Pineapple addendum to Kiwi juice post

A while ago I posted about using kiwi juice to tenderize meat. I also noted that pineapple also has a protease enzyme, bromelain, that will tenderize meat. It does this by breaking down the proteins in the meat and therefore breaking the cellular structure.

One thing I did not mention is that the bromelain also does its wonders on your tongue if you eat the pinapple, especially more green.  I cut up a beautiful pineapple the other day and was happily munching away when  my tongue started to tingle and felt burnt!  Turns out the bromelain was also breaking down the proteins on my tongue...fortunately, the surface of our tongues is replenished almost daily so the effects are not long lasting but in future I think I will eat my pineapple with something a but more creamy such as yogurt to help coat  my tongue from the effects.  I have read that truly ripe from the tree pineapples do not have the same effect as the amount of bromelain is reduced as the pineapple ripens.

One downside of the protein attack is that you cannot put raw pineapple in gelatin since it will break down the gelatin (which is a protein).  The canned pineapple would work since it is usually  cooked and will have inactivated  the bromelain (need to try this experiment). To make pineapple jelly, you would need to use pectin not gelatin.

Links:
http://science.howstuffworks.com/innovation/edible-innovations/pineapple-enzyme-tenderize-steak1.htm

Pineapple strawberry jelly
http://www.cooks.com/rec/view/0,1623,146161-225195,00.html

Dickson, S R and Bickerstaff, G F Pineapple bromelain and protein hydrolysis. Journal of Biological Education 25, 164–166 (1991)

Pineapple bushes

http://www.mnn.com/your-home/organic-farming-gardening/questions/do-pineapples-grow-on-trees

Tenderizing meat with kiwi juice

I read somewhere that Kiwi juice can tenderize meat.

So, of course, I did an experiment!

I took two beef fast-fry steaks and marinated one in crushed kiwi and the other in some soy sauce and vinegar ('cause I like that marinade)

I let the meat marinade for a couple of hours - although some recipes say that might be too long.

The steak in the kiwi marinade felt a lot floppier than the soy sauce marinade:

I fried up some onions and garlic in olive oil and then placed the steaks in the pan.  I used a trick I had recently seen on a cooking show - to brown the meat well, since fast-fry steaks often curl a bit in the pan, fill a pot half full with water and place it on top of the steaks to press them down. Choose a pot that is slightly smaller at the base than the frying pan so most of the meat is covered.  The increased contact with the bottom of the pan will brown the meat better.  Leave it for a few minutes and then turn the meat.  I just threw in the marinade from both the steaks so the gravy it produced was both sweet, salty and tart - a lovely combo.  Served with egg noodles it was delicious.

I had cut each steak in half and served my son and I one of each marinade for the taste test.  The verdict was that the kiwi marinade was a bit more tender (although with fast-fry steaks it is a bit hard to differentiate) but we liked the marinade of the soysauce better - need to work on adding other flavours to the kiwi marinade. But the gravy I made with the pan drippings were delicious!

So why did the meat tenderize more?

Turns out that kiwis, pineapples, mango and papaya contain an enzyme that will break down the protein in meats.  The enzyme, actinidin, is called a protease enzyme.  Enzymes are very large molecules - so large that scientists need a shorthand to describe them - they make them look like ribbons:

Actinidin

Sequence - each letter represents part of the molecule and the squiggles and arrows indicate how the molecule folds and twists

Parts of the enzyme react with the proteins to break the bonds which degrade the cellular structure of the meat.

"protease is any enzyme that conducts proteolysis, that is, begins protein catabolism by hydrolysis of the peptide bonds that link amino acids together in the polypeptide chain forming the protein." http://en.wikipedia.org/wiki/Protease

One protein involved is Actin (which is involved with the muscular tissues)

From Wikicommons:  http://en.wikipedia.org/wiki/File:Actin_with_ADP_highlighted.png

As you can see proteins and enzymes are similar since they are both macromolecules.  The actinidine reacts with the amino acid parts of the protein to break the big chains and therefore break down the strength of the muscle meat and tenderize it...

By the way, our bodies also contain proteases such as pepsin and serine to help us break down and digest the rest of the protein we eat.

Addendum (Sept 7, 2011): Just found this M.Sc.(Food Science) thesis by Jin Han on tenderizing lamb with kiwi juice:

THE EFFECT OF PRE-RIGOR INFUSION OF LAMB WITH KIWIFRUIT JUICE ON MEAT QUALITY