Omdat er altijd wordt gezegd dat er geen wetenschappelijk bewijs is voor problemen met de magnetron nogmaals wat huiswerk......
Ron
hieronder nogmaals informatie over een Spaanse studie naar het verlies van vitamine C en kankerremmende anti-oxidanten bij het bereiden van brocolli.
Het totale verlies bij magnetronnen:
Vitamine C : 40%
Glucosinolates (anti-oxidanten) : 74%
Koken van broccoli zorgde voor een verlies van 55% van de anti-oxidanten. Het stomen van broccoli echter gaf bijna geen verlies dus adviseerden de onderzoekers
dat stomen de beste methode van bereiding is.
Total aliphatic and indole/aromatic glucosinolates and vitamin C content (ascorbic+dehydroascorbic acid) were evaluated in the edible portions of fresh harvested broccoli (Brassica oleracea L. var. italica) florets (Marathon cv.) before and after cooking and in the cooking water. High pressure boiling, steam cooking, microwaving and low pressure boiling (conventional) were the four domestic cooking processes used in this work. Results showed great differences among the four cooking processes and their influence on the content of glucosinolates and vitamin C. Thus, clear disadvantages were detected when cooking in a microwave due to the high loss of vitamin C (40%) and total glucosinolates (74%) in comparison with the rest of treatments. High pressure and conventional boiling had a significant loss rate of total glucosinolates (33% and 55% respectively) regarding fresh raw broccoli, due to the leaching into the cooking water. On the other hand, steaming had minimal effects on glucosinolates and vitamin C. Therefore, we can conclude that a large quantity of glucosinolates and vitamin C will be consumed in steamed broccoli when compared to the other cooking processes.
http://www.springerlink.com/content/a2v7f2vv0adxpnbd/
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74-97% verlies van anti-oxidanten in Brocolli door magnetron
Certain methods of preparation and cooking can cause vegetables to lose their cancer-fighting compounds, with microwaving the biggest culprit, finds a new study published in the Journal of the Science of Food and Agriculture.
A study investigating various cooking methods of broccoli concluded that microwaving is the clear loser: microwaved broccoli had lost 97 per cent, 74 per cent and 87 per cent of three major antioxidant compounds - flavonoids, sinapics and caffeoyl-quinic derivatives. By stark comparison, steamed broccoli had lost only 11 per cent, 0 per cent and 8 per cent, respectively, of the same antioxidants.
"Most of the bioactive compounds are water soluble, during heating they leach in a high percentage to the cooking water, reducing their nutritional benefits in the foodstuff.
http://www.foodnavigator.com/news/ng.as ... -zaps-body
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Verlies van Vitamine B12
Effects of Microwave Heating on the Loss of Vitamin B12 in Foods
Fumio Watanabe,* Katsuo Abe, Tomoyuki Fujita, Mashahiro Goto, Miki Hiemori, and Yoshihisa Nakano
Department of Food and Nutrition, Kochi Women's University, Kochi 780, Japan, and Department of Applied Biological Chemistry, Osaka Prefecture University, Sakai 593, Japan
Abstract:
To clarify the effects of microwave heating on the loss of vitamin B12 in foods, raw beef, pork, and milk were treated by microwave heating and then their vitamin B12 contents were determined according to a chemiluminescent vitamin B12 assay with hog intrinsic factor. Appreciable loss (~30-40%) of vitamin B12 occurred in the foods during microwave heating due to the degradation of vitamin B12 molecule by microwave heating. When hydroxo vitamin B12, which predominates in foods, was treated by microwave heating and then analyzed by silica gel 60 thin layer chromatography, two vitamin B12 degradation products were found. One of the compounds with a Rf of 0.16 was purified and partially characterized. The vitamin B12 degradation product did not show any biological activity in the growth of a vitamin B12 requiring microorganism, Euglena gracilis Z, and was not bound to hog intrinsic factor, a mammalian vitamin B12 binding protein. Intravenous administration of the compound (1 g/day) for 7 days to rats showed that the compound neither has toxicity nor acts as a vitamin B12 antagonist in mammals. These results indicate that the conversion of vitamin B12 to the inactive vitamin B12 degradation products occurs in foods during microwave heating.
http://pubs.acs.org/cgi-bin/abstract.cgi/jafcau/
1998/46/i01/abs/jf970670x.html
http://findarticles.com/p/articles/mi_m ... i_20346932
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Studie mbt verlies van CLA (geconjugeerd linolzuur) in kaas
Effect of heating and processing methods of milk and dairy products on conjugated linoleic acid and trans fatty Acid isomer content
Herzallah SM, Humeid MA, Al-Ismail KM. Department of Nutrition and Food Technology, Faculty of Agriculture, University of Mu'tah, Jordan.
[email protected]
The conventional heating methods of milk did not cause any significant increase in the trans isomer content, with the exception of milk heated at 63 +/- 1.0 degrees C for 30 min and milk microwaved for 5 min, which were significantly increased by 19 and 31%, respectively. The chemical changes of lipids were generally accelerated with the severity of the heat treatment and duration of storage.
The conjugated linoleic acid content of cheese heated in a microwave oven for 5 min decreased by 21%, and microwave heating for 10 min caused a decrease of 53% compared with that of freshly boiled cheese.
PMID: 15778297 [PubMed - indexed for MEDLINE]
J Dairy Sci. 2005 Apr;88(4):1301-10
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Studie mbt verlies van kankerremmende stoffen
Changes in Glucosinolate Concentrations, Myrosinase Activity, and Production of Metabolites of Glucosinolates in Cabbage (Brassica oleracea Var. capitata) Cooked for Different Durations.
Rungapamestry V, Duncan AJ, Fuller Z, Ratcliffe B.
School of Life Sciences, The Robert Gordon University, St. Andrew Street, Aberdeen AB25 1HG, United Kingdom, and The Macaulay Institute, Craigiebuckler, Aberdeen AB15 8QH, United Kingdom.
In cabbage, glucosinolates such as sinigrin are hydrolyzed by plant myrosinase to allyl isothiocyanate (AITC), allyl cyanide, and, in the presence of an epithiospecifier protein, 1-cyano-2,3-epithiopropane (CEP). Isothiocyanates have been implicated in the cancer-protective effects of Brassica vegetables. The effect of processing on the hydrolysis of glucosinolates was investigated in cabbage. Cabbage was steamed or microwaved for six time durations over 7 min. Glucosinolate concentrations were slightly reduced after microwave cooking (P < 0.001) but were not influenced after steaming (P < 0.05). Myrosinase activity was effectively lost after 2 min of microwave cooking and after 7 min of steaming. Hydrolysis of residual glucosinolates following cooking yielded predominantly CEP at short cooking durations and AITC at longer durations until myrosinase activity was lost. Lightly cooked cabbage produced the highest yield of AITC on hydrolysis in vitro, suggesting that cooking Brassica vegetables for a relatively short duration may be desirable from a health perspective.
J Agric Food Chem. 2006 Oct 4;54(20):7628-34
PMID: 17002432 [PubMed - in process]
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Effect op anti-infektie factoren van moedermelk, meer E-coli groei
Effects of microwave radiation on anti-infective factors in human milk.
Quan R, Yang C, Rubinstein S, Lewiston NJ, Sunshine P, Stevenson DK, Kerner JA Jr.
Department of Pediatrics, Stanford University School of Medicine, CA.
In intensive care nurseries it has become common practice to use microwave thawing of frozen human milk for more rapid accessibility. Twenty-two freshly frozen human milk samples were tested for lysozyme activity, total IgA, and specific secretory IgA to Escherichia coli serotypes 01, 04, and 06. The samples were heated by microwave for 30 seconds at a low- or high-power setting and then reanalyzed. One-mL aliquots of 10 additional human milk samples were microwaved at low (20 degrees C to 25 degrees C), medium (60 degrees C to 70 degrees C), and high (greater than or equal to 98 degrees C) setting before the addition to each of 1 mL of diluted E coli suspension. E coli growth was determined after 3 1/2 hours of incubation at 37 degrees C. Microwaving at high temperatures (72 degrees C to 98 degrees C) caused a marked decrease in activity of all the tested antiinfective factors. E coli growth at greater than or equal to 98 degrees C was 18 times that of control human milk. Microwaving at low temperatures (20 degrees C to 53 degrees C) had no significant effect on total IgA, specific IgA to E coli serotypes 01 and 04, but did significantly decrease lysozyme and specific IgA to E coli serotype 06. Even at 20 degrees C to 25 degrees C, E coli growth was five times that of control human milk.
Microwaving appears to be contraindicated at high temperatures, and questions regarding its safety exist even at low temperatures.
PMID: 1557249 [PubMed - indexed for MEDLINE]
Pediatrics. 1992 Apr;89(4 Pt 1):667-9