Evaluation of ascorbic acid and sugar degradation products during fruit dessert processing under conventional or ohmic heating treatment

The effects of conventional heating (C) or ohmic heating (O) treatment on the degradation of sugar and ascorbic acid (AA) were evaluated in chunky fruit desserts prepared with apple puree (Golden Delicious var.) and chunky peach (Panavi var.) pieces. Concentrations of 5-HMF, furfural (F), 3-hydroxy-2-pyrone (3H2P) and 2-furoic acid (FA) were determined to assess the importance of oxidative and/or thermal reactions during processing. Depending on the thermal processing, 5-HMF and F levels in samples ranged from not detected to 3260 and from not detected to 570 μg/100 g FW respectively. Production of 3H2P and FA ranged from 480 to 2670 and from 84 to 420 μg/100 g FW respectively. Results showed that the impact of final heating treatment on the formation of AA degradation products (3H2P and FA) was minor, if any. Thus, AA degradation during apple products processing mainly depended on oxidative reactions pathway. Likewise, ohmic heating processing had very little effect on the formation of 5-HMF and F, in opposite to conventional heating.     

Inactivation kinetics of food enzymes during ohmic heating

Ohmic heating of milk and fruit and vegetable juices was carried out at several incubation temperatures to investigate inactivation of alkaline phosphatase, pectin methylesterase and peroxidase. Mechanisms of inactivation of these enzymes and corresponding kinetic models were verified for each food material, using the multitemperature evaluation of inactivation data. Compared to inactivation by conventional indirect heating, kinetic parameters were changed but inactivation mechanisms remained the same. The kinetic parameter changes were relatively minor for pectin methylesterase and alkaline phosphatase. A significant destabilization of the labile isozyme fraction of peroxidase occurred by the effect of ohmic heating when the greatest decrease of stability was obtained for carrot juice.     

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。     

Modeling the degradation kinetics of ascorbic acid

Most published reports on ascorbic acid (AA) degradation during food storage and heat preservation suggest that it follows first-order kinetics. Deviations from this pattern include Weibullian decay, and exponential drop approaching finite nonzero retention. Almost invariably, the degradation rate constant's temperature-dependence followed the Arrhenius equation, and hence the simpler exponential model too. A formula and freely downloadable interactive Wolfram Demonstration to convert the Arrhenius model's energy of activation, E_a, to the exponential model's c parameter, or vice versa, are provided. The AA's isothermal and non-isothermal degradation can be simulated with freely downloadable interactive Wolfram Demonstrations in which the model's parameters can be entered and modified by moving sliders on the screen. Where the degradation is known a priori to follow first or other fixed order kinetics, one can use the endpoints method, and in principle the successive points method too, to estimate the reaction's kinetic parameters from considerably fewer AA concentration determinations than in the traditional manner. Freeware to do the calculations by either method has been recently made available on the Internet. Once obtained in this way, the kinetic parameters can be used to reconstruct the entire degradation curves and predict those at different temperature profiles, isothermal or dynamic. Comparison of the predicted concentration ratios with experimental ones offers a way to validate or refute the kinetic model and the assumptions on which it is based.     

Temperature dependent electrical conductivities of fruit purees during ohmic heating

Ohmic heating takes its name from Ohm’s law; the food material switched between electrodes has a role of resistance in the circuit. In this study, the apricot and peach purees were heated on a laboratory scale static ohmic heater by applying voltage gradients in the range of 20–70 V/cm. The voltage gradient was statistically significant on the ohmic heating rates for both purees (P < 0.05). The linear temperature dependent electrical conductivity relations were obtained. Bubbling was observed above 60 °C especially at high voltage gradients. The ohmic heating system performance coefficients were in the range of 0.49–1.00. The unsteady-state heat conduction equation for negligible internal resistance was solved with an ohmic heating generation term by the finite difference technique. The predictions of the mathematical model using obtained electrical conductivity equations were found to be very accurate.     

Migration of electrode components during ohmic heating of foods in retort pouches

During space missions, life support technologies must satisfy mission constraints, including maximizing safety and acceptability of food and minimizing crew time, storage volume, power, water usage, and maintenance down-time. Ohmic heating appears to be a feasible potential solution to meet food reheating and waste sterilization requirements; however, it is necessary to verify if electrochemical reactions such as gas generation and electrode corrosion occur. A pulsed ohmic heating system and reusable pouch were tested to ensure the food safety and quality by minimizing the undesired electrochemical reactions. Results of gas generation during ohmic heating show that stainless steel is far superior to aluminum since there were no noticeable gas bubbles even at the temperature of 70 °C. A study of migration of the major key metal ions from stainless steel, such as Fe, Cr, Ni, Mn, and Mo, measured by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) shows that pulsed ohmic heating produced comparable or lower migration of most targeted metal ions, compared to the conventional retorting when electrodes were present. The intakes of individual metal contaminants evaluated with respect to a typical meal (8 oz) after ohmic treatment were, as a maximum, 13.5% of recently published upper-level daily dietary exposure estimates. Consequently, pouches with stainless steel electrodes powered by a pulsed ohmic heater shows promise as a potential reheating and sterilization technology for space missions.Industrial relevanceOhmic heating has been used for many years in different industries and proved to be a promising food processing technology due to its rapid, yet uniform and high energy efficient heating capability. This paper demonstrates the potential of direct ohmic heating for foods in retort pouches at the household level as well as the mass production level, ensuring food safety by suppressing the metal ions migration far less than the dietary exposure estimates.     

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。     

A study on degradation kinetics of ascorbic acid in drumstick (Moringa olifera) leaves during cooking

The kinetics of ascorbic acid degradation in drumstick (Moringa olifera) leaves as well as in pure ascorbic acid solutions at the initial concentrations present in drumstick leaves over a temperature range of 50–120 °C (isothermal temperature process) has been studied. The degradation kinetics of ascorbic acid was also evaluated in normal open‐pan cooking, pressure‐cooking and a newly developed and patented fuel‐efficient eco cooker (non‐isothermal heating process). The ascorbic acid degradation followed first‐order reaction kinetics where the rate constant increased with an increase in the temperature. The temperature dependence of degradation was adequately modelled by the Arrhenius equation. A mathematical model was developed using the isothermal kinetic parameters obtained to predict the losses of ascorbic acid from the time–temperature data of the non‐isothermal heating/processing method. The results obtained indicate the ascorbic acid degradation is of similar order of magnitude in all the methods of cooking. Copyright © 2005 Society of Chemical Industry     

在高温油脂中叶黄素的热降解动力学

应用HPLC法监测叶黄素在高温油脂中的变化,进而了解叶黄素的降解规律,以期为改善油炸食品加工、油脂精炼工艺和开发含叶黄素的功能性食用油提供一定的指导作用。该方法采用C30-HPLC-DAD监测叶黄素分别在130、150、170、190℃大豆油和棕榈油中的保留率变化,计算出相应的动力学参数。结果表明,叶黄素在大豆油和棕榈油中的降解遵循一级反应动力学模型;对任一组来说,温度越高,热处理时间越长,则全反式叶黄素及其顺式异构体在油脂中的浓度越小;在同一温度时,与棕榈油相比,它们在大豆油中的残存量相对较大,但在190℃时,在两种油脂中的降解反应都很剧烈;在同一温度下的同种油脂中,各顺式异构体的降解速率常数大于全反式叶黄素,13-顺式/13’-顺式叶黄素比9-顺式/9’-顺式叶黄素更易降解。      

Goat milk free fatty acid characterization during conventional and ohmic heating pasteurization

The disruption of the milk fat globule membrane can lead to an excessive accumulation of free fatty acids in milk, which is frequently associated with the appearance of rancid flavors. Solid-phase microextraction and gas chromatography techniques have been shown to be useful tools in the quantification of individual free fatty acids in dairy products providing enough sensitivity to detect levels of rancidity in milk. Therefore, the aim of this study was to characterize the short-chain and medium-chain free fatty acid profile in i) raw untreated goat milk; ii) raw goat milk passing through pumps and heating units (plate-and-frame heat exchanger and ohmic heater); and iii) processed goat milk by conventional and ohmic pasteurization to determine the influence of each treatment in the final quality of the milk. Multivariate statistical analysis has shown that the treatments studied were not responsible for the variability found on free fatty acid contents. In particular, it was possible to conclude that ohmic pasteurization at 72°C for 15 s did not promote an extended modification of free fatty acid contents in goat milk when compared with that of conventional pasteurization. Furthermore, principal component analysis showed that the capric acid can be used to discriminate goat's milk with different free fatty acid concentrations. Hierarchical cluster analysis showed evidence of the existence of correlations between contents of short and medium chain free fatty acids in goat milk.     

