Extraction And Characterisation Of Proteins From Farmed Red Seaweed (Porphyra umbilicalis) And Wild Red Seaweed (Pyropia columbina)

Abstract

There is considerable demand in providing alternative sources of proteins, especially in developing countries. Proteins extracted from seaweeds could be a promising choice due to their availability and nutrient balance. This study aims to find the optimum extraction condition and to analyse the protein characteristics and functional properties of two red seaweeds, namely the farmed species (Porphyra umbilicalis, in short form FRS) and the wild species (Pyropia columbina, in short form WRS). The single-factor experiment, followed by an orthogonal design experiment, was applied to optimise the extraction condition of protein from these samples. Four factors were studied: solubilisation time, sample-to-solvent ratio, sonication power, and sonication time. Following the extraction and isolation steps were carried out. The protein extracts were then subjected to characterisation assays. Amino acid profiles, protein secondary structures, and molecular weight distribution were analysed using MCF derivatisation by GCMS, FTIR-ATR, and SDSPAGE, respectively. The functional properties of the proteins were analysed, including solubility, emulsifying activity and stability (EAI/ESI), and foaming capacity and stability (FC/FS) assays. The optimum extraction condition for the extraction of alkaline soluble seaweed protein was 40 min solubilisation with 0.4 M NaOH at a sample-to-solvent ratio of 1:25 followed by applying sonication at 225 W for 15 min. For the farmed and wild seaweeds, the protein contents of raw samples were 39.23 ± 2.88 g/100g DW and 32.50 ± 9.14 g/100g DW. The protein content was more concentrated after extraction, and isolation accounting for 65.63 ± 0.48 g/100g DW and 54.16± 0.94 g/100g DW, respectively. Amino acid profiles of both protein extracts showed comparable composition as a recommendation by FAO with EAA (essential amino acid) ratio of 46.30% and 45.67%, respectively. FTIR spectra expressed a low level of denaturation. SDS-PAGE imaging displayed a low molecular weight distribution at around 50 (i.e., only for the farmed seaweed), 20, 15, and 10 kDa. However, the wild seaweed showed smeared bands. Both seaweeds were identified to have an isoelectric point at pH 2–4.5. In general, protein functional properties had a positive correlation with pH conditions. Of the farmed and wild seaweeds, the highest EAI was at pH 12 for both seaweeds (i.e., accounting for 89.74 m2/g and 82.45 m2/g), while ESI was 63.00 min (at pH 12) and 179.33 min (at pH 6), respectively. On the other hand, pH 12 was the best condition of FC and FS. FC was determined as 43.40% and 57.65%, while FS was accounting for 39.66% and 47.64% for FRS and WRS protein extracts, respectively. The seaweed species exhibited suitable essential amino acid composition with comparable functional attributes that can be used as an alternative protein source for human consumption. However, further fractionation steps should be considered to improve protein yield and molecular weight distribution that can benefit from further biorefinery study.