Gelation of kappa carrageenan as studied by electron spin resonance spectroscopy

Experiments have been carried out to study the thermally induced gelation of kappa carrageenan using electron spin resonance spectroscopy (ESR). Nitroxide spin probe experiments have suggested that the gel is comprised of aggregated polymer chains and that it contains large pockets of mobile solvent. The spin labelling technique used to monitor the molecular motion of the polymer chains themselves has indicated that the gel exists as a two-phase system containing precipitated aggregates dispersed within a homogeneous solution of dissolved molecules. The proportion of molecules in each phase has been calculated by computer analysis of the ESR spectra. Further evidence for the existence of a two-phase system was gained by centrifuging the gel. The supernatant removed was found to contain about 28% of the total carrageenan and intrinsic viscosity measurements showed that it consisted of molecules with a lower average mol. mass than the original starting material. Analysis showed that chemical fractionation had also occurred on gelation.     

Mechanism of initiation of oxidation in mayonnaise enriched with fish oil as studied by electron spin resonance spectroscopy

 Electron spin resonance spectroscopy (spin trapping technique) has been used to identify the most important single factor for initiation of lipid oxidation in mayonnaise enriched with fish oil. Low pH increases the formation of radicals during incubation under mildly accelerated conditions at 37  °C as quantified using 12-doxylstearic acid. Sugar, NaCl and potassium sorbate have no effect on radical formation while EDTA (down to 50 μg/g) has an antioxidative effect. Iron bound to phosvitin in egg yolk, inactive at pH∼6, is considered to be exposed to the solvent (the aqueous phase) at low pH and capable of initiating peroxide cleavage reactions when not protected by EDTA in a mixed complex. Received: 11 February 2000     

电子自旋共振波谱法评价花生油氧化稳定性的可行性研究

为探究花生油加速氧化过程中的自由基链式反应,利用电子自旋共振波谱法（ESR）研究花生油的加速氧化过程,结果发现加速氧化过程中产生大量的烷基自由基（R·）以及少量的烷氧基（RO·）和过氧化自由基（ROO·）。对ESR法与Rancimat法（经典油脂氧化稳定性测定方法）进行比较研究,分别利用这两种方法测定添加不同抗氧化剂花生油的氧化稳定性,发现ESR法的滞后时间（Lagtime）和Rancimat法的诱导时间（IP）结果一致,即加入0.02%TBHQ和0.01%柠檬酸（CA）的花生油中自由基生成量最少,滞后时间最长,且诱导时间最长。此外,滞后时间与诱导时间之间具有良好的线性关系,回归方程为[Lagtime]=79.724[IP]-165.630（R2=0.9688）。综上所述,ESR法可预测Rancimat法的结果,也可作为一种评价花生油氧化稳定性的方法。      

Activity and thermal stability of antioxidants by differential scanning calorimetry and electron spin resonance spectroscopy

Heat flux differential scanning calorimetry (DSC) and electron spin resonance spectroscopy (ESR) were used to assess the activity and the thermal stability of antioxidants in four vegetable oils. Sunflower oil (SO) and high oleic sunflower oil (HOSO), both rich in diunsaturated fatty acids (FA), low trans oil (LT) and partially hydrogenated palm oil (PHPO), both containing monounsaturated FA, were analyzed by isothermal heat flux DSC, with or without 300 mg/kg of antioxidant: ascorbyl palmitate (AP), α-tocopherol (αT), δ-tocopherol (δT) and propyl gallate (PG). DSC experiments showed that δT is the most effective antioxidant for SO and PG for the less unsaturated oils. SO and PHPO were also analyzed by ESR at 120 and 145 °C, respectively. ESR results confirm the strongest antioxidant activity of δT and PG for SO and PHPO, respectively. Therefore, the present study demonstrates that DSC and ESR are valuable technologies to study activity and stability of antioxidants at high temperature. Moreover, experiments performed in the presence of the spin-trap N-tert-butyl-α-phenylnitrone (PBN), suggest that δT delay lipid oxidation through a different reaction mechanism when compared to αT. A different mechanism between tocopherols isomers in delaying lipid oxidation has been hypotized.     

