Non-volatile taste components of several cultivated mushrooms

Food Chemistry 143 (2014) 427–431

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Non-volatile taste components of several cultivated mushrooms Wen Li a, Zhen Gu b, Yan Yang a,⇑, Shuai Zhou a, Yanfang Liu a, Jingsong Zhang a a b

National Engineering Research Center of Edible Fungi; Key Laboratory of Edible Fungi Resources and Utilization (South), Ministry of Agriculture, the People’s Republic of China College of Life and Environment Science, Shanghai Normal University, 100 Haisi Road, Shanghai 200234, China

a r t i c l e

i n f o

Article history: Received 19 June 2013 Received in revised form 19 July 2013 Accepted 1 August 2013 Available online 9 August 2013 Keywords: Cultivated mushrooms Soluble sugar/polyol Free amino acid 50 -Nucleotide Organic acid Equivalent umami concentration

a b s t r a c t Five species of dried mushrooms are commercially available in China, namely Agrocybe cylindracea, Pleurotus cystidiosus, Agaricus blazei, Pleurotus eryngii, and Coprinus comatus, and their nonvolatile taste components were studied. Trehalose (12.23–301.63 mg/g) and mannitol (12.37–152.11 mg/g) were considered as the major mushroom sugar/polyol in the five test species. The total free amino acid levels ranged from 4.09 to 22.73 mg/g. MSG-like components contents ranged from 0.97 to 4.99 mg/g. 50 -Nucleotide levels ranged from 1.68 mg/g in P. eryngii to 3.79 mg/g in C. comatus. Fumaric acid (96.11 mg/g) in P. cystidiosus were significantly higher compared with the other mushrooms, and citric acid (113.13 mg/ g), as the highest of any organic acid among the five mushrooms, were found in A. blazei. Equivalent umami concentrations values in these five test mushrooms ranged from 11.19 to 88.37 g/100 g dry weight. A. blazei, C.comatus and A. cylindracea possessed highly strong umami taste. Ó 2013 Elsevier Ltd. All rights reserved.

1. Introduction Edible mushrooms have long been used as traditionally seasoning materials in soups and sauces, due to their special and subtle flavors. The typical flavor of mushrooms consists of nonvolatile components and volatile compounds. The taste of edible mushrooms is primarily due to the presence of several small water soluble substances, including soluble sugars, free amino acids and 50 -nucleotides. Five such species, Agrocybe cylindracea, Pleurotus cystidiosus, Agaricus blazei, Pleurotus eryngii and Coprinus comatus, are cultivated commercially in China, and have become increasingly popular recently due to their delicious taste and unique texture. With the exception of P. cystidiosus, these mushrooms generally have long stripes and closed caps when grown commercially. It is considered by many people that A. cylindracea, also called the black poplar mushroom (Leu, 1992), has a more chewy texture than oyster mushrooms (Pleurotus spp.) dose, and it has a better taste than shiitake (Lentinula edodes) (Mau, 2005) dose. P. cystidiosus, also called the ‘summer oyster mushroom’, has oyster-like tastes but is of vegetable nature (Stamets, 1993), while A. blazei, commonly known as the almond mushroom or ‘mushroom of the sun’ has the fragrance of almonds, and is native to Brazil. Aqueous extracts of this species have also been used as a food additive to provide an

⇑ Corresponding author. Tel.: +86 21 62209765; fax: +86 21 62201337. E-mail address: [email protected] (Y. Yang). 0308-8146/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodchem.2013.08.006

agreeable bitter taste (Kuroiwa et al., 2005). P. eryngii, also known as the ‘king trumpet mushroom’, is the largest of the oyster mushroom species, young specimens of which have a thick, white, meaty stem and a small tan cap. The natural habitat of this mushroom, which is considered to be of high gastronomic quality due to its delicate almond flavor and abalone texture, ranges from the Atlantic Ocean through the Mediterranean Basin and Central Europe into Western Asia and India (Zervakis, Venturella, & Papadopoulou, 2001). C. comatus, the ‘shaggy ink cap’, ‘lawyer’s wig’ or ‘shaggy mane’, is a common fungus, often seen growing on lawns, along gravel roads and wasteland. Young fruit bodies, before the gills start to turn black, are edible, have a mild taste, and can be used in mushroom soup together with the parasol mushroom, Macrolepiota procera. Microwaved-then-frozen shaggy manes are delicious when used as the liquid component of risotto, replacing the usual chicken stock. The taste components of mushrooms, including fruit bodies and mycelia, have been extensively studied and their equivalent umami concentrations were calculated (Chiang, Yen, & Mau, 2006; Cho, Choi, & Kim, 2010; Huang, Tsai, Lee, & Mau, 2006; Tsai, Huang, & Mau, 2006; Tseng, Lee, Li, & Mau, 2005; Yang, Lin, & Mau, 2001). However, little was known about the chemical composition and taste component profiles of these five mushrooms, especially the organic acids of these mushroom seldom has been reported. Therefore, we had compared the levels of putative nonvolatile taste components in these five mushrooms, including soluble sugars, free amino acids, 50 -nucleotides and organic acids, and determined their equivalent umami concentrations (EUC).

