Development and validation of methodologies for the quantification of phytosterols and phytosterol oxidation products in cooked and baked food products

•GC–MS methods for phytosterols (PS) and phytosterol oxidation products (POPs) analysis in processed foodstuffs were developed.•Fat extraction from entire sample servings makes the method an exact representation of the typical use of the food by the consumer.•Method reliability, selectivity, sensitivity and accuracy allowed the analysis of over 600 samples.•First application of methodologies for monitoring PS retention and POP formation when complex food matrices are cooked/baked with PS-margarine.