Ohmic heating assisted vacuum evaporation of pomegranate juice: Electrical conductivity changes

A novel electrical heating method, named as ohmic heating, was successfully integrated to vacuum evaporation system, and pomegranate juice was concentrated until its total soluble dry matter content reached to 40% by applying three different voltage gradients (7.5, 10, and 12.5 V/cm) at 180 mm Hg absolute pressure in this system. Total evaporation times were determined as 152, 78, and 53 min at the voltage gradients of 7.5, 10, and 12.5 V/cm, respectively. The concentration time of pomegranate juice was shortened about 56% by ohmic heating relative to conventional evaporation. The electrical conductivity values were increased up to reach 25% TSDM for 7.5 V/cm and at 35% TSDM for 10 V/cm, then showed a decreasing pattern. However, it was constant (0.55 ± 0.01 S/m) during evaporation process at 12.5 V/cm. It is recommended that the ohmic heating method could be successfully integrated to vacuum evaporation process to shorten the processing time significantly.Industrial relevanceOhmic heating has been utilized as alternative method for the purpose of heating, pasteurization, cooking etc., and relatively better products can be obtained by ohmic heating. Nowadays, energy efficient systems are needed in concentrated juice production. The integration of ohmic heating to the conventional vacuum systems could serve the production high quality juice concentrates with efficient use of energy. In present study, ohmic heating assisted vacuum evaporation of pomegranate juice was conducted, successfully. This method decreased the total process time for juice concentration, which is critically important for industrial scale productions. This novel method can be implemented to the fruit juice production lines by taking into account of design characteristics of ohmic systems such as electrical conductivity changes depending on both temperature and total soluble solids concentration. The effects of main process parameter, named as voltage gradient, on electrical conductivity changes during electrical heating assisted evaporation process has been also reported in the present study.     

Pasteurization of citrus juices with ohmic heating to preserve the carotenoid profile

This study was carried out to assess, for the first time, the effect of ohmic heating on the carotenoid profile of two citrus fruit juices: grapefruit and blood orange. Two heat treatments were designed to obtain pasteurization values of 50 and 150 min (Tref = 70 °C and z-value = 10 °C) with ohmic heating as compared to conventional heating. The results showed that xanthophyll losses could reach 70% for epoxyxanthophylls (cis-violaxanthin and cis-antheraxanthin) and 40% for hydroxyxanthophylls (β-cryptoxanthin, lutein, and zeaxanthin) with conventional heating, but losses were under 30% and 20%, respectively, with ohmic heating. Carotene species (lycopene and β-carotene) were stable regardless of the treatment. No negative non-thermal effects of ohmic heating were shown on carotenoids. Loss simulations of the studied carotenoids showed that the high temperatures reached with ohmic heating during pasteurization could substantially increase the organoleptic and nutritional quality of acid carotenoid-rich juices.Industrial relevanceCitrus are the top fruit crops in terms of world trade. This craze for them -particularly orange and grapefruit- is notably due to their high content in organoleptic and nutritional compounds of interest and among them carotenoids. About 50% of the Citrus production is processed in juice. From the growing variety of products, minimal processed juices now have a significant market share. This work assessed for the first time the effect of ohmic heating, a thermal method for stabilizing juices while minimizing the impact on the juice quality, on the carotenoid profiles of blood orange and grapefruit juice. Pasteurization with ohmic heating was proven to be a very good alternative for protecting carotenoids and especially xanthophylls compared to conventional heating. These results will help in designing ohmic heating process parameters for optimizing the overall quality of carotenoid-rich fruit juices.     

Improvement of radio frequency (RF) heating uniformity on low moisture foods with Polyetherimide (PEI) blocks

