The OPA method was employed for a more detailed comparison
of amino acid release kinetics of raw and boiled EW during
digestion (Nielsen et al., 2001). The results of the OPA assay were
consistent with the initial SDS-PAGE analysis. There was a two- to
three-fold higher DH for boiled EW throughout the duration of the
in vitro digestion assay. An increased DH of boiled EW was present
during peptic as well as pancreatic hydrolysis, as shown in Fig. 2.
Analysis by SDS-PAGE and OPA gave an excellent comparability
between differently treated protein samples. Our study confirms
that ovalbumin from raw EW was resistant to pepsin. However,
we found that under the tested conditions raw EW, including
ovalbumin, was hydrolysed partially by pancreatin within 30–
60 min. The degree of hydrolysis for raw EW was much lower than
for heated EW. Interestingly, other studies found that ovalbumin
was also resistant to pancreatic digestion (Martos et al., 2010, 2013;Jime´nez-Saiz et al., 2013; Nyemb et al., 2014). The discrepancy
between the findings may be due to different assay conditions and
enzyme formulations.