Potential use of electron spin resonance spectroscopy for evaluating the oxidative status of potato flakes

During storage for up to 52 weeks, under mildly accelerated conditions (22 °C, atmospheric air), potato flakes (1% lipid, dried to a_w=0.4) were found to undergo oxidative changes as indicated by a slight decrease in headspace oxygen. The headspace concentration of hydrocarbons (ethane and pentane) steadily increased during storage, and the increase was reduced with added antioxidants. For a product without added antioxidants, three short-chain aldehydes increased slightly, but other secondary oxidation products did not change significantly (including thiobarbituric acid reactive substances). Long chain aldehydes (identified by GC–MS) were abundant in fresh products, but decreased during storage. The level of free radicals, as a marker of early events in oxidation and measured directly by electron spin resonance spectroscopy (ESR), increased significantly during the first 2 weeks of storage, followed by a marked decrease for the period of 2–22 weeks of storage to reach a steady state level. Throughout the period of storage, ESR spectrometry was able to rank products protected by natural antioxidant extracts according to increasing level of free radicals: Unprotected>Coffee>Green tea, Grape skin>Rosemary. Hydrocarbons evolved according to a similar pattern and it can be concluded that ESR spectrometry provides a method for detecting early stages of oxidation in this type of low fat dried products.     

Analysis of irradiated jujube (Zizyphus jujuba) by photostimulated luminescence and electron spin resonance spectroscopy

Possibility of photostimulated luminescence (PSL) and electron spin resonance (ESR) to detect γ-irradiation of jujube (Zizyphus jujuba) was investigated. The jujube samples were exposed to γ-irradiation at doses of 1, 3, 5, and 10 kGy. The PSL results showed that jujube exposed to at 1 kGy or more had a photon count of greater than 5,000 count/60 sec (positive), while the non-irradiated jujube yielded a photon count of less than 700 photon count/60 sec (negative). However, physical parameters (light exposure, storage, and thermal treatment) of irradiated jujube samples gave a strong effect on the PSL signal, resulting in decrease of the photon counts from the initial counts. ESR spectroscopy analysis of irradiated jujube revealed specific signals derived from cellulose radicals, and irradiation caused a significant increase in the ESR signal intensity of the jujube samples without any changes in the spectral patterns. Light exposure, storage, and thermal treatment of jujube resulted in significant decreases in the ESR signal intensities of cellulose radicals.     

Rosemary as antioxidant in pressure processed chicken during subsequent cooking as evaluated by electron spin resonance spectroscopy

The potential of rosemary (Rosmarinus officinalis L.) to inhibiting lipid oxidation in minced chicken breast and thigh muscle processed at 600 MPa for 10 min during subsequent heat treatment was investigated using electron spin resonance (ESR) spectroscopy and electrochemical detection of oxygen consumption. Chicken breast cooked at 95 °C was found to have significantly higher rate of formation of free radicals and oxygen consumption rate than the samples cooked at 70 °C and 120 °C and this intermediate cooking temperature was used to evaluate the effect of pressure on oxidation during subsequent cooking. Rosemary was found effective in retarding lipid oxidation since the pressurized, minced chicken breast and thigh with rosemary added showed lower rate of oxygen consumption and lower tendency of free radical formation following heat treatment than the samples without rosemary. Pressurized chicken thigh showed a higher susceptibility to oxidation than chicken breast upon subsequent heat treatment. Oxidation in pressurized and subsequently heat-treated chicken breast was from a higher tendency of radical formation concluded to be in an earlier phase of oxidation compared to thigh subjected to the same treatment.Industrial relevanceHigh-pressure processing has a great potential for microbial control of raw chicken meat as a “fresh” chill-stored, convenience product for wok cooking. While raw chicken meat is oxidatively stable, high-pressure treatment at 600 MPa and above induces lipid oxidation resulting in off-flavors during subsequent cooking. Addition of 0.1% dried rosemary to minced chicken thighs or breasts prior to high-pressure processing inhibit lipid oxidation during subsequent cooking and could form the basis for product development.     

