Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:The cultured AF (50 mg AFB1/kg) was produced using Aspergillus parasiticus (NRRL 2999) on ground corn at University of Missouri as described by Gowda et al. (2008). Six premixes, contributing 4.
Category: