Taste Quality of the Hot Water Extract from Flammulina velutipes and its Application in Umami Seasoning

Abstract

Flammulina velutipes, also called enokitake, is usually used for soup cuisine in Taiwan. For health concern to reduce the use of monosodium glutamate (MSG), mushrooms are a particular alternative of interest. Accordingly, we prepared the extract using thermal processing. Commercial protease was added before extraction. Contents of total free amino acids in Bromelain and commercial enzyme extracts (100.74 and 97.34 mg/g dry matter) were higher than that in the hot water extract (WE, 84.94 mg/g dry matter) but contents of umami amino acids were not increased. However, WE showed the highest equivalent umami concentration (241.29 g MSG/100 g dry matter). Sensory study showed that 0.3% WE or 0.3% powder was equivalent to 0.3% MSG but less sweet than 2% sucrose. In vegetable soups, 0.1% WE showed sensory results of 4.83-5.50 at a nine-point hedonic scale. Nevertheless, 0.05% WE and 0.05% MSG was comparable to 0.1% MSG. Overall, WE could be developed for umami seasoning.

Introduction

Many edible mushrooms are delicious and have long been consumed as food and food flavoring. The typical mushroom flavor consists of water-soluble taste components including soluble sugars, polyols, free amino acids and 5′-nucleotides (Litchfield, 1967). The main flavor of mushrooms is the umami taste, which is also called the palatable taste or the perception of satisfaction and it is an overall perception induced or enriched by monosodium glutamate (MSG) and 5′-nucleotide (Yamaguchi, 1979). The umami taste can alleviate a salty, sour, or bitter taste; improve the perception of a sweet taste; and lower the sharp irritation of onion, the raw odor of meat, and the earthy note of potatoes (Mau, 2005). As a result, mushrooms can be widely used as a seasoning in most foods such as meat, seafood, soup, stews, and cooked vegetables. The development of umami seasonings has been diversified in Taiwan. MSG and other complex seasonings such as chicken powder, beef powder and yeast powder are very popular in seasoning companies. For health concern to reduce the use of MSG in umami seasonings, mushrooms are a particular alternative of interest since they contain high amounts of water-soluble taste components in addition to umami amino acids and umami 5′-nucleotides.

Flammulina velutipes    [Curtis: Fries] Sing., also called enokitake, winter and golden mushroom, is cultivated as an abnormal feature of small caps and long stipes and usually used for soup cuisine in Taiwan (Yang et al., 2001). It is one of the most popular mushrooms through its attractive taste and high nutrition values of essential amino acids, vitamins and fiber (Dong et al., 2017; Donglu et al., 2017). Furthermore, it contains a numerous bioactive compounds, such as polysaccharide, ergothioneine, and γ-aminobutyric acid (GABA), and lovastatin (Chen et al., 2012; Zhang et al., 2013). Many studies have shown that hot water extracts extracted from Flammulina velutipes contain bioactive compounds, especially polysaccharides, are good antioxidants, antimicrobial activity, antiinflammatory, and antitumor (Leung et al., 1997; Pang et al., 2007; Wu et al., 2010; Chang et al., 2013; Zhang et al., 2013; Dong et al., 2017).

In addition to fresh market, Flammulina velutipes has been also processed into canned food in Taiwan. However, there is little information is available regarding the umami seasoning processing. Besides, the application of protease in making umami seasonings can enhance the umami taste by releasing more amino acids, especially umami amino acids, aspartic and glutamic acids. Accordingly, our objective is to make the extract from F. velutipes for umami seasoning using thermal processing. In addition, since enzyme would be heat-inactivated, the commercial protease was added before the thermal extraction. The content of taste components of the extract was analyzed and its sensory intensity was evaluated. Finally, the vegetable soup with the extract added was sensory evaluated.

Materials and Methods

Extract and powder preparation    Fresh F. velutipes were purchased from Taiwan Fresh Supermarket (Taichung, Taiwan). Two-stage thermal processing including 50°C holding and 100°C extraction was applied. First, F. velutipes was blended with water at the ratio of 1:2 (w/w) for 10 sec, put into a steam-jacketed kettle, held at 50°C for 1 h and then heated to 100°C for 30 min. After extraction, the mixture was passed through a 0.6 mm filter. The extract filtered was freeze dried whereas the residue was not pressed further and saved for other product, such as an extruded granulate seasoning. The extract prepared without enzyme added was called the hot water extract (WE).

