|The effect of microwave steaming, i.e. steaming with the microwave by the means of one of those microwave steaming bags has not been tested in the study at hand, but it should be relatively harmless... assuming your steaming bag is BPA free.|
With the latest study from the Unidad de Investigación y Desarrollo de Alimentos the previously discussed and often (falsely) ignored formation of oxysterols, i.e. oxidized cholesterol that's bad for your metabolic and cardiovascular health microwave (MW) foods or I should say fish just got even more attractive.
As Leal-Castañeda et al. point out in the introduction to their paper, "cholesterol oxidation products (COPs) formation depends on the conditions of MW heating and the composition of the food matrix" (Leal-Castañeda. 2016).
It is thus only logical that the Mexican researchers compared different oils / foods, namely palm, extra virgin olive, soybean and fish oils. All oils were heated in a two different microwaves:
- a Panasonic, Model NN-6653, 900 W, operating at in multimode
- Thermo CEM DISCOVER series SP-D, operating in monomode
But wait, where's the cholesterol in palm, olive ad soybean oils? Obviously, there is none. Accordingly, the scientists added a standardized amount of 2.5 mg of cholesterol/g of oil to all four test oils before MW heating them.
|Table 1: Temperature reached by in lipid systems made of oils and cholesterol during heating in multimode MW oven; the monomode MW was set to heat until the temperature was 180°C (Leal-Castañeda. 2016).|
"MW heating of edible oils may cause its degradation by oxidation, hydrolysis and polymerization. It has been suggested that the unsaturated components of the oils are usually the most susceptible to these degradation processes, altering their physicochemical properties and FA profile. However, it has been reported that heating time and temperature, and the presence of natural antioxidants (tocopherols, chlorophylls, carotenoids and phenolic compounds) have a significant influence on the extent of the oxidative processes. [In the study at hand, the] most relevant change was the decrease of PUFAs presen[t] in fish oil (Figure 1)" (Leal-Castañeda. 2016).).As Leal-Castañeda, et al point out (2016), the significant decrease of PUFAs in fish oil heated in MW (both unimode and multimode) and conventional oven is in agreement with Weber et al. (2008) and Zhang, et al. (2013), who observed a slight decrease in the PUFA content in silver catfish fillets and grass carp (ctenopharynyodon idellus) fillet (this is important, because this is a whole food) baked in conventional oven, and a greater reduction when MW oven was employed.
- Overall, the maximum total COPs contents "largely varied (46.4-250.4 μg/g lipids), depending on the type of heating system and oil matrix" (Leal-Castañeda. 2016).
- In that, the multimode MW heating caused greater COPs formation than the unimode MW.
- On the other hand, the COP formation in the allegedly healthier was significantly higher - albeit only for fish oil - than during either of the two microwaving treatments.
|The contents of vitamin C and total carotenoids, aliphatic and indole glucosinolate in broccoli cooked by different methods Effects of cooking methods (1. raw; 2. boiled; 3. steamed; 4. microwaved; 5. stir-fried; 6. stir-fried/boiled | Yuan. 2016).|
In that, the effects may differ not just based on the macronutrient composition of the food, it may also differ for individual micronutrients such as vitamins or indoles.
- Fabbri, Adriana DT, and Guy A. Crosby. "A Review of the Impact of Preparation and Cooking on the Nutritional Quality of Vegetables and Legumes." International Journal of Gastronomy and Food Science 3 (2016): 2-11.
- Mansour, Abd Allah, et al. "Effect of Domestic Processing Methods on the Chemical Composition and Organoleptic Properties of Broccoli and Cauliflower." American Journal of Food and Nutrition 3.5 (2016): 125-130.
- Otaegui-Arrazola, Ana, et al. "Oxysterols: a world to explore." Food and Chemical Toxicology 48.12 (2010): 3289-3303.
- Sottero, Barbara, et al. "Cholesterol oxidation products and disease: an emerging topic of interest in medicinal chemistry." Current medicinal chemistry 16.6 (2009): 685-705.
- Staprans, Ilona, et al. "Oxidized cholesterol in the diet is a source of oxidized lipoproteins in human serum." Journal of lipid research 44.4 (2003): 705-715.
- Tian, Jinhu, et al. "Domestic cooking methods affect the phytochemical composition and antioxidant activity of purple-fleshed potatoes." Food chemistry 197 (2016): 1264-1270.
- Yuan, Gao-feng, et al. "Effects of different cooking methods on health-promoting compounds of broccoli." Journal of Zhejiang University Science B 10.8 (2009): 580-588.
- Zhang, Jinjie, et al. "Effect of cooking styles on the lipid oxidation and fatty acid composition of grass carp (ctenopharynyodon idellus) fillet." Journal of Food Biochemistry 37.2 (2013): 212-219.