Investigation of some Energy and Exergy Factors during Ohmic Heating Processing of Sour Orange

Heating is an important step in food processing. A new method of heating uses the natural electrical resistance of the food to generate heat. In this method electrical energy is transformed into thermal energy. This kind of food heating processing operation is called ohmic heating. The rate of ohmic heating critically depends on the Electrical Conductivity of the food during the process. Reviewing a number of researches shows that the usage of direct current for ohmic heating process causes electrolyze in liquid beverages. Moreover, usage of alternating current eliminates the probability of adverse electrochemical reaction. In addition, when the frequency increases, the risk of oxidation in electrodes will decrease. In this regard, for heating different kinds and sizes of food, it is necessary to have an electrical power source with variable output voltage and frequency. This research attempts to design and simulate the variable voltage and frequency electrical power source to feed a 10 kW ohmic heating process at high frequency (10 kHz). The ohmic heating load is simulated by three-phase resistive load. According to Joulepsilas first law, the temperature in heat generation process is closely related to electrical power and time of process. Hence, in this simulation, the value of temperature is controlled by value of power that is generated by current which flows through resistive load with control of the time period and the duty cycle. Furthermore, one of the most important things to have an effective ohmic heating process is supplying the continuous current during the process. The result of this study indicated a simple method to supply a continual current for load during the ohmic heating process.

Ohmic heating uses electric resistance heat which occurs equally and rapidly inside food when an electrical current is passed throught. In this study, we observed the physical & chemical characteristics changes which occurs in soybean protein during heating denaturation by using ohmic and conventional heating. After the ohmic heating process, we could not find any change of the primary protein structure in the denaturated soy protein samples. However, the rate of imbibed water(RIW) of the ohmic samples was 2 times faster than that of the conventional samples. Also the ANS-surface hydrophobicity was decreased, which is very closely related to RIW. In the differential scanning calorimeter(DSC) analysis result, all 7S soyprotein fraction samples were completely denaturated by ohmic and conventional heating. However, the 11S samples were completely denatured only by ohmic heating. According to the DSC result, we decided that soyprotein was damaged by temperature and electrical current during ohmic heating. The damage of electrical current was a cause of the characteristic changes.

The energy balance and life cycle assessment (LCA) of ohmic heating and appertization systems for processing of chopped tomatoes with juice (CTwJ) were evaluated. The data included in the study, such as processing conditions, energy consumption, and water use, were experimentally collected. The functional unit was considered to be 1 kg of packaged CTwJ. Six LCA impact assessment methodologies were evaluated for uncertainty analysis of selection of the impact assessment methodology. The energy requirement evaluation showed the highest energy consumption for appertization (156 kWh/t of product). The energy saving of the ohmic heating line compared to the appertization line is 102 kWh/t of the product (or 65% energy saving). The energy efficiencies of the appertization and ohmic heating lines are 25% and 77%, respectively. Regarding the environmental impact, CTwJ processing and packaging by appertization were higher than those of ohmic heating systems. In other words, CTwJ production by the ohmic heating system was more environmentally efficient. The tin production phase was the environmental hotspot in packaged CTwJ production by the appertization system; however, the agricultural phase of production was the hotspot in ohmic heating processing. The uncertainty analysis results indicated that the global warming potential for appertization of 1 kg of packaged CTwJ ranges from 4.13 to 4.44 kg CO2eq. In addition, the global warming potential of the ohmic heating system ranges from 2.50 to 2.54 kg CO2eq. This study highlights that ohmic heating presents a great alternative to conventional sterilization methods due to its low environmental impact and high energy efficiency.

A distinguishing quality or characteristics of apple puree was determined considering the effect of different processing practices: thermal (4 T), ohmic heating (OHM) and high-pressure processing (HPP). In the thermal treatment, the flow rate was set to 1700 L/h and SHP was approximately 40 s; HPP was conducted at 600 MPa for 3 min and ohmic heating at a flow rate of 2000 L/h, at 107 °C (sample preheated from 25 to 60 °C). Effects on colour, viscosity, particle size distribution (PSD), total phenol content (TPC), ascorbic acid content and sensorial quality were comparatively studied. Results showed that a very low reduction of ascorbic acid in HPP is observed. The highest ascorbic acid loss was observed for 4 T and in a lower extent for OHM ascribable to the thermal degradation, as hypothesized for pigments. The TPC content was not changed during processing. The other quality parameters evaluated (viscosity, colour, PSD, turbidity, consistency, sensorial analysis) were affected by treatments, with particular reference to 4 T. This is one of the first study applying commercial industrial-scale equipment’s. Concluding, as compared to 4 T, OHM and HPP demonstrated feasible technologies for the treatment of apple puree, having obtained also a good organoleptic response. Apple puree preparation by means of high-pressure processing, ohmic or mild thermal treatments could imply new opportunities for the apple processing industry in developing more fresh like value-added products with reasonable shelf life.

Evaluation of non-thermal effects of electricity on anthocyanin degradation during ohmic heating of jaboticaba (Myrciaria cauliflora) juice

The role of emergent processing technologies in tailoring plant protein functionality: New insights

Ohmic heating of blended citrus juice: Numerical modeling of process and bacterial inactivation kinetics

The use of ohmic heating (OH) processing technologies in beverages might provide a higher quality value to the final product; consumers tended to prefer more natural products with minimum preservative substances. The aim of this work was to evaluate the effect of OH over the presence of microorganisms in “aguamiel” as well as to study the effects on physicochemical analysis like total sugars, soluble solids, electric conductivity pH, and color. The results showed that the conductivity of “aguamiel” was 0.374 s/m, this as temperature increased, conductivity rose as well. During OH a bubbling was observed when reaching 70 °C due to the generation of electrochemical reactions during the OH process. OH had a significant effect in the reduction of E. coli, yeast, and lactobacillus compared to conventional pasteurization, reaching optimal conditions for its total inactivation. Regarding its physicochemical properties, both treatments, conventional pasteurization and OH, did not show negative changes in aguamiel, demonstrating that OH technology can be a feasible option as a pasteurization technique. In conclusion it is important to notice that negative changes were not found in quality, color and sugars of “aguamiel”. Therefore, ohmic heating can be an option to replace traditional methods used for pasteurization.