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.     

Influence of storage temperature and ascorbic acid addition on pomegranate juice

Our recent work shows that in pomegranate juice the destructive effect of ascorbic acid on anthocyanins is not well correlated with changes in the observed colour. However, the addition of vitamin C to this juice has no additional benefit, since ascorbic acid degradation is very rapid and a slightly orange hue results, after a period of storage, in those juices to which ascorbic acid was added. Data are also included on the influence of storage temperature on juice colour stability, indicating that this parameter is more specific for colour alteration and anthocyanin degradation. © 2001 Society of Chemical Industry     

Reducing the formation of glucose degradation products in peritoneal dialysis solutions by ultrahigh temperature ohmic heating

Peritoneal dialysis (PD) is commonly performed by using preprepared dialysis solutions containing glucose, which are thermally treated to achieve commercial sterilization. A series of glucose degradation products (GDPs) are being formed, which react with the tissue during the dialysis procedure, thus baring a negative effect on the patient and the dialysis process. The present study tested the efficacy of ohmic heating as an alternative thermal treatment for continuous sterilization of PD solutions. The process was compared to conventional retort treatment, and GDPs accumulation was measured. Thermal treatments using the ohmic heating system were performed at three temperatures (105, 125, and 150 degrees C) with residence time at each temperature ranging from 0.84 to 12.0 s. The resulting concentrations of glyoxal (GO), methylglyoxal (MGO), and 3-deoxyglucosone (3-DG) in the PD solutions were measured. None of these GDPs were found in PD fluids treated by ohmic heating at 105 degrees C. The concentration of 3-DG, after a standard sterilization treatment (121 degrees C, 20 or 40 min) was one order of magnitude higher (approximately 140 and 242 microM) than after ohmic heating treatment at 125 degrees C. The results of the present study suggest that this technique can be used to produce solutions with much lower content of GDPs. It also demonstrates the advantage of using the ohmic heating technology as a tool for high temperature short time treatment of PD fluids.     

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.     

Apple polyphenoloxidase inactivation during heating in the presence of ascorbic acid and chlorogenic acid

It was recently reported that during osmotic dehydration of ascorbic acid (AA)-treated apple cubes, losses in AA and phenolics could partly arise from enzymatic oxidation, provided polyphenoloxidase (PPO) was still active under the processing conditions. To determine the impact of dehydration temperatures on PPO action, as well as chemical and enzymatic oxidation reactions, apple PPO inactivation alone or with AA (1 mM) and/or chlorogenic acid (CG, 3 mM), as well as AA and CG levels evolution, during heating of the model solutions at 45 and 60 °C were investigated. At pH 3.8, PPO was still functional, keeping 61 and 4% residual activity after 2 h of heating at 45 and 60 °C, respectively. The combined treatment of heating and AA was more effective in reducing PPO activity, while incubation at 60 °C with AA and CG minimised the losses of PPO activity. CG remained stable during heating, even in the presence of AA which, in turn, was more affected by heating. Thus, during heating, provided PPO remained active with enough available O₂ in the model systems, CG oxidation and coupled oxidoreduction with AA could readily develop.     

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.     

The temperature prediction of some botanical beverages,concentrated juices and purees of orange and pineapple during ohmic heating

In this research, 10 kinds of botanical beverages, concentrated juices and purees of orange and pineapple were heated applying a static ohmic heating system. The objectives were (1) to develop the mathematical models for predicting the temperature changes of these samples during ohmic heating and (2) to compare between the qualities of ohmically-heated and conventionally-heated specimens. The results indicated that the mathematical models can precisely predict the temperature variations of the concentrated purees during ohmic heating although the heat losses to the surroundings and evaporated moisture are neglected. However, the temperature estimation of botanical beverages and concentrated juices were more accurate if the heat losses to the surroundings and evaporated moisture were included in the mathematical models. Furthermore, at the same heating rate the ohmic and conventional heating methods resulted in the insignificant difference in the sensorial qualities and remaining vitamin C contents of orange and pineapple juices.