Tuesday, July 5, 2011

Meat Science: To Cook or Not to Cook? The Raw Truth About Antioxidants in Raw and Cooked Meat and Fish.

Image 1: Now, that we know that meat is not
bad for you. Let's get to the meat of the matter:
Is raw meat better than cooked meat?
"Eat Raw!" If its referring to peppers, tomatoes and salads, even the Vegan lobby won't disagree with this slogan, yet when it comes to eating raw meat, dairy and eggs, hell breaks lose. "Don't do that you will kill yourself!" is what you will hear even from respected scientists. Strangely, I am eating raw eggs and other raw stuff on a daily basis without noticing any detrimental health effects whatsoever. All bacteria-hysteria aside (this would be the topic for a whole new blogpost, cf. red info-box at the bottom), the idea that meat has to be cooked before it is eaten is actually counterintuitive. I do not want to bring up the "Look at the lion, does he cook his pray before savoring on his bloody prey?"-debate, but didn't you ever ask yourself, why the same people who are scared of a medium steak, order their veggies steamed, or even raw (again see red info box at the bottom of the page), so that the antioxidants in them do not get damaged by the heat. Assuming that these people are aware that raw meat is full of healthy antioxidants (I assume many or them are not, though), common wisdom about the effects of heat on anti-oxidants tells us that they should be eating all our foods raw. As it turns out, though, even that may not be the optimal strategy to boost your antioxidant defenses...

A recently published study by Serpen et al. (Serpen. 2011) showed that the total antioxidant capacity (TAC) of meat and fish actually peaked after brief (<5 min) heating at 180°C - intriguing, no?

The Turkish scientists had bought four samples of your favorite meats and fish - chicken (breast), pork (tenderloin), beef (tenderloin) and fish (Sea bream, fillet) - at a local market, determined the proximate composition (cf. fig 1) of the samples and cut identical cylindrical (5x2cm) slices from the samples.
Figure 1: Composition of raw meat extracts (data adapted from Serpen. 2011)
In the next step, Serpen and his colleagues determined the total antioxidant value of raw and thermally treated meat / fish samples using a process that is called the QUENCHER method. The method was described by the same authors in a previous paper (Gökmen. 2009) and has already become a widely used and generally accepted way of determining the total antioxidant content of foodstuff.
Figure 2: Total antioxidant capacity (calculated average from ADPS and DPPH probes) of meat and fish samples after 0, 5, 10, 15 and 20 minutes of heating at 180°C (data calculated based on Serpen. 2011)
As can be seen in figure 2, where I plotted the mean total antioxidant values of the meat / fish samples as measured by ABTS and DPPH challenges, heating at 180°C does not - as common wisdom would have it - lead to a linear or even exponential decline of the antioxidant capacity of raw meats and fish. The total anti-oxidant capacity rather peaks at around 5 minutes, decreases thereafter, just to rise again at about 20 min. According to the scientists, the highly non-linear effects of heating on the antioxidant value of various meats and the observable variety in heat responses among the different samples can be explained by the interaction of the following processes
  1. denaturation and exposure of reactive sites of proteins; 
  2. thermoxidation and degradation of endogenous antioxidants; 
  3. formation of antioxidant MRPs (Maillard Reaction Products)
While some antioxidants are destroyed in the course of the heating process, others are created. This interplay appears to be most pronounced in the case of chicken (breast) and is the least obvious in fish (Sea bream fillet). Yet, despite the fact that short-fried <5 min meat and fish appears to be the best choice in terms of its overall antioxidant properties, specific anti-oxidants, amino acids and proteins, such as L-cysteine could get damaged even in the course of very brief heating processes. Furthermore it should be mentioned that other than a chef would do it, the scientists removed their probes from the oven and cooled them down immediately, in order to stop the continuing chemical processes. To see the same results as the scientists did for their 5min-steak, you would thus have to fry it for no more than let's say 2 minutes (this is just a very rough estimation) to make up for the ongoing reactions that won't stop if you do not shock-freeze your food before you eat it.
Note for the non-Europeans: Just in case you did not see it on CNN - the EHEC bacteria that killed people in Germany and all over Europe did not come from raw meats, but from sprouts. And it was the prejudice that raw meat, dairy and eggs were the worst (if not only) offenders, when it comes to food poisoning, that significantly hindered the investigations into the roots of an infection that has killed 37 people (according to Bild.de, 07-02-2011) in Germany, alone, when the first patients were hospitalized a few weeks ago.
Bottom line: While heating is obviously less detrimental to the overall antioxidant capacity of meat and fish, as some raw food eaters (and interestingly even the steam cooker faction) would have it, it remains questionable how you can reproduce the optimal fyring time of 5 minutes without immediately deep freezing your meat in a way, which would not leave you with your a steak that would be at least pretty rare. In turn, this means that a steak without a few drips of blood will not provide an optimal level of total antioxidants (TAC). Now, its up to you to decide whether a 2.3% decrease in mean TAC values are worth eating your steak rare - I would say no, but I don not love my steak rare, anyways, but I also read Sean Casey's formidable article on AGE formation, so if you cannot get over your socialized aversion against raw meat, dairy and eggs for what it does contain, i.e. antioxidants, then maybe for what it does not contain, which is advanced glycation end-products ;-)