Structural and functional properties of hemp seed storage proteins

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Date
2020
Authors
Ajibola, Comfort
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Abstract

This study aimed to determine the structural and functional properties of hemp seed storage protein fractions (2S, 7S, and 11S) in comparison to hemp seed protein isolate (HPI). The protein content of 11S, 7S, 2S, and HPI were 91%, 90%, 83%, and 90% respectively. The 11S fraction was the predominant protein in hemp seed and accounted for 72% of the total seed protein. In vitro protein digestibility of the hemp seed proteins ranged from 72.54 to 88.28%. Hemp seed proteins were rich in glutamic acid and sulfur-containing amino acids while limiting in tryptophan and lysine. The SDS-PAGE profiles revealed that the 7S fraction consists of basic subunits (18 kDa to 20 kDa) and high MW polypeptides (47 kDa and 85 kDa). The 11S and HPI fractions had similar polypeptides bands that consist of the basic subunit (18 to 20 kDa), acidic subunit (30 to 40 kDa) and other high MW polypeptides. The 2S profile has seven polypeptides (15 kDa, 19, 80 and 125 kDa) with the 15 kDa in the highest proportion. The intrinsic fluorescence and near-UV data showed that the aromatic amino acids of the protein samples were more exposed to the polar environment. The far-UV data showed that the secondary structures of all the proteins were mostly dominated by -sheet conformation at all the pH values. The 2S fraction was relatively soluble at all the pH values. The 11S fraction and HPI were more soluble at the acidic pH while 7S fraction was soluble at alkaline pH. The 2S and HPI exhibited good oil absorption capacity. The 7S fraction showed better gelling properties when compared to HPI and other fractions. The 2S fraction exhibited higher foaming capacity at all the pH values when compared to HPI and other fractions. The 2S, 7S, and 11S fractions formed better emulsions when compared to HPI emulsions. Overall, the hemp seed protein fractions differ from one another in terms of amino acid composition, polypeptide composition, and protein conformation while their functional properties are superior to those of HPI.

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Keywords
Structural properties, Functional properties, Hemp seed, storage proteins
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