English abstract
The coastline in Sultanate of Oman is rich in different raw natural materials such as
seaweed plants. Red seaweeds contain various nutritional compositions such as
carbohydrates, protein, minerals, vitamins, polyphenols, and lipids. These compounds are
used in various applications in food industries or pharmaceutical, nutraceutical, or
cosmetic applications. Hypnea bryoides species belonging to the Rhodophyta group (Red
seaweed) were found to contain a good amount of protein. This study aimed to determine
the proximate composition of the species Hypnea bryoides, extract its organic solvent soluble compounds and investigate its polyphenols contents (TPC, TFC, and TTC), and
extract protein and study its functional and chemical properties. The non-water-soluble
molecules were extracted using five different organic solvents sequentially (Hexane,
DCM, ethyl acetate, acetone and methanol). The protein was extracted in an alkaline
solution (0.3 M NaOH, pH 12). High-Performance Liquid Chromatography (HPLC) was
performed to study the molecular weight of protein and amino acid composition and
profiling. The structural characteristics of the organic solvent extracts and protein were
analyzed by Fourier Transform Infrared (FTIR-ATR) technique. The finding of this study
showed that the carbohydrates (67.57 ± 0.00%) were the most abundant components in
H. bryoides, followed by protein (19.48 ± 0.07%), and the lipid content was found the
lowest (1.01 ± 0.07%). The ash content was 11.87 ± 0.05%, and the main essential
minerals found in the sample were Na, K, Ca, P, Fe, where the Na was detected with the
highest concentration (30.19 ± 0.43 mg/g). The methanolic extract exhibited the highest
polyphenols contents (141.3 ± 0.59, 115.11 ± 3.25 and 36.77 ± 1.05 mg/g of TPC, TFC
and TTC, respectively) among the five fractions. The total yield of protein was 6.00 ±
0.35% and the purity was 88.50 ± 0.71%. The protein showed a higher oil holding
capacity (13.56 ± 0.26 g oil/ g protein) than water capacity (9.61 ± 0.15g water/g protein).
The best protein solubility, emulsifying capacity, emulsifying stability, and foaming
capacity were observed at pH 8 and 10 (P≤0.05). However, pH 4 revealed the best
foaming stability. The in-vitro digestibility of the protein extract was 62.62 ± 3.29%. In
addition, the structural characteristics analyzed by FTIR-ATR demonstrated presence of
α-helix (1,638.2 cm-1
) and β-sheet (1,537.92 cm-1
) structures in the protein extract.
Different protein molecules with a wide range of MWs (0.4 -125.2 kDa) were detected
by HPLC. The result of amino acid profiles showed that the essential amino acids counted
for 35.08% of the total amino acids; and methionine + cysteine was the limiting amino
acid (Amino acid score: 0.003). In conclusion, the organic solvent extracts from H.
bryoides were found with high polyphenols content. The protein content of this seaweed
showed great functional and chemical properties. Therefore, the isolated protein can be
utilized in different food products as an emulsifying or foaming agents. Moreover, future
work could be conducted to focus more on nutritional value (i.e. protein quality and
digestibility) and biological activities of H. bryoides protein.
