It looks like using parabens Sodium salts is a must
even if they get initially dissolved by heating water, some then precipitates out of solution in the finished formulation, once it has cooled down.
Is making paraben Sodium salts as simple as weighn parabens and NaOH stochiometrically proportional to each other, heat water and stir?
I see that paraben has a -OH (hydroxy) group, so it ain't as simple as neutralizing a carboxylic acid.
I was unable to find the compete study:
Study on Synthesis of Sodium Methylparaben
Sodium methylparaben,a derivant of methylparaben,is a new type of multifunctional and high performance food or cometic additive。The preparation of sodium methylparaben by methylparaben and sodium hydroxide as raw materials was studied。The main factors affecting the quality of product were determined by experiments。The optimal reaction conditions for the synthesis of sodium methylparaben were obtained by studying the influence of reagent ration,reaction temperature and methods of feeding materials。The final purity of products reached 99.5% which meeted the pharmacopoeia standards.