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Pulsed electric field (PEF) treatment consists of exposing food to electrical fields between electrodes within a treatment chamber, which can improve the preservation of fresh-like products such as milk. Although several studies support the use of PEF technology to process milk at low temperature, these studies reported microbial reductions of around 3 log10 cycles and also indicated a limited impact of PEF on some endogenous and microbial enzymes. This scenario indicates that increasing the impact of PEF on both enzymes and microorganisms remains a major challenge for this technology in milk processing. More recently, combining PEF with mild heating (below pasteurization condition) has been explored as an alternative processing technology to enhance the safety and to preserve the quality of fresh milk and milk products. Mild heating with PEF enhanced the safety of milk and derived products (3 log10–6 log10 cycles reduction on microbial load and drastic impact on the activity enzymes related to quality decay). Moreover, with this approach, there was minimal impact on enzymes of technological and safety relevance, proteins, milk fat globules, and nutrients (particularly for vitamins) and improvements in the shelf-life of milk and selected derived products were obtained. Finally, further experiments should consider the use of milk processed by PEF with mild heating on cheese-making. The combined approach of PEF with mild heating to process milk and derived products is very promising. The characteristics of current PEF systems (which is being used at an industrial level in several countries) and their use in the liquid food industry, particularly for milk and some milk products, could advance towards this strategy.
Dehydration is a technique that has been used since ancient times. The need to develop more efficient processes to obtain dehydrated foods of higher quality from the organoleptic and nutritional point of view has led to the study of different techniques. For instance, convection drying, freeze-drying, spray drying, vacuum drying, microwave vacuum drying, infrared radiation drying, osmotic dehydration, among others have been investigated.
Over the last years, pulsed electric fields (PEF)-assisted drying has attracted the interest of several researchers due to its ability for reducing drying time, preserving at the same time some thermolabile compounds which are responsible for the aroma, nutritional and bioactive properties of food products.
Therefore, in this article, some of the most important studies regarding the application of PEF-assisted drying in food processing will be discussed.
The aim of this study was to analyze the impact of pulsed electric field (PEF) pre-treatment of apple tissue on kinetics of freeze-drying preceded by vacuum freezing and physical properties of such processed material. PEF intensified freeze-drying kinetics and thus reduced processing time by 57% in comparison to untreated apples slices. Furthermore, the effective water diffusion coefficient increased by 44% as a result of PEF application. Water activity changes during storage of freeze-dried apple tissue were more evident in the case of untreated material albeit initial water activity was higher in the case of electroporated samples. As proved by thermal properties measurements these differences were linked to higher crystallinity of the PEF treated samples (35.5%) in comparison to the untreated material (11.0%). The freeze-dried fruits subjected to PEF pretreatment absorbed more water than the untreated samples while no changes were observed for hygroscopicity and loss of the soluble solids during rehydration.
In this study, the impact of a pulsed electric field (PEF) treatment on the final quality of freeze-dried apples was investigated. The PEF treatment has been performed at an electric field intensity equal to 1.07 kV/cm and a specific energy input of 0.5, 1 and 5 kJ/kg. The samples were freeze-dried (without a separate pre-freezing step) at varying temperatures (set on 40 °C and 60 °C) and pressures (0.1, 0.25 and 1 mbar). The quality of dried material was evaluated by the analysis of residual moisture content, macro- and microscopic properties, colour, the total content of phenolic compounds and the antioxidant activity as well as texture and acoustic properties. It was found that the residual moisture content of PEF treated samples was reduced by up to ∼82% in comparison to the intact tissue. For electroporated samples, a good preservation of macro-shape, an inhibition of shrinkage and the development of large pores were observed. The PEF treated material exhibited a higher total phenolic content, but a smaller antioxidant activity. Mechanical and acoustic analysis showed a higher crunchiness and brittleness for PEF-treated tissue, whereas untreated tissue was characterised by a harder and rather crackly texture.
