# Comparison of the Nutritional and Taste Characteristics of 5 Edible Fungus Powders Based on the Composition of Hydrolyzed Amino Acids and Free Amino Acids

Authors: Jian Li; Junmei Ma; Sufang Fan; Shengquan Mi; Yan Zhang
Journal: Journal of Food Quality
 (2022)

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## Abstract

The nutritional characteristics and taste of some edible fungus powders were scientifically evaluated and compared. Five common edible fungus powders were used as test materials (Agrocybe chaxinggu edible fungus powder, Pleurotus citrinopileatus edible fungus powder, Flammulina velutipes edible fungus powder, Lentinus edodes edible fungus powder, and Hericium erinaceus edible fungus powder). The hydrolyzed amino acid and free amino acid content were measured by an automatic amino acid analyzer, and the ratios of hydrolyzed amino acid and free amino acid components and the taste characteristics of these eatables were systematically compared. The results showed that the total amount of hydrolyzed amino acids contained in the 5 edible fungus powders was between 2.583 and 14.656 g/100 g. The total amount of free amino acids contained in the 5 edible fungus powders was between 0.550 and 2.612 g/100 g. Comparative analysis of the mass fractions and composition of amino acids indicated that Pleurotus citrinopileatus edible fungus powder best met the ideal protein standard. The taste characteristics of protein were evaluated by calculating the taste active value (TAV) of taste-producing free amino acids. The most significant TAV values of the 5 edible fungus powders appeared in glutamic acid, and this amino acid is an umami amino acid. Principal component analysis (PCA) suggested that four principal components could reflect all the information on the free amino acids with a total cumulative variance contribution rate of 100%, and three principal components could reflect most of the information on the hydrolyzed amino acids with a total cumulative variance contribution rate of 99.143%, which could represent the main trends of free amino acids and hydrolyzed acids in edible fungus powder. The comprehensive evaluation model was established, and the comprehensive score indicated that Agrocybe chaxinggu edible fungus powder had the best comprehensive amino acid quality.


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## Body

## 1. Introduction

Edible funguses are widely grown all over the world. There are at least 2,000 species of edible funguses in the world, of which about 200 are wild edible funguses [1]. China is the largest producer of edible funguses in the world, accounting for two-thirds of the world’s production [2, 3]. Edible funguses are widely cultivated for their medicinal and nutritional value. Some edible funguses have been reported as therapeutic foods, useful in preventing diseases such as hypertension, hypercholesterolemia, atherosclerosis, or cancer [4–7]. Edible funguses are valuable health foods, low in calories, lipids, and essential fatty acids, and high in vegetable proteins, minerals, and vitamins [8]. As a delicacy, edible funguses have unique umami, texture, and increasingly high-rated nutritive value. Umami is produced by glutamic acid, ribonucleotide and chemicals that make edible funguses tasty and are widely used in food preparation [2].An amino acid is a biologically active substance that plays an important role in human metabolism. Its composition and content are important indicators for evaluating the nutritional value of edible funguses [9, 10]. Free amino acids (FAA), also known as nonprotein amino acids, are an important class of taste active ingredients [11], and their content and types are often used as important indicators for food nutritional value and taste and taste evaluation [12]. Some studies have shown that the main taste substances that have a significant impact on the taste of edible funguses are nucleotides, soluble sugars, organic acids, free amino acids, and other taste substances. Among them, free amino acids play an extremely important role in the presentation of the taste and deliciousness of edible funguses [13]. The typical umami taste of edible funguses is attributed to aspartic acid and glutamate [2]. Umami not only alleviates salty, sour or bitter tastes and improves the perception of sweetness, it also reduces the pungent meaty smell and the earthy taste [14, 15]. At present, the analytical methods for amino acids in edible funguses include ninhydrin colorimetry [16], high performance liquid chromatography [14, 17, 18], gas chromatography [19], gas chromatography-mass spectrometry [6, 20], nuclear magnetic resonance [21], amino acid analyzers [22–27], and high performance liquid chromatography-triple quadrupole mass spectrometry [28]. In the present study, the amino acid analyzer was used to analyze the nutritional characteristics of hydrolyzed amino acids and free amino acids of five common edible funguses powder, and their differences in nutritional and taste components were compared. The research results not only provide scientific data for revealing the nutritional value and taste characteristics of edible funguses, but also provide a scientific basis for guiding people to establish a scientific and healthy diet structure.


## 2. Materials and Methods

### 2.1. Materials and Reagents

Aspartic acid, threonine, serine, glutamic acid, glycine, alanine, valine, methionine, isoleucine, leucine, tyrosine, phenylalanine, lysine, histidine, arginine, and proline mixed standard solution were obtained from Wako Pure Chemical Industries, Ltd. (2.5μmol/mL, Tokyo, Japan). Water was purified using a Milli-Q-System (Millipore, Guyancourt, France). Ethanol was HPLC grade and was purchased from Merck (Darmstadt, Germany). Sodium citrate dihydrate, citric acid monohydrate, sodium chloride, sodium hydroxide, sodium borohydride, and hydrochloric acid were premium grade pure and were purchased from Beijing Chemical Reagent Factory (Beijing, China). Anhydrous sodium acetate, ninhydrin, ethylene glycol monomethyl ether, acetic acid, and phenol were analytical grade and were purchased from the Guangfu Fine Chemical Research Institute (Tianjin, China).Agrocybe chaxinggu edible fungus powder, Pleurotus citrinopileatus edible fungus powder, Flammulina velutipes edible fungus powder, Lentinus edodes edible fungus powder, and Hericium erinaceus edible fungus powder were supplied by Henan Longfeng Edible Funguses Industry Research Institute.


### 2.2. Methods

#### 2.2.1. Determination of Hydrolyzed Amino Acids

Refer to GB 5009.124-2016 [29] for the determination of hydrolyzed amino acids. 0.5 g of each sample was hydrolyzed by an electric heating blast drying oven (Boxun GZX-9240MBE, China) with 10 mL of 6 mol/L hydrogen chloride at 110°C for 22 h under a nitrogen atmosphere, and then filtered through a 0.45 mm membrane filter prior to analysis. The amino acid profiles of each sample were determined by an automatic amino acid analyzer (Hitachi L-8900, Japan). All determinations were carried out in triplicate.


#### 2.2.2. Determination of Free Amino Acids

Refer to the first method in GB/T 30987-2020 [30] for the determination of free amino acids. 0.5 g of the sample was diluted with 100 mL of boiling water. The sample was water bathed by a water bath constant temperature oscillator (Runhua SHA-B, China) at 95°C for 10 min. and then filtered through a 0.45 mm membrane filter prior to analysis. The amino acid profiles of each sample were determined by an automatic amino acid analyzer (Hitachi L-8900, Japan). All determinations were carried out in triplicate.


