Slow acidification process

I'm trying to find a substitute of Glucono delta-lactone (GDL). This food additive is usually used to produce silk tofu. Because of its slow hydrolysis the pH decreases very smoothly, which results in a tofu(coagulated soy milk protein) very soft. At the same time it is neutral in flavour, which is a great feature for a food additive. Now, my problem is that I'm trying to find an alternative because GDL is not allowed in organic food (in EU). Does anyone know any possible alternative compatible with the allowed additives (Annex III in:


<http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2008:250:0001:0084:EN:PDF>)


Or, how can I know the reaction rates of these acidifiers? For example, does Lactic acid hydrolyses slowly? 
Note: When I refer to fast or slow, my time reference is a minute (fast) or hours (slow).