电子自旋共振技术分析植物油氧化

采用电子自旋共振（ESR）从微观角度分析了棕榈油、菜籽油、葵花籽油、亚麻籽油4种植物油在120、150、180 ℃加热氧化时的自由基变化,并对自由基信号强度与过氧化值的相关性进行了研究。结果表明：同一温度下加热0～36 h,自由基信号强度随着加热时间的延长而增加,表明氧化程度与自由基加合物的量成正相关;同时,自由基信号强度与过氧化值的相关性较强（P<0.05）。ESR方法可表征植物油的热氧化程度。     

啤酒中自由基的ESR研究

利用自旋捕集技术，采用电子自旋共振（ESR）仪研究了啤酒经保温产生自由基以及啤酒清除二苯代苦昧酰肼自由基（DPPH）的过程，结果表明：啤酒具有产生和清除自由基的双重性质，探讨了啤酒酿造及贮存过程中易于形成自由基和发生自由基链反应的工艺阶段，以及清除自由基的物质及来源。     

Identification of irradiated meat using electron spin resonance spectroscopy: results of blind trials

Two blind trials on bone‐in meat chunks are reported. In total 30 or 35 coded samples were analysed for irradiation treatment using electron spin resonance (ESR) spectroscopy. In the first trial 30 samples were received from other research institutes. All samples were qualitatively identified correctly. The second trial consisted of 35 samples. They were either left unirradiated or had been irradiated at doses of 1, 2.5 or 4 kGy. All samples were qualitatively identified on the basis of the ESR spectra. Using re‐irradiation, the doses received by the samples were determined with linear, quadratic or exponential equations. The quadratic or exponential equations gave more successful estimates of the irradiation dose whereas linear fit equations tended to overestimate the dose.     

Structural changes of myoglobin in pressure-treated pork meat probed by resonance Raman spectroscopy

Pork meat was pressurised at 600–700 MPa under conditions applicable for non-thermal food preservation and studied by resonance Raman spectroscopy with 413-nm excitation to probe selectively myoglobin, which is the origin of the red colour of meat. The spectra of intact, non-pressurised meat tissue exclusively display the resonance Raman bands of the ferrous deoxy-form of myoglobin whereas upon pressure treatment a new six-coordinated low spin ferrous species is formed (>60%), that is assigned to a bis–histidine complex including the distal histidine 64. This structural change is associated with a shift of the electronic transitions of the haeme and thus affects the colour of the meat. In contrast, solutions containing myoglobin extracted from pressurised and non-pressurised pork meat give rise to resonance Raman spectra characteristic of the ferrous oxy-form of myoglobin, evidently due to the accessibility of the proteins for oxygen in solution. Upon pressure treatment of the extracted myoglobin solution, the oxy-form is partially converted to the met-(like) ferric form implying a pressure-induced oxidation of the haeme. Thus, this structural transition does not only cause a colour change but also may initiate unwanted oxidative side reactions involving further components of meat. Evidently, such effects can be largely avoided when the oxy- to deoxy-myoglobin ratio is kept small prior to pressure treatment.     

Redox processes in pressurised smoked salmon studied by resonance Raman spectroscopy

Non-thermal food preservation technology is based on the application of high pressures up to 600 MPa. Here we report a resonance Raman (RR) spectroscopic analysis of smoked salmon meat after high pressure processing. High quality spectra, which can be obtained even from packed salmon without spectral interference of the packing foil, allow determining pressure-dependent irreversible changes of the main RR-active components of salmon meat, astaxanthin and myoglobin/haemoglobin. High pressure-treatment causes a decrease of the relative RR intensities of astaxanthin as probed with 514 nm excitation which is in line with a slight attenuation of the originally intense red colour of the salmon meat. 413-nm excited RR spectra indicate a heterogeneous broadening of astaxanthin bands accompanied by the formation of deoxy-myoglobin or deoxy-haemoglobin. The results suggest that pressure-treatment facilitates the oxidative degradation of astaxanthin coupled to the reduction of metmyoglobin (methaemoglobin).     

