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:Literature values for hydrolysis of DG and DGS range from 100 to 180 mg/g (Kim et al., 2008b; Tucker et al., 2004; Bals et al., 2009; Noureddini et al., 2009).
Category: