Characterization and peptide identification of umami fractions from rusip—a traditional fermented anchovy product

Rusip is a spontaneously fermented anchovy product originating from Bangka Belitung province in Indonesia, used as umami seasoning. This study investigated the characteristics of rusip and its umami fractions to reveal umami peptides in rusip. Six commercial rusip samples from Bangka were analyzed for their proximate composition, pH, total titratable acids, NaCl, total sugars, free glutamic acid, nucleotide (adenosine monophosphate), and total amino acid composition. Umami taste intensity of water-soluble extracts (WSE) was analyzed by a sensory panel. Total plate count and total lactic acid bacteria were also analyzed to assess the microbial variations between the samples. Stepwise ultrafiltration on the highest umami intensity WSE was conducted to obtain three fractions: >5 kDa, 3-5 kDa, and <3 kDa, followed by chromatography fractionation of fraction <3 kDa by Sephadex G-15 gel to acquire umami fractions (F1-F4). Protein (28.94%-44.53% dry weight basis [db]) and NaCl (30.86%-55.73% db) were the major solids of rusip. Concentrations of free glutamic acid (5.79%-8.99% db) in rusip are related with umami intensities of WSE. F1 was the umami fraction with its residual umami amino acids higher than its free ones; therefore, F1 was also a peptide fraction. It contained peptides of 3-12 residues within the highest relative area. Their sequences contained those of umami peptides listed in BIOPEP database. Some of these peptides were also associated with bioactivities. This information could broaden the insight of umami peptides and their bioactivities in fermented foods. PRACTICAL APPLICATION: Rusip is used as a source of umami ingredient in food. The characteristics of product quality of rusip were reported in this study. In addition, the chemical and sensory characteristics as well as peptides of its umami fraction were also described. This information is important for the exploration of umami peptides from fish fermented products.