Antioxidant activity of enzymatic extracts from the brown seaweed Undaria pinnatifida by electron spin resonance spectroscopy

Enzyme assisted extraction of Undaria pinnatifida was performed using five proteases (Alcalase, Flavourzyme, Neutrase, Trypsin and Protamex) and six carbohydrases (AMG, Dextrozyme, Maltogenase, Promozyme, Viscozyme and Celluclast) in order to acquire extracts rich in antioxidants. Antioxidant activity of the extracts was investigated using electron spin resonance (ESR) spectroscopy on 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydroxyl and superoxide radicals. Extracts exhibited strong radical scavenging activity on DPPH and hydroxyl radical, and activity increased with increasing extract concentration. In contrast to DPPH and hydroxyl radical scavenging activity, extracts showed weak scavenging activity on superoxide radical. Extracts exhibited weak radical scavenging activity compared to vitamin C as a reference compound. However, they are still a good source of antioxidant materials that are safe for consumption and show water-soluble properties.     

Detection of gamma irradiated fig seeds by analysing electron spin resonance

Seeds of fig produced in Turkey were studied by electron spin resonance (ESR) technique for detection purposes. Unirradiated fig seeds (control) exhibited a weak ESR singlet at g = 2.0052 ± 0.0003 (native signal). Irradiation induced at least one additional intense singlet overlapping to the control signal and caused a significant increase in signal intensity without any changes in spectral patterns. Variation of ESR signal intensity of irradiated samples at room temperature with time in a long-term showed that free radicals responsible from the ESR spectrum of fig seeds were not stable but detectable after 80 days. Annealing studies at five different temperatures were used to determine the kinetic behaviour and activation energy of the radiation-induced radicals in fig seeds. A study on microwave saturation characteristics and thermal behaviour of the ESR singlet (g = 2.0052) in irradiated and unirradiated fig seed samples was also carried out by using ESR technique. These preliminary results indicate that microwave saturation characteristics of the ESR signal at room and low temperatures may be useful method to distinguish irradiated fig seeds from unirradiated ones.     

Texture changes in frozen cod mince measured by low-field nuclear magnetic resonance spectroscopy

Studies were carried out on changes in water proton relaxation, Instron parameters, dimethylamine (DMA) content and sensory texture scores during storage of cod mince at -10°C, -20°C and -70°C. The longest transverse proton relaxation time measured by pulsed low-resolution nuclear magnetic resonance (NMR) spectroscopy increased with temperature and duration of frozen storage. These variations in the NMR parameter paralleled changes observed with analytical methods commonly used for evaluating fish texture, ie Instron measurements, as well as dimethylamine and sensory analyses. It is concluded that the NMR method can be an alternative tool to study textural modifications of cod during frozen storage. © 1997 SCI.     

Induction of a lag phase by chiller temperatures in Escherichia coli growing in broth or on pork

