Dear Ghalib, many factors might contribute to increases in acidy after harvest. Normally, we see decreases (depending on the species - very steep ones) since acids are a fast and the first source of respiratory substrate to produce energy. Results in increases might be a concentration effect - when your tissues loose water... a second point is that part of the depolimerization processes going on in cell walls could release acids (uronic acids) that, again, depending on species, could result in detectable increases of titratable acidity after harvest. What is triggering is that after six months you detect such increases. Are they very significant?

Simply, it is due to concentration.

Drying evaporates water, Total solids will increase

 Probably its due to loss of water and increase the concentration.

 I thank everyone on the answer.

I think the moisture loss is part of the high acidity

The second thing is the disintegration of the cell walls and release  Galictronic acid.

Perhaps the most important thing anaerobic respiration. or some microbiology.

Dr. Renar Joao Bender have agood answer.

To proof the answer is correct for the question, I think it would make us easier to seek the possible answer if you could give us: more information on:

1. Firstly,  I agree with you all,  that majority cause is the dehydration it self that makes the acid concentration in dried product increased. This case is the same as in any vacuum fried products that I experienced in. Not only the total acidity but also the taste is getting more sour for acidic fruits when it is dried. That's why many of the sold dried fruit product need an addition of sugar powder of crystals to make it more palatable.

2. But, the second thing is about not to jump into conclusion, i.e. how could you conclude that it was an un-aerobic respiration? Was it stored in a vacuum packaging and what is the temperature of storage during the 6 months period? What was the aw of the dried apricots? Is your hypothesis testing methods proved it so? I would presumed that as long as the dried apricot's aw lower than 0.7, and storage condition is maintained safe for any chemical (including biochemical), microbiological and physical changes to occur the change in total acids will not be significant. This includes maintenance of internal and external products' factors of the storage system of the dried apricots, such as moisture content of the dried apricots, storage temperature, packaging materials, atmosphere conditions. Only if the aw is too low (say like 0.2-0.4) then the threats of auto oxidation may occur. But is it, really?