Color and viscosity of watermelon juice treated by high-intensity pulsed electric fields or heat

The effects of high-intensity pulsed electric field (HIPEF) processing (35 kV/cm for 1727 μs applying 4-μs pulses at 188 Hz in bipolar mode) on color, viscosity and related enzymes in watermelon juice were evaluated during 56 days of storage and compared to thermal treatments (90 °C for 60 s or 30 s). HIPEF-treated juice maintained brighter red color than thermally treated juices along the storage time. In addition, the application of HIPEF as well as heat at 90 °C for 60 s led to juices with higher viscosity than those untreated for 56 days of storage. On the other hand, peroxidase (POD) was inactivated more efficiently after HIPEF processing than after applying heat treatments. However, the thermally processed juice at 90 °C for 60 s kept the lowest residual POD activity values beyond day 7 of storage. Differences in lipoxygenase (LOX) activity among treatments were not appreciated at day 0. However, storage time had a strong reducing influence on the enzyme activity of heat-treated samples. A substantial loss of pectin methylesterase (PME) activity (more than 50%) was observed in all the treated juices, whereas a slight reduction in polygalacturonase (PG) activity was only achieved after the HIPEF treatment. The use of HIPEF technology could be an alternative to thermal treatments and could contribute to better maintain valuable attributes of watermelon juice.Industrial RelevanceHIPEF processing is a feasible alternative to thermal treatments to obtain watermelon juice, achieving optimal inactivation of deleterious microorganisms and quality-related enzymes. HIPEF-treated watermelon juices exhibit better physical properties such as color or viscosity than thermally treated juices throughout storage. Thus, HIPEF technology can help processors to obtain juices that keep their fresh characteristics, thus being better accepted by consumers.     

Carotenoid transfer to oil during thermal processing of low fat carrot and tomato particle based suspensions

Carotenoid solubilization in the oil phase is a prerequisite for carotenoid bioaccessibility during digestion. However, the level of bioencapsulation and the hydrophobicity of carotenoids were proven to strongly affect their transfer to oil during in vitro digestion. Therefore, thermal processing (95–110 °C) was exploited to favor carotenoid transfer from tomato- and carrot-based fractions to the oil before digestion. Initially, the total (all-trans + cis) carotenoid content in the oil increased quickly, thereafter, depending on the temperature applied, either a drop or a plateau was reached at longer treatment times. Treatment conditions of > 100 °C for 10 min significantly favoured carotenoid transfer to oil (≥ 75%). The rates of transfer to oil were as follows: β-carotene ≈ α-carotene > lycopene. The results revealed that the cell wall hinders carotenoid transfer to oil during thermal processing. Overall, the results indicate that typical high temperature short time thermal processing can be sufficient to achieve maximal carotenoid transfer to oil with minimal degradation in real food systems/food emulsions and this can be crucial to improve the nutritional quality of carrot and tomato based products.     

Influence of high-intensity pulsed electric field processing parameters on antioxidant compounds of broccoli juice

The effect of high-intensity pulsed electric field (HIPEF) processing parameters (electric field strength, treatment time, and polarity) on broccoli juice carotenoids, vitamin C, total phenolic (TP) content and antioxidant capacity (AC) was evaluated. Results obtained from HIPEF-processed broccoli juice were compared with those of thermally treated (90 °C/60 s) and untreated juices. HIPEF processing parameters influenced the relative content (RC) of bioactive compounds, and the relative AC (RAC). Maximum RC of lutein (121.2%), β-carotene (130.5%), TP (96.1%), vitamin C (90.1%) and RAC (5.9%) was reached between 25 and 35 kV/cm and from 2000 μs to 500 μs. The highest RAC and RC of bioactive compounds were observed in HIPEF treatments applied in bipolar mode, except for vitamin C. HIPEF-treated broccoli juice exhibited greater RC of bioactive compounds and RAC than juice treated by heat. HIPEF technology could be considered a promising option for preserving the antioxidant quality of broccoli juice.Industrial relevanceVegetable juices are becoming more and more popular because of their wide range of health-related compounds. Particularly, broccoli juice is attracting the food industry attention because it contains high amounts of vitamins, carotenoids and phenolic compounds, among other bioactive compounds. Broccoli juice requires treatment conditions that protect its microbial, nutritional and sensorial quality. HIPEF is a non-thermal technology for liquid food preservation that inactivates microorganisms and enzymes without compromising the nutritional and sensorial features of foods. Consequently, this technology could be used in the food industry as an alternative for thermal treatment to preserve the bioactive compounds present in vegetable juices, offering to consumers a healthy product.     