This study investigated polyphenol oxidase (PPO) inactivation in a viscous solution of carboxymethyl cellulose (CMC) by ohmic processing (OH) and conventional thermal processing (CTP) at several temperatures and to assess the impact of CMC consistency on PPO inactivation. OH affects the PPO activity in temperatures higher than 50°C (reduction to 20% at 50°C, 12 min and complete inactivation after 2 min at 80°C), whereas CTP caused a significant reduction in PPO activity only above 60°C (reduction to 90% at 60°C, 8 min and complete inactivation after 2 min at 80°C). The rate of PPO inactivation by ohmic heating was higher than by CTP under all conditions tested, represented by a reduction of D70°C (OH: 3.61 min, CTP 7.32 min), except D80°C was ∼0.5 for both techniques. The Z‐value was higher for OH (14.68°C) than for CTP (8.60°C). Consistency did not have a major impact on inactivation rate.Practical ApplicationsInactivating enzymes that alter quality aspects of food products, such as polyphenol oxidase (PPO), is an important objective of a food processing technology. PPO is an enzyme commonly found in fruits and vegetables that catalyzes browning reactions. Ohmic heating (OH) is a technology known for its potential for processing highly viscous products. This study corroborates the potential of OH for processing highly viscous fluids over conventional thermal processing (CTP), having a great potential to be an alternative technique to food processing. In addition, it gave more evidence of the nonthermal effects due to the electrical current during the ohmic processing.

Unraveling the nature of ohmic heating effects in structural aspects of whey proteins – The impact of electrical and electrochemical effects

Phycocyanin is a highly valued pigment present in Spirulina platensis biomass with applications in the food industry in terms of biorefinery concepts; specifically, its antioxidant and antimicrobial capacity are an advantage that could be incorporated into a food matrix. This study aims to use rice husk as an alternative culture medium for S. platensis biomass growth and phycocyanin extraction by ohmic heating processing using a 3D-printed reactor. S. platensis was cultivated in rice husk extract (RHE) from 0-100% (v/v). The highest content of microalgal biomass was 1.75 ± 0.01 g/L, with a specific growth rate of 0.125 ± 0.01 h-1. For the phycocyanin extraction under an ohmic heating process, a 3D-printed reactor was designed and built. To optimize phycocyanin extraction, a central composite rotatable design (CCDR) was evaluated, with three factors: time (min), temperature (°C), and pH. The highest phycocyanin content was 75.80 ± 0.98 mg/g in S. platensis biomass grown with rice husk extract. Ohmic heating is a promising method for rapid phycocyanin extraction, and rice husk as a culture medium is an alternative for the growth of S. platensis biomass in the integration of second- and third-generation biorefineries.

Low-frequency dielectric changes in cellular food material from ohmic heating: Effect of end point temperature

The technology of heating materials by passing a current through them has been variously termed Ohmic or Joule heating, in honor of Georg Ohm (who elucidated the Ohm’s law) and James Prescott Joule (who showed that passage of electricity resulted in heating effects). In the latter part of the 19th century, a number of inventions were developed for the heating of flowable materials. The technology saw periodic revival with industrial applications, for example, in milk pasteurization in the 1930s, before being discontinued. In the 1980s, the technology was again revived, and it has achieved some industrial applications that include the pasteurization of liquid eggs and processing of fruit products.

Stabilization of ohmic pretreated peach cubes (ohm) in syrup, representative of semifinished fruit products, was finalized by ohmic heating (OHM) and high pressure processing (HPP), proposed respectively as thermal and nonthermal pasteurization, in comparison to a conventional pasteurization treatment (DIM). The samples were then studied in terms of histological, physical (dimensional distribution, tenderometry, texture, viscosity of syrup and colour), chemical (total phenolic and ascorbic acid content), and sensorial (triangle test) properties. Severe modifications of the cell walls were observed in ohm-DIM and ohm-OHM samples, with swelling and electroporation, respectively. From chemical analyses, significant reduction of ascorbic acid and simultaneous increase of total phenolics content were observed for ohm-DIM and ohm-OHM, probably in relation to the cell wall damages. ohm-HPP showed the best preservation of the dimensional characteristics and hardness, followed by ohm-OHM and ohm-DIM. In addition, textural and colour parameters evidenced similar results, with ohm-HPP as the less different from ohm. Finally, the sensorial analysis confirmed ohm-HPP and ohm-OHM samples as the most similar to ohm as well as the most appreciated in terms of colour and consistency.

: Two methods of food sterilization were studied with a variety of foods. The methods were ohmic heating and split-phase aseptic processing. The method of operation of these systems is discussed in depth. ne final products were tested by a sensory panel. Products from both systems compared favorably to thermally processed tray pack items. The recipes used for these products were identical to the tray packs. Although the products received satisfactory ratings, they could be improved by using formulations specifically developed for the systems. The study demonstrated that either of these reduced-temperature sterilization processes will produce an acceptable product that is an alternative to thermal sterilization.