Characterization of Umami Fractions Obtained from Spirulina platensis and Its Acid Hydrolysate

Abstract

Spirulina platensis is known as unicellular and fibrous blue-green phytoplankton which grows in both fresh and saltwater through photosynthesis. Spirulina platensis has high reproductive power because biomass can reach 20 times the initial weight within 4-6 days after cultivation. Dried Spirulina platensis has been consumed as a nutraceutical dietary supplement due to its health benefits. Spirulina platensis powder contains high protein which is dominated by glutamic acid. Due to its composition, Spirulina platensis exhibits a fairly high development potential for the umami material. This research is the first research to explore the umami compounds from Spirulina platensis. Hydrolyzed foods commonly have higher umami taste intensity than unhydrolyzed food, for example, the hydrolyze soybeans with strong acid such as acid-hydrolyzed vegetable protein (aHVP) have a much stronger umami taste. In this research, the Spirulina platensis was also hydrolyzed with strong acid to produce simple peptides and free amino acids that may increase the umami taste intensity. To identify the umami compounds, the water soluble extracts (WSEs) of unhydrolyzed and hydrolyzed Spirulina platensis were fractionated using ultrafiltration membrane and gel filtration chromatography. Determination of umami taste intensity in WSEs, ultrafiltration fractions, and chromatography fractions was carried out through the sensory evaluation using the taste dilution analysis (TDA). The analyses of SDS PAGE, pH, total salt, total sugar, total soluble protein, total peptide and amino acid, RP-HPLC profile, organic acid composition, amino acid composition, and peptide sequencing were carried out to determine some simple peptides that contribute to the umami taste in Spirulina platensis. The result showed that hydrolyzed WSE had umami intensity twice higher (DF = 1024) than unhydrolyzed WSE (DF = 512). Each WSE was fractionated using an ultrafiltration membrane (MWCO 3000 Da) to obtain two ultrafiltration fractions, < 3000 Da and > 3000 Da. The ultrafiltration fraction < 3000 Da of hydrolyzed WSE had four times (DF = 1024) higher umami intensity than another fraction, > 3000 Da (DF = 256). On the other hand, the ultrafiltration fraction < 3000 Da of unhydrolyzed WSE had twice (DF = 512) higher umami intensity than fraction > 3000 Da (DF = 256). The chemical composition, especially total peptide and amino acid was more abundant in the ultrafiltration fractions < 3000 Da compared with ultrafiltration fractions > 3000 Da in both treatments. Therefore, the peptides with molecular weight less than 3000 Da have the potential to give the umami taste in algal hydrolyzate. Both ultrafiltration fractions < 3000 Da were fractionated using a gel filtration chromatography (Sephadex-G25). The hydrolyzed fraction was separated into four chromatography fractions (H1, H2, H3, and H4) while the unhydrolyzed fraction was separated into three chromatography fractions (U1, U2,and U3). The umami fraction H2 and U3 had rich in salt with DF umami 512 and 256 which mean that they had high umami intensity. The free glutamic acid concentrations of fraction H2 and U3 were about 3 and 1,5 times higher than the glutamic acid threshold, however, their intensity of the umami taste can reach up to 256 and 512 times. This result indicated the role of peptides or other components which caused the high intensity of umami taste. Both fractions H2 and U3 had succinic acid concentration about 20 and 6 times higher than the succinic acid threshold. The succinic acid is known to contribute to the umami taste. These fractions had also some dominant hydrophilic peaks in RP-HPLC profiles that indicated the presence of hydrophilic compounds such as free amino acids, succinic acid, and hydrophilic peptides. Moreover, 19 peptides were identified in fraction H2 while in fraction U3, the peptide which had low molecular weight was not detected by HR-LC-ESI-MS-MS. Nine of 19 simple peptides (Asn-Lys-Pro-Ala-Leu-Ala-Val-Glu-Ala-Phe, Asn-Gln-Arg-Gln-Trp-Arg-Glu-Ala-Ile-Asp, Ser-Arg-Ile-Glu-Glu-Ile-His-Arg, Glu-Phe-Val, Pro-Ser-Glu, Glu-Leu-Glu, Glu-Leu, Glu-Met, and Glu-Ala) or almost half of identified peptides had glutamic acid (Glu) residue(s) that may play an important role in the umami taste of hydrolyzed Spirulina platensis.