Epigallocatechin-3-gallate enhances sterilization of irradiated whole
bovine casein and protects alpha and beta caseins from gamma radiation:
depending on polyphenol/protein ratio
Abstract
The increasing use of milk proteins in medicine requires the development
of effective processes for sterilization of milk formulations. We found
that epigallocatechin-3-gallate (EGCG) was able to reduce bacterial
flora in total casein, depending on the concentration of EGCG.
Furthermore, the combination of EGCG and gamma radiation reduced the
dose D10 to 0.88 kGy and 0.63 kGy with 250 and 500 µM EGCG,
respectively, instead 2.01 kGy without EGCG. We also examined the effect
of gamma radiation on alpha- and beta-casein in the absence and presence
of epigallocatechin-3-gallate (EGCG). Milk proteins in solution were
exposed to different doses of gamma radiation with and without EGCG.
Unirradiated and irradiated samples were analyzed by SDS-PAGE and
matrix-assisted laser desorption ionization time-of-flight mass
spectrometry (MALDI-MS). Our results suggest that EGCG (10 µM) protects
α- and β-casein from degradation and subsequent polymerization, possibly
by scavenging oxygen and protein free radicals generated during
irradiation. Although we used a ratio of polyphenols to protein that was
higher for alpha-casein (1/5) than beta-casein (1/10), beta-casein was
better protected with EGCG. According to previous studies, this result
could be explained by differences in protein primary structure and its
interaction with EGCG. The interaction of EGCG with casein is
hydrophobic rather than hydrophilic, so the interaction with β-casein is
stronger than with α-casein. In conclusion, we found that low EGCG
concentrations enhances the sterilization of total casein by gamma
radiation and it provided an excellent radioprotection of α- and
β-casein, especially β-casein, against degradation and aggregation.