### 2.3. Statistical Analysis

All analyses were conducted in triplicate. The results reported were the average of these three replicates. Normal distribution tests of multielements and PCA analysis were performed with SPSS 25.0 software (SPSS, IBM Corp., USA).


## 2.1. Materials and Reagents

Aspartic acid, threonine, serine, glutamic acid, glycine, alanine, valine, methionine, isoleucine, leucine, tyrosine, phenylalanine, lysine, histidine, arginine, and proline mixed standard solution were obtained from Wako Pure Chemical Industries, Ltd. (2.5μmol/mL, Tokyo, Japan). Water was purified using a Milli-Q-System (Millipore, Guyancourt, France). Ethanol was HPLC grade and was purchased from Merck (Darmstadt, Germany). Sodium citrate dihydrate, citric acid monohydrate, sodium chloride, sodium hydroxide, sodium borohydride, and hydrochloric acid were premium grade pure and were purchased from Beijing Chemical Reagent Factory (Beijing, China). Anhydrous sodium acetate, ninhydrin, ethylene glycol monomethyl ether, acetic acid, and phenol were analytical grade and were purchased from the Guangfu Fine Chemical Research Institute (Tianjin, China).Agrocybe chaxinggu edible fungus powder, Pleurotus citrinopileatus edible fungus powder, Flammulina velutipes edible fungus powder, Lentinus edodes edible fungus powder, and Hericium erinaceus edible fungus powder were supplied by Henan Longfeng Edible Funguses Industry Research Institute.


## 2.2. Methods

### 2.2.1. Determination of Hydrolyzed Amino Acids

Refer to GB 5009.124-2016 [29] for the determination of hydrolyzed amino acids. 0.5 g of each sample was hydrolyzed by an electric heating blast drying oven (Boxun GZX-9240MBE, China) with 10 mL of 6 mol/L hydrogen chloride at 110°C for 22 h under a nitrogen atmosphere, and then filtered through a 0.45 mm membrane filter prior to analysis. The amino acid profiles of each sample were determined by an automatic amino acid analyzer (Hitachi L-8900, Japan). All determinations were carried out in triplicate.


### 2.2.2. Determination of Free Amino Acids

Refer to the first method in GB/T 30987-2020 [30] for the determination of free amino acids. 0.5 g of the sample was diluted with 100 mL of boiling water. The sample was water bathed by a water bath constant temperature oscillator (Runhua SHA-B, China) at 95°C for 10 min. and then filtered through a 0.45 mm membrane filter prior to analysis. The amino acid profiles of each sample were determined by an automatic amino acid analyzer (Hitachi L-8900, Japan). All determinations were carried out in triplicate.


## 2.2.1. Determination of Hydrolyzed Amino Acids

Refer to GB 5009.124-2016 [29] for the determination of hydrolyzed amino acids. 0.5 g of each sample was hydrolyzed by an electric heating blast drying oven (Boxun GZX-9240MBE, China) with 10 mL of 6 mol/L hydrogen chloride at 110°C for 22 h under a nitrogen atmosphere, and then filtered through a 0.45 mm membrane filter prior to analysis. The amino acid profiles of each sample were determined by an automatic amino acid analyzer (Hitachi L-8900, Japan). All determinations were carried out in triplicate.


## 2.2.2. Determination of Free Amino Acids

Refer to the first method in GB/T 30987-2020 [30] for the determination of free amino acids. 0.5 g of the sample was diluted with 100 mL of boiling water. The sample was water bathed by a water bath constant temperature oscillator (Runhua SHA-B, China) at 95°C for 10 min. and then filtered through a 0.45 mm membrane filter prior to analysis. The amino acid profiles of each sample were determined by an automatic amino acid analyzer (Hitachi L-8900, Japan). All determinations were carried out in triplicate.


## 2.3. Statistical Analysis

All analyses were conducted in triplicate. The results reported were the average of these three replicates. Normal distribution tests of multielements and PCA analysis were performed with SPSS 25.0 software (SPSS, IBM Corp., USA).


## 3. Results and Discussion

### 3.1. Hydrolyzed Amino Acid Concentrations in 5 Edible Fungus Powders

The hydrolyzed amino acid is to hydrolyze the protein, polypeptide, and other amino acid chains in the plant to be tested into a single amino acid through acid hydrolysis. Therefore, the hydrolyzed amino acid can fully reflect the kind and content of all single amino acids in the sample. The hydrolyzed amino acid composition and content of 5 kinds of edible fungus powder are shown in Table1. Results showed that 15 hydrolyzed amino acids were present in all samples tested. The total amount of hydrolyzed amino acids contained in the 5 edible fungus powders was between 2.583 and 14.656 g/100 g. The total hydrolyzed amino acid content of Pleurotus citrinopileatus edible fungus powder was the highest, reaching 14.656 g/100 g, and the total hydrolyzed amino acid content of Hericium erinaceus edible fungus powder was the lowest, at 2.583 g/100 g. Glutamic acid was the most abundant among the 5 kinds of edible fungus powder, accounting for 17.41%, 19.75%, 25.16%, 24.92%, and 16.72% of the total hydrolyzed amino acids, respectively.Table 1
Contents∗ of hydrolyzed amino acids in 5 kinds of edible fungus powders.
CompoundAgrocybe chaxinggu edible fungus powderPleurotus citrinopileatus edible fungus powderFlammulina velutipes edible fungus powderLentinus edodes edible fungus powderHericium erinaceus edible fungus powderAspartic acid and asparagine1.571 ± 0.0150.613 ± 0.0010.531 ± 0.0020.737 ± 0.0020.247 ± 0.005Threonine0.744 ± 0.0120.510 ± 0.0090.147 ± 0.0030.192 ± 0.0020.107 ± 0.005Serine0.768 ± 0.0030.469 ± 0.0060.280 ± 0.0060.399 ± 0.0040.099 ± 0.003Glutamic acid and glutamine2.536 ± 0.0122.894 ± 0.0012.198 ± 0.0312.969 ± 0.0300.432 ± 0.001Glycine0.799 ± 0.0080.867 ± 0.0040.468 ± 0.0040.650 ± 0.0020.165 ± 0.003Alanine1.491 ± 0.0041.427 ± 0.0591.065 ± 0.0241.859 ± 0.0140.414 ± 0.005Valine1.021 ± 0.0141.202 ± 0.0230.585 ± 0.0020.809 ± 0.0140.207 ± 0.012Methionine0.022 ± 0.0020.113 ± 0.011NDNDNDIsoleucine0.583 ± 0.0110.677 ± 0.0030.301 ± 0.0040.423 ± 0.0050.068 ± 0.002Leucine1.379 ± 0.0171.703 ± 0.0370.821 ± 0.0011.135 ± 0.0090.298 ± 0.002Tyrosine0.507 ± 0.0040.636 ± 0.0080.414 ± 0.0010.406 ± 0.0150.111 ± 0.000Phenylalanine0.714 ± 0.0100.849 ± 0.0040.537 ± 0.0030.567 ± 0.0250.112 ± 0.006Lysine0.754 ± 0.0021.082 ± 0.0060.622 ± 0.0020.710 ± 0.0050.102 ± 0.001Histidine0.300 ± 0.0040.410 ± 0.0050.217 ± 0.0030.257 ± 0.0030.057 ± 0.003Arginine0.943 ± 0.0091.204 ± 0.0270.554 ± 0.0090.799 ± 0.0120.165 ± 0.001Proline0.434 ± 0.016NDNDNDNDTotal14.567 ± 0.02414.656 ± 0.2878.739 ± 0.01611.912 ± 0.0922.583 ± 0.010∗Value (g/100 g) = mean ± SD (n = 3). ND: not detectable.


