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Plant-based proteins are rapidly emerging, while novel technologies are explored to offer more efficient extraction processes. The current study aimed to evaluate the effects of pulsed electric fields (PEFs) and temperature on the extraction of soluble proteins from nettle leaves (Urtica dioica L.) and identify an optimal operational range for the highest yield of soluble proteins. Extractions and kinetic modeling were conducted with whole and ground dried leaves at different temperatures (30–70 °C) and specific energy of PEF (0–30 kJ kg−1) with extraction times of up to 60 min. The influence of temperature and specific energy on the soluble protein extraction yields was investigated and modeled using composite central design and response surface methodology. The experimental results were fitted to Peleg's kinetic model, which satisfactorily described the extraction process (R2 > 0.902), and PEF treated samples resulted in a higher soluble protein yield and shortened processing time. Response surface methodology showed that the linear effect of temperature and quadratic effect of PEF (p < 0.01) were highly significant for protein yield. In the optimized PEF-extraction region (specific energy between 10 and 24 kJ kg−1, and 70–78 °C), soluble protein yield was higher than 60% after 5 minutes of extraction. The achieved results are relevant for developing processes for PEF assisted extraction of soluble proteins from leaves. Understanding the effects of PEFs and process parameters is crucial to obtain high protein yields, while requiring low energy and short processing time.
The kiwifruit processing industry is focused on product yield maximization and keeping energy costs and waste effluents to a minimum while maintaining high product quality. In our study, pulsed electric field (PEF) pretreatment enhanced kiwifruit processing to facilitate peelability and specific peeling process and enhanced valorization of kiwifruit waste. PEF optimization was applied to obtain the best treatment parameters. A 32 factorial design of response surface methodology was applied to find the effect of time elapsed after PEF treatment and the PEF-specific energy input on specific peeling force and kiwifruit firmness as response criteria. Under the optimized condition, the specific peeling force decreased by 100, and peelability increased by 2 times. The phenolic content and antioxidant capacity of PEF-treated kiwifruit bagasse were 5.1% and 260% richer than the control sample. Overall, the optimized PEF pretreatments incorporated into kiwifruit processing led to decreased energy demand and increased productivity.
PEF is an innovative technology to extend the shelf life of fresh liquid food products, mainly juices, with minor impact on the quality. Many lab scale studies have been published, indicating the great potential of PEF for the juice industry. For industrial realization, the PEF systems have been adapted to the industrial requirements, establishing HACCP and hygienic design concept. Important process parameters have been identified from research and integrated in industrial PEF processes. Juice producers are now able to use PEF for their production lines.
Pulsed Electric Field (PEF) processing has been investigated in the past for gentle preservation and for the disintegration of biological tissue. The principle is based on polarization of the cell membrane by an external electric field, which results in electroporation. This increases the permeability of the membrane, which positively affects processes in which mass transfer is important. Extraction, such as sugar from sugar beet or juice from fruit, aims to separate ingredients from a matrix. By disintegrating the cells by PEF, a facilitated extraction of sugar or a higher juice yield can be achieved. Beneficial effects were also observed during water removal, as the drying time or the drying temperature can be reduced using PEF as a pre-treatment. Furthermore, a softening of PEF-treated tissue was observed, which can be highly beneficial for the vegetable industry such as in processing French fries or potato chips. The cutting force is reduced and smoother surface with less breakage can be achieved. The chapter gives an overview on the effects achieved in the PEF treatment of solid material.
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.
Повышение эффективности снятия покровной ткани с плодов томата импульсным электрическим полем
(2022)
Electrophysical technologies are a global trend of sustainable agriculture and food industry. Peeling is an energy-intensive procedure of fruit and vegetable processing. The research featured the effect of pulsed electric field (PEF) treatment on tomato peeling effectiveness. The assessment included such factors as specific effort, energy costs, and product losses in comparison with thermal and electrophysical methods. Tomatoes of Aurora variety underwent a PEF treatment at 1 kV/cm. The expended specific energy was 1, 5, and 10 kJ/kg. The tomatoes were visually evaluated with optical microscopy before and after processing. The peeling effectiveness and mass loss were measured with a texture analyzer and digital scales. The PEF treatment decreased the specific force of mechanical peel removal by 10% (P < 0.05). The mass loss decreased by 4% (P < 0.05) at 1 kJ/kg. The PEF method resulted in cell electroporation, which activated the internal mass transfer of moisture from the endocarp region between the mesocarp and the integumentary tissue. The hydrostatic pressure produced a layer of liquid, which facilitated the peeling. In comparison with thermal treatment (blanching), ohmic heating, and ultrasonic processing, the PEF technology had the lowest production losses and energy costs. The research proves the prospects of the PEF treatment in commercial tomato processing.
The impact of Pulsed Electric Fields (PEF) on the peeling ability of different fruits and vegetables in particular tomatoes, peaches, peppers, and oranges were investigated. Samples were exposed to a fixed electric field strength of 2.15 kV/cm. The specific energy ranged from 0.6 kJ/kg to 50.3 kJ/kg. The treated raw materials were analysed regarding to the peeling ability, skin size and weight and firmness. The best result for tomatoes at a specific energy of 1.2 kJ/kg induced a high score of peeling ability that led to less product loss and could therefore increase the yield by 33.84%–41.53% compared to untreated samples. Moreover, an increased skin size by a factor of 3.7 was observed. However, PEF had no significant impact on peeling ability of oranges, peppers, and peaches. Although oranges showed an improvement in peeling ability by up to 32%, this cannot be traced back to the PEF treatment. The different properties and structures of the raw materials were discussed and provided indications about the limitation of PEF.
The increased consumption of reduced-fat or non-fat products leads to a reduced intake of fat-soluble bioactive substances, such as fat-soluble vitamins. Due to their natural role as transport systems for hydrophobic substances, casein micelles (CM) might depict a viable system. The structure of CM is characterized by a lipophilic core stabilized by an electric double layer-like structure. Modification allows accessibility of the core and, therefore, the inclusion of fat-soluble bioactive substances. Well-known modifications are pH reduction and use of rennet enzyme. A completely new procedure to modify CM structure is offered by pulsed electrical fields (PEF). The principle behind PEF is called electroporation and affects the electric double layer of CM so that it is interrupted. In this way, lipophilic substances can be incorporated into CM. In this work, we evaluated integration of β-carotene into native CM by an industry-compatible process to overcome disadvantages associated with the use of Na-caseinate and avoid great technical effort, e.g., due to treatment with high hydrostatic pressure. Our research has shown that PEF can be used for disintegration of CM and that significant amounts of β-carotene can be incorporated in CM. Furthermore, after disintegration using PEF, a combination of another PEF and thermal treatment was applied to restructure CM and trap significant amounts of β-carotene, permanently, ending up with an encapsulation efficiency of 78%.