Lipase enzyme digestion of milk experiment - effects of stale milk - Help needed understanding how stale milk could affect my experiment... (Feb/28/2006 )

I conducted the following experiment to investigate the speed at which lipase digests the fats in milk.

I prepared the concentrations of lipase by diluting my 1% solution of lipase further. Having prepared some solutions I would then add the phenolphthalein (indicator), bile salts (emulsify the fats – this provides a larger surface area for the enzymes to react with and so speeds up the reaction), the carbonate solution (makes the PH higher so that the enzymes react at their optimum rate – as in the small intestine) and the milk which is the substrate (what we are digesting).

I timed the experiments (obviously) and these are my results:

-------- 1---------- 2---------3 ----- Avr
1.0% -- 414 ------428 ------335 ------392
0.8% -- 533 ------517 ------367 ------472
0.6% -- 759 ------677 ------444 ------627
0.4% -- 873 ------735 ------509 ------706
0.2% -- 1431 ---1026 ------957 ------1138

I took test one results first along with the first 3 of the second test (up to 677), it was at this point I stopped my experiment. I continued it the following week, but I strongly suspect the milk of being stale.

As you can see the results were less (from T2, 0.4% - T3, 0.2%) without exception than the previous results.

My question: if the milk were stale - why would this speed up the experiment?

Ideas? Suggestions? All appreciated!
Thanks,
Ben

you did not say what the numbers mean? (what exactly are you measuring; OD based on phenolphthalein or something?)

anyways, if the milk is old and the reaction progresses faster, what do YOU think it's telling you? What would happen to the fats in milk, if it is getting too old?

also, is this dry (powdered) milk, or fresh?