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PubMed1996

Microwave-antigen retrieval: the importance of pH of the retrieval solution for MIB-1 staining.

Using microwaves for microscopy almost invariably implies working at elevated temperatures. In microwave studies it became evident that high temperatures do not inevitably damage the tissues. On the contrary very high temperatures can even be beneficial. The most striking example is the 'heat shock' of formalin-fixed paraffin sections in the microwave oven with temperatures higher than 100 degrees C, revealing otherwise hidden epitopes. These microwave applications have triggered a breakthrough in pathology. The pH of the microwave-retrieval solution is decisive for the staining results, particularly for MiB-1. There is no staining of proliferating cells between pH 3.5 and 5.0. Between pH 5.0 and 6.5 we observed an increase in the number of MiB-1-positive stained nuclei. Our findings indicate that in quantitative work it is of extreme importance to standardise the pH of the retrieval solution and to choose pH 6.5 for optimal results.

Antibodies, Monoclonal↗

PubMed2001

A quick microwave histochemical stain for copper.

A rapid microwave method is described for staining copper in liver. This procedure was compared with a conventional method for copper. To this end, liver sections obtained from patients affected by several liver diseases associated with copper overload, were stained both with the standard rubeanic acid method for copper and with our modification of the same method, incorporating microwave treatment. Liver sections from a normal human newborn were used as a positive control. In Wilson's disease in the cirrhotic stage, copper was detected by the conventional method solely in periportal cells; following the microwave treatment, we were able to demonstrate copper in the whole lobule. In alcoholic cirrhosis, rubeanic acid stained copper only in a few periportal cells, while, by our modified method, copper was detected in almost all periportal hepatocytes. In chronic biliary tract disease, and in the newborn liver, copper was demonstrated in a few periportal cells by both the two histochemical procedures. In conclusion, although copper was detected by both procedures, a different degree of positivity was sometimes observed by using microwaves. Moreover, the microwave-treated sections showed more contrast and less artifacts. From a practical point of view, for the simplicity of employment and, above all, for its quickness (10 min), we suggest the use of our method in all conditions where copper overload is suspected.

Autopsy↗

PubMed1992

Influence of age and body mass on the heating effect of microwave radiation in broilers.

1. A total of 648 broilers was used in a factorial combination of 3 ages x 3 body masses x 4 microwave treatments to examine the possible interaction between bird age and body mass on the heating effect of microwaves. 2. As age or body mass increased, the increase in body temperature following exposure to microwaves decreased curvilinearly. 3. A significant interaction was evident between age and body mass. For the same body mass, microwave radiation exerted a greater heating influence at the younger age. 4. A model for the heating effect of microwaves is presented which takes into account the influence of both bird age and irradiated body mass.

Aging↗

PubMed2001

A comparison of techniques for preparing fish fillet for ICP-AES multielemental analysis and the microwave digestion of whole fish.

Four catfish fillet homogenate treatments before multielemental metal analysis by simultaneous inductively coupled plasma/atomic emission spectroscopy were compared in triplicate. These treatments were: nitric acid wet-ashing by Parr bomb digestion; nitric acid wet-ashing by microwave digestion; tetramethylammonium hydroxide/nitric acid wet digestion; and dry-ashing. The tetramethylammonium hydroxide/nitric acid method was imprecise (coefficients of variation > 20%). The dry-ashing method was fast and sensitive but had low recoveries of 50% for spiked Pb and Al and was not as precise as the Parr bomb or microwave treatments. The Parr bomb method was the most precise method but was less sensitive than the microwave method which had nearly the same precision. The microwave method was then adapted to homogenates of small whole fish < or = 3 cm in length. The whole fish homogenate required more vigorous digestion conditions, and addition of more acid after the evaporative step because of the presence of less oxidizable and acid-soluble components than fillet. The whole fish homogenate was also more heterogeneous than catfish fillet. A quality assurance protocol to demonstrate homogenate uniformity is essential. The use of a non-specialized microwave oven system allowed precise results for fillet and whole fish homogenates.

Animals↗

PubMedDate not supplied

Migration testing with olive oil in a microwave oven.

