I filter sterilize the coconut , boiled and added directly to the MS medium,then autoclaved it in 121(15 min).but lots of contamination is coming in the medium itself.
Autoclaving should kill any contamination so you might need to have your autoclave checked. There are test kits you can use to check if your autoclave is working correctly. You don't need to filter sterilise or boil the coconut water prior to autoclaving.
HiI I wonder to listen sterilizing coconut water. Until you break and open the nut I believe that is in perfect sterilized condition. Is it not? Take care in such a way partly break the nut and collect water in a laminar add to medium or where ever you want, so that there will not be any contamination from coconut water. Generally once you autoclave there should not be any contamination. As per your question I believe it is not with coconut water something thing wrong. First check all things right from your autoclave working condition and pressure development in that.