### 3.2. Free Amino Acid Concentrations in 5 Edible Fungus Powders

Free amino acids refer to amino acids that exist in a free state in plants as a single amino acid molecule and can be directly absorbed and utilized. The free amino acid composition and content of 5 kinds of edible fungus powder are shown in Table2. The total amount of free amino acids contained in the 5 edible fungus powders was between 0.550 and 2.612 g/100 g. The total free amino acid content of Flammulina velutipes edible fungus powder was the highest, reaching 2.612 g/100 g, and the total free amino acid content of Hericium erinaceus edible fungus powder was the lowest, at 0.550 g/100 g. Glutamic acid was the most abundant among the 5 kinds of edible fungus powders, accounting for 25.21%, 23.99%, 28.29%, 36.48%, and 18.18% of the total free amino acids, respectively.Table 2
Contents∗ of free amino acids in 5 kinds of edible fungus powders.
CompoundAgrocybe chaxinggu edible fungus powderPleurotus citrinopileatus edible fungus powderFlammulina velutipes edible fungus powderLentinus edodes edible fungus powderHericium erinaceus edible fungus powderAspartic acid0.070 ± 0.0010.016 ± 0.0000.018 ± 0.0000.022 ± 0.0000.016 ± 0.001Threonine0.139 ± 0.0030.286 ± 0.0000.373 ± 0.0010.327 ± 0.0040.037 ± 0.001Serine0.079 ± 0.0020.107 ± 0.0000.068 ± 0.0020.015 ± 0.0000.004 ± 0.000Glutamic acid0.505 ± 0.0030.396 ± 0.0000.739 ± 0.0030.448 ± 0.0070.100 ± 0.002Glycine0.047 ± 0.0000.032 ± 0.0000.049 ± 0.0000.022 ± 0.0000.019 ± 0.001Alanine0.326 ± 0.0020.207 ± 0.0000.409 ± 0.0010.135 ± 0.0020.085 ± 0.003Valine0.164 ± 0.0020.117 ± 0.0000.118 ± 0.0000.053 ± 0.0010.047 ± 0.002MethionineND0.007 ± 0.000NDNDNDIsoleucine0.101 ± 0.0010.033 ± 0.0000.060 ± 0.0000.012 ± 0.0000.022 ± 0.000Leucine0.168 ± 0.0020.063 ± 0.0000.103 ± 0.0000.017 ± 0.0000.064 ± 0.002Tyrosine0.064 ± 0.0010.086 ± 0.0010.159 ± 0.0000.032 ± 0.0010.038 ± 0.001Phenylalanine0.115 ± 0.0020.131 ± 0.0000.216 ± 0.0010.046 ± 0.0000.046 ± 0.003Lysine0.066 ± 0.0020.079 ± 0.0000.151 ± 0.0010.035 ± 0.0000.007 ± 0.000Histidine0.027 ± 0.0000.028 ± 0.0000.052 ± 0.0000.009 ± 0.0000.008 ± 0.000Arginine0.106 ± 0.0020.062 ± 0.0000.057 ± 0.0010.055 ± 0.0010.024 ± 0.001Proline0.026 ± 0.002ND0.039 ± 0.002ND0.034 ± 0.002Total2.003 ± 0.0181.651 ± 0.0012.612 ± 0.0051.228 ± 0.0170.550 ± 0.018∗Value (g/100 g) = mean ± SD (n = 3). ND: not detectable.


### 3.3. The Difference in the Ratio of Essential Amino Acids and Nonessential Amino Acids

In order to scientifically evaluate the component structure of hydrolyzed amino acids, indicators such as the ratio of essential amino acids (EAAs) to nonessential amino acids (NEAAs) have been introduced. According to the essential amino acid model of protein nutritional value proposed by the World Health Organization (WHO) and the United Nations Food and Agriculture Organization (FAO) in 1973, the EAA/(EAA + NEAA) value in an ideal protein should reach about 40%, and the EAA/NEAA value should be above 60% [31]. The results (Table 3) showed that the value of EAA/(EAA + NEAA) was between 32.20% and 41.87%, and the value of EAA/NEAA was 47.48%–72.03%. In contrast, among the 5 kinds of edible fungus powders, Lentinus edodes edible fungus powder had the lowest EAA/(EAA + NEAA) and EAA/NEAA values, and Pleurotus citrinopileatus edible fungus powder best met the ideal protein standard.Table 3
Comparative analysis of the mass fractions and composition of amino acids in 5 edible fungus powders.
SampleEAA/NEAAEAA/(EAA + NEAA)Agrocybe chaxinggu edible fungus powder55.8135.82Pleurotus citrinopileatus edible fungus powder72.0341.87Flammulina velutipes edible fungus powder52.6234.48Lentinus edodes edible fungus powder47.4832.20Hericium erinaceus edible fungus powder52.8534.58


