Processing of cauliflower by ohmic heating: influence of precooking on firmness

The feasibility of processing cauliflower by ohmic heating was investigated. Firstly, cauliflower florets were precooked in tap water at low temperatures (40–70 °C) for 0 to 60 min. A control sample was cooked at 95 °C for 5 min. No significant textural differences were found between samples treated at 40 or 50 °C and fresh samples, but the firmness of samples cooked above 60 °C decreased. The effect of precooking time was not found to be significant. Secondly, low temperature precooking was performed in salted water for 30 min and followed by ohmic heating (holding time 30 s at 135 °C). After ohmic heating, florets pretreated at low temperatures were firmer than control samples. The firmness of florets precooked at 40 °C or 50 °C was considerably increased (>300%) compared to those precooked at 95 °C. Low-temperature precooking increased the firmness of cauliflower subjected to ohmic heating. The experimental results show that ohmic heating combined with low-temperature precooking in saline solutions offers a viable solution to high temperature/short time sterilisation of cauliflower florets. © 1999 Society of Chemical Industry     

Effects of ohmic heating for pre-cooking of meatballs on some quality and safety attributes

Effectiveness of ohmic treatment on some quality attributes of semi-cooked meatballs was studied. Meatball samples were semi-cooked by 15.26 V/cm voltage gradient and 0 s holding time at 75 °C. Although ohmic cooking significantly reduced the numbers of total mesophilic aerobic bacteria, mould-yeast, Staphylococcus aureus and completely eliminated Salmonella spp. from meatball samples (p < 0.05), it was not found efficient to inactivate all Listeria monocytogenes cells. Ohmic semi-cooking process was resulted at higher cooking yields, which were supported by high fat and moisture retention values in meatball samples. Metal levels (iron, chromium, nickel and manganese) of ohmically semi-cooked meatball samples were found below the upper level of dietary exposure levels. Ohmic cooking procedure was found to be safe in terms of PAH formation and mutagenic activity. Sensory evaluation showed that the overall acceptance of the semi-cooked meatball samples were good. These results demonstrate considerable potential for the application of ohmic process for semi-cooking of meatballs.     

Effects of infrared radiation heating on peeling performance and quality attributes of clingstone peaches

Salinity and wastewater disposal problems associated with the conventional wet-lye method for peeling clingstone peaches result in considerable negative environment impacts. The efficacy of using infrared (IR) heating as an alternative method for peach peel removal was investigated to eliminate the use of water and chemicals. Peaches sorted into three size categories were double-sided heated under IR with three emitter gaps for a range of heating times from 90 s to 180 s. Wet-lye peeling was used as a control. Results showed that 180 s IR heating for medium sized peaches under an emitter gap of 90 mm yielded 84 mm²/100 mm² peelability and 90 g/100 g peeling yield, produced peeled products with comparable firmness and color to wet-lye peeled peaches. Surface temperature increased rapidly (> 00 °C) during IR heating whereas the flesh temperature at 16 mm beneath skin remained relatively low (<45 °C). Thermal expansion of cell walls and collapse of cellular layers adjacent to skins were found in IR heated peaches and differed from the micro-structural changes observed in lye heated samples, indicating their mechanistic difference. Promoting uniform and rapid surface heating is essential to further develop IR heating as a non-chemical method for peach peeling.     

Chilling pig carcasses: Effects on temperature, weight loss and ultimate meat quality

Effects of conventional (4°C, air velocity 0·5 m/s) and forced chilling at -5°C (120 min) or -30°C (30 min) with air velocities of 1, 2 or 4 m/s, followed by conventional chilling till 24 h post mortem on temperatures, meat quality and weight losses, were studied. Experiments were carried out in six batches of six slaughter pigs each (crossbred gilts, weighing 105-110 kg. The subcutaneous temperature decreased very rapidly to values below 0°C when 'ultra' rapid chilling (-30°C) at high air velocities (4 m/s was used. Immediately after rapid chilling, when the carcasses were railed into a conventional chiller, the subcutaneous temperature increased above the air temperature, after which the decline in temperature was continued. Temperature inside the biceps femoris muscle decreased from the start of chilling rather slowly according to an asymptotic curve until ultimate values of 4°C were reached. Theoretically calculated temperatures during slaughter and chilling were comparable with the measured values; indicating that a finite-element calculation method in combination with a cylindrical model for heat transport can be used to predict muscle temperatures for various chilling regimes. Losses in carcass weight, 24 h after conventional and forced chilling at -5°C, were about 2%. After 'ultra' rapid chilling (-30°C) the losses were reduced to 1·3% when air velocity was increased to 4 m/s. Meat quality of the longissimus lumborum muscle was not significantly affected by the various chilling regimes except for the variables related to tenderness. The Warner-Bratzler shear forces were higher (P < 0·05) together with shorter sarcomere lengths (P < 0·10) after 'ultra' rapid chilling at a high (4 m/s) air velocity, indicating an increased risk of cold shortening.     

无包装条件下大白菜失水与硬度的研究

主要研究在不同湿、温度环境下无包装大白菜失水与硬度的变化规律。研究表明,虽然相对湿度的提高有利于大白菜重量的保持,但55％RH的失重率高于35％RH;随处理时间延长,在35％RH、55％RH条件下,30℃明显加剧大白菜的重量损失,而在75％RH、95％RH下,15℃则有利于大白菜重量的保持;在35％RH、55％RH、75％RH、95％RH下,仅15℃在3h、6h、12h、12h时间段内较好的保持了大白菜的硬度。     

Effects of ohmic heating on technological properties of whole egg

The aim of this work was to study the effects of different ohmic heating conditions on color, rheology, foaming, and gelling properties of whole egg. Industrial products treated by conventional heat pasteurization and the corresponding raw materials were also evaluated. Ohmic treatments accomplished in a static cell (65.5 °C × 3 min, 70 °C × 1 min, and 67 °C × 4.5 min) increased whole egg apparent viscosity (up to 190%), but also foam overrun (up to 28%) and gel hardness (up to 15%). The performance improvement was confirmed by treatments carried out in a continuous pilot plant (71 °C × 0.6 min, 68 °C × 1.4 min) and the products resulted stable during storage at 4 °C for 30 days. In conclusion, this study demonstrated that ohmic heating is a suitable alternative to conventional pasteurization. Low temperature treatments are preferable to avoid possible rheological issues due to protein denaturation.Industrial relevanceWhole egg is a protein ingredient with multiple technological properties, used in many foods. Due to safety reasons, food manufacturers often use pasteurized liquid egg products, microbiologically safer and easier to handle with respect to shell eggs. In order to satisfy the required sanitary levels for liquid egg products, thermal pasteurization treatments are needed. However, since egg proteins are very sensitive to high temperatures, attention must be paid to avoid coagulation entailing deleterious effects against egg quality. In this study, different ohmic heating treatments were evaluated as milder alternatives to conventional pasteurization. The lab- and pilot-scale experiments and the subsequent statistical analyses of the obtained results contributed to assess the effects of the different ohmic treatments on technological features (e.g. color, rheology, foaming, and gelling properties) of liquid whole egg. This study demonstrated that ohmic heating is a suitable technology for whole egg treatment, paving the way for new opportunities in order to produce safe food ingredients with improved technological functionalities.     