When log phase cultures of Escherichia coli in brain–heart infusion (BHI) were cooled from 12°C to temperatures below 7°C (the minimum required for growth), the optical densities of cultures increased at declining rates for up to 6 days during incubation at temperatures between 6 and 3°C inclusive, but did not increase at temperatures ≤2°C. However, the numbers of E. coli recovered from cultures on selective or non-selective agars were similar at all times of incubation up to 8 days at temperatures below the minimum for growth. From optical density measurements it appeared that when log phase cultures were cooled to 2°C, then returned to 15°C, a lag developed with time at 2°C to reach a maximum of about 1 h after about 4 h. When cultures were returned to 12°C after times at 2°C between 0·5 and 8 days, the time during which optical densities did not increase was constant at about 2 h, but the initial rate of optical density increase declined with time at 2°C. On pork fat tissue the lag time, determined by increases in the numbers of E. coli cfu on tissues inoculated with cells returned from incubation at 2°C for 16 h to a growth permitting temperature between 7 and 30°C, was longer than the lag time determined from optical density measurements of broth cultures subjected to the same temperature regime. Lag times for E. coli adapted to and growing on normal pH pork lean tissue were longer than for E. coli on fat tissue, while unadapted E. coli did not initiate growth on lean tissue, after incubation at 2°C, at 12°C or lower temperatures. The observations indicate that lag phase development in log phase E. coli subjected to chiller temperatures is complex, and that prediction of lag resolution in log phase cells exposed to temperatures that fluctuate around the minimum for growth will require modeling of lag induction as well as lag resolution.     

Studies in vivo by electron spin resonance of free radical mechanisms implicated in UV-induced skin photocarcinogenesis

Solar ultraviolet radiation (UVR) is implicated in many types of skin damage, such as photodermatoses, photoageing, erythema, pigmentation, skin cancer etc. Free radicals and reactive oxygen species are considered to play an important role in cutaneous photocarcinogenesis. But skin is endowed with photoprotective agents, namely melanins and antioxidant enzymatic and non-enzymatic mechanisms. In this study we describe the in vivo electron spin resonance (ESR) signals of melanins after UVR exposure, using skin specimens of various types of mice, which were taken from different parts of their bodies. The ESR signals were used as a model for testing the antioxidant properties of butylated hydroxyanisole, tocopherol acetate, and octyl p -methoxycinnamate with butyl methoxy dibenzoyl methane and superoxide dismutase (SOD). Additional UVB radiation was applied to the skin samples in situ (in the cavity of the ESR spectrometer). Suppression of ESR signals of melanins was observed in all cases.
Etudes in vivo par resonance paramagnetique electronique, après exposition au rayonnement UV, des méchanismes radicalans impliqués a la photocarcinogénèse cutanée     

基于低场核磁共振技术分析冷冻和冷却猪肉乳化香肠的品质差异

本文主要研究以冷却猪肉和冷冻猪肉加工乳化香肠后色差、蒸煮损失、质构等品质的差异,并采用低场核磁共振技术,分析冷却猪肉和冷冻猪肉香肠中水分分布和水分迁移的特征,得到冷却猪肉和冷冻猪肉两种原料来源对香肠保水性的影响。与冷冻猪肉香肠相比,冷却猪肉香肠有较高的L*值、硬度、弹性、内聚性和咀嚼性等,有较低的a*值、b*值和蒸煮损失。低场核磁共振结果表明:冷却猪肉香肠中T22弛豫时间较短,T21的峰比例增加,而T22的峰比例降低,说明可移动水的比例增加。综上,使用冷却猪肉加工乳化香肠能够提高保水性和产品品质。      

Identification and stability study of irradiated chicken,pork, beef,lamb, fish and mollusk shells by electron paramagnetic resonance (EPR) spectroscopy

The application of electron paramagnetic resonance (EPR) spectroscopy to the detection of irradiation treatment of bones of chicken, pork, beef, lamb, fish and mollusk shells was described. Induced radicals in irradiated samples gave distinguishable EPR patterns for differentiation from the unirradiated samples. The EPR signals were found to be relatively stable in mammalian bones and mollusk shells; but significant loss was observed in fish samples. Dose–response relationships of the samples were found to be linear at 0–5 kGy range (r ²>0.95). Using calibration curve method, the irradiation status of all the 64 blind samples (14 unirradiated and 50 irradiated) was correctly identified. The estimation of irradiation doses was satisfactory with mean values ranging from 86 to 116% of those of the nominal values, and precision (%RSD) ranged from 15 to 29%. The validated analytical procedure was applied in the surveillance monitoring of about 400 food samples during the period of 2001–2004.