Radio frequency (RF) heating is rapid, volumetric, and can penetrate most food packaging material. Thus, it is suited for in-packaged food pasteurization applications. However, the non-uniform heating problem needs to be resolved. In this study, a method of adding Polyetherimide (PEI) cylindrical blocks on top of and at the bottom of peanut butter samples in a cylindrical jar (d = 10 cm, h = 5 cm) was evaluated to improve RF heating uniformity. A computer simulation model built with COMSOL Multiphysics® was used for heating pattern prediction, and a new temperature uniformity index was proposed to suitably evaluate pasteurization process heating uniformity. Results showed that a pair of PEI blocks with a diameter of 8 cm among all five diameters (2, 4, 6, 8, and 10 cm) added to the cold spots of a given peanut butter sample could make the sample reach the best heating uniformity. Furthermore, the best height of PEI blocks with a diameter of 8 cm that allows the sample to be heated most uniformly was found to be 1.3 cm after sweeping from 0.1 to 2.3 cm with a step of 0.1 cm. Simulation results also showed that the combination of PEI surrounding and the addition of 8 cm diameter PEI blocks could further control the temperature distribution range in peanut butter within 7.1 °C when the peanut butter was heated from 23 to 70 °C. The newly developed temperature uniformity index provided a more reasonable evaluation on heating uniformity of pasteurization process than the traditional uniformity index.     

Pressure–ohmic–thermal sterilization: A feasible approach for the inactivation of Bacillus amyloliquefaciens and Geobacillus stearothermophilus spores

The efficacy of a pressure–ohmic–thermal sterilization (POTS) for Bacillus amyloliquefaciens and Geobacillus stearothermophilus spore inactivation was investigated. Spores (2.5 × 10⁸ cfu/ml) were inoculated in 0.1% NaCl solution (pH 5.0 and 7.0), green pea puree (pH 6.1), carrot puree (pH 5.0) or tomato juice (pH 4.1). Samples were ohmically (50 V/cm) treated at 600 MPa and 105 °C for various holding times using a laboratory-scale high-pressure processor. B. amyloliquefaciens and G. stearothermophilus spores suspended in 0.1% NaCl solution (pH 7.0) were inactivated by 4.6 and 5.6 log, respectively, for a 30-min holding time. B. amyloliquefaciens and G. stearothermophilus spores in tomato juice were reduced by 3.1 and 4.8 log, respectively, for a 10-min holding time. Spore germination was highest in the G. stearothermophilus suspended in 0.1% NaCl solution (pH 7.0). POTS treatment appears to be a potent method for inactivating pressure–thermal resistant bacterial spores.Industrial RelevanceFood industry is interested in developing superior quality low-acid shelf-stable foods. This study evaluated the pressure–ohmic–thermal sterilization (POTS) for the inactivation of Bacillus amyloliquefaciens and Bacillus stearothermophilus endospores. The impact of food matrices and acidity on the spore resistance was also investigated. Knowledge gained from the study will help the food processors for understanding the importance of various POTS treatment parameters for sterilization of low-acid foods.     

Mathematical modeling of ohmic heating of two-component foods with non-uniform electric properties at high frequencies

The ohmic heating (OH) of two-component foods (consisting of mashed potato and mashed potato with 1% NaCl) configured using four different filling patterns (parallel, series, and two concentric patterns) was investigated experimentally and by modeling. The electrical conductivities of the samples at 50 Hz and 20 kHz were obtained in the range of 20–85 °C. The differences between the thermal behaviors of the two-component foods were analyzed using internal thermal images and temperature profiles from four positions. A three-dimensional OH model for high frequencies was developed based on electric field analysis using Maxwell's equations. The model agreed sufficiently with the measured results and was able to confirm that the current applied to the sample follows the path that presents minimum electrical resistance, which is independent of the filling pattern configuration. Analysis of the heat flux density provided a better understanding of the heating behavior of two-component foods during OH.Industrial relevanceAlthough several mathematical approaches used to simulate the OH process of solid foods have been published in recent years, the simulation of temperature and electric field distributions using simplified methods, such as by the solution of Laplace's equation, is still a problem for two-component solid foods with special configurations of the internal components treated using an OH process at high frequencies. This problem can be solved using a more fundamental solution based on Maxwell's equations and electric field analysis via computer simulation. A comprehensive mathematical simulation of the thermal behavior and the effect of the orientation of the current within the two-component foods can be used to accurately predict the heat during OH. Therefore, the modeling of heating patterns of complex foods can assist in the design of food sterilization and pasteurization processes. Moreover, it will contribute in industrial applications for a better design of OH systems and electrode configurations for rapid and uniform heating.     

Fermented minced pepper by high pressure processing,high pressure processing with mild temperature and thermal pasteurization

High pressure processing (HPP) and thermal pasteurization (TP) of fermented minced pepper (FMP) were comparatively evaluated by examining their impacts on microbial load, titratable acid (TA), pH, a_w, firmness, color, capsanthin, ascorbic acid (AA), and biogenic amines (BAs) after processing and during 12 weeks of storage at 25 and 37 °C. The total plate count (TPC) in FMP samples was reduced by 1.48, 0.12 and 1.58 log₁₀ CFU/g after TP (83 °C/15 min), HPP1 (500 MPa/20 °C/5 min) and HPP2 (500 MPa/50 °C/5 min), respectively. The population of spores was reduced by 1.21 log₁₀ CFU/g only after HPP2. During storage at 25 or 37 °C, the TPC in TP, HPP1, and HPP2 samples increased by 0.88/1.21, 0.41/0.62 and 0.60/0.86 log₁₀ CFU/g, respectively, while the spores decreased below the detection limit. The retention of firmness after TP, HPP1 and HPP2 was 36.91, 91.15 and 66.48% respectively, and HPP-treated samples exhibited more retention during the storage. Color of FMP samples was not changed by TP, but slightly changed by HPP1 and HPP2. The content of capsanthin retained 78.99, 93.71 and 88.19% after TP, HPP1 and HPP2, it showed a small decrease during storage. Levels of biogenic amines (BAs) in HPP2 samples were lower than that of TP and HPP1 ones. There were better sensory quality and lower microbial level in HPP-treated samples during storage, indicating that HPP is a better choice for the preservation of FMP.Industrial relevanceConsumption of fermented minced pepper (FMP), as a traditional Chinese food, is becoming increasingly popular. Considering that heat treatment may destroy some heat-sensitive quality of the products, this study evaluated the effects of high pressure processing (HPP) on quality of FMP. Findings of this study could help processors commercialize HPP to replace current thermal processing in industrial production.     

Proofing of bread dough assisted by ohmic heating

Proofing of bread dough was studied under ohmic heating for a target temperature of 35°C. An experimental device based on PLC monitoring was developed to study the effect of heating rates and voltages on the proofing process. Conventional and ohmic heating-assisted proofing were compared; the results showed that the process itself had no impact on the proofing when identical heating rates (0.065°C·min^− 1) were used. However, increasing the heating rate could significantly reduce the time needed to reach an expansion ratio of 3 (from 122 min during conventional proofing to 65–70 min during ohmic heating in the range of 1–10°C·min^− 1). This was due to the shortening of the lag phase at the beginning of proofing (from 58 min during conventional heating to 20 min at 10°C·min^− 1 in ohmic heating). Results also showed that the voltage intensity had no significant effect on the proofing kinetics in the range of 50–150 V. The evolution of expansion ratios with proofing time could be fitted by a Gompertz model with a very high accuracy (R² > 0.999)     

Gelation characteristics of tropical surimi under water bath and ohmic heating

Gelation characteristics of tropical surimi, namely threadfin bream (TB), bigeye snapper (BS), goatfish (GF) and lizardfish (LF) prepared in the absence and presence of 10 g kg^?1 egg white proteins were evaluated using either ohmic (OH) or water bath (WB) heating. LF and GF surimi exhibited higher endogenous proteolytic activity than BS and TB. Ohmic heating markedly minimized proteolysis of LF and GF surimi as evidenced by a reduction of trichloroacetic acid (TCA)-soluble oligopeptide content of gels and more retention of myosin heavy chain (MHC). Ohmic heating increased breaking force and deformation of TB and BS surimi by 1.3 and 1.6 times, respectively, as compared to water bath heating. However, TB surimi gels heated by a higher applied voltage gradient of 16.7 V cm^?1 exhibited lower breaking force than those heated at 6.7 V cm^?1. Gels heated ohmically contained lower total sulfhydryl concentration, indicating the greater extent of disulfide bond formation as compared to gels heated in a 90 °C water bath. The rapid heating method with shorter heating time could improve water holding capacity and preserve color of tropical surimi gels when compared to water bath heating.     

