In vitro digestibility of b-casein and b-lactoglobulin under simulated human gastric and duodenal conditions: A multi-alboratory evaluation

Initially the resistance to digestion of two cow's milk allergens, b-casein, and b-lactoglobulin (b-Lg), was compared using a ''high-protease assay" and a ''low-protease assay" in a single laboratory. The low-protease assay represents an alternative standardised protocol mimicking conditions found in the gastrointestinal tract. For the high-protease assay, both proteins were incubated with either pepsin or pancreatin and digestion monitored by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and reverse phase-high performance liquid chromatography. The low-protease assay involved gastroduodenal digestion in the presence or absence of phosphatidylcholine (PC). Both b-casein and b-Lg were susceptible to hydrolysis by pepsin and pancreatin in the high-protease assay. In contrast, the kinetics of b-casein digestion in the low-protease assay were slower, b-Lg being pepsin resistant. During duodenal digestion, b-Lg was gradually degraded and addition of PC slowed digestion. Subsequently, the reproducibility of the low-protease assay was assessed in 12 independent laboratories by visual assessment of the gels and densitometric analysis: the inter- and intra-laboratory variability was affected by sampling and electrophoresis method employed. The low-protease assay was shown to be reproducible. Future studies will extend these findings using a broader panel of proteins.