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2. Materials and methods 2.1. Mushrooms Air-dried, artificially-cultivated A. blazei, A. cylindracea, P. cystidiosus, P. eryngii, and C. comatus fruit bodies were purchased from Shanghai Baixin Bio-Tech Co. Ltd, China. Samples (50 g) of each species were ground to fine powder (60 mesh) using an ultracentrifugal mill and sieving machine. 2.2. Assay of soluble sugars and polyols Soluble sugars and polyols were extracted and analyzed according to Ajlouni, Beelman, Thompson, and Mau (1995). Suspensions of powdered mushroom (0.5 g) in 50 ml 80% ethanol were shaken at 80 rpm for 45 min at room temperature. After filtration through Whatman No. 3 filter paper, the residue was washed five times with additional 25 ml volumes of 80% ethanol and the combined filtrate and rinsed water were evaporated to dry at 40 °C on a rotary evaporator. Extracted solids were redissolved in deionized water to a final volume of 10 ml and the solution was filtered (0.22 lm cellulose filter, Millipore) prior to analysis. Components were identified by high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) using the Dionex ICS2500 HPAEC-PAD system (Thermo Fisher China Ltd, Shanghai). Arabitol, trehalose and mannitol were assayed using a CarboPac MA1 column (4  250 mm), the mobile phase was 0.48 M NaOH and the flow rate was 0.4 ml/ min. Fucose, glucose, fructose, mannose and ribose were assayed using a CarboPac PA20 column (3  150 mm), the mobile phase was 0.25 M NaOH and the flow rate was 0.45 ml/min. The oven temperature was maintained at 30 °C, and injection volume was 25 ll. Each sugar or polyol was identified and quantified using authentic sugar or polyol standards (Sigma–Aldrich, St. Louis, United States). 2.3. Assay of free amino acids Powdered mushroom samples (1.0 mg) were suspended in 50 ml of 0.1 N HCl (36%) for 45 min with shaking speed of 80 rpm at ambient temperature and then filtered through Whatman No. 3 filter paper. The filtrate was mixed with 8% 5-sulfosalicylic acid dihydrate reagent in an Eppendorf tube, centrifuged at 10,000 rpm (11,100g) for 15 min, and the retained supernatant was filtered (0.22 lm cellulose filter; Millipore) prior to analysis by HPAEC-PAD. The HPAEC-PAD system was the same as for soluble sugars and polyols analysis but included an Amino Pac PA-10 column (2  250 mm). HPAEC-PAD conditions were as follows: mobile phase, 1 M NaAc and 0.25 M NaOH; flow rate 0.22 ml/min; oven temperature 30 °C; injection volume 20 ll (Zhou et al., 2010). Each amino acid was identified and quantified using the authentic amino acid standards (Thermo Fisher China Ltd, Shanghai, China). 2.4. Assay of 50 -nucleotides 50 -Nucleotides were extracted and analyzed as described by Taylor, Hershey, Levine, Coy, and Olivelle (1981). A suspension of mushroom powder (1 g in 25 ml deionized water) was boiled for 1 min, cooled, and then centrifuged at 12,000 rpm (16,000g) for 15 min. The extraction was repeated with 20 ml deionized water, the combined supernatants were evaporated to dry and filtered through a 0.22 lm cellulose membrane (Millipore) prior to analysis by high-performance liquid chromatography (HPLC) using a Waters Alliance e2695 instrument (Waters Corporation, Shanghai, China) equipped with an Ultimate AQ-C18 column (4.6  250 mm,

5 lm). HPLC conditions were as follows: mobile phase, 0.01 M KH2 PO4/H3PO4 (pH 4.68); flow rate 1.0 ml/min; UV detection wavelength, 259 nm; oven temperature 30 °C; injection volume 10 ll. Each 50 -nucleotide was identified and quantified using 50 -nucleotide standards (Sigma–Aldrich, St. Louis, United States). 2.5. Assay of organic acids Powdered mushroom samples (1.0 mg) were suspended in 20 ml deionized water and subjected to ultrasound (400 W, 30 min, ambient temperature) using a 1500 W High Intensity Ultrasonic Processor (Sonics & Materials Inc., Newtown, CT, USA). The suspension was centrifuged at 12,000 rpm (16,000g) for 15 min and the supernatant was filtered through a 0.45 lm cellulose membrane (Millipore) prior to analysis by HPLC. The HPLC system above was fitted with a Green ODS-AQ column (4.6  250 mm, 5 lm) (Boston Analytics, Shanghai, China). HPLC conditions were as follows: mobile phase, 0.01 M KH2PO4 (pH 2.8), flow rate 1.0 ml/min, UV detection wavelength, 210 nm; oven temperature, 30 °C; injection volume, 10 ll. Each organic acid was identified and quantified using authentic standards (Sinopharm Chemical Reagent Co. Ltd, Shanghai, China). 2.6. Equivalent umami concentration The equivalent umami concentration [EUC, g monosodium glutamate (MSG) per 100 g dry raw material weight] is the concentration of MSG equivalent to the umami intensity of that given by the mixture of MSG and a 50 -nucleotide and is represented by the following addition equation (Yamaguchi, Yoshikawa, Ikeda, & Ninomiya, 1971):

Y¼

X

ai bi þ 1218

X

ai bi

X

aj bj



where Y is the EUC of the mixture in terms of g MSG per 100 g dry raw material weight; ai is the concentration (mg per 100 g dry raw material weight) of each umami amino acid [aspartic acid (Asp) or glutamic acid (Glu)]; aj is the concentration (mg per 100 g dry raw material weight) of each umami 50 -nucleotide [50 -inosine monophosphate (50 -IMP), 50 -guanosine monophosphate (50 -GMP), 50 -xanthosine monophosphate (50 -XMP) or 50 -adenosine monophosphate (50 -AMP)]; bi is the relative umami concentration (RUC) for each umami amino acid to MSG (Glu, 1 and Asp, 0.077); bj is the RUC for each umami 50 -nucleotide to 50 -IMP (50 -IMP, 1; 50 -GMP, 2.3; 50 -XMP, 0.61 and 50 -AMP, 0.18); and 1218 is a synergistic constant based on the concentration of g per 100 g dry raw material weight used. 2.7. Statistical analysis For each mushroom, three samples were used for the determination of every quality attribute. Experimental data were subjected to an analysis of variance for a completely random design with a single factor, as described by Dean and Voss (1999). The least significant difference among means was at the level of 0.05. 3. Results and discussion Total soluble sugar/polyol levels ranged from 151.3 mg/g in P. cystidiosus to 316.59 mg/g in P. eryngii. Trehalose was the predominant sugar in every case apart from A. blazei where mannitol was the major component. Trehalose and mannitol were also found to be major components in P. cystidiosus, A. cylindracea and A. blazei by Yang et al. (2001) and Tsai, Tsai, and Mau (2008). Low levels of glucose and fructose were also recorded in all the test fungi except P. eryngii, which was the only mushroom containing fucose.