Investigation and kinetic evaluation of furan formation in tomato paste and pulp during heating

Due to its high ascorbic acid content and acidic environment, tomato is susceptible for furan formation during heat treatment. In this study, kinetics of furan formation was analyzed in order to have an understanding of the reactions taking place in tomato pulp during heating. Also several tomato paste samples were investigated in terms of their furan and hydroxymethylfurfural (HMF) concentrations, and the possible furan precursors. Paste samples were found to contain 3.3–13 ng/g furan and 0.9–39.4 μg/g HMF (dry weight basis). Freshly prepared tomato pulps were heated at 70, 80, and 90 °C for different times, and analyzed for ascorbic acid, dehydroascorbic acid, and furan concentrations. The formation rates of furan in the very first 5 min of heating at 70, 80, and 90 °C were 0.0071, 0.0130, and 0.0168 nmol/g·min, respectively. Rate constants related to reactions taking place during furan formation were estimated by multi-response kinetic modeling. The results revealed that ascorbic acid oxidation is the critical step in furan formation reaction mechanism during heating of tomato pulp, and prevention of oxidation during processing might help to limit furan formation.     

Pasteurized and sterilized maple sap as functional beverages: Chemical composition and antioxidant activities

Maple sap has been consumed for centuries as a tonic by the indigenous peoples of eastern North America but is primarily utilized in this region to produce maple syrup. The natural watery form of maple sap makes its application as a functional beverage appealing but due to microbial growth, sterilization or pasteurization would be necessary before sap could be consumed. This study was designed to investigate the chemical composition (sugars, amino acids, organic acids, minerals, and phenolics) and antioxidant effects of maple sap after undergoing pasteurization and sterilization. After both processes, sugars, amino acids, organic acids, and minerals were preserved in the sap samples and they had similar phenolic contents (0.25–0.27 mg/100 g gallic acid equivalents) and antioxidant activities (IC₅₀ ca. 550 μg/mL by DPPH assay). HPLC-DAD analyses revealed over 25 constituents in the sap samples of which 15 were identified using phenolic standards. In addition, one compound, 3′,5′-dimethoxy-4′-hydroxy-(2-hydroxy)acetophenone, not previously reported from maple syrup, was isolated and identified (by NMR) for the first time from maple sap. Therefore, the preservation of chemical constituents and antioxidant activity in maple sap after pasteurization and sterilization warrants its application as a functional beverage beyond its primary use for maple syrup production alone.     

Ohmic heating treatment for Gac aril oil extraction: Effects on extraction efficiency,physical properties and some bioactive compounds

The effects of ohmic heating on Gac aril oil extraction in comparison with conventional heating were studied. The experiments were conducted using three extraction stages with the selected ratio of Gac aril powder to n-hexane (solvent) and time for each stage of 1:7 (7 h), 1:6 (6 h) and 1:5 (5 h), respectively. The aims were to (1) study the possibility of applying ohmic method in Gac aril oil extraction and (2) compare between oil extraction using ohmic and conventional treatments. It appeared that the electrical conductivities of fresh Gac aril, Gac aril powder with water and Gac aril powder with hexane ranged between 0.54 and 1.16, 0.50–1.46 and 0.18–0.31 S·m^− 1 respectively. The extraction efficiency, color characteristics and the contents of β-carotene and lycopene of Gac aril oil were enhanced by extraction with ohmic method. Three extraction stages with ohmic heating treatment at 50 °C in all stages resulted in the highest extraction efficiency (81.40%). The SEM micrographs proved that the cell wall of the Gac aril powder after extraction with ohmic heating was more ruptured than that of conventional heating. Physical properties of Gac aril powder and residues collected from different extraction methods were diverse due to their dissimilar compositions and structures.     

Ohmic heating for cooking rice: Electrical conductivity measurements,textural quality determination and energy analysis

In this study, an innovative technique, namely ohmic heating was applied in rice cooking and compared with conventional method using electric rice cooker. Four types of rice samples including white rice of two varieties (KDML105 and Sao Hai), brown rice and germinated brown rice of one variety (KDML105) were used. Electrical conductivities of mixtures between rice samples and 0.1 M salt solution at various ratios were measured. Empirical models were developed for predicting electrical conductivities of rice samples as a function of temperatures. Textural properties of cooked rice samples and energy consumption were compared between ohmic and conventional cooking methods. The purposes of this work were to (1) study the possibility of applying ohmic method in rice cooking and (2) compare between cooking rice by ohmic and conventional method. The results revealed that it is possible to apply ohmic method for cooking all rice samples by using 0.1 M salt solution in the mixtures. The electrical conductivities of white rice (KDML105), white rice (Sao Hai), brown rice and germinated brown rice (KDML105) mixtures were 0.246–0.900, 0.375–1.005, 0.617–1.370 and 0.485–1.182 S/m respectively. The rice cooked by ohmic method had significantly different textural properties from that cooked by electric rice cooker. The magnitude of difference depended on the rice types. The electrical energy consumption of ohmic cooking system was approximately 73–90% of energy required for conventional rice cooker.     

Influence of high intensity ultrasound on microbial reduction,physico-chemical characteristics and fermentation of sweet whey

The aim of this study was to investigate the influence of high intensity ultrasound on quality of reconstituted sweet whey in order to substitute thermal treatments i.e. pasteurization. Also, it was intended to study the influence of ultrasound on fermentation process of pasteurized or thermo-sonicated whey with respect to culture activation and sensory properties of the fermented whey. In the first stage, whey was subjected to treatments with different power inputs (480 W, 600 W) over 6.5, 8 and 10 min at constant temperature (45 °C, 55 °C). Treated whey samples were analyzed for microbiological quality, particle size distribution, protein content, acidity, electrical conductivity, viscosity and sensory properties. All of the analyzed parameters were compared with the control sample (pasteurized) and fresh whey. Subsequently, influence of high intensity ultrasound on pasteurized or thermo-sonicated whey fermentation with yoghurt culture and with monoculture Lactobacillus acidophilus La-5 was investigated. Ultrasound treatments were applied for culture activation prior to or after the inoculation. Whey thermo-sonication by nominal power of 480 W for 10 min at 55 °C resulted in better microbiological quality and sensory properties in comparison to whey pasteurization. Ultrasound treatments with nominal input power of 84 W over 150 s resulted in the highest increase of the viable count during the activation process. Whey fermentation by ultrasonicated culture La-5 lasted 30 min shorter and resulted in higher viable cells count.Industrial relevanceAttached paper (“Influence of high intensity ultrasound on microbial reduction, physico-chemical characteristics and fermentation of sweet whey”) reports the influence of high intensity ultrasound on quality and fermentation process of sweet whey. Also, the influence of high intensity ultrasound on pasteurized or thermo-sonicated whey fermentation with yoghurt culture and with monoculture Lactobacillus acidophilus La-5 was investigated.Whey proteins are thermo-labile proteins and degradable at higher temperatures (above 60 °C), and at conventional processing (pasteurization), denaturation and precipitation of proteins occur. Ultrasound gives a great replacement for pasteurization where precipitation does not occur. Also, ultrasonic treatment of the whey results in homogenization and thus, stability is increased. When microbiological cultures for fermentation, prior to the inoculation in the samples, are treated by ultrasound their activity is higher (explained in the paper) and thus fermentation is faster.From an economical point of view, processing by ultrasound can reduce costs a lot, since fermentation time is shorter, and the same effect as pasteurization is achieved. Ultrasonic treatment is a future in the dairy industry.     

Screening for and characterization of Lactococcus lactis bacteriophages with high thermal resistance

Fifty-six Lactococcus lactis phage isolates collected from different German dairies and obtained from a starter culture manufacturer were tested for their heat resistance. About 40% of these isolates resisted treatment at 80 °C for 5 min when they were heated in milk. The most resistant phage isolate, P1532, was collected from sour cream. Plaque-formation was still detectable even after heating at 97 °C for 5 min. The second heat-resistant one, P680, showed some plaque-forming ability after heating at 95 °C for 5 min. Kinetic parameters for the thermal inactivation of these two resistant phages were determined for temperatures ranging from 70 to 97 °C. The inactivation of phage P1532 in skim milk and in buffer medium were found to follow first-order kinetics and did not exhibit tailing, whereas in the inactivation curves of phage P680 tailing was observed. The D-value of P1532 at pasteurization temperature of 72 °C was calculated as 112 min.     

