Chelating Properties of Peptides from Red Seaweed Pyropia columbina and Its Effect on Iron Bio-Accessibility

Abstract

The aim of this work was to evaluate copper-chelating, iron-chelating and anticariogenic activity of peptides obtained by enzymatic hydrolysis of P. columbina protein concentrate and to study the effects of chelating peptides on iron bio-accessibility. Two hydrolyzates were obtained from P. columbina protein concentrate (PC) using two hydrolysis systems: alkaline protease (A) and alkaline protease + Flavourzyme (AF). FPLC gel filtration profile of PC shows a peak having molecular weight (MW) higher than 7000 Da (proteins). A and AF hydrolyzates had peptides with medium and low MW (1013 and 270 Da), respectively. Additionally, AF presented free amino acids with MW around 82 Da and higher content of His and Ser. Peptides from AF showed the highest chelating properties measured as copper-chelating activity (the lowest β-carotene oxidation rate: Ro; 0.7 min(-1)), iron-chelating activity (33%), and phosphorous and Ca(2+) release inhibition (87 and 81%, respectively). These properties could indicate antioxidant properties, promotion of iron absorption and anticariogenic activity, respectively. In fact, hydrolyzates promoted iron dialyzability (≈ 16%), values being higher than that found for P. columbina seaweed. Chelating peptides from both hydrolyzates can maintain the iron in a soluble and bio-accessible form after gastrointestinal digestion.

Protein Hydrolysates as Promoters of Non-Haem Iron Absorption

“…Several iron-chelatable peptides were identified from soybean proteins that were hydrolysed by pepsin, trypsin, protease, deamidase and other enzymes [49,51]. Hydrolysates of shrimp, fish and seaweed also have the ability to chelate iron, and several iron-chelatable peptides have been isolated from these sources [32,43,45,46]. …”

“…Peptides that are rich in His have higher iron-chelating activities than other peptides in the hydrolysates of some proteins [31,43,71]. Serine is also an important amino acid that affects the stability of iron-containing peptides, likely due to its hydroxyl group [23].…”

“…Serine is also an important amino acid that affects the stability of iron-containing peptides, likely due to its hydroxyl group [23]. Peptides containing Ser have higher iron and zinc chelating abilities [19,43]. Similar to serine, cysteine also contributes to iron-chelating activity of a peptide due to its sulfhydryl group.…”

“…If the peptides are smaller in size, the proportion of amino and carboxyl groups (the oxygen of the C-terminus and the nitrogen of the N-terminus) will be higher, and the iron chelation activity may be higher as well, and it has been shown that peptides with lower molecular weights have higher iron-chelating activities in protein hydrolysates of P. columbina [43]. The iron-binding capacity of sea cucumber ( Stichopus japonicus ) ovum hydrolysates increased significantly, from 55.7% to 92.1%, as their molecular weight decreased and as the proportion of fractions larger than 1000 Da decreased markedly from 58.5% to 36.4% [74].…”

“…For example, Cys and reduced cysteinylglycine can significantly increase the solubility of iron in a solution containing insoluble iron [58]. Additionally, the hydrolysates of red seaweed ( P. columbina ) protein can maintain iron in a soluble and bioaccessible form after gastrointestinal digestion [43]. CPPs derived from milk proteins with a special sequence of three phosphoseryl residues followed by two glutamic acid residues, Ser(P)-Ser(P)-Ser(P)-Glu-Glu, act as mineral absorption enhancing peptides [8,79,80].…”