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Mannose and ribose were also found in some extracts but arabitol was not detected (Table 1). Total soluble sugar/polyol concentrations recorded for P. eryngii in this study are considerably higher than the 6.96–20.8 mg/g range reported by Mau, Lin, Chen, Wu, and Peng (1998) but comparable to those documented by Tsai et al. (2008). Levels reported here for P. cystidiosus and A. cylindracea are also appreciably higher than the 64.9 mg/g (P. cystidiosus) and 56–86.14 mg/g (A. cylindracea) recorded by Yang et al. (2001) and Mau et al. (1998), respectively. However, our data are consistent with total sugar/polyol levels in A. cylindracea (139.13 mg/g) and A. blazei (162.01 mg/g) reported by Tsai et al. (2008). Qualitative and quantitative differences in sugar/polyol levels reported by different laboratories are most likely due to the adoption of different strains for research purposes. Soluble sugars present in mushroom fruit bodies are thought to contribute to the perceived sweet taste of certain species (Litchfield, 1967). The five test species exhibited considerable variation in their free amino acid profiles, and total free amino acid levels ranged from 4.0 to 6.0 mg/g in the two Pleurotus species, 13 mg/g in A. cylindracea and C. comatus, and 22.73 mg/g in A. blazei (Table 2). Levels in A. cylindracea and A. blazei were slightly higher compared to corresponding values reported by Tsai et al. (2008), but marginally lower in P. cystidiosus compared to the data of Yang et al. (2001). Concentrations of individual amino acids exceeded 3 mg/g in the case of glutamic acid in C. comatus, and alanine, histidine and lysine in A. blazei. Glutamate and phenylalanine levels in A. cylindracea exceeded 2.0 mg/g, as did glutamate and proline concentrations in A. blazei. Amino acids in edible mushrooms had been divided into several groups on the basis of their taste characteristics (Mau, Lin, Ma, & Song, 2001) (Table 3). Aspartic and glutamic acids represent the monosodium glutamate-like (MSG-like) components responsible for the most typical mushroom taste, the umami or palatable taste (Yamaguchi, 1979). Levels of MSG-like components ranged from 4.99 mg/g in C. comatus to 0.97 mg/g in P. cystidiosus. According to Yang et al. (2001), who defined low (<5 mg/g), medium (5– 20 mg/g) and high (>20 mg/g) ranges of MSG-like components, levels of MSG-like constituents in the five mushrooms all fell within the former category. In C. comatus and A. blazei, MSG-like components were present at relatively high and low levels, respectively compared with elements of other taste groups. A. cylindracea contained relatively high levels of bitter components and comparable levels of MSG-like and sweet tasting constituents (3.62/3.86 mg/g, respectively). Bitter and sweet components were present at similar concentrations in A. blazei (7.85–7.00 mg/g) and C. comatus (3.37– 3.35 mg/g). In comparison with the previous data results reported by other researchers, levels of MSG-like components in A. cylindracea were slightly higher compared to those reported by Tsai et al. (2008)

but lower than detected by Mau et al. (1998), whereas concentrations in A. blazei and P. cystidiosus were lower than those reported by Tsai, Weng, Huang, Chen, and Mau (2006) and Yang et al. (2001), respectively. Levels found in P. eryngii were comparable to those detected by Mau et al. (1998). Chen (1986) conducted a series of sensory evaluations on synthetic mushroom extracts prepared by omitting and adding soluble components, and found that sweet amino acids (alanine, glycine, threonine) and MSG-like amino acids (aspartic acid, glutamic acids) have taste activities. Conversely, none of the bitter components (valine, methionine, leucine, isoleucine, phenylalanine, histidine, arginine, tryptophan) has taste activities. Any bitterness in these five mushrooms would probably be masked by the high amounts of soluble sugars, polyols and other sweet components, and by MSG-like amino acids, which together appear to be responsible for their natural taste. 50 -Nucleotide levels in the five test mushrooms were relatively low, ranging from 1.68 mg/g in P. eryngii to 3.79 mg/g in C. comatus (Table 4). Trace amounts of 50 -XMP were found in P. cystidiosus but this nucleotide was not detected in the other mushrooms. Flavor 50 -nucleotides responsible for the umami or palatable taste were previously identified as 50 -guanosine monophosphate (50 -GMP), 50 -inosine monophosphate (50 -IMP) and 50 -xanthosine monophosphate (50 -XMP) (Chen, 1986). 50 -GMP imparts a meaty flavor, and is a stronger flavor enhancer than MSG (Litchfield, 1967). Levels of these nucleotides were generally higher in A. blazei (50 -IMP levels were slightly higher in P. eryngii) compared with the other tested mushrooms. Yang et al. (2001) defined three ranges of flavor 50 -nucleotides: low (<1 mg/g), medium (1–5 mg/g) and high (>5 mg/g), according to which A. blazei falls within the medium category and the remaining mushrooms in the low range. Overall, flavor 50 -nucleotide levels were lower compared with previously reported concentrations in P. cystidiosus (Yang et al., 2001), P. eryngii (Mau & Tseng, 1998), A. cylindracea and A. blazei (Tsai et al., 2008). Total organic acid levels in the five mushrooms ranged from 59.42 mg/g in A. cylindracea to 237.81 mg/g in A. blazei (Table 5). Fumaric acid levels in P. cystidiosus were significantly higher compared with the other mushrooms, but malic, ascorbic and acetic acid were not detected. High concentrations of citric acid were found in A. blazei (the highest of any organic acid among the five mushrooms), which were approximately 2-fold, 3-fold and 5-foldhigher compared with C. comatus, P. eryngii, and both P. cystidiodus and A. cylindracea, respectively. Citric acid is the major organic acid produced by fungal fermentation and the second of all fermentation commodities following industrial ethanol. Organic acids are essential flavor components in alcoholic beverages such as wine and sake, and the high citric acid levels in A. blazei may serve to make the mushroom a useful food flavoring additive.