Application of ohmic heating/vacuum impregnation treatments and air drying to develop an apple snack enriched in folic acid

The changes of lifestyle and eating habits of consumers have induced a growth in the demand for functional food. The aim of this work was to study the incorporation of folic acid into apple slices by using ohmic heating (OH) and vacuum impregnation (VI) at 30, 40 and 50 °C and air drying at 50, 60 and 70 °C to obtain an apple snack that is rich in folic acid. The kinetic impregnation of folic acid, texture and color were evaluated. The impregnated samples (VI) at 40 °C and vacuum-impregnated samples with ohmic heating (VI/OH) at 50 °C presented a high content of folic acid, whereas the samples air dried at 60 °C presented an important retention of folic acid. The lowest loss of firmness and color was obtained with the VI/OH treatment at 50 °C with drying at 60 °C. Therefore, the VI/OH treatment at 50 °C followed by drying at 60 °C was determined to be the best process for creating dehydrated apple slices that are rich in folic acid.Industrial relevanceThe aim of this research was to study the incorporation of folic acid into dehydrated sliced apples by using vacuum impregnation/ohmic heating (VI/OH) treatments and air drying technologies and evaluating the mechanical and optical properties of the resulting product. Two technologies, vacuum impregnation (VI) and ohmic heating (OH) were performed at 30, 40 or 50 °C with an electric field intensity of 13 V/cm using conventional heating. The results showed that the samples impregnated of apple slices by VI and VI/OH treatments reached the highest content of folic acid. However, the samples that were dried at 60 °C after impregnation by the VI/OH treatment at 50 °C exhibited an increase in folic acid due to the electropermeabilization effect, which induces retention of folic acid and an increase in the folic acid concentration by decreasing the water content. Under the investigated conditions, the VI/OH treatment at 50 °C followed by air drying at 60 °C may be considered the best processing method to obtain an apple snack that is rich in folic acid.     

Radio frequency heating of corn flour: Heating rate and uniformity

Non-uniform heating is a major challenge for using radio frequency (RF) heat treatment in pasteurization of low moisture food products. The objective of this study was to evaluate the effect of different electrode gaps, moisture content (MC), bulk density and surrounding materials on RF heating uniformity and rate in corn flour. Additionally, the dielectric and thermal properties of corn flour were determined as affected by MC, temperature (°C), and frequency (MHz). Changes in MC, water activity (a_w) and color in the sample after RF heating were measured to evaluate treatment effect on food quality. A precision LCR meter and a liquid test fixture were used to study DP of the sample at RF frequency ranging from 1 to 30 MHz. The RF heating uniformity and temperature profiles of corn flour as exposed to RF heating were obtained with an infrared camera and a data logger connected to a fiber optic sensor. The DP values increased with increasing MC and temperature, but decreased with frequency. The heating rate increased from 3.5 to 6.8 °C min^− 1 with increasing MC (from 10.4 to 16.7%), but decreased from 12.7 to 5.2 °C min^− 1 with increasing electron gap (from 11 to 15 cm). The corner and edge heating were observed at all layers of the samples for all the distances, and the hottest and the most uniform layer were determined as the middle layer at an electrode gap of 15 cm. Glass petri dish provided better uniformity than those of polyester plastic petri dish. Covering by foam led to more uniform RF heating uniformity in corn flour, and better moisture and a_w distribution. This study provided useful information to develop an effective RF process as an alternative of conventional thermal treatments for pasteurization of low-moisture products.Industrial relevanceThis paper describes a novel methodology based on Radio Frequency heating to pasteurize food powder while maintaining the quality. The study addresses the ever-increasing global demand from consumers for safe food products.     

Heat transfer modeling of chicken cooking in hot water

To calculate the slowest heating point and optimum cooking time of whole chicken cooking in hot water, a 2-dimensional heat transfer model was developed to predict temperature profile and history of the chicken cooked in hot water at 85, 90 and 95 °C. Chickens were divided into 12 sections and the heat transfer model was applied to each cross section. These models were solved with an I-DEAS program. Specific heat and thermal conductivity were measured at temperatures ranging from 25 to 95 °C. The temperature of chicken did not significantly affect the thermal properties. The average values of specific heat of white and dark meats were 3.521 and 3.654 kJ/(kg K), respectively, and the average thermal conductivity values were 0.5093 and 0.4930 W/(m K), respectively. The model was validated against experimental results, and provided an average root mean square error of 2.8 °C. Temperature distributions showed that the slowest heating point was deep in the breast part of the second cross section (3.6 cm far from shoulder) at the symmetric line of the chicken, around 2.1–2.5 cm deep from breast skin. For food safety consideration, the recommended cooking times, for whole chickens in weight range of 2.3–3.2 kg with different initial temperatures (5–30 °C), were around 74–84, 64–74 and 57–67 min for cooking temperatures of 85, 90, and 95 °C, respectively.     