High pressure thermal processing for the inactivation of Clostridium perfringens spores in beef slurry

The spores of Clostridium perfringens can survive and grow in cooked/pasteurized meat, especially during the cooling of large portions. In this study, 600 MPa high pressure thermal processing (HPTP) at 75 °C for the inactivation of C. perfringens spores was compared with 75 °C thermal processing alone. The HPTP enhanced the inactivation of C. perfringens spores in beef slurry, resulting in 2.2 log reductions for HPTP vs. no reductions for thermal processing after 20 min. Then, the HPTP resistance of two C. perfringens spore strains in beef slurry at 600 MPa was compared and modeled, and the effect of temperature investigated. The NZRM 898 and NZRM 2621 exhibited similar resistance, and Weibull modeled well the log spore survivor curves. The spore inactivation increased when HPTP temperature was raised from 38 to 75 °C. The results confirm the advantage of high pressure technology to increase the thermal inactivation of C. perfringens spores in beef slurry.Industrial relevanceC. perfringens spores may cause food/meat poisoning as a result of improperly handled and prepared foods in industrial kitchens. Thermal processes at 100 °C or higher are generally carried out to ensure the elimination of these pathogenic spores. High pressure processing (HPP) is a food pasteurization technique which would help to maintain the sensorial and nutritional properties of food. Preservation of foods with HPP in conjunction with mild heat (HPTP) would enhance the spore inactivation compared to thermal processing alone at the same temperature, due to a known germination–inactivation mechanism. This technology, together with the application of Good Manufacturing Practices, including rapid cooling, is a good alternative to the traditional methods for producing safe processed meat and poultry products with enhanced sensory and nutritional quality.     

Simultaneous optimization of heat transfer and reciprocation intensity for thermal processing of liquid particulate mixtures undergoing reciprocating agitation

Simultaneous optimization of heat transfer and reciprocation intensity (RI) was carried out for reciprocating agitation thermal processing (RA-TP) of liquid-particulate foods. Heat transfer data under various processing conditions (temperature, frequency, and headspace) and product properties (liquid viscosity, particle concentration, and particle density) during RA-TP were utilized to develop a composite model using quadratic stepwise regression analysis. Heat transfer coefficients were maximized individually and simultaneously with minimal RI using multiple-variable optimization. High RI (37–45 ms^− 2) was recommended to maximize heat transfer alone, whereas lower RI (16–19 ms^− 2) was found optimal for simultaneous optimization of heat transfer & RI. Product formulations containing low viscosity liquids filled with 23–27% volume of particles with density of 1130–1350 kg/m³ were found most desirable for maintaining good quality under RA-TP. Optimal conditions were also reported for applying RA-TP under different operating temperatures, liquid viscosities, particle concentrations and particle densities.Industrial significanceReciprocating agitation of containers is receiving interest from thermal processing industry for enhancing product quality. The aim of this study was to optimize the use of reciprocating agitation thermal processing for processing particulate liquid foods. This study attempts to predict optimal conditions of processing conditions and product compositions for reciprocating agitation thermal processing. Multi-variable optimization based on data from multiple experimental designs is conducted in this study, which will be directly relevant to be used by industry seeking to employ reciprocating agitation thermal processing.     

Prediction of convective heat transfer coefficient during deep-fat frying of pantoa using neurocomputing approaches