### 3.4. The Difference in Taste Characteristics and Taste Activity Values

The determination of hydrolyzed amino acids was mainly to study their nutritional properties. The flavored amino acids in structural proteins are mostly in a combined state and have little effect on flavor, while free amino acids are mainly used to participate in the formation of taste substances. Therefore, the taste characteristics of free amino acids in the five test samples were compared, and they were divided into 4 categories: umami amino acids, sweet amino acids, bitterness amino acids, and tasteless amino acids [32]. The results (Table 4) showed that Pleurotus citrinopileatus edible fungus powder, Flammulina velutipes edible fungus powder, and Lentinus edodes edible fungus powder had the highest content of sweet amino acids. Agrocybe chaxinggu edible fungus powder and Hericium erinaceus edible fungus powder had the highest content of bitterness amino acids.Table 4
Flavored amino acid content (g/100 g) in 5 kinds of edible fungus powders.
SampleUmami amino acidsSweet amino acidsBitterness amino acidsTasteless amino acidsAgrocybe chaxinggu edible fungus powder0.5740.6160.6820.131Pleurotus citrinopileatus edible fungus powder0.4120.6330.4410.163Flammulina velutipes edible fungus powder0.7570.9690.6060.310Lentinus edodes edible fungus powder0.4690.4990.1930.067Hericium erinaceus edible fungus powder0.1150.1790.2110.045The absolute content and relative ratio of flavored amino acids may be closely related to the taste of the food. Therefore, the taste active value (TAV) of 16 amino acids in 5 kinds of test samples was analyzed and compared. TAV is the ratio of the content of each taste amino acid in the sample to its corresponding taste threshold [33]. In general, when TAV > 1, the taste-producing substance is considered to have a significant impact on the taste-producing effect of the sample; when TAV < 1, it means that the substance has no significant taste-producing effect [34]. The results (Table 5) showed that among the 5 edible fungus powders, the TAV values of aspartic acid, glutamic acid, alanine, and arginine were also greater than 1. The TAV values of serine, glycine, methionine, leucine, tyrosine, and proline were also less than 1. The TAV of free amino acid in Agrocybe chaxinggu edible fungus powder was between 0.00 and 100.93. The TAV of free amino acid in Pleurotus citrinopileatus edible fungus powder was between 0.00 and 79.30. The TAV of free amino acid in Flammulina velutipes edible fungus powder was between 0.00 and 147.84. The TAV of free amino acid in Lentinus edodes edible fungus powder was between 0.00 and 89.50. The TAV of free amino acid in Hericium erinaceus edible fungus powder was between 0.00 and 19.95. According to the TAV value, the most significant free amino acid that affects the taste of the 5 edible fungus powders that can be screened out was glutamic acid in the umami amino acid, followed by aspartic acid in umami amino acids, arginine in bitterness amino acids, and alanine in sweet amino acids. And Flammulina velutipes edible fungus powder has the most outstanding umami.Table 5
The TAV of free amino acid in 5 kinds of edible fungus powders.
CompoundTaste characteristicsTaste threshold (mg/100 g) [34]TAV of 5 kinds of edible fungus powdersAgrocybe chaxingguPleurotus citrinopileatusFlammulina velutipesLentinus edodesHericium erinaceusAspartic acidUmami3.0023.225.306.037.295.24ThreonineSweet260.000.531.101.441.260.14SerineSweet150.000.520.720.450.100.02Glutamic acidUmami5.00100.9379.30147.8489.5019.95GlycineSweet110.000.420.290.450.200.17AlanineSweet60.005.443.456.822.251.42ValineBitterness150.001.090.780.780.350.32MethionineBitterness30.000.000.240.000.000.00IsoleucineBitterness90.001.130.370.670.140.25LeucineBitterness380.000.440.170.270.040.17TyrosineTasteless260.000.250.330.610.120.15PhenylalanineBitterness150.000.770.871.440.310.31LysineTasteless50.001.331.593.020.690.14HistidineBitterness20.001.341.392.600.440.38ArginineBitterness10.0010.646.235.735.532.38ProlineSweet300.000.090.000.130.000.11


### 3.5. Correlation Analysis and PCA of Free Amino Acids

A correlation analysis was performed on the 16 free amino acid components of 5 edible fungus powders, and the results are shown in Table6. There were positive correlations and negative correlations between amino acids, and most of them were positive. The results showed that there was a strong correlation between the free amino acids of the five edible fungus powders, which could be comprehensively evaluated by PCA.Table 6
Correlation analysis of free amino acids in 5 kinds of edible fungus powders.
Amino acidsAspartic acidThreonineSerineGlutamic acidGlycineAlanineValineMethionineIsoleucineLeucineTyrosinePhenylalanineLysineHistidineArginineProlineAspartic acid1Threonine−0.3201Serine0.2710.3491Glutamic acid0.2000.7830.5021Glycine0.5190.3330.6800.8191Alanine0.3850.4570.6240.888∗0.983∗∗1Valine0.6990.1220.8390.5830.889∗0.7991Methionine−0.2960.2140.670−0.101−0.073−0.1060.1951Isoleucine0.842−0.1190.5450.4930.8670.7720.910∗−0.1971Leucine0.802−0.2760.4930.3530.8070.7020.860−0.1980.980∗∗1Tyrosine−0.1530.5770.5590.7670.7630.8430.4920.1110.3790.3511Phenylalanine0.0070.5570.6820.8080.8560.908∗0.6460.1600.5150.4750.982∗∗1Lysine−0.0230.6970.6340.894∗0.8330.906∗0.5910.1170.4490.3750.968∗∗0.981∗∗1Histidine0.0470.5550.6570.8320.8780.930∗0.6550.1000.5460.5010.978∗∗0.998∗∗0.983∗∗1Arginine0.8740.1190.6240.5270.7070.6050.8750.0230.8320.7280.1340.3110.3200.3371Proline0.146−0.343−0.1730.1180.4190.4310.159−0.5930.4490.5560.4320.3820.2840.408−0.1021Note: relevance is Pearson’s type;∗significant correlation (p < 0.05); ∗∗extremely significant correlation (p < 0.01).PCA is a multivariate statistical analysis method that analyses a few variables which can reveal the internal structure sufficiently by studying the relationship between multiple original variables [35]. According to the rule that the characteristic value is greater than 1 and the cumulative variance contribution rate is greater than 80%, four principal component factors were obtained through rotation and extraction factors, and the total contribution rate was 100%, indicating that the experimental data can fully reflect the original information (Table 7).Table 7
Results of principal component analysis.
ComponentInitial eigenvalueRotate the sum of squares loadingTotalVariance (%)Accumulate (%)TotalVariance (%)Accumulate (%)19.24157.75957.7597.12544.53244.53223.45521.59279.3515.25932.86977.40232.18313.64592.9961.91611.97789.37841.1217.0041001.69910.622100The first principal component was mainly composed of glycine, alanine, histidine, phenylalanine, lysine, valine, glutamic acid, tyrosine, isoleucine, serine, leucine, and arginine. The second principal component was mainly composed of aspartic acid, leucine, isoleucine, and arginine. And the third principal component was mainly composed of methionine and serine (Table8).Table 8
Contribution value of element principal component.
Amino acidsComponent1234Aspartic acid0.4320.8540.178−0.228Threonine0.417−0.7500.176−0.482Serine0.745−0.1030.5890.296Glutamic acid0.843−0.301−0.045−0.443Glycine0.9910.112−0.064−0.031Alanine0.984−0.040−0.148−0.089Valine0.8820.3340.3150.104Methionine0.037−0.3970.7760.488Isoleucine0.8090.587−0.0110.029Leucine0.7430.634−0.0890.195Tyrosine0.814−0.490−0.2560.176Phenylalanine0.902−0.377−0.1310.163Lysine0.884−0.454−0.112−0.017Histidine0.917−0.344−0.1640.117Arginine0.6750.5100.443−0.295Proline0.3490.253−0.8470.311