Mechanical and thermal characteristics of amaranth starch isolated by acid wet-milling procedure

Effects of soaking conditions during acid wet-milling of amaranth grain on mechanical and thermal properties of amaranth starch were investigated. A factorial design based on temperature (40–60 °C) and SO₂ concentration (0.1–1.0 g/L) was used. Dynamic oscillatory tests involved heating and cooling cycles (25–90 °C) with tempering at 90 °C followed by a frequency sweep (0.1–20 Hz) at constant temperature. Thermal properties of starch suspensions were based on DSC tests. Viscoelastic modulus and thermal properties were affected by both factors, being significant the interaction effect. Maximum values of viscoelastic modulus at the end of heating and cooling steps were determined for samples corresponding to soaking conditions of 50 °C and 1.0 g/L SO₂. Based on Ross-Murphy index from frequency sweep analysis it was found that paste behavior occurs at 60 °C and 0.1 g/L, while at 47.4 °C and 0.72 g/L starch suspension gave a strong gel. Onset (61.7 °C) and peak (66.2 °C) temperatures showed a minimum at 50 °C and 1.0 g/L. As SO₂ concentration decreased, the end of gelatinization took place at lower temperature. Maximum gelatinization enthalpy (12.7 J/g) was found at 40 °C and 0.1 g/L SO₂.     

Ohmic heating and pulsed vacuum effect on dehydration processes and polyphenol component retention of osmodehydrated blueberries (cv. Tifblue)

Blueberries are highly perishable fruits; therefore, emerging technologies focus on improving the bioactive compound retention and extending the shelf life. The aim of this study was to evaluate the effect of ohmic heating and vacuum pulses on the dehydration processes and polyphenol compound retention of osmodehydrated blueberries (cv. Tifblue). The treatments were performed using a 65% (w/w) sucrose solution, an electric field of 13 V/cm (100 V) at 30 °C, 40 °C or 50 °C for 300 min, and air drying at 50, 60 or 70 °C to obtain dried blueberries. The moisture content, soluble solids and phenolic compounds were analyzed. The combination of ohmic heating/pulsed vacuum treatments intensifies mass transfer in osmodehydrated blueberries, especially at higher temperatures. Nevertheless, the polyphenol retention was greater at lower temperatures; hence, the application of an intermediate process temperature (40 °C) was selected as a pre-treatment prior to further drying. The treated samples improve the retention of polyphenols after drying compared with untreated samples. Therefore, the results of this research study suggest that the use of a pulsed vacuum and ohmic heating in the osmotic dehydration (PVOD/OH) treatment at 40 °C for 240 min and subsequent drying at 60°C could be the best process for dehydrating blueberries, considering that it improved mass transfer, achieved lower losses of phenolic components and reduced the drying time.Industrial relevanceBlueberries are an important fruit due their high bioactive compound content, especially polyphenols. Studies that involve emerging technologies application could add value to blueberries. Ohmic heating and pulsed vacuum as pre-treatments improve the efficiency of dehydration processes, focused toward bioactive compounds retention and achieving commercial viability. In this work have been applied PVOD/OH treatments at moderated temperatures and subsequently dried at 60 °C, obtaining promissory results.     

Electrical conductivity of particle–fluid mixtures in ohmic heating: Measurement and simulation

The electrical conductivity (EC) of food systems is a key parameter of the ohmic heating process. Ohmic heating experiments were conducted using a Teflon cylindrical cell. Electrical conductivity values were evaluated for the ohmic processing (25–125 °C) of blanched, 2-cm cubic particles (carrot, potato, radish, beef muscle, pork muscle and commercial ham) dispersed in carrier fluid (5% w/w starch–water solution with 0.15–1.5% w/w salt concentrations). Assuming an analogy between thermal conductivity (TC) and EC five existing TC theoretical models (series, parallel, two forms of Maxwell–Eucken models and effective medium theory) were applied and evaluated for EC of various solid–fluid structural systems. Parallel and Series models are not practically applicable in real food system, however they can indicate the useful limit values of highest and lowest EC among all two-phase structures. The first Maxwell–Eucken model, which describes solid particles dispersed in continuous liquid, showed the best agreement between predicted EC values and experimental data. This model provided a useful and relatively simple new approach to predict the effective EC for mixtures of different types of solid food particles immersed in liquid food.