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:Fractions 1, 2 and 3 were identified to contain different proteases, while fraction 4 showed four main peaks PhTx1, PhTx2, PhTx3 and PhTx4, containing polypeptides and enhancing different toxicological effects [19,20].
Category: