Title: Umami taste characteristics of water extract of Doenjang, a Korean soybean paste:Low-molecular acidic peptides may be a possible clue to the taste Source: Food Chemistry 127 (2011) 1210–1215 Impact factor：3.458 Speaker：Chen,Yi-Lin 5100043001 Moderator：Wei, Shang-Ying Date：101.6.16 The order of reporting：14 1.Introduction： Doenjang is made from fermented soybeans, salt and koji. Koji is a food additive made from grains fermented with Aspergillus oryzae and Bacillus subtilis.Doenjang is widely used in Korea as a soup base or as a seasoning agent. Given the high soybean content,and with koji serving as an enzyme source, we suspected that doenjang proteins are hydrolysed to peptides and amino acids during fermentation and that these compounds contribute to overall taste. Therefore, we investigated the taste characteristics of a water extract of doenjang to determine the contribution of peptides and amino acids, produced during fermentation, to the taste of doenjang. 2. Materials and methods： Doenjang was prepared using steamed soybean (21%), salt(10%), and water (43%), with soybean-based koji (11%) and wheat-based koji (13%) as starters, and fermented at 30℃ for 30 days. (1) Sensory evaluation: Sensory evaluation panellists were recruited from the Korea Food Research Institute and trained to recognise basic tastes. (2) Taste profile analysis: To evaluate the taste profile of DWE, nine pre-trained panelists performed a quantitative descriptive analysis test. Taste profiles for a 1% DWE solution were analysed using a 15-point intensity scale. (3) Difference tests: To evaluate flavour-enhancing and monosodium glutamate (MSG)-substitution effects of DWE,six panellists performed an overall difference tests, using a 5-point intensity scale. (4) Stepwise ultrafiltration: The DWE was fractionated into five different fractions by successive treatments with ultrafiltration membranes. (5) Group fractionation: Fraction IV (F-IV) was further separated into aromatic, basic, acidic,and neutral peptide fractions by a multi-stage process, using systematic column chromatography with activated charcoal. (6) Peptide and amino acid analysis: Total and free amino acid contents were analysed before and after hydrolysis. Free amino acid content was determined using a Hitachi amino acid analyzer. 3. Results and discussion： (1) Taste characteristic of DWE: Umami taste had the highest rating among the five basic tastes for the 1% DWE solution (Fig. 1A). Salty taste had the second highest rating, followed by sour, sweet, and bitter (Fig. 1B). The umami taste intensity of the solution without either MSG or DWE (Model 1) was 0.3, significantly lower than all other solutions (Fig. 2A). With MSG (from 2% to 11.4%),umami taste increased to between 2.5 (Model 2) and 4.7 (chicken bouillon base). With 3% DWE and 2% MSG (Model 3), umami taste intensity was statistically similar to that of the chicken bouillon base. The dilution of HAP in water did not affect the bitter taste sensation, but adding DWE significantly reduced bitter taste intensity (Fig. 2B; P < 0.01). This result also supports the finding that the bitter taste of DWE had the lowest rating(Fig. 1B). (2) Successive DWE fractions and their umami taste intensity characteristics: Total solids content was high in fraction V (F-V), but total peptide content was highest in F-IV (Table 1). Indicating that low-MW compounds contributed to their umami taste.The acidic peptide fraction elicited the highest umami taste (+++); the aromatic peptide fraction was only slightly umami (+), and the basic and neutral peptide fractions had no umami taste. (3) Amino acid profiles of DWE and its successive fractions: Glu was the major total, free, and bound-type amino acid component of DWE (Fig. 4). In our results, the umami tasting-DWE and its taste-active fractions had the highest molar ratio of Glu, followed by Asp, Gly, Ser or Lys or Thr, indicating that these are responsible for the stronger umami taste characteristics. 4. Conclusion： Doenjang water extract (DWE) had a characteristic umami taste profile, and was composed of low-MW compounds produced during fermentation of doenjang. Proteolytic peptides, which had a higher molar ratio of bound-type Glu and Asp, were abundant and considered important contributors to umami taste of DWE. 5.References： (1) Jo, M. N., & Lee, Y. M. (2008). Analyzing the sensory characteristics and taste-sensor ions of MSG substitutes. Journal of Food Science, 73(5), S191–S198 (2) Kuninaka, A., Kibi, M., & Sakaguchi, K. (1964). History and development of flavor nucleotides. Food Technology, 18(3), 29–33. (3) Oka, S., & Nagata, K. (1974). Isolation and characterization of neutral peptides in soy sauce. Agricultural and Biological Chemistry, 38, 1185–1194.