Table 3.

Comparison of recovery obtained with the different extraction method.

	Buffer	Extraction method	Recoverya	Reference
1	50 mM NH4HCO3, 1 M urea, pH 8.0	2 g sample added with 20 ml preheated (60°C) buffer, homogenised, shake for 15 min	24.4% ± 0.8%	Lutter et al. (2011)
2	Tris-buffer, pH 8.2	2 g sample added with 20 ml buffer, homogenised, incubated at 60°C for 3 h	21.5% ± 0.5%	Heick et al. (2011)
3	1 M guanidine hydrochloride, 20 mM DTT, 10 mM sodium citrate, pH 6.75	1 g sample added with 25 ml buffer, homogenised, shake for 30 min	35.9% ± 0.8%	Monaci et al. (2010)
4	4.3 mM Na2HPO4, 1.4 mM KH2PO4, 137 mM NaCl, 2.7 mM KCl, pH 7.4	2 g sample added with 20 ml buffer, homogenised, incubated at 4°C for 3 hb	19.9% ± 0.8%	Kim et al. (2002)
5	Water	2 g sample added with 20 ml water, homogenised, shake for 3 h	23.1% ± 1.4%
6	Method described in the ‘Tryptic digestion and peptide extraction’ section		50.8% ± 1.6%

Notes: ^aRecovery = detected β-casein/spiked β-casein*100%.

^bThe ratio of sample to water was increased from 1:3 in the literature to 1:10.