通电加热条件对豆浆中脂肪氧化酶活性的影响

采用通电加热和传统(油浴)加热两种方式处理豆浆样品,研究通电加热过程中电源电压、电源频率和保温时间对豆浆中脂肪氧化酶活性的影响。结果表明:采用的电源电压越高,通电加热处理后的豆浆中脂肪氧化酶活性越高;较高的电源频率对脂肪氧化酶的钝化具有显著的促进作用,但是当电源频率超过500 Hz后,电源频率的提高对脂肪氧化酶的活性影响较小;延长保温时间会促进脂肪氧化酶的钝化,通电加热过程中电场的存在会促进脂肪氧化酶的钝化。各因素对脂肪氧化酶活性的作用规律,可以对通电加热设备的设计与生产产生积极的指导作用。     

Processing and stabilisation of cauliflower by ohmic heating technology

Cauliflower is a brittle product which does not resist conventional thermal treatments by heat. The feasibility of processing cauliflower by ohmic heating was investigated. Cauliflower florets were sterilised in a 10 kW APV continuous ohmic heating pilot plant with various configurations of pre-treatments and processing conditions. The stability of final products was examined and textural qualities were evaluated by mechanical measurements. Ohmic heating treatments gave a product of attractive appearance, with interesting firmness properties and a high proportion of particles >1 cm. Stabilities at 25 °C and 37 °C were verified, and in one case, the product was even stable at 55 °C. Low temperature pre-cooking of cauliflower, high flow rate and sufficient electrical conductivity of florets seem to be optimal conditions. The interest of using this electrical technology to process brittle products such as ready meals containing cauliflower was highlighted.     

The effect of log heating temperature on the peeling process and veneer quality: beech, birch, and spruce case studies

Heating green-wood prior to peeling is necessary to improve both peeling process and quality of veneer. This study investigates optimum heating temperatures by soaking of beech, birch and spruce. Experiments have studied the influence of heating temperatures from 20 to 80 °C on thickness deviations and veneer lathe checking using a pneumatic rugosimeter and image analysis of opening checks with the SMOF device (Système de Mesure de l’Ouverture des Fissures). Conclusions account for reduced heating temperatures compared to the temperatures currently in-use in the industry. Already at 50 °C, positive effects of heating ensure efficient peeling process. Low temperatures produce veneers with deeper and more spaced checks than high temperatures when checks are closer and less deep, becoming even unpredictable especially in case of spruce. These results establish the SMOF as an essential non-destructive control device to control the quality of the veneer produced at research level.     

High amylose starch thermally processed by ohmic heating: Electrical,thermal, and microstructural characterization

High amylose starch (HAS) exhibits restricted granular swelling, limiting its use in many food applications. In this work, we investigated for the first time the potential of ohmic heating (OH) to enhance the swelling of HAS granules in a very efficient manner in terms of processing times. Specifically, the impact of OH at two voltages (130 and 150 V), two moisture conditions (1:3 and 1:5 w/v), and two final temperatures (160 and 180 °C) on the structural, thermal, pasting, and digestion of HAS (70% amylose, AM) was investigated. The electrical conductivity of native HAS showed a transition at 168 ± 1 °C consistent with the thermal transition at 139–192 °C (DSC) with an enthalpy of 11.39 J/g. Furthermore, OH caused a reduction of resistant starch (RS) from 52.0 to 34.5%, and a significant increase in granular swelling (as represented by the increased initial, maximum, and final viscosities). The above was further corroborated by SEM micrographs, which showed the disruption of the granular structure that aligned with a decrease in the relative crystallinity and shift to a B-type polymorphism. Results showed that the high temperatures reached during ohmic heating result in partial HAS gelatinization and enhanced granular swelling.     

欧姆加热的电参数对杀菌效果的影响

采用欧姆加热杀菌与水浴加热杀菌对比的方法。以豆浆的总菌数为试验菌群,通过改变电源的电压和频率,得出电源的电压和频率与杀菌效果的关系。对比水浴加热杀菌的效果可知:当电压超过60V时,欧姆加热方法的杀菌效果明显好于水浴加热方法的杀菌效果,残菌率随处理电压的增加以指数规律减少;随着频率的增加,欧姆加热的杀菌好,但当频率超过一定值时杀菌效果降低;频率在30～300Hz时其杀菌效果明显优于水浴加热方法的杀菌。     

冷冻猪肉欧姆加热解冻电势梯度与尺寸对解冻效果的影响

欧姆加热解冻是一种潜力很大的解冻方法。试验中研究冻结物料的尺寸、电势梯度对解冻时间、解冻速率、失水率、解冻均匀性和能量利用率的影响。选用尺寸不同的冻猪肉进行了解冻试验,尺寸分别为直径3、4、5 cm,长度为6 cm。解冻时从中心温度-18～5℃。试验过程中,变换解冻材料中的电势梯度,分别为20、30、40V/cm。结果表明:电势梯度和尺寸对解冻均匀性、失水率、能量利用率的影响不大。电势梯度和样品尺寸对解冻时间的影响较明显,电势梯度变大,解冻时间变小,尺寸增大,解冻时间变长。电势梯度和尺寸对解冻速率的影响分为两个阶段。电势梯度和尺寸对内部冻结温度以下的解冻速率影响不明显。在内部冻结温度以上,电势梯度增大,解冻速率变大,解冻加快,样品尺寸变大,解冻速率降低。欧姆加热解冻较传统解冻中的水解冻具有很大的优势。     

Influence of ohmic heating on lentil protein structure and protein-pectin interactions

Proteins are essential for creating structured food systems due to their interactions with other molecules, but their structure is highly affected by temperature. This study aimed to evaluate the effects of different thermal processes (conventional and ohmic heating) on lentil protein structure and its interactions with pectin. The results showed that thermal processes can modify lentil protein structure, with the extent of modifications depending on the treatment temperature, electric field strength, and pH of the protein fraction extraction. Lentil protein extracted at pH 9 was more stable to temperature variation under ohmic heating. When a low electric field strength (5 V/cm) was applied, there was an increase in the hydrophobic surface and accessibility of sulfhydryl groups. In contrast, lentil protein extracted at pH 7 was highly affected by all thermal treatments. Although structural changes were observed in some protein features, no influence was identified regarding lentil protein-pectin interactions. In conclusion, ohmic heating treatment has the potential to modify lentil protein structure, but the outcomes may depend on the extraction method used, which can dictate different structural arrangements of the native protein fraction.Industrial relevanceThe development of plant-based products have increased in the last years and other proteins, instead of soybean and pea, are required to meet new consumers' needs. Lentil protein is a non-soy, gluten free, and plant-based protein that could be an alternative to the plant-based market. These proteins can act as texturizing, emulsifying, foaming, and gelling agents but their suitable performance is dependent on protein structure. Thermal processes are a necessary component of food production, requiring careful control of the conditions involved as heat can drastically modify the structure of proteins, Therefore, in this study, the effects of two thermal processes (conventional and ohmic heating) on lentil protein structure and its interactions with pectin were evaluated. These findings may provide insights for developing more appropriate processes to preserve protein structure during food processing at industry.     

蛋清、蛋黄溶液的通电加热特性研究

研究了温度、蛋清、蛋黄浓度和电压对蛋清溶液和蛋黄溶液的电导率的影响;研究了蛋清、蛋黄浓度和电压对蛋清溶液、蛋黄溶液加热速率的影响。结果表明,蛋清溶液、蛋黄溶液的电导率随温度、蛋清和蛋黄浓度和电压的增高而增大,且电导率与温度呈线性关系;加热速率随蛋清和蛋黄浓度和电压的增高而加快,且温度与时间呈指数关系。     

Effects of high pressure and ohmic heating on shell loosening,thermal and structural properties of shrimp (Pandalus borealis)

This study aimed at understanding the effects of high pressure (HP) and ohmic heating (OH) on the peelability, the underlying mechanisms of HP- and OH-induced shell tightening, the thermal and structural properties of shrimp parts. HP improved the peelability of shrimp at low pressure level (<350 MPa) and short holding time (≤3 min) and the optimum condition for peeling was at 100 MPa for 3 min at 5 °C. However, a higher pressure level (>350 MPa) led to a decrease in the peelability. High pressure at 600 MPa stabilized cuticular and epidermal collagen and formed new collagen-like structures by new linkages, which strengthened the muscle-shell connection and reduced the peelability. Shrimp meat induced from HP at 100 MPa and 600 MPa had minorly denatured myofibrillar proteins. OH as a blanching method did not significantly improve the peelability of shrimp at most of the studied conditions. Some extreme conditions (e.g. at 50 °C) caused a markedly low peelability due to occurrence of collagen gelatinization. The gel formation from collagen-gelatin transformation under heating added strength to adherence of shell to epidermis and muscle, as a consequence, a difficult peeling was experienced. OH also denatured proteins in shrimp meat and caused loss of astaxanthin.Industrial relevance.The industrial processing of ready-to-eat shrimp involves the on-ice or in-brine maturation process which loosens the shrimp's shell from its meat, and therefore enable the mechanical peeling. However, the traditional maturation is time consuming (up to several days), inevitably leads to reduced quality of shrimp meat. This study shows the possibility of the application of HP at mild pressure levels to promote the shell loosening at short HP processing time (≤3 min). However, at more severe HP conditions could lead to the shell tightening which was caused by HP-induced stabilization of collagen in shell and epidermis. The study also shows that ohmic heating (<5 min) might not be a significant blanching method to support the maturation since OH had minor positive effect on shell loosening at some OH conditions (e.g. 2 or 10% NaCl, 92 V, and 30 or 35 °C), but had a counter effect at most OH conditions especially at high temperature.     

Inactivation of pectin Methylesterase and Lactobacillus Plantarum by ohmic heating in pomelo juice

The use of ohmic heating (OH) to inactivate damaging elements in pomelo juice was evaluated. The work investigated the effect of frequencies (50–20 000 Hz) on pectin methylesterase (PME) and Lactobacillus plantarum (L. plantarum) in pomelo juice at 30 V cm⁻¹ of electric field strength. The results show that frequency does not affect PME inactivation (P > 0.05) but affects bacterial reduction and has the most efficiency at 60 Hz, followed by 50 Hz, and in the frequency range at or higher than 500 Hz (P < 0.05). Additionally, the inactivation kinetics of PME and L. plantarum and the impact of nonthermal factors were given. The nonthermal element has contributed to the inactivation enhancement of L. plantarum and PME to reduce the necessary treatment temperature and time. The major spoilage bacteria and enzyme destruction in pomelo juice occurred faster under OH than under conventional heating (CH) suggesting that OH can be effectively used to pasteurise pomelo juice.     

Inactivation kinetics of Agaricus bisporus tyrosinase treated by ohmic heating: Influence of moderate electric field

The tyrosinase is a binuclear copper enzyme that catalyzes the oxidation of phenolics compounds to quinones in presence of molecular oxygen, which subsequently polymerized to dark brown pigments. To evaluate the effect of ohmic heating (OH) on the inactivation kinetics of Agaricus bisporus tyrosinase the independent variables were: electric field strength (25, 30, 35 V/cm), process time (0–15 min) and temperature (50–58 ± 1 °C). The conventional thermal treatment (CT) was used as a control. The results showed that the electric field decreased the time (D-value) required obtaining the same degree of tyrosinase inactivation at a target temperature compared to the CT. This indicates that the electric field acted synergistically with temperature to inactivate tyrosinase. The activation energy (E_a) calculated for the CT was 227.32 kJ mol⁻¹, while for the OH they were 146.52, 135.14 and 124.87 kJ mol⁻¹ for electric field strengths of 25, 30, and 35 V/cm respectively. In this study, a direct relationship between the E_a and the electric field is shown. Results demonstrated that the OH is an effective technology to inactivate tyrosinase, allowing it to be used in thermal process such as pasteurization or blanching.