Hagen's Nutrafin flake food line has this feature which is supposed to do some great things. I have used this food in the past and can't say that I ever saw anything different (except lower phosphates) than other foods.
According to Hagens website this what PDP will do for you:
High natural astaxanthin pigment levels to enhance fish colors
Superior nutritional profiles (excellent amino acid profile, high levels of highly unsaturated fatty acids, etc.)
Increased growth and survival rates for fish
Improved digestibility and palatability
Potent flavourant/feed attractant, resulting in improved feed uptake and Food Conversion Ratios