Solution for microbial dilutions

Hi everyone!

We are currently launching two new products in the fermented milk category, one being an ambient drinking yogurt made from reconstituted milk. I am doing basic microbial tests on the products, but I am unsure as to which water I should be using for my dilutions. 

I am testing for Total aerobic Microorganisms, Yeasts and Moulds, Enterobacteriaceae and Bacillus cereus. 

Is it a must to use Buffered Peptone water for my serial dilutions? What solution would be the best for these tests? 

I will appreciate your advice! Thank you :)

The best think to use is Maximum Recovery Diluent (MRD) which is a saline solution containing peptone lower than in Buffered Peptone Water. The osmotic pressure is isotonic to the cell plasma, therefore, it doesn't harm the microbial cells and the cells do not divide in the 45 mins duration of preparing the diluent and testing because of minimal amount of peptone.