A study was carried out to compare the overall migration from packaging materials into olive oil during heating in a microwave oven, and the overall migration from the same materials into olive oil but applying time and temperature conditions stipulated in the current EC and Dutch legislation on food packaging. Application of additional test conditions (e.g. 30 min and 1 h in combination with test temperatures exceeding 121 degrees C, and a test temperature of 130 degrees C) have demonstrated the need for extension of the test conditions mentioned in existing food packaging regulations to enable realistic migration testing of microwave packaging materials under conventional test conditions. It is concluded that the overall migration into olive oil from packaging materials intended for microwave oven use, including susceptor materials, can be judged on the basis of migration testing using conventional heating. For testing film or susceptor materials in a microwave oven by one-sided contact, a migration cell transparent to microwaves was developed and used up to 200 degrees C. In conventional high-temperature tests applying hot-filling of trays or migration cells, a temperature drop was observed, while handling oil at temperatures of 150 degrees-175 degrees C may be considered perilous. To prevent problems of this kind it is proposed to start migration tests at room temperature and to heat the simulant rapidly to the final test temperature. This procedure is comparable to migration tests carried out with aqueous food simulants at 121 degrees C in an autoclave.(ABSTRACT TRUNCATED AT 250 WORDS)

Food Contamination↗

PubMedDate not supplied

Temperature measurement during microwave cooking.

Product development of microwavable foods originally suffered from a high degree of non-uniform heating which is generic in microwave heating. Typically, foods have suffered from either overheated edges or under heated centres. This was compounded by short reheat times which allowed little opportunity for temperature equilibration. A crucial step in overcoming this problem has been the understanding provided from time-temperature data. Conventional temperature measurements by thermocouple, etc. are inappropriate in microwave cooking due to the high electric fields which are present (ca 15 kV/m). The result is either very significant interference, or even failure of the sensor. Therefore, alternative methods were developed to meet the need, some of which are discussed in this paper. One such measurement system is the now commonplace fibre optic probe, originally from Luxtron. The discrete data provided from this system are compared with the surface imaging data delivered by thermal imaging. These techniques are discussed in the context of microwave packaging materials heated in situ in a microwave oven and the need for temperature data as a basis for establishing testing regimes.

Cooking and Eating Utensils↗

PubMed2006

Thermal characteristics of microwave ablation in the vicinity of an arterial bifurcation.

PURPOSE: The objective of this research was to reveal the thermal characteristics of microwave ablations in the vicinity of an arterial bifurcation. METHODS: The temperature distribution after microwave heating of a liver-like material in the close proximity of an arterial bifurcation was simulated using the finite element method. Coupled fluid flow and solid heat transfer were taken into consideration and a three-dimensional analysis was performed. An experimentally determined SAR (specific absorption rate) generated by the absorption of microwaves in liver-like material was used in the analysis instead of utilizing electromagnetic calculations. Several different tests of time-controlled ablations with varying distances between the microwave antenna and the bifurcation were performed and detailed temperature distributions near the bifurcation were obtained. RESULTS: The interaction between the recirculation flow in the bifurcation and the heat transfer in the surrounding tissue makes the temperature distribution near the bifurcation complicated. Most importantly, after a period of continuous heating with constant microwave output power, the maximum temperatures caused by the ablation did not always increase with the distance between the antenna and the bifurcation. CONCLUSION: It can be concluded that inadequate ablations can be the result not only from a close proximity between the antenna and the blood vessel, but also from a complicated blood flow in large vessels whose structure causes recirculation flow.

Arteries↗

PubMed2004

Microwave or autoclave treatments destroy the infectivity of infectious bronchitis virus and avian pneumovirus but allow detection by reverse transcriptase-polymerase chain reaction.

A method is described for enabling safe transit of denatured virus samples for polymerase chain reaction (PCR) identification without the risk of unwanted viable viruses. Cotton swabs dipped in avian infectious bronchitis virus (IBV) or avian pneumovirus (APV) were allowed to dry. Newcastle disease virus and avian influenza viruses were used as controls. Autoclaving and microwave treatment for as little as 20 sec destroyed the infectivity of all four viruses. However, both IBV and APV could be detected by reverse transcriptase (RT)-PCR after autoclaving and as long as 5 min microwave treatment (Newcastle disease virus and avian influenza viruses were not tested). Double microwave treatment of IBV and APV with an interval of 2 to 7 days between was tested. After the second treatment, RT-PCR products were readily detected in all samples. Swabs from the tracheas and cloacas of chicks infected with IBV shown to contain infectious virus were microwaved. Swabs from both sources were positive by RT-PCR. Microwave treatment appears to be a satisfactory method of inactivating virus while preserving nucleic acid for PCR identification.

Animals↗

PubMed1994

D-aspartate and D-glutamate in microwaved versus conventionally heated milk.

OBJECTIVE: It has been reported that microwave heating of infant formulae can isomerize and racemize amino acids in the milk proteins, causing toxicity or affecting the nutritional value of the milk formulae. Therefore, we investigated whether microwave heating vs conventional heating would produce any D- enantiomers of aspartic acid (Asp) and glutamic acid (Glu) in milk. METHODS: Whole and skim milk samples were heated for 10 minutes in either a microwave oven at medium power or on a hot water bath at 80 degrees C. D-Asp and D-Glu were determined by high performance liquid chromatography. RESULTS: Unheated (control) samples were found to contain 0.40-0.45% D-Asp and D-Glu, inherent from the original pasteurizing process. Both conventional heating and microwave heating induce < 0.25% more racemization when compared to the control samples. CONCLUSION: Within experimental error, there is no significant difference in the levels of these D-amino acids between the conventionally heated and microwave heated milks, thus having no significant effect on the nutritional value of the milk proteins.