Bromelain (Shing Jih Perfumery Co., Taipei, Taiwan) was added at 0.3% (enzyme to mushrooms, w/w) during the 50°C holding stage, held for 1 h and then heated to 100°C for 30 min. After extraction, the mixture was passed through a 0.6 mm filter and freeze dried. The extract prepared with Bromelain added was called the bromelain extract (BE). In addition, commercial enzymes Protamex and Flavourzyme (Trump Chemicals Co., Taipei, Taiwan) were used. Protamex was added first at 1% (enzyme to mushrooms, w/w) during the 50°C holding stage, held for 2 h and Flavourzyme was then added at 0.5%, held for 1 h and finally heated to 100°C for 30 min. After extraction, the mixture was passed through a 0.6 mm filter and freeze dried. The extract prepared with commercial enzymes added was called the commercial enzymes extract (CEE). For the comparison, fresh F. velutipes was cut, freeze-dried, ground and screened through a 0.6 mm sieve as powder.

Determination of free amino acids and 5′-nucleotides and equivalent umami concentration    Free amino acids were analyzed according to the methods used in Chen et al. (2012). 5′-Nucleotides were determined following the methods used in Tsai et al. (2007). Each compound was identified and quantified by the calibration curve of the authentic compound. The equivalent umami concentration [EUC, mg monosodium glutamate (MSG)/100 g] was calculated on the basis of the addition equation established in Yamaguchi et al. (1971). EUC is the concentration of MSG equivalent to the relative umami intensity which is given by the mixture of MSG and 5′-nucleotide.

Proximate analysis and determination of soluble sugars and polyols    The proximate compositions of the extracts and powder, including moisture, crude protein, fat, ash and fiber were analyzed on the basis of the methods of AOAC (1990). The nitrogen conversion factor used for crude protein content was 4.38 (Crisan and Sands, 1978). The carbohydrate content (%, w/w) was calculated by subtracting the contents of crude protein, fat and ash from 100% of dry matter. Reducing sugars were measured using the 3,5-dinitrosalicylic acid (DNS) method described in James (1995) and calculated by the calibration curve of glucose. Sugars and polyols were determined according to the methods used in Tsai et al. (2007). Each sugar or polyol was identified and quantified on the basis of the calibration curve of the authentic compound.

Sensory evaluation of the extract and powder    The umami and sweet tastes of the extract and powder were sensory evaluated by seven trained panelists (two males and five females, 27–38 years old), which had been well-trained in recognizing five basic tastes including sour, sweet, bitter, salty and umami tastes. The test samples prepared were A: 0.3% (w/w) WE, B: 0.3% powder, C: 0.3% powder and 0.1% 5′-inosine monophosphate/5′-guanosine monophosphate (5′-IMP/5′-GMP), D: 0.3% MSG and 0.1% 5′-IMP/5′-GMP, and E: 0.3% MSG and 2% sucrose in 100 g water for umami and sweet tastes, respectively. Two E samples were used as standards to calibrate the results to avoid over-dispersion. First, panelists were seated in individual sensory booth and received two samples with random three-digit numbers, and two E samples. Moreover, the panelists were given distilled water to rinse their mouth between samples. After the test, the panelists rested for 5 min and then received another two samples and two E samples. The samples were served at 25°C and sensory evaluated using a nine-point scale (1 = extremely light umami or sweet, 9 = extremely strong umami or sweet) and 0.3% MSG and 2% sucrose were the umami and sweet standards with a sensory intensity of 5.

Sensory evaluation of vegetable soups    The ingredients for basic vegetable soup powder (100 g) were salt (50 g), sucrose (21 g), glycine (3 g), alanine (3 g), 5′-IMP/5′-GMP (2 g), yeast powder (5 g), onion powder (3 g), tomato powder (3 g), and maltodextrin (10 g). The maltodextrin in basic vegetable soup powder (10 g) was substituted by MSG (10 g), MSG and WE (5 g each) and WE (10 g) for vegetable soup powders F, G and H, respectively. Various vegetable soup powders (basic, F, G and H, 1 g) were dissolved in 100 g of hot water to make vegetable soups. The hedonic test was used to determine the degree of appearance, aroma, umami, sweet, salty, taste and overall preference for the vegetable soups. Untrained consumers (n = 60, 19–24 years old) were recruited from the students at National Chung Hsing University and were asked to rate them based on degree of preference on a nine-point hedonic scale (1 = dislike extremely, 5 = neither like nor dislike, 9 = like extremely). The consumers were seated in individual sensory booths and provided with distilled water to rinse between samples, and the vegetable soups were served at 50°C.

Statistical analysis    Each measurement was conducted in triplicate, except for the sensory evaluation of the extract and powder (n = 7) and vegetable soups (n = 60). All data were analyzed using an analysis of variance followed by Duncan's multiple range tests to determine significant differences among the means at the level of α = 0.05 (SAS Institute, Cary, NC, USA). In addition, principal component analysis (PCA) using Xlstat 2014 (Addinsoft, Inc., Brooklyn, NY, USA), a multivariate analysis in data reduction, was used to identify latent variables that explain the pattern of correlation within the observed variables. The correlations within three different extracts and powder and compounds were present as score and loading plots, respectively.

Results and Discussion

The extract from F. velutipes    The inputs of blended mixture (F. velutipes to water at 1:2, w/w) were ∼ 3000 g but the outputs were 2584.3–2689.3 g (Table 1). During two-stage thermal processing, the steam-jacketed kettle was open to the atmosphere; and therefore, the evaporation caused the weight loss. In addition, enzyme treatments took longer time so that samples lost more moisture and the recovery was less. After extraction, commercial enzymes yielded the highest extract whereas bromelain yielded the lowest. However, after freeze drying, the solids showed the reverse trend. It seems that the extract from BE treatment was thicker. The pH values of the extract were similar (6.38–6.46). Three extracts showed yellow color; with bromelain treated the color was darker; and with commercial enzymes treated the color was the darkest. The color change might be due to the Maillard reaction during enzyme treatment and heat treatment. With more soluble components hydrolyzed from commercial enzymes, CEE was darker than BE.

Table 1. The parameters for the processing of extracts from F. velutipes

	WE1	BE	CEE
Extraction process
Total input (g)	2997.7 ± 2.5a3	3000.0 ± 4.0a	3004.3 ± 5.0a
Total output (g)	2689.3 ± 4.5a	2604.0 ± 5.6b	2584.3 ± 5.5c
Recovery (%)2	89.71 ± 0.23a	86.80 ± 0.14b	86.02 ± 0.24c
Filtration process
Extract (g)	1631.2 ± 1.8b	1375.3 ± 4.1c	1678.3 ± 1.0a
Extract (%)	60.66 ± 0.03b	52.81 ± 0.03c	64.94 ± 0.05a
Solids (% dry matter)	2.03 ± 0.01c	2.54 ± 0.01a	2.47 ± 0.01b
pH	6.46 ± 0.02a	6.38 ± 0.05a	6.42 ± 0.02a

¹  WE, hot water extract; BE, bromelain extract; and CEE, commercial enzymes extract.

²  Recovery (%) = (Total output/Total input) × 100%; Extract (%) = (Extract (g)/Total output (g)) × 100%. Solids (% dry matter): The solids contents are direct values obtained after freeze-drying.

³  Each value is expressed as mean ± SE (n = 3). Means with different letters within a row differ significantly (P < 0.05).

Contents of free amino acids and 5′-nucleotides and equivalent umami concentration    In the freeze-dried samples, total free amino acids contents of the extracts with enzyme treated (BE and CEE) were higher than that of WE, and that of WE was in turn higher than that of the powder (Table 2). It is obvious that hot water could only extract soluble components and enzyme could further hydrolyze protein into free amino acids so that total amino acids contents increased significantly. Therefore, the profiles of amino acids of the freeze-dried extract and powder differed widely. The glycine contents in the freeze-dried CEE and BE are higher than those of WE and powder. The higher glycine content would result in a more intensive sweet perception (Chen, 1986). However, the contents of umami amino acids, aspartic and glutamic acids, was not increased as enzyme treated further. Total 5′-nucleotide contents of the extracts were 3.76–4.59 mg/g dry matter, less than that of the powder (Table 2). In addition, the profile of six 5′-nucleotides also varied entirely. Both of 5′-CMP and 5′-UMP content are the two higher components in the extracts and powder, but they are not related to umami taste (Yamaguchi et al., 1971). The content of relative umami 5′-nucleotide, including 5′-AMP, 5′-GMP, 5′-IMP and 5′-XMP, are lower in the extracts and powder.

Table 2. Content of free amino acids and 5′-nculeotides of freeze-dried extracts from F. velutipes

	Content (mg/g dry matter)
	WE1	BE	CEE	Powder
Amino acid
L-Alanine	5.30 ± 0.13b3	6.73 ± 0.94a	7.41 ± 0.23a	3.65 ± 0.25c
L-Arginine	7.70 ± 0.79a	8.92 ± 0.78a	8.66 ± 0.88a	3.83 ± 0.37b
L-Aspartic acid	8.17 ± 1.07a	6.80 ± 0.68b	4.69 ± 0.50c	5.64 ± 0.17bc
L-Glutamic acid	14.95 ± 0.09b	10.81 ± 0.57c	7.92 ± 1.05d	17.65 ± 1.33a
Glycine	6.88 ± 0.31c	8.09 ± 0.32b	9.04 ± 0.60a	5.51 ± 0.35d
L-Histidine	3.23 ± 0.03c	4.29 ± 0.58b	5.68 ± 0.39a	1.01 ± 0.05d
L-Isoleucine	2.70 ± 0.33c	4.11 ± 0.55b	5.49 ± 0.48a	1.80 ± 0.05d
L-Leucine	3.56 ± 0.39c	6.26 ± 0.83b	8.22 ± 0.69a	2.53 ± 0.04c
L-Lysine	11.84 ± 0.46b	16.44 ± 0.88a	11.63 ± 0.99b	7.70 ± 0.81c
L-Phenylalanine	7.07 ± 0.94b	9.13 ± 1.31a	8.36 ± 0.71ab	7.66 ± 0.33ab
L-Serine	2.07 ± 0.06c	3.21 ± 0.34a	2.49 ± 0.14b	1.79 ± 0.03c
L-Threonine	6.88 ± 0.31c	8.09 ± 0.32b	9.04 ± 0.60a	5.51 ± 0.35d
L-Valine	4.59 ± 0.68b	7.86 ± 1.05a	8.71 ± 0.06a	2.51 ± 0.36c
Total	84.94 ± 2.77b	100.74 ± 5.40a	97.34 ± 2.88a	66.79 ± 0.87c
5′-Nculeotide2
5′-AMP	0.23 ± 0.02a	0.19 ± 0.01b	0.05 ± 0.01d	0.17 ± 0.01c
5′-CMP	2.25 ± 0.02b	1.98 ± 0.04c	0.97 ± 0.06d	2.58 ± 0.05a
5′-GMP	0.32 ± 0.02a	0.28 ± 0.04b	0.08 ± 0.01d	0.23 ± 0.02c
5′-IMP	0.21 ± 0.02c	0.35 ± 0.01b	0.45 ± 0.01a	0.09 ± 0.01d
5′-UMP	1.13 ± 0.02c	0.84 ± 0.02d	1.21 ± 0.04b	1.70 ± 0.04a
5′-XMP	0.45 ± 0.11c	0.53 ± 0.03b	1.00 ± 0.06a	0.28 ± 0.01d
Total	4.59 ± 0.07b	4.17 ± 0.08c	3.76 ± 0.06d	5.05 ± 0.11a

¹  WE, hot water extract; BE, bromelain extract; and CEE, commercial enzymes extract.

²  5′-AMP, 5′-adenosine monophosphate; 5′-CMP, 5′-cytosine monophosphate; 5′-GMP, 5′-guanosine monophosphate; 5′-IMP, 5′-inosine monophosphate; 5′-UMP, 5′-uridine monophosphate; 5′-XMP,5′-xanthosine monophosphate.

³  Each value is expressed as mean ± SE (n = 3). Means with different letters within a row differ significantly (P < 0.05).

Using the addition equation established from sensory evaluation in Yamaguchi et al. (1971), EUC values of the freeze-dried extracts (WE, BE and CEE) and powder were 241.29, 188.26, 127.80 and 182.89 g MSG/100 g dry matter, respectively (Table 3). A EUC of 100% represents that the umami intensity per 1 g dry matter is equivalent to the umami intensity given by 1 g of MSG. In other words, WE, BE, CEE and powder were equivalent to 2.41, 1.88, 1.28 and 1.83 g MSG/g dry matter. It seems that WE and CEE showed higher and lower umami intensity than powder, respectively whereas BE and powder were comparable. Accordingly, WE and BE would be used for umami seasoning and their proximate composition and contents of soluble sugars and polyols were studied further.

Table 3. The equivalent umami concentration (EUC) of extracts from F. velutipes

	Content (g/100 g dry matter)
	WE1	BE	CEE	Powder
Total MSG	1.56 ± 0.09b3	1.13 ± 0.06c	0.83 ± 0.11d	1.81 ± 0.13a
Total IMP	0.13 ± 0.02a	0.14 ± 0.01a	0.13 ± 0.01a	0.08 ± 0.01b
EUC2	241.29 ± 27.01a	188.26 ± 10.85b	127.80 ± 21.84c	182.89 ± 4.77b

¹  WE, hot water extract; BE, bromelain extract; and CEE, commercial enzymes extract.

²  Calculated based on the equation: Y = ∑a_ib_i + 1218 (∑a_ib_i) (∑a_jb_j) (Yamaguchi et al., 1971), where Y is the EUC of the mixture in terms of g MSG/100 g; a_i is the concentration (mg/100 g) of each umami amino acid [aspartic acid (Asp) or glutamic acid (Glu)]; a_j is the concentration (g/100 g) of each umami 5′-nucleotide (5′-IMP, 5′-GMP, 5′-XMP or 5′-AMP); b_i is the relative umami concentration (RUC) for each umami amino acid to MSG (Glu, 1 and Asp, 0.077); b_j is the RUC for each umami 5′-nucleotide to 5′-IMP (5′-IMP, 1; 5′-GMP, 2.3; 5′-XMP, 0.61 and 5′-AMP,0.18); and 1218 is a synergistic constant based on the concentration (g/100 g) used.

³  Each value is expressed as mean ± SE (n = 3). Means with different letters within a row differ significantly (P < 0.05).

To visualize 19 compounds detected in the extracts and powder and provide the relative interpretations, PCA was used in data reduction to obtain several orthogonal variables, known as principal components. For 19 compounds, the first two components (F1 and F2) explained the 90.50% (68.10% + 22.40%) of the total variation (Figure 1). PCA score plot shows that the freeze-dried extracts and powder were quantitatively distinguished as four sets of three replicates, indicating that four samples had entirely different profiles of compounds. Besides, in plots for compounds (Figure 1A), BE and CEE had positive values in F1 whereas WE and BE had positive values in F2.

Fig. 1.

PCA of free amino acids and 5′-nculeotides of freeze-dried extracts from F. velutipes. Score (A) and loading plots (B). WE, hot water extract; BE, bromelain extract; and CEE, commercial enzymes extract.

The compounds were dispersed actinomorphically from the origin (Figure 1B). About two thirds of compounds (13/19) had positive values in F1 whereas near two thirds of compounds (12/19) had positive values in F2. From the score and loading plots, BE and CEE positively correlated with 11 amino acids and two umami 5′-nucleotides (5′-IMP and 5′-XMP) in F1; WE positively correlated with five compounds including two umami acids (aspartic and glutamic acids), two umami 5′-nucleotides (5′-GMP and 5′-AMP) and 5′-CMP; and powder only positively correlated with 5′-UMP. It can explain why WE showed the strongest umami intensity. It is obvious that enzyme treatment increased contents of amino acids other than umami amino acids and thereby, diluting the concentration of umami amino acids in the freeze-dried extracts. Since enzyme could increase the content of other amino acids other than the content of umami amino acids, the enzyme should be used to make products for nutrient supplement such as chicken essence instead of umami seasoning.

In summary, the freeze-dried extracts and powder were well-separated in score plots and compounds were individually dispersed using PCA. These results could also confirm that the freeze-dried extracts and powder contained different profiles of free amino acids and 5′-nucleotides.

Proximate composition and contents of soluble sugars and polyols    The freeze-dried extracts and powder showed low amounts of moisture and were 2.57–3.87% (Table 4). The WE showed higher carbohydrate content but the lowest reducing sugar and crude fiber contents, indicating that the soluble polysaccharide content (carbohydrate content - reducing sugar content - crude fiber content) (Ulziijargal and Mau, 2011) was the highest (60.81%). Several studies have displayed that the polysaccharides is the major component in the hot water extract, which possess good antioxidant, antimicrobial, antiinflammatory, and antitumor activities (Leung et al., 1997; Pang et al., 2007; Wu et al., 2010; Chang et al., 2013; Zhang et al., 2013; Dong et al., 2017). The crude protein content of BE was the highest, which was the result of bromelain hydrolysis. Crude ash content was higher in the freeze-dried WE extract whereas crude fat and fiber contents were lower in the freeze-dried WE and BE extracts. It seems that ash was solubilized during thermal processing and fat and fiber were absorbed by the residue.

Table 4. Proximate composition of extracts from F. velutipes

	Content (%)
	WE1	BE	Powder
Moisture2	2.57 ± 0.05c3	3.17 ± 0.03b	3.87 ± 0.04a
Carbohydrate	74.66 ± 1.84a	71.34 ± 1.13b	73.31 ± 0.54b
Reducing sugar	13.28 ± 0.34c	16.26 ± 0.19b	19.64 ± 0.13a
Crude fiber	0.57 ± 0.06c	1.49 ± 0.13b	5.35 ± 0.56a
Crude protein	13.24 ± 1.66c	18.25 ± 1.42a	16.43 ± 0.43b
Crude fat	0.77 ± 0.04b	0.36 ± 0.04c	2.12 ± 0.05a
Crude ash	11.33 ± 0.08a	10.05 ± 0.2b	8.14 ± 0.02c

¹  WE, hot water extract; BE, bromelain extract; and CEE, commercial enzymes extract.

²  Moisture was presented on air-dried matter basis; others were presented on dry matter basis.

³  Each value is expressed as mean ± SE (n = 3). Means with different letters within a row differ significantly (P < 0.05).

The freeze-dried WE and BE extracts showed higher amounts of soluble sugars and polyols, indicating that thermal processing could extract more sugars and polyols (Table 5). Among five sugars and polyols detected, glucose content was the first highest (27.83–37.87 mg/g) and mannitol content (12.75–15.48%) was the second highest in the freeze-dried extracts and powder. These soluble sugars and polyols would contribute a moderately sweet taste.

Table 5. Content of soluble sugars and polyols of extracts from F. velutipes

	Content (mg/g dry matter)
	WE1	BE	Powder
Arabinose	6.05 ± 0.18b2	6.55 ± 0.32a	5.63 ± 0.12c
Glucose	35.23 ± 0.83a	37.87 ± 1.44a	27.83 ± 2.84b
myo-Inositol	9.12 ± 0.31b	9.69 ± 0.34ab	11.03 ± 1.44a
Mannitol	12.95 ± 0.82b	15.48 ± 0.91a	12.75 ± 0.58b
Trehalose	8.69 ± 0.21b	9.35 ± 0.36a	6.84 ± 0.71c
Total	72.04 ± 2.25b	78.94 ± 3.32a	64.08 ± 5.12c

¹  WE, hot water extract; BE, bromelain extract; and CEE, commercial enzymes extract.

²  Each value is expressed as mean ± SE (n = 3). Means with different letters within a row differ significantly (P < 0.05).

Sensory results of the extract and powder    Since WE showed the strongest umami intensity, WE was used to study its sensory umami and sweet intensities and powder, 5′-IMP/5′-GMP and MSG were used for comparison. Besides, two standards 0.3% MSG and 2% sucrose were used to calibrate the sensory results. Samples A and B were prepared from 0.3% WE and 0.3% powder, respectively. Based on their EUC in Table 3, samples A and B were equivalent to 0.72% and 0.55% MSG, higher than sample E. It is consistent that samples A and B were perceived more umami than sample E at 5 but both did not differ in umami intensity (Table 6). Undoubtedly, 0.3% WE or 0.3% powder was equivalent to 0.3% MSG. In addition, samples C and D were prepared from 0.3% powder with 0.1% 5′-IMP/5′-GMP and 0.3% MSG and showed significantly stronger umami taste than sample E. It is obvious that the umami taste was enhanced by the addition of 5′-nucleotides or MSG (Yamaguchi, 1979).

Table 6. Sensory intensity of freeze-dried F. velutipes extract and powder

	Sample1
	A	B	C	D	E
Umami	5.71 ± 1.25b2	5.43 ± 0.98b	8.14 ± 1.07a	7.29 ± 0.76a	53
Sweet	3.00 ± 0.82c	3.14 ± 0.69c	6.57 ± 1.51a	5.00 ± 1.29b	53

¹  A, 0.3% hot water extract; B, 0.3% powder; C, 0.3% powder + 0.1% 5′-IMP/5′-GMP; D, 0.3% MSG + 0.1% 5′-IMP/5′-GMP; E-umami, 0.3% MSG; E-sweet, 2% sucrose.

²  Each value is expressed as mean ± SE (n = 7). Means with different letters within a row differ significantly (P < 0.05).

³  Umami, 0.3% MSG as the standard with the sensory intensity of 5; sweet, 2% sucrose as the standard with the sensory intensity of 5.

Based on their contents in Table 5, samples A and B contained 0.022% and 0.019% soluble sugars and polyols. Besides, all these sugars and polyols were much less sweet than sucrose (Ensminger and Ensminger, 1993). Therefore, the sweetness of samples A and B would be extremely low and insignificant. However, the sweet intensities of samples A and B were evaluated to be 3.00 and 3.14, less sweet than sample E (Table 6). Nevertheless, samples C showed significantly more sweet taste than sample E and sample D was as sweet as sample E. It proves that the umami taste could improve the perception of a sweet taste (Mau, 2005). Overall, using sensory evaluation to validate EUC, we found that the calculated values and the actual sensory results had a positive correlation. Besides, the addition of 5′-IMP/5′-GMP to the sample could significantly increase its umami and sweet perception.

Sensory results of vegetable soups    The vegetable soup was prepared by dissolving vegetable soup powder (1 g) in 100 g of hot water. After calculation, the amount of the ingredients in vegetable soup powder was divided by 100. Therefore, the major test ingredient in vegetable soups F, G and H was 0.1% MSG, 0.05% MSG and 0.05% WE, and 0.1% WE, respectively. Sensory results in seven attributes were 4.83–6.00 (Figure 2). Four vegetable soups perceived similar in appearance, aroma and sweet attributes. Basic vegetable soup and vegetable soups F and G were comparable. However, vegetable soup H (0.1% WE) showed sensory results of 4.83–5.50 but was lower in scores of umami, sweet, salty, taste and overall perception. It seems that 0.1% WE could not completely replace 0.1% MSG. The reason for the lower sensory scores might be due to a unique mushroom flavor introduced. Nevertheless, WE could replace MSG by 50%. For further application, the formulation of vegetable soup could be manipulated to find the better combination. Besides, WE used as umami seasoning in other products such as instant drink or sauce would be an area of investigation.

Fig. 2.

Radar plot of sensory results of vegetable soups. Basic, ; F (+ 0.1% MSG), ; G (+ 0.05% MSG and 0.05% WE), ; and H (+ 0.1% WE), . WE, hot water extract from F. velutipes; MSG, monosodium glutamate.

Conclusion

For umami seasoning, the extract of F. velutipes was prepared using two stage thermal processing. Enzyme was added at the 50°C holding stage before 100°C extraction. With enzyme treated, contents of total free amino acids were higher but contents of umami amino acids were not increased. Besides, with enzyme treated, crude protein content of BE increased. However, WE showed the highest EUC. Sensory results showed that 0.3% WE or 0.3% powder was equivalent to 0.3% MSG in umami intensity but less sweet than 2% sucrose. In vegetable soups, 0.1% WE showed slightly lower sensory results in umami, salty, taste and overall attributes. Nevertheless, 0.05% WE and 0.05% MSG was comparable to 0.1% MSG. Overall, WE could be used in umami seasoning.

Acknowledgement    This study was supported by the Ministry of Science and Technology, Taiwan, Republic of China (MOST-105- 2911-I-005-301, MOST-104-2911-I-005-301) and the Ministry of Education, Taiwan, R.O.C. under the ATU plan.

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