers to investigate milder preservation processes and stimulate the current trend to use hurdle technologies. Pulsed electric field (PEF) and high pressure carbon dioxide (HPCD) are emerging non-thermal technologies which have antimicrobial capabilities when applied alone or in combination with other physicochemical hurdles. The present work demonstrated, for the first time, the feasibility of combined PEF-HCPD process based on the coupling of a PEF pretreatment stage to HPCD treatment in a continuous flow unit. The results support the view that the combined process is able to induce substantial microbial inactivation at mild treatment conditions and at room temperature suggesting the idea that this process could be applied to foods with thermosensitive components.

The effects of electrical parameters (field strength E, total specific energy input W-T and pulse frequency) and product composition on the release of the main metallic elements (Fe, Cr, Ni and Mn) of stainless steel (type 316L) electrodes of a continuous flow parallel plate PEF chamber into the treatment medium were investigated. Experiments were carried out by subjecting two different buffer solutions (McIlvaine and Trizma-HCl) with the same values of pH (7) and electrical conductivity (sigma = 2 mS/cm) to PEF treatments (mono-polar exponential decay pulses, lasting 3.1 mu s) at different intensities (E = 12-21-31 kV/cm, W-T = 20-60-100 J/mL) and flow rates (2-3-4 L/h). The results showed that, for each field strength applied, the concentration of metallic elements increased upon increasing the total specific energy input. At constant total energy input, it was noticed that the metal concentration decreased upon increasing the field strength applied. These results were mainly attributed to the key role played by the pulse frequency in the charging process of the double layer capacitors at the electrode-solution interface. Moreover, it was shown that the amount of metal released from the electrodes markedly depended on the presence of halides in the composition of the processed product.Industrial relevance: Electrochemical reactions at the electrode solution interfaces are unavoidable when typical conditions for PEF processing are applied. For the acceptability of PEF processing as a non-thermal method for liquid food pasteurization, the occurrence of these reactions should be avoided or minimized since they may determine undesired phenomenon of contamination of the food product, electrode-fouling and electrode corrosion. In this paper, electrode corrosion was studied, for the first time, in a continuous flow parallel plate PEF treatment chamber. The present investigation contributes to clarifying the effects of some electrical parameters and food composition on electrode corrosion or release of electrode materials under real PEF treatment conditions. (c) 2013 Elsevier Ltd. All rights reserved.

In the present study the effect of ohmic heating processing on the quality and shelf-life of apricots in syrup was investigated.Each 100 g of product contained 30 g of pre-heated syrup (15 degrees Brix) and 70 g of blanched apricot pieces with a cubic shape (size 1.2 cm). The liquid solid mixture (pH < 4) was pasteurized at 90 degrees C for about 113 s in a 30 kW aseptic continuous pilot ohmic system using a 25 kHz alternating electric current. The aseptically packaged samples were stored at 25 degrees C and periodically examined over one year period. The parameters measured during the preservation period were: pH, degrees Brix, color, ascorbic acid content, and microbial spoilage.During the shelf-life, no swelling of the packages was detected. Moreover, the product kept its microbiological stability during the whole storage period of 52 weeks. The ascorbic acid content was slightly reduced by the elctrothermal treatment. However, it was well preserved for the entire storage time. Similarly, the quality characteristics of the fresh apricots in syrup were not adversely affected by ohmic processing and a high retention of the quality attributes was observed during the storage time. (C) 2011 Elsevier Ltd. All rights reserved.

The High Pressure (HP) treatment induces significant changes on the milk macromolecules (proteins, whey proteins and caseins), as well as on its functional properties, which allow its application in innovative dairy productions. The aim of this work was to setup the process condition and product formulation to produce a milk cream under pressure and evaluate and model its rheological behaviour. Some preliminary experiments (pressure level=400-500 MPa, time=5-10 min, temperature=25°C) were carried out to optimize the processing parameters inducing milk coagulation. Moreover, different milk concentrations (50%, 60%, 70%) were tested to identify the concentration values able to achieve the optimal creaminess of the high pressure milk cream. The latter information was obtained analyzing the results of rheological static and dynamic tests. According to several literature studies, preliminary results indicate that the milk coagulation occurs at a pressure level of 500 MPa and ambient temperature after 10 minutes of treatments. The dynamic rheological analysis demonstrate that the compactness of HP milk cream increases with increasing the milk concentration of the product, while the values of the G ‘and G” modules of the unprocessed concentrated milk are similar to those of the fresh milk. Therefore, as milk concentration doesn’t affect the rheological behaviour of the cream, the higher compactness observed can be attributed to milk coagulation under pressure. The stationary rheological tests, indeed, indicate that the HP milk cream behaves as a non-Newtonian pseudo-plastic fluid, whose stress-strain relationship can be described by a power law model equation. This rheological behaviour is due to the milk macromolecules, which conglomerate under pressure, tend to align and provide greater resistance to flow.

The effects of both the electric and flow parameters on the lethality and energy efficiency of a pulsed electric fields (PEF) treatment were studied. An experimental plan was designed in order to study the microbial inactivation of Saccharomyces cerevisiae and Escherichia coli cells inoculated in a buffer solution. The following process parameters were taken into consideration: electric field strength (13-30 kV/cm), total specific energy input (20-110 J/mL), flow rate of the processed stream (1-4 L/h) and number of passes through the chamber (up to 5).The results showed that, at a fixed flow rate (2 L/h), microbial inactivation of both microbial strains increased with increasing field strength and applied energy input. The maximum inactivation level (5.9 Log-cycles for S. cerevisiae and 7.0 Log-cycles for E. coli) corresponded to the more intensive PEF treatment (30 kV/cm and 110 J/mL). However, for any given field strength applied, the inactivation rate decreased by increasing the energy input. This behavior was attributed to the presence of heterogeneous treatment conditions due, for example, to a different morphology (size and shape) or cell membrane (composition, structure), a local variation of the electric field strength in the treatment chamber, the tendency of microbial cells to form clusters, or a non-uniform distribution of the residence time of the product in the PEF chamber.A more effective stirring of the microbial suspensions which was achieved, at a fixed field strength (18 kV/cm), either by increasing the flow rate with a single pass operation through the PEF chamber, or by operating in re-circulating mode at a constant flow rate, provided a significant increase in the effectiveness and energy efficiency of the pulse treatment.A mathematical model based on the Weibull distribution adequately described the inactivation kinetics of both microbial strains under different flow dynamic conditions. (C) 2011 Elsevier Ltd. All rights reserved.

The use of pulsed high hydrostatic pressure was investigated as a possible approach to stabilize foodstuffs. The objective of this article was to investigate the effect of the main processing variables (pressure [150 to 300 MPa], temperature levels [25 to 50 degrees C], and pulse number [1 to 10]) on the sanitation of nonpasteurized clear Annurca apple juice as well as freshly-squeezed clear orange juice. The aim of the article was the optimization of the process parameters in step-wise pressure treatment (pressure holding time of each pulse: 60 s, compression rate: 10.5 MPa/s, decompression time: 2 to 5s). The shelf life of the samples, processed at optimized conditions, was evaluated in terms of microbiological stability and quality retention. According to our experimental results, the efficiency of pulsed high pressure processes depends on the combination of pulse holding time and number of pulses. The pulsed high pressure cycles have no additive or synergetic effect on microbial count. The efficacy of the single pulses decreases with the increase of the pulse number and pressure level. Therefore the first pulse cycle is more effective than the following ones. By coupling moderate heating to high pressure, the lethality of the process increases but thermal degradation of the products can be detected. The optimization of the process condition thus results in a compromise between the reduction of the pressure value, due to the synergetic temperature action, and the achievement of quality of the final production. The juices processed under optimal processing conditions show a minimum shelf life of 21 d at a storage temperature of 4 degrees C.

Flowsheet simulation is widely used in industries as a computer aided tool for the conceptual design of processes involving fluids. Only recently a new simulation environment was developed specifically for more complex solids processing. However, unit operation models describing the storage and handling of bulk solids have not been implemented yet. In this work a unit model for the design and the rating of storage units for flow, following the well established design procedure due to Jenike, has been implemented. The unit operation model requires as inputs the bulk solids physical properties and flow properties and the frictional properties of the silo wall material. Main outputs of the simulation block are the geometrical characteristics of the hopper and the maximum solid flow rate.

Arching can occur during silo discharge of cohesive powders. In general this happens when the outlet size is not wide enough. Flow aid devices, such as aeration pads, are commonly used in the industry to achieve proper flow of cohesive materials. However, no design criteria are presently available for such kind of devices and, in particular, for the intensity of aeration to be used to avoid arching. Aim of this paper is the evaluation of the limiting aeration condition to produce the collapse of established arches and the minimum aeration rate necessary for no arching discharge flow. Experimental tests are carried out in an aerated flat bottom silo. The measured quantities are the aeration rate at arch collapse and the arch size. Powder permeability is characterized by fluidization experiments. A simplified model is proposed to assess on the prevailing physical phenomena and predictively evaluate the minimum aeration rate to determine no arching discharge flow.

Fluidization behaviour of a fine aeratable FCC powder assisted by mechanical vibration was studied in a 85 mm i.d. transparent column. The investigated parameters of vibration were the peak acceleration value (a/g = 0.5, 1 and 2) and the frequency (between 7 and 200 Hz). The most significant variations obtained by changing these parameters regard the voidage of the fixed bed, the effects of aeration on bed expansion and fluidization, the maximum bed expansion and the onset of bubbling conditions. The typical fluidization curve in presence of mechanical vibration is characterized with the introduction of key fluidization velocities: a minimum bed expansion velocity, a minimum velocity for fluid dynamic suspension, the minimum bubbling velocity and a minimum velocity for stable bubbling. The possibility to apply the Ergun equation under gas fluidization assisted by vibration was also verified. Differential pressure drops at different heights inside the bed were used to investigate on the effects of vibrations on the gas fluidized bed. Changes of differential pressure drop along the bed were interpreted in the light of some internal bed structure.