Animals↗

PubMed1988

Bacterial survival and thermal responses of beef loaf after microwave processing.

The effects of wrapping product in polyvinylidene chloride (PVDC) film, load size (150, 600 and 1200 g loaves), microwave output power (713 +/- 5 W and 356 +/- 3 W at 2450 MHz) and processing time on bacterial survival were evaluated in beef loaf. Specifically the survival of aerobic flora, and inoculated Staphylococcus aureus (ATCC 6538) and Escherichia coli (O157:H7) were assessed. Results showed that beef loaf wrapped in PVDC film had lower levels of survival for aerobic bacteria, S. aureus and E. coli than unwrapped beef loaf. When beef loaf was exposed to the same microwave dose (watts x minutes processed/grams of food), the percent of survival remained the same, regardless of load size or microwave output power. Exposed microwave dose, which correlated highly to percent of bacterial survival (R2 = 0.8-0.83) and end point temperature (R2 = 0.84), is suggested in place of output power, time or temperature as a predictor of microbial quality in foods that have been microwave processed.

Animals↗

PubMed1999

Thawing of foods in a microwave oven: I. Effect of power levels and power cycling.

Microwave thawing is faster than other methods, but it can produce significant non-uniformity of heating. The objective of this study was to perform comprehensive experimentation and heat transfer modeling to relate the time to thaw and the non-uniformity of thawing to power cycling, power level and the surface heat transfer coefficient. The governing energy equation was formulated with an exponential decay of the microwave flux from the surface. Surface microwave flux was obtained from the measured temperature rise using inverse heat transfer analysis. Gradual phase change was formulated as an apparent specific heat, and was obtained for the experimental material tylose from differential scanning calorimetry (DSC) measurements. The temperatures were measured immediately following heating with a fast response thermocouple. Dielectric properties were measured above freezing. Results show that the microwave flux at the surface and its decay are affected by the changes in the power level. Power cycling has an almost identical effect as continuous power at the reduced level of the average cycled power. As power level increases, the surface flux increases by the same fraction. At higher power levels, however, the outside thaws relatively faster. A "shield" develops due to a much reduced microwave penetration depth at the surface. This thawing time at higher power levels is reduced considerably. Temperature increases initially are non-uniform since the surface is heated at a faster rate than the interior. In keeping with the assumption that once the temperature reaches 100 degrees C, all energy absorbed goes into evaporation, and subsequent temperature is maintained at 100 degrees C. Thus, eventually, non-uniformity starts to decrease.

Food Handling↗

PubMed2000

A tunable microwave applicator for extraction of date-juice and similar products.

A tunable microwave applicator for extraction of date juice and similar products has been developed, designed and constructed. It consists of two main units: a microwave unit and a press/filter unit. The microwave unit consists of a tunable cylindrical cavity resonator, a section of aluminum waveguide with aperture coupling and tuning mechanism and a locally assembled microwave generator working at 2.45 GHz. The press/filter unit is made from a low-loss, heat-resistant material that works inside the cavity. Performance tests at both low and high power levels showed good performance characteristics with power conversion efficiency of more than 70%. Comparison with a commercial microwave oven and an electric heater showed the superiority of the present applicator, in terms of heating rate and power coupling efficiency.

Food-Processing Industry↗

PubMed2000

Modification of a household microwave oven for continuous temperature and weight measurements during drying of foods.

The main objective of this study was to modify a conventional household microwave oven for recording temperature and weight measurements continuously during microwave drying of foods. A household microwave oven with digital control was equipped with an electronic balance and a set of standard thermocouples that were connected to a PC for continuous data collection. The efficiency of the modified thermocouples was tested against the built-in probe of the oven. It was found that this microwave oven dryer set-up could be used for drying kinetics studies of foods since both the temperature and weight of the sample could be recorded continuously during the microwave drying operation.

Food Preservation↗

PubMed1987

Thermal effects of 2.45 GHz microwaves on survival and viability of Chinese hamster V-79 cells.

The possible existence of thermal effects specific to microwaves at 2.45 GHz and not found with classical heating in a waterbath was studied by measuring cell survival (colony-forming ability) and cell viability (the ability to exclude trypan blue) in Chinese hamster V79 cells. The microwaves were employed at high power densities (125 to 175 mW/cm2) corresponding to specific absorption rates ranging between 62 and 87 mW/g. When matching the rises in temperature, the effects of microwave-induced hyperthermia at 125 mW/cm2 on cell survival were comparable to those of classical heating. However, they were statistically significantly different when using power densities of 150 and 175 mW/cm2. The response obtained in terms of cell viability appeared to be comparable. The conclusions are also valid when taking into account a correction factor for energy losses during microwave treatment. The apparent specific effect of microwaves appears to be associated with exposures at high power densities involving short treatment times and rapid rises in temperature.