Table 1 Soluble sugar/polyol levels in five edible mushrooms.

a b c

Sugar/polyol

A. cylindracea

P. cystidiosus

A. blazei

P. eryngii

C. comatus

Trehalose Mannitol Arabitol Glucose Fucose Fructose Mannose Ribose Totalc

157.8 ± 4.9 c a 12.37 ± 0.49 d ndb 0.25 ± 0.01 c nd 2.11 ± 0.06 a nd nd 170.42 ± 1.80 c

124.9 ± 9.41 d 24.37 ± 1.49 c nd 2.03 ± 0.02 a nd 0.57 ± 0.02 c 0.49 ± 0.04 a 0.12 ± 0.01 a 151.3 ± 3.64 d

12.23 ± 1.34 e 152.11 ± 11.84 a nd 0.17 ± 0.01 d nd 1.25 ± 0.02 b 0.11 ± 0.01 c nd 164.51 ± 4.40 c

301.63 ± 10.44 a 14.96 ± 0.7 cd nd nd 2.34 ± 0.01 a nd 0.21 ± 0.01 b 0.07 ± 0.01 b 316.59 ± 5.57 a

174.3 ± 9.16 b 83.92 ± 2.97 b nd 0.34 ± 0.03 b nd 0.25 ± 0.01 d nd nd 258.56 ± 4.05 b

Values (mg/g dry weight) are the means ± SD (n = 3). Means with different letters within a row are significantly different (P < 0.05). Not detected. Trehalose + mannitol + arabitol + glucose.

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Table 2 Free amino acid levels in five edible mushrooms. Amino acid

A. cylindracea

L-Alanine

1.50 ± 0.02 c

L-Arginine

0.55 ± 0.02 c

C. comatus

1.03 ± 0.06 d

3.46 ± 0.06 a

0.96 ± 0.05 d

1.91 ± 0.02 b

0.05 ± 0.01 e

1.61 ± 0.02 a

0.36 ± 0.01 d

0.97 ± 0.03 b

0.05 ± 0.01 e

0.53 ± 0.02 b

0.19 ± 0.01 d

0.27 ± 0.01 c

0.05 ± 0.01 d

0.26 ± 0.01 a

0.05 ± 0.01 d

0.13 ± 0.01 c

2.70 ± 0.03 b

0.67 ± 0.02 d

2.09 ± 0.09 c

0.51 ± 0.02 e

3.97 ± 0.11 a

L-Histidine

0.28 ± 0.01 b 0.72 ± 0.02 c

0.09 ± 0.01 d 0.04 ± 0.01 e

0.63 ± 0.02 a 3.24 ± 0.05 a

0.18 ± 0.01 c 0.61 ± 0.02 d

0.19 ± 0.01 c 0.90 ± 0.03 b

L-Aspartic

0.93 ± 0.03 b

0.30 ± 0.01 d

0.88 ± 0.04 b

0.57 ± 0.03 c

1.02 ± 0.07 a

0.21 ± 0.01 c

0.08 ± 0.01 e

1.07 ± 0.03 a

0.23 ± 0.01 c

0.40 ± 0.02 b

0.29 ± 0.02 c

0.07 ± 0.01 e

4.16 ± 0.06 a

0.23 ± 0.01 d

0.90 ± 0.01 b

0.31 ± 0.01 a

0.02 ± 0.01 d

0.21 ± 0.01 b

0.07 ± 0.01 c

0.05 ± 0.01 c

L-Glutamic

acid

Glycine

L-Leucine L-Lysine

acid

a

a

L-Methionine

a

L-Phenylalanine

a

L-Proline L-Serine L-Threonine

a

L-Tryptophan

a

L-Tyrosine L-Valine

a

Total Essential AA

c

P. eryngii

0.77 ± 0.01 a

a

L-Cystine

a

A. blazei

0.18 ± 0.01 b

L-Isoleucine

b

P. cystidiosus

b

2.08 ± 0.03 a

0.89 ± 0.03 c

0.70 ± 0.02 d

1.12 ± 0.03 b

0.48 ± 0.03 e

0.98 ± 0.02 b

0.40 ± 0.02 d

2.05 ± 0.05 a

0.26 ± 0.02 e

0.83 ± 0.02 c

0.45 ± 0.03 a

0.11 ± 0.01 e

0.37 ± 0.02 b

0.15 ± 0.01 d

0.21 ± 0.01 c

0.65 ± 0.05 a

0.03 ± 0.01 e

0.50 ± 0.02 b

0.15 ± 0.01 d

0.21 ± 0.01 c

ndc

nd

nd

nd

nd

0.25 ± 0.02 c

0.11 ± 0.01 e

0.48 ± 0.01 b

0.16 ± 0.01 d

0.84 ± 0.03 a

0.38 ± 0.01 b

0.10 ± 0.01 e

0.49 ± 0.02 a

0.14 ± 0.01 d

0.30 ± 0.02 c

13.21 ± 0.02 c 4.68 ± 0.02 b

4.09 ± 0.01 e 1.25 ± 0.01 c

22.73 ± 0.03 a 7.67 ± 0.02 a

5.93 ± 0.01 d 2.11 ± 0.01 c

13.57 ± 0.03 b 2.61 ± 0.02 b

Essential amino acid. Values, expressed as mg/g dry weight, are the mean ± SD (n = 3). Means with different letters within a row are significantly different (P < 0.05). Not detected.

Table 3 Levels of amino acid taste components in five edible mushrooms.

a b

Taste componenta

A. cylindracea

Bitter MSG-like Sweet Tasteless Total

5.01 ± 0.02 3.62 ± 0.03 3.86 ± 0.02 0.72 ± 0.01 13.21 ± 0.02

bb b b c c

P. cystidiosus

A. blazei

1.23 ± 0.01 0.97 ± 0.02 1.66 ± 0.02 0.24 ± 0.01 4.09 ± 0.01

7.85 ± 0.02 2.97 ± 0.07 7.00 ± 0.03 4.90 ± 0.03 22.73 ± 0.03

e e d e e

P. eryngii a c a a a

2.71 ± 0.01 1.08 ± 0.02 1.70 ± 0.02 0.44 ± 0.01 5.93 ± 0.01

C .comatus d d d d d

3.37 ± 0.02 4.99 ± 0.09 3.35 ± 0.01 1.87 ± 0.02 13.57 ± 0.03

c a c b b

MSG-like (Asp + Glu); sweet (Thr + Ser + Gly + Ala + Pro); bitter (Val + Met + Ile + Leu + Phe + His + Arg + Trp); tasteless (Cys + Tyr + Lys). Values, expressed as mg/g dry weight, are the mean ± SD (n = 3). Means with different letters within the same row are significantly different (P < 0.05).

Table 4 50 -Nucleotide levels in five edible mushrooms. 50 -Nucleotidea

A. cylindracea

50 -AMP 50 -CMP 50 -GMP 50 -IMP 50 -UMP 50 -XMP Flavor 50 -nucleotideb Total

0.16 ± 0.03 1.23 ± 0.12 0.53 ± 0.06 0.09 ± 0.02 0.31 ± 0.01 nd 0.62 ± 0.04 2.32 ± 0.04

dc b c b b c c

P. cystidiosus

A. blazei

P. eryngii

0.70 ± 0.07 0.27 ± 0.04 0.61 ± 0.11 0.03 ± 0.01 0.23 ± 0.03 0.03 ± 0.01 0.67 ± 0.04 1.87 ± 0.04

0.55 ± 0.05 bc 1.24 ± 0.13 b 1.37 ± 0.08 a 0.10 ± 0.01 b 0.32 ± 0.02 b nd 1.47 ± 0.04 a 3.58 ± 0.05 b

0.60 ± 0.01 ndd 0.60 ± 0.01 0.18 ± 0.02 0.30 ± 0.01 nd 0.78 ± 0.01 1.68 ± 0.01

a c bc d c a c d

C. comatus b bc a b b e

0.52 ± 0.03 1.92 ± 0.07 0.70 ± 0.03 0.05 ± 0.01 0.60 ± 0.03 nd 0.75 ± 0.02 3.79 ± 0.03

c a b c a b a

a 50 -AMP, 50 -adenosine monophosphate; 50 -CMP, 50 -cytosine monophosphate; 50 -GMP, 50 -guanosine monophosphate; 50 -IMP, 50 -inosine monophosphate; 50 -UMP, 50 uridine monophosphate; 50 -XMP, 50 -xanthosine monophosphate. b Flavor nucleotide, 50 -GMP + 50 -IMP + 50 -XMP. c Each value, expressed as mg/g, is the mean ± SD (n = 3). Means with different letters within a row are significantly different (P < 0.05). Where a mean is followed with ‘‘bc’’, this mean was not significantly different from a mean with ‘‘b’’, and was not significantly different from another mean with ‘‘c’’. d Not detected.

Synergistic effects between flavor 50 -nucleotides and MSG-like components may greatly increase the umami taste of mushrooms (Yamaguchi et al., 1971). Using the equation derived from sensory evaluation (Yamaguchi et al., 1971), EUC values were relatively high in the case of A. blazei and C. comatus (88.37 and 86.86 g/100 g, respectively), moderate in A. cylindracea (45.40 g/100 g), and low in P. cystidiosus and P. eryngii (13.32 and 11.19 g/100 g, respectively) (Table 6). Our EUC value for A.

cylindracea is comparable to that reported by Tsai et al. (2008) but lower than that calculated by Mau et al. (1998). Tsai et al. (2008) also reported that A. blazei had a higher EUC compared with our value. Mau (2005) designated EUC values, expressed as MSG/g dry matter, to one of four levels: >10 g, 1–10 g, 0.1–1 g and <0.1 g. Hence, EUC values of the five mushrooms included in this study were all at the third level (Table 6).

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W. Li et al. / Food Chemistry 143 (2014) 427–431 Table 5 Organic acid levels in five edible mushrooms. Organic acid Tartaric acid Malic acid Ascorbic acid Acetic acid Citric acid Fumaric acid Succinic acid Total a b

A. cylindracea a

nd 22.41 ± 0.27b 0.93 ± 0.04b 5.94 ± 0.06 d 22.2 ± 0.29 d 3.17 ± 0.04 c 4.77 ± 0.06 d 59.42 ± 0.12 e

P. cystidiosus b

1.18 ± 0.07 nd nd nd 22.13 ± 0.22 d 96.11 ± 0.57a 0.89 ± 0.03 e 120.31 ± 0.22b

A. blazei a

64.52 ± 0.57 16.01 ± 0.18 c nd 14.6 ± 0.17b 113.13 ± 1.52a 2.87 ± 0.07 c 26.68 ± 0.27b 237.81 ± 0.47a

P. eryngii

C. comatus

nd 5.29 ± 0.09 d nd 18.26 ± 0.14a 43.58 ± 0.33 c 1.56 ± 0.05 d 29.31 ± 0.20 a 98 ± 0.16 d

nd 23.9 ± 0.29a 2.09 ± 0.08a 6.58 ± 0.07 c 60 ± 0.43b 5.4 ± 0.10b 15.4 ± 0.13 c 113.37 ± 0.19 c

Not detected. Each value, expressed as mg/g, is the mean ± SD (n = 3). Means with different letters within a row are significantly different (P < 0.05).

Table 6 Equivalent umami concentration (EUC) values of five edible mushrooms. EUCa (g/100 g dry weight) bb c a c a P  P P a Calculation based on the equation: Y ¼ ai bi þ 1218 ð ai bi Þ aj bj (Yamaguchi et al., 1971) where Y is the EUC of the mixture in terms of g MSG/100 g; ai is the concentration (g/100 g) of each umami amino acid (Asp or Glu); aj is the concentration (g/100 g) of each umami 50 -nucleotide (50 -IMP, 50 -GMP, 50 -XMP or 50 AMP); bi is the relative umami concentration (RUC) for each umami amino acid to MSG (Glu, 1 and Asp, 0.077); bj is the RUC for each umami 50 -nucleotide to 50 -IMP (50 -IMP, 1; 50 -GMP, 2.3; 50 -XMP, 0.61 and 50 -AMP, 0.18); and 1218 is a synergistic constant based on the concentration of g/100 g used. b Each value is expressed as the mean ± SD (n = 3). Means with different letters within a row are significantly different (P < 0.05). A. cylindracea P. cystidiosus A. blazei P. eryngii C.comatus

45.40 ± 5.18 13.32 ± 2.50 88.37 ± 8.02 11.19 ± 0.62 86.86 ± 5.00

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