Deep-fat frying (DFF) is the major processing step in preparation of pantoa, a popular Indian dairy sweetmeat. In this study, the dough for pantoa was rolled into balls of 15 g, and fried in sunflower oil at 125, 135 and 145 °C for 8 min. Convective heat transfer coefficient, which defines the heat transfer characteristics of the product during DFF, was determined using one-dimensional transient heat conduction equation as 92.71–332.92 W·m^− 2·K^− 1. Neurocomputing techniques such as connectionist models and adaptive neurofuzzy inference system (ANFIS) were compared vis-à-vis multiple linear regression (MLR) models for prediction of heat transfer coefficient. A back-propagation algorithm with Bayesian regularization optimization technique was employed to develop connectionist models while the ANFIS model was based on Sugeno-type fuzzy inference system. Both connectionist and ANFIS models exhibited superior prediction abilities than the classical MLR model. Amongst the three approaches, the hybrid ANFIS model with triangular membership function and frying time and temperature as input factors gave the best fit of convective heat transfer coefficient with R² as high as 0.9984 (99.84% accuracy) and %RMS value of 0.1649.Industrial relevanceConvective heat transfer coefficient defines the heat transfer characteristics of a product during frying. Accurate prediction of heat transfer coefficient is important for design of process equipment and saving energy during commercial production. Developing models to predict heat transfer and the coefficients have been a challenge. Neurocomputing is one of the emerging intelligent technologies with analogies to biological neural systems. Therefore, it has the capability to predict complex relationships in food systems. Neurocomputing approaches such as connectionist and ANFIS models are now widely used in the food industry to predict various engineering properties of food, optimization of various transport processes, unit operations and formulating new products and product characteristics. No attempt has been made to predict the heat transfer coefficient during frying of pantoa. In this study, the convective heat transfer coefficient of pantoa was predicted using connectionist models and ANFIS techniques. These neurocomputing techniques are expected to alleviate the difficulties in conventional heat transfer modeling.     

Determination,analysis and prediction of the volumetric behavior of milk at high pressure

High pressure preservation technologies are consolidating in the food industry as an interesting alternative to traditional thermal processes. Process modeling contributes to its progress and requires the input of food properties like density for calculations. The dependency on pressure of these properties is indispensable but it is rarely available in the literature. The sector of dairy products is an important target for the development of novel foods by high pressure treatments (both high hydrostatic pressure processing and ultra-high pressure homogenization). Thus, the main objective of this research was to characterize the volumetric properties of raw whole milk and skim milk. A variable-volume piezometer with a solid-piston volumeter was employed for this purpose. Density, specific volume, isothermal compressibility and thermal expansion coefficient were determined between 0 and 60 °C under pressures up to 350 MPa; at atmospheric pressure, measurements cover temperatures up to 90 °C. Results show that milk solutes and fats, although present in low quantities in milk compared to water, have an influence which is worthy of consideration on milk volumetric properties. Irregularities appear from 200 MPa in the dependencies on temperature of the studied milk properties. From a composition-based model, it is highlighted that milk solutes' specific volume behavior is inverted around 55 °C and that milk fats' compressibility goes through a maximum around 30 °C. The composition-based model is further developped for the calculation of milk properties as a function of pressure at different temperatures; prediction errors are below 2%. Useful data and equations for high pressure processing simulation are provided together with an original view on the combined effects of pressure and temperature on milk solutes and fats.     

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.     

High pressure thermal processing of pears: Effect on endogenous enzyme activity and related quality attributes

The effect of high pressure-thermal (HPT) processing (600 MPa, 20–100 °C) on the activity of pear enzymes and related quality attributes was investigated. HPT processing at 20 °C for 5 min resulted in 32%, 74% and 51% residual activities of polyphenol oxidase (PPO), peroxidase (POD) and pectin methylesterase (PME), respectively. Increasing processing temperature to 40 and 60 °C reduced the level of PPO and POD inactivation, with the maximum residual activities of 64% and 123%, respectively observed after 3-min treatments at 40 and 60 °C. Overall, HPT at 20 to 60 °C had minimal effect on quality, although enzymatic browning was observed upon air exposure. HPT at 80 to 100 °C caused almost complete inactivation of PPO and POD with 90% and 92% inactivation respectively after 3-min processing at 100 °C, which reduced browning upon air exposure. Nevertheless, the lowest texture retention of 22% was observed under this condition.Industrial relevanceThe study examined the effects of combined high pressure thermal processing on quality related pear enzymes and related instrumental quality attributes such as colour and texture. The study enabled identification of processing regimes for enzyme inactivation and quality retention. The excellent quality retention following HPP at 20 to 40 °C makes this condition suitable for ‘fresh-like’ small portion products for immediate consumption after unpacking that do not require complete PPO and POD inactivation. On the other hand, the almost complete inactivation of oxidative enzymes PPO and POD at 100 °C makes this condition more appropriate for the production of bulk products for food service applications or pureed ingredients for baby food, or pear pieces for yoghurt, that require PPO inhibition but not necessarily high firmness retention.     

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.     

On-line and non-destructive measurement of core temperature in heat treated fish cakes by NIR hyperspectral imaging

During industrial heat treatment of food products the core temperature is a critical control parameter with respect to food quality and in particular food safety. This paper presents a method based on near-infrared (NIR) spectroscopy that enables on-line and non-contact monitoring of the complete product volume on a typical industrial belt cooking system. Two NIR systems (760–1040 nm) were evaluated on heat treated fish cakes, one point measurement system and one hyperspectral imaging system. Both systems measured several millimetres into the product. Core temperature in the fish cakes (at 10 mm depth) varied between 53 and 99 °C. The point system performed best with a root mean square error of prediction of 2.3 °C, while the imaging system was less accurate with an error of 4.5 °C. It was demonstrated that temperature changes down to 11–13 mm depth in the fish cakes could be registered by the NIR point system.Industrial relevanceDuring industrial heat treatment of food products the core temperature is a critical control parameter with respect to food quality and in particular food safety. Especially for ready-made products this is important since they can be consumed without further heat treatment. Today, most temperature measurements during processing are typically based on spot checks on a small number of products. The core temperature of heat treated products is usually the most critical and needs to be measured by insertion of thermo couplers. This procedure is insufficient since it leaves the producer with a large degree of uncertainty; only a few products are checked and a very tiny volume of the checked products is actually measured. Due to these limitations, current practise is to over-cook much of the food to ensure that everything has reached the critical core temperature. This might reduce quality of the end product and also requires overspending of energy. In the food industry there is a need for non-contact on-line temperature measurements for improved control of the cooking process. The ideal system should be able to log the temperature in the entire production volume.The method presented in this article can allow complete monitoring of the heat treated products. In this way the producer could have full control of the heating process and be sure that sufficient core temperature is reached in all product units. Such a system can also be used to control the temperature to a certain target that ensures safe products of high quality.     

UV-C irradiation as an alternative disinfection technique: Study of its effect on polyphenols and antioxidant activity of apple juice

Ultraviolet (UV-C) irradiation is a non-thermal disinfection method, effective against a range of bacteria and viruses, which is being considered as an alternative to pasteurization of fruit juices. The objective of this study was to investigate the effect of UV-C irradiation on the polyphenolic content and in-vitro total antioxidant activity of apple juice. UV irradiation doses ranging from 0 to 240 mJ·cm^− 2 were delivered to apple juice and polyphenols, sugars, in-vitro total antioxidant activity and total phenols were profiled. The results demonstrated that UV-C irradiation in apple juices at relevant commercial disinfection doses induced significant reduction in the concentrations of chlorogenic acid, phloridzin, and epicatechin (p < 0.05). The induced changes were relatively minor for the above mentioned polyphenols, except phloridzin (50% reduction) at 240 mJ·cm^− 2. Epicatechin concentrations were reduced significantly (p < 0.05), whereas increase in catechin concentration was observed with increase in UV-C exposure to 240 mJ·cm^− 2. There was a minor reduction in sugar (glucose and fructose) concentrations with increasing exposure levels from 0 to 40 mJ·cm^− 2 (p > 0.05). In contrast, a slight increase in sugar concentrations as increase in UV-C exposure after 40 mJ·cm^− 2 was observed. These changes were not significantly different from control. Total phenolic content was well retained regardless of the UV-C exposure for apple juice. In-vitro total antioxidant activity changed when UV-C exposure exceeded 40 mJ·cm^− 2, but remained unchanged at the maximum UV-C dose of 240 mJ·cm^− 2. These results suggested that UV-C irradiation could be an effective alternative to conventional thermal processing for production of high quality apple juice.Industrial RelevanceThis research paper provides scientific evidence of the potential for UV-C irradiation to achieve meaningful levels of disinfection while retaining important bioactive compounds (polyphenols) in apple juice. In-vitro antioxidant activity and individual polyphenols were well retained at commercially relevant doses of 40 mJ·cm^− 2. From a nutritional perspective, UV-C irradiation is an attractive food preservation technology and offers opportunities for horticultural and food processing industries to meet the growing demand from consumers for healthier food products. Therefore, UV-C irradiated foods could be sold at a premium price to their thermally-processed counterparts, as they have retained their fresh-like properties. This study would provide technical information relevant for commercialization of UV-C treatment of juices.     

Impact of high pressure processing on total antioxidant activity,phenolic, ascorbic acid,anthocyanin content and colour of strawberry and blackberry purées

The present study was undertaken to assess the effect of high pressure treatments and conventional thermal processing on antioxidant activity, levels of key antioxidant groups (polyphenols, ascorbic acid and anthocyanins) and the colour of strawberry and blackberry purées. Bioactive compounds (cyanidin-3-glycoside, pelargonidin-3-glucoside, ascorbic acid) and antioxidant activity were measured in strawberry and blackberry purées subjected to high pressure treatment (400, 500, 600 MPa/15 min/10–30 °C) and thermal treatments (70 °C/2 min). Samples were assessed immediately after processing. Different pressure treatments did not cause any significant change in ascorbic acid (p > 0.05). In contrast, following thermal processing (P₇₀ ≥ 2 min) ascorbic acid degradation was 21% (p < 0.05) as compared to unprocessed purée. However, no significant changes in anthocyanins were observed between pressure treated and unprocessed purées (p > 0.05), whereas conventional thermal treatments significantly reduced the levels (p < 0.05). In general, antioxidant activities of pressure treated strawberry and blackberry purées were significantly higher (p < 0.05) than in thermally processed samples. Colour changes were minor (ΔE) for pressurised purées but the differences were slightly higher for thermally treated samples. Redness of purées was well retained in high pressure treated samples. Therefore processing strawberry and blackberry by high pressure processing could be an efficient method to preserve these products quality. Hence high pressure processing (HPP) at moderate temperatures may be appropriate to produce nutritious and fresh like purées.Industrial relevanceThis research paper provides scientific evidence of the potential benefits of high pressure processing in comparison to thermal treatments in retaining important bioactive compounds. Antioxidant activity (ARP), ascorbic acid, and anthocyanins after exposure to high pressure treatments (400–600 MPa) were well retained. Our results also show that redness and colour intensity of strawberry and blackberry purées were better preserved by high pressure processing than conventional thermal treatment. From a nutritional perspective, high pressure processing is an attractive food preservation technology and offers opportunities for horticultural and food processing industries to meet the growing demand from consumers for healthier food products. Therefore high pressure processed foods could be sold at a premium than their thermally processed counterparts as they will have retained their fresh-like properties.     

Influence of high isostatic pressure on structural and functional characteristics of potato protein

Potato protein possesses promising nutritional and techno-functional properties, but distinct heat sensitivity. Therefore, the potential of high isostatic pressure as an alternative preservation and modification method was investigated. Pressures of 200, 400 and 600 MPa were applied at isothermal conditions of 20 and 40 °C to dispersions made of potato protein concentrate and isolated patatin for dwell times of 10 min. Process induced changes in solubility, foaming properties and selected structural characteristics were compared to results of pure thermal treatments from 20 to 80 °C. Potato protein solubility in neutral solutions made of concentrate was reduced to 21% after heating to 70 and 80 °C whereas it only decreased to 74% after pressurization at 600 MPa. Processing of isolated patatin at pH 6 and pH adjustment from 7 to 6 after processing reduced protein solubility to 12% for heat treatments and to 55 and 89%, respectively, for pressure treatments indicating different denaturation or aggregation mechanisms. Hydrogen bonds and hydrophobic interactions were involved in pressure induced aggregation, whereas aggregates formed during heat treatments were primarily stabilized by hydrophobic interactions. The surface hydrophobicity of soluble protein increased by factor 2.5 to 4.5 after heat treatments and by factor 1.3 at maximum after pressure treatments. High pressure processing provides therefore a good alternative to conventional heat pasteurization as initial potato protein quality may be preserved to a higher extent. Foam stability was increased to 177% by pressure treatments, but this modification was not long-term stable. Applying high pressure with the aim of a functional modification therefore requires further investigations.     

Antioxidant capacity,phenolic composition and microbial stability of aronia juice subjected to high hydrostatic pressure processing

The aim of this study was to characterize the effect of high hydrostatic pressure (200–600 MPa/15 min) and storage (4 °C/80 days) on aronia juice quality. The total antioxidant capacity, phenolic content and composition were assessed using an updated analytical strategy. Microbial growth was also analyzed following juice storage. Among all the analyzed juices, the untreated aronia juice had the greatest reduction (36%) in total polyphenols over the entire storage period. At the end of the storage period, the pressurized juices demonstrated ABTS and FRAP values higher by 14% and 5% as compared to the untreated juices. The main antioxidants identified in the aronia juice were: chlorogenic acid; neochlorogenic acid; cyanidin 3-galactoside; cyanidin 3-xyloside; cyanidin 3-arabinoside; cyanidin 3-glucoside. Cyanidin 3-glucoside was the most stable compound during juice storage. Microorganism growth in juices pressurized at 400–600 MPa was below the detection limit (< 1 CFU mL^− 1) upon storage.Industrial relevanceAronia berries are rarely consumed fresh since they give off several negative sensory attributes. Multiple health-promoting properties of aronia berries make them a valuable raw material for juice production. However, processing involves pasteurization or hot-filling strongly diminishes the product quality due to the changes in quantity and quality of thermolabile phytochemicals. The objective of this work was to characterize the effect of high hydrostatic pressure on the antioxidant capacity, polyphenol content and composition and microbial stability of aronia juice. Results of this study may be useful for the juice industry commercialize this technology for the development healthy, nonclarified aronia juices with desired level of quality.     

Numerical modelling of the food freezing process in a quasi-hydrofluidisation system

The paper presents a study of food freezing using hydrofluidisation method, characterised by very high heat transfer coefficients exceeding 2500 W · m⁻² K⁻¹, which constitutes a novel and promising technology. A numerical analysis of a system with a stationary group of food products was performed. This study aimed to investigate the geometrical parameters governing the freezing process, i.e., the position of food products above the orifices (from 50 mm to 70 mm), their mutual position, the diameter of orifices (3 mm or 5 mm), and the spacing of the orifices in an array (from 8 mm to 12 mm). In this method, the freezing time was from 3 min for 10 mm spherical food sample in moderate refrigerating medium temperatures up to 12 min for 30 mm spherical sample. Moreover, the freezing times at different liquid temperatures were compared in the range of −20 °C to −5 °C. Reducing the temperature by 5 K may lead to shortening the process by up to 50%. The hydrofluidisation method was assessed versus the immersion freezing for spherical products of different sizes showing the reduction of the process time from about 35% to over 60%.     

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.     

Thermal and dielectric properties of shucked oysters

Thermal conductivity, thermal diffusivity and specific heat were measured for shucked oysters. Thermal conductivity increased from 0.577 to 0.677 W/m °C as temperature increased from 0 to 50 °C measured by a line heat source thermal conductivity probe. Specific heat was measured using a differential scanning calorimeter. It increased from 3.795 to 4.047 kJ/kg °C when temperature was raised from 10 to 50 °C. Thermal diffusivity of oysters was calculated from thermal conductivity, specific heat and density values. Dielectric properties of oysters were determined by an open-ended coaxial cable connected to a network analyser between 300 MHz and 3 GHz. At microwave frequencies of 915 and 2450 MHz, it was observed that the dielectric constant decreased (64.02–50.89 at 915 MHz and 59.10–47.67 at 2450 MHz), while the loss factor increased (13.84–20.14) at 915 MHz as temperature increased from 1 to 55 °C. Models were developed to describe the temperature effects on thermal and dielectric properties of shucked oysters.     

Comparative study on cloudy apple juice qualities from apple slices treated by high pressure carbon dioxide and mild heat

Qualities of cloudy apple juices from apple slices treated by high pressure carbon dioxide (HPCD) and mild heat (MH) were evaluated. Temperatures were from 25 to 65 °C, time 20 min, and pressure 20 MPa. Polyphenol oxidase (PPO) was completely inactivated by HPCD and its minimal residual activity (RA) by MH at 65 °C was 38.6%. RA of pectin methylesterase (PME) with HPCD was significantly lower than MH and its minimum was 18%. L value of cloudy apple juice from HPCD-treated apple slices was significantly greater than that from MH-treated apple slices, however, b value, browning degree (BD) and turbidity were lower. And no differences in a value, total soluble solids, pH and conductivity were observed. After 7-day storage at 4 °C, HPCD caused no BD alteration but a significant turbidity loss. MH increased BD at 55 and 65 °C, and led to turbidity loss from 35 to 65 °C. The turbidity was not well related to RA of PME.Industrial relevanceCloudy apple juice is one of the popular fruit juices, and it requires strict processing treatment conditions to protect its quality, especially to prevent enzymatic browning and cloud loss. HPCD is one promising novel non-thermal technique and is likely to replace or partially substitute thermal processes. This study analyzed the effect of HPCD as a pretreatment means on qualities of cloudy apple juice, including inactivating enzymes which are crucial to quality control. Available data provided in this study will benefit the fruit juice industry.     

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.