Today's the first installment of Food Science Friday.
The article today is
"Effect of Beef Product Physical Structure on Salmonella Thermal Inactivation"by Maria Avelina Mogollon et al. from The Journal of Food Science 2009 Vol. 74
I really enjoyed this article because it put 2 things into perspective:
- The structure of meat really does make a difference in the effect of bacterial growth (whether you have a whole piece of meat or whether it is ground)
- I really love this field, and reading this article really made my decision to go to Grad School worthwhile.
Basically, its always been understood that whole muscle meat is contaminated through surface area and not likely to be highly affected like ground meat, which has tons of surface area. Well... the study kind of supported that the opposite is true. Whole meat actually is able to "house" bacterial pathogens because of its inside. Think about it... if you wanted to hide, you'd go in a deep dark hole right? That's exactly what bacteria does, with whole meat it can go to the most inner center and stay there and grow. With ground meat, you're dealing with tiny particles and not much "protection", if you will.
Salmonella in particular, has greater thermal resistance (basically, won't die as easily if exposed to heat - aka - cooking) when unattached or suspended in a liquid... think marination.
Why
Salmonella? Well, it's pretty much the basis of study for USDA performance standards (which is that there should be a 6.5log10 reduction (99.99998%) of
Salmonella for all cooked beef products - more info on guidelines found
here ). However, through all the lethality guidelines used for calculating this, physical structure (grind size of meat) of the meat itself has never been factored in.
The stated objective of the study was to evaluate the relationship between thermal resistance of
Salmonella and degree of grinding (whole-muscle, coarsely ground, finely ground, and beef puree (sounds appetizing, eh?))
Methods of the experiment:Preparation of meat: beef chuck, shoulder clods, all taken from the same place (Packerland-Plainwell, Inc.) 48 hours after slaughter. Samples were then taken to the Michigan State University lab and irradiated (rid of all background bacterial flora).
For whole muscle: cyclinders were obtained (about 6-8 cm long) using a sterile coring device.
For coarsely and finely ground beef: beef was ground in a sterile grinder by putting the beef through a plate two times with 16 mm holes for coarsely ground, and two times with 6 mm holes for finely ground.
For beef puree: beef was put through sterile grinder and passed through a plate with 6 mm holes 5 times, then blended in a sterile blender at puree speed for 1 minute. (yummy)
Then bacterial cultures were obtained for 8 different serotypes (similar to strains, but not exactly) of
Salmonella - including serotypes from beef, chicken, turkey, and humans.
A "Marinade" was then prepared (and definitely like the type of marinade you and me are used to) by using 96% filtered and deionized water, 3.2% NaCl (salt), and 0.8% potassium phosphate solution. Mixture was poured into 520mL glass bottles and stored at room temperature.
Inoculation of the samples began with the 8 serotypes of each
Salmonella (about 9 mL of each) combined by centrifuge and resuspended in the marinade mix. This resulted in 10 to the 8th CFU (colony forming units)/mL... that 100,000,000
Salmonella colonies PER mL of a 520mL bottle... you can imagine that's a pretty large number.
To inoculate the whole muscle: the cyclinders were placed into the marinade for about 20 minutes, resulting in a 0.15 g uptake of the marinade.
To inoculate coarsely and finely ground beef: samples were inoculated dropwise with the marinade mixture after their 1st grind, and then ground for the 2nd time, also resulting in a 0.15 g uptake.
To inoculate the beef puree: the samples were inoculated dropwise after grinding was complete and before blending step, resulting in 0.15 g uptake.
To test for Thermal inactivation, each of the samples were packed into sterile brass tubes, sealed with rubber stoppers and place in an agitated 60.5 C (140.9 F) water bath. Once the internal temperatures of the samples reach 60 C, they were removed and placed on an ice bath.
Results found were all within a similar range, but whole-muscle was found to inactivate at a slower rate than that of the ground beef products. (The degree of grind was shown not to make a difference because all 3 grind products produced about the same rate of inactivation).
So what exactly does this all mean? Well, they suggest in the article, that the higher fat content found in whole muscle product could provide an area for bacterial attachment that allows for it to be thermally protected. You don't get at much fat surface area in ground meat, so that could explain the difference in thermal inactivation.
Now, what I take from the study, is not to never buy whole meat products because not ALL
Salmonella or bacterial pathogens are bad for you. Whole meat products are pretty much the best ways to use meat, but I think that it should, based on this study, be exposed to
more heat longer. Now, will I live up to that? Probably not, because personally, I think a medium rare steak is the way to go, but can I live with a few bacterial bodies floating around because of that? Sure thing. Mainly because, even if you don't like to admit it, there's millions of bacteria living in us all, regardless of how many times a day you shower or clean yourself. And without them... you honestly wouldn't be able to survive.
Phew... that was a hefty piece of work. I included a PDF file of the article for those of you that want to read it in depth. It's a pretty easy read, for the most part, and I would definitely like to hear some feedback on what you guys think! Do you agree with me? Do you take a different message home from the article? Is this segment a little too scientific or nerdy for you? I want to hear it all! The good and the bad!
Anyway, on a lighter note, here's a non-beef recipe for you!
Ingredients:3 chicken thighs, skinned and de-boned, cut into thin strips or cubes
1 & 1/2 cups chicken stock
2 teaspoons grated ginger
4 garlic cloves, crushed
2 teaspoons tumeric
4 teaspoons curry powder
1 teaspoon chili powder
2 teaspoons garam masala
4 onions, chopped
2 sticks of celery, chopped
2 carrots, peeled and chopped
1/2 to 1 cup plain yogurt
2 tablespoons tomato paste
2 teaspoons unsalted butter
Dupiaza, at first, sounds Italian to me. But no, it's actually a type of Indian curry, and "piaza" actually means onion... so hence why there's so much onion in this dish. But don't worry, it doesn't overpower anything.
In a medium sauce pan, add enough water to fill it halfway and bring to a boil. Add half of the chopped onions and cook until soft. About 10-15 minutes or so. Drain the onions and puree until semi-smooth. This will be your onion paste, but you can set it aside for right now.
In a large skillet, under medium high heat, add the butter and melt. Once melted, add in the remaining onions, celery, and carrots. Reduce heat to medium-low and cook until vegetables are soft and starting to turn brown in color, about 10-15 minutes.
Meanwhile, you can make your curry paste. In a food processor, add ginger, garlic, curry powder, garam masala, tumeric, and about 1-2 tablespoons of water. Pulse to get a nice paste-like consistency. You may add more water if it is still too thick. Add paste to saucepan with vegetables and stir for about 2-3 minutes.
Add in chicken and coat well with mixture.
In a medium bowl, mix yogurt, tomato paste, onion paste, and chicken stock. Mix until tomato paste is dissolved. Then add mixture to pan with vegetables and chicken. Mix well and simmer for about 15 minutes and chicken is cooked all the way through.
I served this with some red rice and it was phenomenal. You could sense the onion flavor, but it wasn't too much. The curry really mellowed the onion out. It was definitely sensationally delicious and great the next day! Enjoy!
