3.6. Ferrous chelating capacity assay
Since the transition metals such as ferrous ion could generate
hydroxyl radicals via Fenton reaction in biological systems, in the
present study we tested the effect of gastrointestinal digestion
and food matrix on chokeberry juice chelating capacity. The results
presented in Table 2 showed that diluted juice (J) exhibited the
lowest chelating capacity among examined samples, even lower
than control of matrix digestion at zero time (DMC). Digested juice
(DJ) showed mildly increased chelating capacity probably due to
release of small peptides originating from matrix proteins. It has
been previously reported that hydrolysis of both plant and animal
proteins resulted in elevated ferrous chelating capacity (Chan,
Decker, Lee, & Butterfield, 1994; Stanisavljevic et al., 2013; Zhang
et al., 2009). Comparing DMC and DM almost doubled chelating
capacity was observed after digestion of food matrix alone, supporting
the previously mentioned claim that matrix derived peptides
could be partially responsible for the increase in ferrous
chelating capacity in DJ. The most interesting result was obtained
by comparing the chelating capacity in digested matrix in the presence
and absence of chokeberry juice (DJ and DM). It was determined
that digestion of food matrix in the presence of
chokeberry juice yielded an extract with significantly lower chelating
capacity than the extract of digested food matrix without
chokeberry juice. This result could implicate that phenolic compounds
of chokeberry juice inhibited the digestion of matrix proteins
and formation of peptides with high chelating capacity,
probably due to interactions and formation of complexes with proteins
making them unavailable for enzymatic digestion. This was
supported by studies describing formation of stable protein–phenolic
complexes (Xu & Diosady, 2000).