1,721,070 research outputs found
PEF treatment for the valorization of agri-food byproducts
No full textCell membrane acts as a physical barrier when removing the intracellular substances (water, juices and solutes) from food tissues in common unit operations of food industry such as drying and extraction. The permeabilization of the cell membrane by means of food tissue pre-treatments may positively affect the mass transport rates, and, thus, higher yield and shorter residence time in the processing plants can be obtained.
However, the conventional pre-treatments of the raw material utilized to increase the extraction yield, namely grinding, heating, addition of chemicals/enzymes, have a negative impact on the quality of the solutions and extracts (e.g., purity, turbidity, color, flavor and nutrient content).
Pulsed electric fields (PEF) treatments has been proved to bea promising mild and more efficient physical method alternative to conventional cell disintegration techniques. The exposure of food tissue to an electric field of moderate intensity (0.5-10 kV/cm) and relatively low energy (1-10 kJ/kg), applied in the form of repetitive very short voltage pulses, typically from few μs up to 1 ms, induces thepermeabilization of cell membranes by electroporation, facilitating the release of liquids and valuable compounds from the inner parts of the cells.
PEF pretreatment may exert a selective permeabilization of the membranes (tonoplast and plasma membrane), while the cell wall remains intact. Consequently, the yield and the purity of the extractsare improved. Moreover, since PEF is a non-thermal technology, the reduction of the impact on the thermo-sensitive and thermo-labile compounds in the extracts is avoided.
Interestingly, PEF treatment can be used to recover valuable compounds from food wastes and by-products,which have been matter of concern by the agri-food industry due to their environmental impact. The compounds that can be recovered show great potential industrial applications as natural colorants (anthocyainins, carotenoids, betanines, etc.) or nutraceuticals(polyphenols).
In this paper a brief description of the basic mechanisms of electroporation of plant tissues is presented and the experimental results on the recovery of valuable compounds from fruit and vegetable by-products are presented.
The influence of PEF processing parameters on extraction effectiveness is also discussed
Mathematical modelling of the electric field distribution in a co-field chamber of a PEF system
No full textThe treatment chamber is one of the crucial component of a PEF system, whose design is critical for successful treatment as its main function is to uniformly transfer the high voltage pulsed electric field to the food. Electrodes arranged in a co-field- or co-linear configuration are widely used due to their advantages fluid dynamics as well as high intrinsic resistance. However, the distribution of the electric field in the treatment zone is typically non uniform and the average field strength can be significantly
different from the expected values derived from dividing the applied voltage by the electrode gap.
In this work a total of 36 models of co-field chambers of different gap between electrodes (2-6 mm) and inner radius of the tube (1-3 mm) were developed by using Comsol MultiphysicsTM software. For each of these models, different setting of applied voltage (1-25 kV) were simulated for a model liquid food (aqueous solution with electrical conductivity of 2 mS/cm) and the values of the average electric field were computed.
Results showed that homogeneity of the electric field distribution can be improved by decreasing the inner radius of the bore and/or increasing the electrode gap. The average electric field strength of the PEF treatment zone, was significantly lower than the expected values estimated assuming a parallel plate
configuration. Finally, a relationship between the relative ratios of theoretical electric field strength to actual (average) electric field strength and the ratio of electrode radius and gap was also obtained
Campi elettrici pulsati per la stabilizzazione microbiologica di alimenti
No full textThe 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
Estrazione di succo di mirtillo mediante pressatura assistita da PEF
No full textPEF treatments of different electric field intensity (E=0-7 kV/cm) and
total specific energy (WT=0-20 kJ/kg) were applied during the pressing process
(0.35-1.65 bar) to enhance the expression of fresh and thawed blueberry juice.
Results demonstrate that PEF treatment is able to induce the permeabilization of
blueberry tissues. The higher is the intensity of the applied electric field, the
lower is the energy required to obtain the desired degree of cell membrane
disintegration. The application of a PEF treatment of moderate intensity (E=1
kV/cm, WT=12 kJ/kg) in combination with pressures below 1 bar allows to obtain
higher extraction yields (up to 75%) and the production of juices with a higher
content of polyphenols and antioxidant activity than those achievable with a
conventional pressing process
Changes in the electrical conductivity of selected juices during ohmic heating: influences of temperature, solid content and electric field strength
No full textThe influence of operating temperature on the dense phase properties of bubbling fluidized beds of solids
No full textThe paper analyses the dependence on process temperature of parameters that characterize the dense phase of a freely bubbling bed. Application of the bed collapse technique to beds of FCC, silica sand, and corundum in experiments covering a temperature field ranging from room level up to 700 jC demonstrates that the increase of interparticle forces at superambient temperatures leads to significant modifications of the fluidization dynamics. These include clear changes of the particulate phase voidage and dense phase velocity as well as of bubble hold-up. Changes induced in the partition of the total gas flow rate and, consequently, in the characteristics of the bubble phase of the fluidized bed are also discussed
Post-harvest UV-C and PL Irradiation of Fruits and Vegetables
No full textThe 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
Pulsed light decontamination of vegetables and fruits before packaging in modified atmosphere
No full textPulsed light (PL) is an emerging technology which has considerable potential as an alternative to thermal and chemical methods for rapid inactivation of microorganisms on food surfaces. The technique involves the use of intense short duration light pulses of a wide broad spectrum light including wavelengths from ultraviolet (UV) to close infrared region (100-1100 nm).
In this work the effect of PL pre-treatment of strawberry before their packaging in modified atmospheric (MAP) on the shelf-life of the fruits was investigated. Samples of strawberries were exposed for 8 s to pulsed light treatments at an energy dose of 10 J/cm2/side before being packed in MAP (20% O2, 5% CO2, 75% N2) and then stored under refrigerated conditions (4°C) for up to 28 days. The parameters measured during the preservation period were: pH, °Brix, color, texture, ascorbic acid content, and microbial spoilage.
During the shelf-life, PL-treated strawberries appeared to better preserve their fresh smelt and appearance than the untreated samples. Moreover, while the microbial population of untreated fruits progressively increased during storage, it was significantly decreased (2 Log-cycles) by the exposure to PL treatment and the product kept its microbiological stability during the whole storage period of 28 days. The initial ascorbic acid content was not affected by the light treatment. Moreover, it was better preserved for PL treated samples for the entire storage time, as compared with the untreated fruits. Similarly, the quality characteristics of the fresh strawberries were not adversely affected by PL processing and a high retention of the quality attributes was observed during the storage time.
In conclusion, our results suggest that the surface decontamination treatment with PL before packaging in MAP has the potential to extend the shelf life of strawberries while preserving the properties of the fresh product
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