Bioaccessible fraction of proteins obtained after in vitro digestion: Impact of the fractionation method on the peptide profile.

Protein digestibility can be determined in vitro from the digesta bioaccessible fraction. Different fractionation methods were compared on casein, ovalbumin, gelatin, lupin and pea globulins digested at high (INFOGEST protocol) or low extent (enzyme reduced 10×). Digesta were centrifuged, alone or after trichloroacetic acid (TCA, 3 or 8.5%), sulfosalicylic acid (SSA, 1.5 or 4.5%) or methanol (80%) precipitation. The supernatants were analyzed by size exclusion chromatography. Real in vitro digestibility values of 15N-labelled casein were compared with those obtained in vivo. Only the chemical agents, offering similar efficiency except methanol and 1.5% SSA somehow differing, allowed large peptide (>10 kDa) depletion. The effectiveness of chemical agents depended both on the protein source and their digestion extent. The real digestibility of casein could be determined appropriately in vitro using 4.5% SSA or methanol, with values similar to that measured previously in humans, at the ileal level, on the same protein source.