PKU Cooler 20 Purple. The PKU cooler system is a range of ready-to-drink phenylalanine free protein substitutes, available in neutral-tasting (white), and flavored (orange, purple and red) options, containing essential and non-essential amino acids, carbohydrate, vitamins, minerals, trace elements and the Omega-3 long chain polyunsaturated fatty acids (LCPs); Docosahexaenoic acid (DHA) and Eicosapentaenoic acid (EPA).