Applications of pulsed electric fields for processing potatoes: Examples and equipment design
(2022)
In the last two decades, pulsed electric fields (PEF) have successfully been introduced into the food industry, as one of the most promising and "game changing" technologies. This review is devoted to the recent applications of pulsed electric fields used in processing potatoes. The potato processing market size was estimated to be ca. USD 24.83 billion (2018) and with an annual growth rate of 5.2%. The physicochemical characteristics of potatoes and the specificity of potato processing lines makes a pulsed electric field very versatile and flexible allowing one to achieve different technological aims by its implementation into technological lines. In this paper, a short analysis of the potato structure and its nutritional properties, applications of moderate electric fields, ohmic heating, and pulsed electric fields are presented. Moreover, the basic electroporation effects, metabolic responses, texture modification and different PEF assisted processes applied to the potato are discussed. Finally, some examples of commercial applications and a brief description of the available equipment for the PEF processing of potatoes are presented.
Currently, the modelling of drying processes of plant tissues pre-treated by pulsed electric field (PEF) is following experimentally identified curves or separate heat and mass transfer and diffusion models with different levels of accuracy. This research had two major objectives: mathematical modeling and control of drying process of different vegetables pretreated by PEF during convective drying. The mathematical modeling was based on Luikov's heat and mass transfer model along with properties of different vegetables. Computer modelling was done using the difference method for predicting moisture and the temperature potentials of untreated and PEF-treated vegetables. The formulation and the solution procedures were applied to simulate the simultaneous heat and mass transfer in selected vegetables subjected to the convective drying. Suggested model had a good correlation with experimental results. Moreover, cell disintegration index can be used as a controllable parameter in heat and mass transfer models to predict drying behavior of potato, onion, and carrot tissues. Obtained drying models can be used as a mathematical tool to predict drying behavior for various types of agricultural products pre-treated by pulsed electric field.
While the Food and Biotechnology industries often use unit operations that have been known for some time, sometimes these processes are not efficient or sustainable. The need to develop more efficient processing lines to obtain higher quality products is of utmost importance. Over the last years, pulsed electric fields (PEF) processing has attracted the interest of numerous researchers and companies due to its ability to reduce processing time, preserve thermolabile compounds, which are responsible for the aroma, nutritional and bioactive properties of food products.
Therefore, in this article, some of the most important studies regarding the application of PEF technology in food and biotechnology processing is discussed.
In this study the effect of PEF pre-treatment on the microstructure of freeze-dried strawberry dices was investigated. The PEF treatment has been performed at an electric field intensity of 1.07 kV/cm and a specific energy input of 1 kJ/kg. The samples were freeze-dried at a temperature of 45 °C and a pressure of 1 mbar. The microstructure of dried material was evaluated by different physical and optical methods, such as SEM, μ-CT and thermogravimetry. Moreover, mechanical and acoustic properties as well as the colour of processed material have been analyzed. PEF pre-treated strawberry dices showed a more uniform shape, a better retention of volume and a visual better quality compared to untreated ones. Moreover, PEF pre-treatment led to a more homogeneous distribution and a greater thickness of pores. In accordance, analysis of textural properties evidenced that PEF treated freeze-dried strawberry dices were crispier than untreated ones. Measurement of L*a*b*-values showed that PEF treated material was characterized by a more preserved colour after freeze-drying than untreated ones.
The study aimed for the analysis of the impact of pulsed electric field (PEF) pre-treatment on convection (CD) and microwave (MW-CD) assisted air drying. Drying kinetics acceleration and retention of bioactive compounds of PEF pre-treated carrots and apples has been demonstrated. Moreover, the direct and indirect environmental energy impacts of CD and MW-CD technologies with consideration of bioactive compounds preservation has been evaluated. PEF assisted CD and MW-CD demonstrated lower energy use, especially for indirect energy consumption, in the case of carotenoids preservation in dried carrots.