Studies On Extraction Of Protein From Cucumber Seed And Properties Of Peptide Produced By Fermentation

In this paper, cucumber seeds were used as raw material, cucumber seed protein was extracted by alkali extraction and acid precipitation and process optimization to ensure the maximum extraction rate, then functional properties of cucumber seed protein were measured. Cucumber seeds were treated with Bacillus subtilis to produce cucumber seed peptide (CSP) and optimum extraction parameters were determined, at the same time,differences between cucumber protein and peptide were compared. Next, CSP was divided into three different molecular weight peptide components by ultrafiltration, after that theanti-hypertensive activity and calcium chelating ability of each molecular weight peptide were compared. Furthermore, the structure of peptides and peptide-calcium chelate were investigated to confirm the chelating reaction.The optimal extraction process of cucumber seed protein were: extraction solution pH11,solid-liquid ratio 1:30, extraction temperature 90? extraction time 2.5h. When the extraction ratio was considered as the primary index, four factors including extraction solution pH, solid-liquid ratio, extraction temperature, extraction time had important influence.The optimal parameters of fermentation were: fermentation time 2d, fermentation temperature 28?, inoculation amount 8%. When the concentration was considered as the primary index, three factors including fermentation time, fermentation temperature,inoculation amount had important influence.SDS-PAGE analysis suggested that cucumber seed protein was degraded into low-molecular-weight peptide after fermentation; there were changes of structure between protein and peptides with DCS, CD, FTIR spectrums, the molecular forces among residues were weakened and rigid structure changed into flexible structure, which made CSP more digestible and absorbable.CSP was separated into three components which were CSP1 (MW>10KDa), CSP2(6KDa<MW<10KDa) and CSP3 (MW<6KDa) by ultrafiltration, meanwhile, the CSP3 displayed the most excellent ability to with calcium and its calcium chelate ratio was 34.64%. Beyond that, CSP3 combined with bile acid salt effect was superior to other components and hypolipidemic effect is better.CSP3 and CSP3-Ca were selected to investigate structural properties. The microstructures of CSP3 have changed after chelate with calcium were observation by SEM,surfaces of CSP3 and CSP3-Ca wae irregular, however, CSP3-Ca was more loosely and with many different size holes like a floccules structure. The calcium content of CSP-Ca was significantly higher than that of CSP3 by EDS. There were distinctions in the internal structure between CSP3 and CSP3-Ca by UV, FTIR, fluorescence spectroscopy. The result indicated that the chelation reaction has taken place and metal binding sites in CSP3 were involved in coordination with Ca2+ to form the CSP3-Ca chelates, which could be considered as a potential production for calcium supplement.