Purge command in cronjob not executed?

Question

Hello dear friends,
I need to purge my RAM on my OS X Mavericks Late 2012 iMac every 5 minutes.
I used to run this command in cronjob on Mountain Lion and it was working great:
*/5 * * * * purge
It would seem that the cron job is indeed executed every 5 minutes, but the memory DOES NOT get purged at all, yet if I run the purge command manually it works.
In fact, to ensure that the command is actually performed, I have tempèorarily modified it as follows:
*/5 * * * * purge >/Users/lab/Desktop/cronpurge.txt
The .txt file is modified every 5 minutes but, as I said, no memory purge occurs.
How can I ensure that the command is run successfully by cronjob as it used to be the case with Mountain Lion?
Thanks!

Answer 1

Hi,
Thanks to both.
I forgot to mention that the cronjob is indeed edited as root, with su command first to get an elevated prompt.
I run 6 Parallels Desktop Windows 7 sessions while I am working with Mavericks, that's why I need frequent purging, for them to run smoothly as Parallels Desktop is pretty much memory hungry.
Although I have 32 GB RAM, I prefer to be able to multitask as best as possible by running a frequent memory purge.
@TonyT1: I am indeed aware that memory management in Mavericks is different, however I can't help wondering why the same command "purge" works perfectly when run manually in an elevated prompt.... hence my curiosity about why the cron job, which is supposed to run the same instruction, is not working. Thanks!