Re: what is the rate of denturation of pectinase?

There is no theoretical reason to expect any increases in pectinase activity with increasing denaturation time (the jumps in your graph). The pectinase activity should decrease with increasing exposure to 90 degree temperature, but the relationship is not as clear-cut as you might think. It is not a straight-line ("linear") relationship; I am pretty sure it could be described as an "exponential decay curve"; expect it to drop rapidly at first, and then flatten out (if you want to understand this better, find a basic physics text book, and look up 'half-life' in the index. They will be talking about the decay of radioactive materials, but the idea is the same).

There are many things that could explain the jumps. Almost any experiment has some unusual data points, and often you'll never know why. The way scientists deal with these unusual data points is be replicating each experiment, often 3 or more times. If you methods are good, these funny data points will get averaged out.

And yes, some of the other things you describe, such as doing the experiments on different days of the week, could be responsible for the jumps. Since it can be hard to control ALL the experimental conditions, sometimes it is better to perform your experiments in random order. This also helps to wash out the funny results.

Finally, don't expect your experiments to work right the first time. Mine never do, and I've been doing this a long time.

Good luck!

*Please note: The author is answering on his own behalf, and his answer does not represent a statement from the USDA.