Not by the interactions but by the neutrino propagation itself, neutrinos spontaneously change from one flavor to the other, other en route, this is called neutrino oscillation it's the discovery at 2001, I think it was the 2002 Nobel prize including Ray Davis for his prediction. the PP process as I said produces electron neutrinos, by the time they get here they've all mixed up and only a third of them are electron neutrinos, the other two thirds are mu or tau neutrinos which do not interact in the way that Davis was 