Animals↗

PubMed1999

No effect of short-term exposure to GSM-modulated low-power microwaves on benzo(a)pyrene-induced tumours in rat.

PURPOSE: In view of current interest in the biological effects of amplitude-modulated microwaves arising from the rapid development of mobile communications, the effects of low-level microwaves on cancer development were investigated using a rat sarcoma model. MATERIALS AND METHODS: Two-month-old female Sprague-Dawley rats were treated by injection of benzo(a)pyrene and irradiated with GSM (Global System for Mobile)-modulated 900-MHz microwaves in an anechoic chamber at 55 or 200 microW cm(-2) (75 and 270 mW kg(-1) average whole-body SAR, 2h daily for 2 weeks). Rats were exposed from day 20, 40 or 75 after carcinogen injection. Additional groups of rats were sham-exposed in a second anechoic chamber. Anti-phosphatidylinositol autoantibody levels were evaluated in sera to monitor malignant transformation. RESULTS: Microwave exposure had no effect on the development of tumours. No acceleration or delays in tumour onset were observed. Animal survival was not modified and serum autoantibody levels were similar in exposed and sham-exposed groups. CONCLUSION: Low-level GSM microwave exposure of rat bearing benzo(a)pyrene-induced tumours had no effect on auto-antibody levels, tumour appearance and survival. The low exposure levels used here correspond to exposure limits for whole-body exposure of humans.

Animals↗

PubMed2006

Basic studies on the treatment of volatile organic pollutant in sand by microwave radiation.

The heating characteristics of water and sand were investigated to understand the basic features of a microwave soil pollution treatment system and the reasonableness of this method was examined. The evaporation and temperature change of water by microwave irradiation were dependent on its volume and sand showed a three-fold temperature change compared with water. When microwave energy was applied, water showed an even variation in temperature on the whole, however, there was approximately 30 square difference according to the location inside the sand. Sand temperature was observed to show a larger difference as it was horizontally and vertically closer to the microwave irradiation point and horizontal temperature variations were more evenly distributed than vertical variations. Heating characteristics according to the particle size of sand showed that the temperature change was larger when the particle size became smaller and the moisture content of sand was found to influence its heating behavior. In the conditions of experiment, about 50% of the benzene in sand was volatized after 23 minutes of heating and 85% of the total benzene was removed from the sand after 60 minutes of microwave irradiation. For real soil test, more than 70% of BTEX was successfully removed from the soil after 120 minutes of heating.

Benzene↗

PubMed2006

Immunotropic influence of 900 MHz microwave GSM signal on human blood immune cells activated in vitro.

In an earlier study we reported that G(o) phase peripheral blood mononulclear cells (PBMC) exposed to low-level (SAR = 0.18 W/kg) pulse-modulated 1300 MHz microwaves and subsequently cultured, demonstrate changed immune activity (Dabrowski et al., 2003). We investigated whether cultured immune cells induced into the active phases of cell cycle (G(1), S) and then exposed to microwaves will also be sensitive to electromagnetic field. An anechoic chamber of our design containing a microplate with cultured cells and an antenna emitting microwaves (900 MHz simulated GSM signal, 27 V/m, SAR 0.024 W/kg) was placed inside the ASSAB incubator. The microcultures of PBMC exposed to microwaves demonstrated significantly higher response to mitogens and higher immunogenic activity of monocytes (LM index) than control cultures. LM index, described in detail elsewhere (Dabrowski et al., 2001), represents the monokine influence on lymphocyte mitogenic response. The results suggest that immune activity of responding lymphocytes and monocytes can be additionally intensified by 900 MHz microwaves.

Cell Cycle↗

PubMed1977

Rapid microwave fixation of rat brain.

A new microwave device which inactivates brain enzymes rapidly and uniformly is described. From the results obtained with microwave irradiation at two power levels (0.8 kW and 4.5 kW), it has been demonstrated that the high power microwave irradiation has several advantages over the low power irradiation. In its application to neurochemical studies, significant increase in the DOPAC level was found in the irradiated brain, while there were no statistical differences in the levels of NE, DA, 5-HT and 5-HIAA between microwave irradiation and decapitation. Significant increase in the Ach level and marked reduction of the choline level were observed after microwave irradiation. There were no significant differences in the level of cyclic GMP in the brain between the two methods of sacrifice, while significant reduction of the cyclic AMP level was observed in the irradiated brain.

Acetylcholinesterase↗