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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