The Effect of Vibrations on Fluidized Cohesive Powders

The fluidization of a cohesive silica powder has been tested with the help of mechanical vibration. The experiments showed how the effectiveness of vibrations changed with the vibrational acceleration and frequency. The aggregative behavior of powders has been highlighted and a model procedure is proposed to predict the aggregate size starting from the measurement of powder flow properties with conventional shear testers

Campi elettrici pulsati per la stabilizzazione microbiologica di alimenti

The features of a sanitization process for foods based on Pulsed Electric Fields technology (PEF) is described and discussed. A laboratory experimental apparatus operated under electric fields up to 40 kV/cm and with different pulse length and frequency has been set into operation. Experiments on the inactivation of Saccharomyces cerevisiae have been carried out in different conditions. Results demonstrate that the most critical condition is the realization of a uniform electric field in the treatment chamber. However, a good mixing of the sample can help in enhancing the effectiveness of the process. In these conditions, a reduction up to 6 decades of microorganism viability can be obtained. Preliminary tests on liquid foods demonstrate that PEF processes can be envisaged for industrial applications of food stabilisation

Pasteurization of fruit juices by means of a pulsed high pressure process

ABSTRACT: 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 ◦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: 10.5MPa/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 ismore effective than the following ones. By couplingmoderate 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 ◦C

Metal release from stainless steel electrodes of a PEF treatment chamber: Effects of electrical parameters and food composition

The effects of electrical parameters (field strength E, total specific energy inputWT 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 treatmentmedium 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 (ó=2 mS/cm) to PEF treatments (mono-polar exponential decay pulses, lasting 3.1 ìs) at different intensities (E = 12–21–31 kV/cm, WT = 20–60–100 J/mL) and flow rates (2–3–4L/h). The results showed that, for each field strength applied, the concentration ofmetallic 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

The use of soaking and blanching pre-treatments to improve Ohmic heating uniformity of beans–liquid mixtures

In this work cannellini beans were pre-treated by either blanching or soaking in salt solutions with the aim to improve the ohmic heating uniformity of beans-liquid mixture. Dry beans were pretreated by either soaking (12 h) in sodium chloride solutions of different concentration (0, 0.3, 0.5, 0.7, 1 and 1.5 g/100mL) or blanched for different length of times (35 and 50 s) in a water bath set at 90°C after soaking (12 h) in tap water. Heating curves of solid-liquid mixtures of different pre-treated beans to salt solution (1 g/100mL) ratio (60g of beans/100g of mixture and 53g of beans/100g of mixture) were determined in a static ohmic heating device by applying a constant voltage of 100V. Results showed that the ohmic heating rate of beans increased with increasing the salt concentration of the soaking solution as well as the blanching time as a direct result of the increase of electrical conductivity. The higher was the solid-liquid ratio, the greater was the heating rate of solid phase. Optimal pre-treatment conditions, which allowed the ohmic heating of both phases of solid-liquid mixture at comparable rate, were found when beans were pre-treated either by soaking in solutions with salt concentration of either 0.5 g/100mL (60g of beans/100g of mixture) or 1.5 g/100mL (53g of beans/100g of mixture), or when blanched for 50 s at 90°C (53g of beans/100g of mixture)

Set up of a batch Ohmic Heating system for sterilization of solid-liquid mixture

In present work a batch ohmic heating plant was designed and set up with the aim to obtain a flexible system able to reproduce the three phases (heating, holding and cooling) of a thermal treatment of food matrices, in a wide range of product factor as well as electrical and thermal parameters. The realized system consists of a 15 kW power generator able to deliver electric current in the form of bipolar square wave at 25 kHz to a food matrices (liquid or particulate-liquid product) placed into a batch ohmic heater made of a cylindrical Peek tube (7.6 cm in diameter, 20 cm in length) closed at the ends with two inox electrodes. The electrodes were provided with an internal cavity in which, during the cooling phase, water-ethylene glycol solution was recirculated from an external refrigerated bath. Auxiliary devices were employed for control and measurements of the process parameters. Preliminary tests were carried out to assess the performance of the ohmic system by heating sodium chloride solutions of different concentrations (0.1-0.50% (w/v)) in a wide range of operative variables such as peak voltage (100-1500Vpk), holding temperature (90-121°C), heating time (60-180 s) and electrical conductivity (1-5 mS/cm). Optimal settings of the operative variables were found for different processing conditions

Microbial inactivation by a combined PEF-HPCD treatment in a continuous flow system

A laboratory scale continuous flow unit was set up and used to study the effect of pulsed electric fields (PEF) pretreatments on the inactivation of microbial population by high pressure carbon dioxide (HPCD). McIlvaine buffer solution inoculated with Escherichia coli cells ATCC26 were pretreated with PEF (25 °C) at different field strength (E=6-12 kV/cm) and energy input (WT=10-40 J/mL) and then processed with HPCD (25 °C) at pressures of 8.0, 11.0 and 14.0 MPa and holding times of 4, 7 and 11 min. Results showed that treating microbial suspensions only with PEF the maximum inactivation level achieved was 2.25 Log-cycles at 12 kV/cm and 40 J/mL. On the other hand, when the bacterial cells were treated only with HPCD, the inactivation level was almost independent on the applied CO2 pressure, while gradually increased by increasing the holding time up to a maximum value of 2.41 Log-cycles. The combination of PEF and HPCD treatment (8.0 MPa) resulted in a marked increase of the microbial inactivation with increasing the field strength, energy input and holding time. In particular, a clear synergistic effect was evident for holding times longer than 4 min regardless the PEF treatment intensity applied

Microbial inactivation of E. coli cells by a combined PEF–HPCD treatment in a continuous flow system

A laboratory scale continuous flowunit was set up and used to study the effect of pulsed electric fields (PEF) pretreatments 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 = 6–12 kV/cm) and energy input (WT = 10–40 J/mL) and then processed with HPCD (25 °C) at pressures of 8.0, 14.0 and 20.0 MPa and holding times of 4, 7 and 11 min. 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 12 kV/cm and 40 J/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 maximumvalue of 2.41 Log-cycles. The combination of PEF and HPCD treatment resulted in a marked increase of themicrobial 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 4 min, regardless the intensity of the PEF treatment applied