Effects of different proteases on iron absorption property of egg white hydrolysates

•Effects of egg white albumin hydrolysates on iron binding and absorption were investigated.•Hydrolysates were prepared with pepsin, bacterial and/or fungal enzymes.•In vitro iron absorption from peptide-iron complex or mixture was evaluated using IEC-6 cells.•In vitro iron absorption was higher in peptide-iron complex than post-hydrolysis mixture of iron and peptides.•Results are promising for the development of egg-based functional protein to enhance iron uptake.

One of the causes of iron deficiency in human is poor absorption of non-heme iron from the diet. While proteins from meats have been reported in the literature to enhance the absorption of non-heme iron, other proteins, such as those from egg, are known to inhibit iron absorption. The objective of this study is to investigate non-heme iron binding property of egg white proteins hydrolyzed using pepsin and a combination of bacterial/fungal proteases. The iron bioavailability of non-heme iron, in the presence of egg white (EW) hydrolysates, was evaluated in vitro using a tissues culture model system - rat intestinal epithelial cells (IEC-6). In the first treatment condition, EW was digested in the presence of ferrous gluconate (FeGluc), producing a peptide-FeGluc complex. In the second treatment, EW was digested in the absence of FeGluc followed by the addition of the non-heme iron. In both treatments, the resulting EW hydrolysates were further separated into > 0.1-0.5 kDa and > 6-8 kDa peptide fractions using dialysis. The hydrolysate and FeGluc complex or mixtures were applied to the IEC-6 cells and iron absorption was measured after 2 h or 16 h. Results showed that the peptide-FeGluc complex digested with a combined proteases from Bacillus licheniformis (SDAY) and from Aspergillus melluss (PP) increased the in vitro iron-binding property but did not enhance iron uptake by the in IEC-6 cells (p < 0.05). Peptide-FeGluc complex digested with pepsin alone (> 0.1-0.5 kDa) resulted in significantly higher iron uptake in IEC-6 cells compared with the higher molecular weight complex (> 6-8 kDa) produced using the same hydrolysis treatment. Similarly, enhanced iron uptake was observed with the complexes produced with the combined SDAY and PP enzymatic treatments (> 0.1-0.5 kDa and > 6-8 kDa) (p < 0.05). On the other hand, the enhanced iron absorption effect was not observed when pre-hydrolyzed free peptides were added to FeGluc. Overall, this study suggests that low molecular weight fractions of egg white protein hydrolysates can enhance the bioavailability of non-heme iron. Furthermore, the method by which the egg white proteins are being prepared, i.e., in the presence or absence of FeGluc, can affect the bioavailability of the non-heme iron.

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