### 3.6. Correlation Analysis and PCA of Hydrolyzed Amino Acids

A correlation analysis was performed on the 16 hydrolyzed amino acid components of 5 edible fungus powders, and the results are shown in Table9. The results showed that the correlation coefficients between most hydrolyzed amino acids were greater than 0.7, indicating that there were strong correlations among the 16 hydrolyzed amino acids in 5 kinds of edible fungus powders, so they could be further studied by PCA.Table 9
Correlation analysis of free amino acids in 5 kinds of edible funguses powder.
Amino acidsAspartic acidThreonineSerineGlutamic acidGlycineAlanineValineMethionineIsoleucineLeucineTyrosinePhenylalanineLysineHistidineArginineProlineAspartic acid1Threonine0.8531Serine0.953∗0.927∗1Glutamic acid0.5130.4810.6841Glycine0.6630.7850.8520.903∗1Alanine0.5760.4440.6920.948∗0.8321Valine0.6070.7830.8170.8750.995∗∗0.7851Methionine0.0410.5190.3190.4180.6480.2350.7241Isoleucine0.6300.8070.8340.8610.994∗∗0.7690.999∗∗0.7211Leucine0.5680.7580.7870.8760.990∗∗0.7800.999∗∗0.7460.996∗∗1Tyrosine0.5150.6880.7340.889∗0.956∗0.7340.964∗∗0.7120.963∗∗0.967∗∗1Phenylalanine0.5730.7140.7790.910∗0.974∗∗0.7770.975∗∗0.6730.974∗∗0.975∗∗0.996∗∗1Lysine0.4350.6120.6730.917∗0.952∗0.7770.962∗∗0.7280.955∗0.970∗∗0.989∗∗0.985∗∗1Histidine0.4800.6860.7170.886∗0.969∗∗0.7530.983∗∗0.7690.979∗∗0.989∗∗0.988∗∗0.986∗∗0.993∗∗1Arginine0.5480.7370.7720.885∗0.988∗∗0.7900.997∗∗0.7460.993∗∗0.999∗∗0.966∗∗0.974∗∗0.974∗∗0.990∗∗1Proline0.932∗0.8170.8240.1780.4140.2450.369−0.0570.4020.3240.2660.3180.1580.2250.2971Note: relevance is Pearson’s type;∗significant correlation (p < 0.05); ∗∗extremely significant correlation (p < 0.01).PCA was performed on the hydrolyzed amino acid content of the 5 samples, and the results are shown in Tables10 and 11. It can be seen from Tables 10 and 11 that the cumulative contribution rate of the three principal components reaches 99.143%, indicating that three components can represent the information of all hydrolyzed amino acids in 5 kinds of edible fungus powders and can better reflect the relationship of free amino acids in 5 kinds of edible fungus powders.Table 10
Results of principal component analysis.
ComponentInitial eigenvalueRotate the sum of squares loadingTotalVariance (%)Accumulate (%)TotalVariance (%)Accumulate (%)112.56878.54778.5476.21338.83438.83422.29414.33592.8825.49134.31873.15231.0026.26199.1434.15825.9999.143Table 11
Contribution value of element principal component.
Amino acidsComponent123Aspartic acid0.6740.732−0.100Threonine0.8050.4740.355Serine0.8610.508−0.018Glutamic acid0.889−0.176−0.419Glycine0.998−0.017−0.035Alanine0.805−0.027−0.562Valine0.994−0.0770.049Methionine0.657−0.4670.582Isoleucine0.996−0.0450.073Leucine0.989−0.1260.054Tyrosine0.964−0.1850.022Phenylalanine0.980−0.126−0.023Lysine0.952−0.288−0.037Histidine0.971−0.2320.047Arginine0.985−0.1520.036Proline0.4360.8890.131The first principal component was mainly composed of glycine, isoleucine, valine, leucine, arginine, phenylalanine, histidine, tyrosine, lysine, glutamic acid, serine, alanine, threonine, aspartic acid, and methionine. The second principal component was mainly composed of proline, aspartic acid, and serine. And the third principal component was mainly composed of methionine (Table11).


### 3.7. Comprehensive Evaluation

A comprehensive evaluation model was established based on the contribution rates of the eigenvalues corresponding to the three principal components of hydrolyzed amino acids and the four principal components of free amino acids. The free amino acid model wasF = 0.445F1 + 0.329F2 + 0.120F3 + 0.106F4. The hydrolyzed amino acid model was F′ = 0.392F1′ + 0.346F2′ + 0.262F3′. A comprehensive score was calculated for each sample, followed by ranking and evaluating the amino acid content of each sample. It can be seen from Table 12 that the comprehensive scores of hydrolyzed amino acids and free amino acids of Agrocybe chaxinggu edible fungus powder were greater than those of other varieties, indicating that the comprehensive quality of hydrolyzed amino acids and free amino acids of this variety was higher, and it is a variety with better amino acid quality.Table 12
Comprehensive scores of 5 edible funguses powder.
SampleFree amino acidHydrolyzed amino acidComprehensive scoreRankComprehensive scoreRankAgrocybe chaxinggu edible fungus powder2.04012.0271Pleurotus citrinopileatus edible fungus powder0.06531.1802Flammulina velutipes edible fungus powder0.7332−0.8444Lentinus edodes edible fungus powder−1.4245−0.3813Hericium erinaceus edible fungus powder−1.4134−1.9795


## 3.1. Hydrolyzed Amino Acid Concentrations in 5 Edible Fungus Powders

The hydrolyzed amino acid is to hydrolyze the protein, polypeptide, and other amino acid chains in the plant to be tested into a single amino acid through acid hydrolysis. Therefore, the hydrolyzed amino acid can fully reflect the kind and content of all single amino acids in the sample. The hydrolyzed amino acid composition and content of 5 kinds of edible fungus powder are shown in Table1. Results showed that 15 hydrolyzed amino acids were present in all samples tested. The total amount of hydrolyzed amino acids contained in the 5 edible fungus powders was between 2.583 and 14.656 g/100 g. The total hydrolyzed amino acid content of Pleurotus citrinopileatus edible fungus powder was the highest, reaching 14.656 g/100 g, and the total hydrolyzed amino acid content of Hericium erinaceus edible fungus powder was the lowest, at 2.583 g/100 g. Glutamic acid was the most abundant among the 5 kinds of edible fungus powder, accounting for 17.41%, 19.75%, 25.16%, 24.92%, and 16.72% of the total hydrolyzed amino acids, respectively.Table 1
Contents∗ of hydrolyzed amino acids in 5 kinds of edible fungus powders.
CompoundAgrocybe chaxinggu edible fungus powderPleurotus citrinopileatus edible fungus powderFlammulina velutipes edible fungus powderLentinus edodes edible fungus powderHericium erinaceus edible fungus powderAspartic acid and asparagine1.571 ± 0.0150.613 ± 0.0010.531 ± 0.0020.737 ± 0.0020.247 ± 0.005Threonine0.744 ± 0.0120.510 ± 0.0090.147 ± 0.0030.192 ± 0.0020.107 ± 0.005Serine0.768 ± 0.0030.469 ± 0.0060.280 ± 0.0060.399 ± 0.0040.099 ± 0.003Glutamic acid and glutamine2.536 ± 0.0122.894 ± 0.0012.198 ± 0.0312.969 ± 0.0300.432 ± 0.001Glycine0.799 ± 0.0080.867 ± 0.0040.468 ± 0.0040.650 ± 0.0020.165 ± 0.003Alanine1.491 ± 0.0041.427 ± 0.0591.065 ± 0.0241.859 ± 0.0140.414 ± 0.005Valine1.021 ± 0.0141.202 ± 0.0230.585 ± 0.0020.809 ± 0.0140.207 ± 0.012Methionine0.022 ± 0.0020.113 ± 0.011NDNDNDIsoleucine0.583 ± 0.0110.677 ± 0.0030.301 ± 0.0040.423 ± 0.0050.068 ± 0.002Leucine1.379 ± 0.0171.703 ± 0.0370.821 ± 0.0011.135 ± 0.0090.298 ± 0.002Tyrosine0.507 ± 0.0040.636 ± 0.0080.414 ± 0.0010.406 ± 0.0150.111 ± 0.000Phenylalanine0.714 ± 0.0100.849 ± 0.0040.537 ± 0.0030.567 ± 0.0250.112 ± 0.006Lysine0.754 ± 0.0021.082 ± 0.0060.622 ± 0.0020.710 ± 0.0050.102 ± 0.001Histidine0.300 ± 0.0040.410 ± 0.0050.217 ± 0.0030.257 ± 0.0030.057 ± 0.003Arginine0.943 ± 0.0091.204 ± 0.0270.554 ± 0.0090.799 ± 0.0120.165 ± 0.001Proline0.434 ± 0.016NDNDNDNDTotal14.567 ± 0.02414.656 ± 0.2878.739 ± 0.01611.912 ± 0.0922.583 ± 0.010∗Value (g/100 g) = mean ± SD (n = 3). ND: not detectable.


## 3.2. Free Amino Acid Concentrations in 5 Edible Fungus Powders

Free amino acids refer to amino acids that exist in a free state in plants as a single amino acid molecule and can be directly absorbed and utilized. The free amino acid composition and content of 5 kinds of edible fungus powder are shown in Table2. The total amount of free amino acids contained in the 5 edible fungus powders was between 0.550 and 2.612 g/100 g. The total free amino acid content of Flammulina velutipes edible fungus powder was the highest, reaching 2.612 g/100 g, and the total free amino acid content of Hericium erinaceus edible fungus powder was the lowest, at 0.550 g/100 g. Glutamic acid was the most abundant among the 5 kinds of edible fungus powders, accounting for 25.21%, 23.99%, 28.29%, 36.48%, and 18.18% of the total free amino acids, respectively.Table 2
Contents∗ of free amino acids in 5 kinds of edible fungus powders.
CompoundAgrocybe chaxinggu edible fungus powderPleurotus citrinopileatus edible fungus powderFlammulina velutipes edible fungus powderLentinus edodes edible fungus powderHericium erinaceus edible fungus powderAspartic acid0.070 ± 0.0010.016 ± 0.0000.018 ± 0.0000.022 ± 0.0000.016 ± 0.001Threonine0.139 ± 0.0030.286 ± 0.0000.373 ± 0.0010.327 ± 0.0040.037 ± 0.001Serine0.079 ± 0.0020.107 ± 0.0000.068 ± 0.0020.015 ± 0.0000.004 ± 0.000Glutamic acid0.505 ± 0.0030.396 ± 0.0000.739 ± 0.0030.448 ± 0.0070.100 ± 0.002Glycine0.047 ± 0.0000.032 ± 0.0000.049 ± 0.0000.022 ± 0.0000.019 ± 0.001Alanine0.326 ± 0.0020.207 ± 0.0000.409 ± 0.0010.135 ± 0.0020.085 ± 0.003Valine0.164 ± 0.0020.117 ± 0.0000.118 ± 0.0000.053 ± 0.0010.047 ± 0.002MethionineND0.007 ± 0.000NDNDNDIsoleucine0.101 ± 0.0010.033 ± 0.0000.060 ± 0.0000.012 ± 0.0000.022 ± 0.000Leucine0.168 ± 0.0020.063 ± 0.0000.103 ± 0.0000.017 ± 0.0000.064 ± 0.002Tyrosine0.064 ± 0.0010.086 ± 0.0010.159 ± 0.0000.032 ± 0.0010.038 ± 0.001Phenylalanine0.115 ± 0.0020.131 ± 0.0000.216 ± 0.0010.046 ± 0.0000.046 ± 0.003Lysine0.066 ± 0.0020.079 ± 0.0000.151 ± 0.0010.035 ± 0.0000.007 ± 0.000Histidine0.027 ± 0.0000.028 ± 0.0000.052 ± 0.0000.009 ± 0.0000.008 ± 0.000Arginine0.106 ± 0.0020.062 ± 0.0000.057 ± 0.0010.055 ± 0.0010.024 ± 0.001Proline0.026 ± 0.002ND0.039 ± 0.002ND0.034 ± 0.002Total2.003 ± 0.0181.651 ± 0.0012.612 ± 0.0051.228 ± 0.0170.550 ± 0.018∗Value (g/100 g) = mean ± SD (n = 3). ND: not detectable.


## 3.3. The Difference in the Ratio of Essential Amino Acids and Nonessential Amino Acids

In order to scientifically evaluate the component structure of hydrolyzed amino acids, indicators such as the ratio of essential amino acids (EAAs) to nonessential amino acids (NEAAs) have been introduced. According to the essential amino acid model of protein nutritional value proposed by the World Health Organization (WHO) and the United Nations Food and Agriculture Organization (FAO) in 1973, the EAA/(EAA + NEAA) value in an ideal protein should reach about 40%, and the EAA/NEAA value should be above 60% [31]. The results (Table 3) showed that the value of EAA/(EAA + NEAA) was between 32.20% and 41.87%, and the value of EAA/NEAA was 47.48%–72.03%. In contrast, among the 5 kinds of edible fungus powders, Lentinus edodes edible fungus powder had the lowest EAA/(EAA + NEAA) and EAA/NEAA values, and Pleurotus citrinopileatus edible fungus powder best met the ideal protein standard.Table 3
Comparative analysis of the mass fractions and composition of amino acids in 5 edible fungus powders.
SampleEAA/NEAAEAA/(EAA + NEAA)Agrocybe chaxinggu edible fungus powder55.8135.82Pleurotus citrinopileatus edible fungus powder72.0341.87Flammulina velutipes edible fungus powder52.6234.48Lentinus edodes edible fungus powder47.4832.20Hericium erinaceus edible fungus powder52.8534.58


## 3.4. The Difference in Taste Characteristics and Taste Activity Values

The determination of hydrolyzed amino acids was mainly to study their nutritional properties. The flavored amino acids in structural proteins are mostly in a combined state and have little effect on flavor, while free amino acids are mainly used to participate in the formation of taste substances. Therefore, the taste characteristics of free amino acids in the five test samples were compared, and they were divided into 4 categories: umami amino acids, sweet amino acids, bitterness amino acids, and tasteless amino acids [32]. The results (Table 4) showed that Pleurotus citrinopileatus edible fungus powder, Flammulina velutipes edible fungus powder, and Lentinus edodes edible fungus powder had the highest content of sweet amino acids. Agrocybe chaxinggu edible fungus powder and Hericium erinaceus edible fungus powder had the highest content of bitterness amino acids.Table 4
Flavored amino acid content (g/100 g) in 5 kinds of edible fungus powders.
SampleUmami amino acidsSweet amino acidsBitterness amino acidsTasteless amino acidsAgrocybe chaxinggu edible fungus powder0.5740.6160.6820.131Pleurotus citrinopileatus edible fungus powder0.4120.6330.4410.163Flammulina velutipes edible fungus powder0.7570.9690.6060.310Lentinus edodes edible fungus powder0.4690.4990.1930.067Hericium erinaceus edible fungus powder0.1150.1790.2110.045The absolute content and relative ratio of flavored amino acids may be closely related to the taste of the food. Therefore, the taste active value (TAV) of 16 amino acids in 5 kinds of test samples was analyzed and compared. TAV is the ratio of the content of each taste amino acid in the sample to its corresponding taste threshold [33]. In general, when TAV > 1, the taste-producing substance is considered to have a significant impact on the taste-producing effect of the sample; when TAV < 1, it means that the substance has no significant taste-producing effect [34]. The results (Table 5) showed that among the 5 edible fungus powders, the TAV values of aspartic acid, glutamic acid, alanine, and arginine were also greater than 1. The TAV values of serine, glycine, methionine, leucine, tyrosine, and proline were also less than 1. The TAV of free amino acid in Agrocybe chaxinggu edible fungus powder was between 0.00 and 100.93. The TAV of free amino acid in Pleurotus citrinopileatus edible fungus powder was between 0.00 and 79.30. The TAV of free amino acid in Flammulina velutipes edible fungus powder was between 0.00 and 147.84. The TAV of free amino acid in Lentinus edodes edible fungus powder was between 0.00 and 89.50. The TAV of free amino acid in Hericium erinaceus edible fungus powder was between 0.00 and 19.95. According to the TAV value, the most significant free amino acid that affects the taste of the 5 edible fungus powders that can be screened out was glutamic acid in the umami amino acid, followed by aspartic acid in umami amino acids, arginine in bitterness amino acids, and alanine in sweet amino acids. And Flammulina velutipes edible fungus powder has the most outstanding umami.Table 5
The TAV of free amino acid in 5 kinds of edible fungus powders.
CompoundTaste characteristicsTaste threshold (mg/100 g) [34]TAV of 5 kinds of edible fungus powdersAgrocybe chaxingguPleurotus citrinopileatusFlammulina velutipesLentinus edodesHericium erinaceusAspartic acidUmami3.0023.225.306.037.295.24ThreonineSweet260.000.531.101.441.260.14SerineSweet150.000.520.720.450.100.02Glutamic acidUmami5.00100.9379.30147.8489.5019.95GlycineSweet110.000.420.290.450.200.17AlanineSweet60.005.443.456.822.251.42ValineBitterness150.001.090.780.780.350.32MethionineBitterness30.000.000.240.000.000.00IsoleucineBitterness90.001.130.370.670.140.25LeucineBitterness380.000.440.170.270.040.17TyrosineTasteless260.000.250.330.610.120.15PhenylalanineBitterness150.000.770.871.440.310.31LysineTasteless50.001.331.593.020.690.14HistidineBitterness20.001.341.392.600.440.38ArginineBitterness10.0010.646.235.735.532.38ProlineSweet300.000.090.000.130.000.11


## 3.5. Correlation Analysis and PCA of Free Amino Acids

A correlation analysis was performed on the 16 free amino acid components of 5 edible fungus powders, and the results are shown in Table6. There were positive correlations and negative correlations between amino acids, and most of them were positive. The results showed that there was a strong correlation between the free amino acids of the five edible fungus powders, which could be comprehensively evaluated by PCA.Table 6
Correlation analysis of free amino acids in 5 kinds of edible fungus powders.
Amino acidsAspartic acidThreonineSerineGlutamic acidGlycineAlanineValineMethionineIsoleucineLeucineTyrosinePhenylalanineLysineHistidineArginineProlineAspartic acid1Threonine−0.3201Serine0.2710.3491Glutamic acid0.2000.7830.5021Glycine0.5190.3330.6800.8191Alanine0.3850.4570.6240.888∗0.983∗∗1Valine0.6990.1220.8390.5830.889∗0.7991Methionine−0.2960.2140.670−0.101−0.073−0.1060.1951Isoleucine0.842−0.1190.5450.4930.8670.7720.910∗−0.1971Leucine0.802−0.2760.4930.3530.8070.7020.860−0.1980.980∗∗1Tyrosine−0.1530.5770.5590.7670.7630.8430.4920.1110.3790.3511Phenylalanine0.0070.5570.6820.8080.8560.908∗0.6460.1600.5150.4750.982∗∗1Lysine−0.0230.6970.6340.894∗0.8330.906∗0.5910.1170.4490.3750.968∗∗0.981∗∗1Histidine0.0470.5550.6570.8320.8780.930∗0.6550.1000.5460.5010.978∗∗0.998∗∗0.983∗∗1Arginine0.8740.1190.6240.5270.7070.6050.8750.0230.8320.7280.1340.3110.3200.3371Proline0.146−0.343−0.1730.1180.4190.4310.159−0.5930.4490.5560.4320.3820.2840.408−0.1021Note: relevance is Pearson’s type;∗significant correlation (p < 0.05); ∗∗extremely significant correlation (p < 0.01).PCA is a multivariate statistical analysis method that analyses a few variables which can reveal the internal structure sufficiently by studying the relationship between multiple original variables [35]. According to the rule that the characteristic value is greater than 1 and the cumulative variance contribution rate is greater than 80%, four principal component factors were obtained through rotation and extraction factors, and the total contribution rate was 100%, indicating that the experimental data can fully reflect the original information (Table 7).Table 7
Results of principal component analysis.
ComponentInitial eigenvalueRotate the sum of squares loadingTotalVariance (%)Accumulate (%)TotalVariance (%)Accumulate (%)19.24157.75957.7597.12544.53244.53223.45521.59279.3515.25932.86977.40232.18313.64592.9961.91611.97789.37841.1217.0041001.69910.622100The first principal component was mainly composed of glycine, alanine, histidine, phenylalanine, lysine, valine, glutamic acid, tyrosine, isoleucine, serine, leucine, and arginine. The second principal component was mainly composed of aspartic acid, leucine, isoleucine, and arginine. And the third principal component was mainly composed of methionine and serine (Table8).Table 8
Contribution value of element principal component.
Amino acidsComponent1234Aspartic acid0.4320.8540.178−0.228Threonine0.417−0.7500.176−0.482Serine0.745−0.1030.5890.296Glutamic acid0.843−0.301−0.045−0.443Glycine0.9910.112−0.064−0.031Alanine0.984−0.040−0.148−0.089Valine0.8820.3340.3150.104Methionine0.037−0.3970.7760.488Isoleucine0.8090.587−0.0110.029Leucine0.7430.634−0.0890.195Tyrosine0.814−0.490−0.2560.176Phenylalanine0.902−0.377−0.1310.163Lysine0.884−0.454−0.112−0.017Histidine0.917−0.344−0.1640.117Arginine0.6750.5100.443−0.295Proline0.3490.253−0.8470.311


## 3.6. Correlation Analysis and PCA of Hydrolyzed Amino Acids

A correlation analysis was performed on the 16 hydrolyzed amino acid components of 5 edible fungus powders, and the results are shown in Table9. The results showed that the correlation coefficients between most hydrolyzed amino acids were greater than 0.7, indicating that there were strong correlations among the 16 hydrolyzed amino acids in 5 kinds of edible fungus powders, so they could be further studied by PCA.Table 9
Correlation analysis of free amino acids in 5 kinds of edible funguses powder.
Amino acidsAspartic acidThreonineSerineGlutamic acidGlycineAlanineValineMethionineIsoleucineLeucineTyrosinePhenylalanineLysineHistidineArginineProlineAspartic acid1Threonine0.8531Serine0.953∗0.927∗1Glutamic acid0.5130.4810.6841Glycine0.6630.7850.8520.903∗1Alanine0.5760.4440.6920.948∗0.8321Valine0.6070.7830.8170.8750.995∗∗0.7851Methionine0.0410.5190.3190.4180.6480.2350.7241Isoleucine0.6300.8070.8340.8610.994∗∗0.7690.999∗∗0.7211Leucine0.5680.7580.7870.8760.990∗∗0.7800.999∗∗0.7460.996∗∗1Tyrosine0.5150.6880.7340.889∗0.956∗0.7340.964∗∗0.7120.963∗∗0.967∗∗1Phenylalanine0.5730.7140.7790.910∗0.974∗∗0.7770.975∗∗0.6730.974∗∗0.975∗∗0.996∗∗1Lysine0.4350.6120.6730.917∗0.952∗0.7770.962∗∗0.7280.955∗0.970∗∗0.989∗∗0.985∗∗1Histidine0.4800.6860.7170.886∗0.969∗∗0.7530.983∗∗0.7690.979∗∗0.989∗∗0.988∗∗0.986∗∗0.993∗∗1Arginine0.5480.7370.7720.885∗0.988∗∗0.7900.997∗∗0.7460.993∗∗0.999∗∗0.966∗∗0.974∗∗0.974∗∗0.990∗∗1Proline0.932∗0.8170.8240.1780.4140.2450.369−0.0570.4020.3240.2660.3180.1580.2250.2971Note: relevance is Pearson’s type;∗significant correlation (p < 0.05); ∗∗extremely significant correlation (p < 0.01).PCA was performed on the hydrolyzed amino acid content of the 5 samples, and the results are shown in Tables10 and 11. It can be seen from Tables 10 and 11 that the cumulative contribution rate of the three principal components reaches 99.143%, indicating that three components can represent the information of all hydrolyzed amino acids in 5 kinds of edible fungus powders and can better reflect the relationship of free amino acids in 5 kinds of edible fungus powders.Table 10
Results of principal component analysis.
ComponentInitial eigenvalueRotate the sum of squares loadingTotalVariance (%)Accumulate (%)TotalVariance (%)Accumulate (%)112.56878.54778.5476.21338.83438.83422.29414.33592.8825.49134.31873.15231.0026.26199.1434.15825.9999.143Table 11
Contribution value of element principal component.
Amino acidsComponent123Aspartic acid0.6740.732−0.100Threonine0.8050.4740.355Serine0.8610.508−0.018Glutamic acid0.889−0.176−0.419Glycine0.998−0.017−0.035Alanine0.805−0.027−0.562Valine0.994−0.0770.049Methionine0.657−0.4670.582Isoleucine0.996−0.0450.073Leucine0.989−0.1260.054Tyrosine0.964−0.1850.022Phenylalanine0.980−0.126−0.023Lysine0.952−0.288−0.037Histidine0.971−0.2320.047Arginine0.985−0.1520.036Proline0.4360.8890.131The first principal component was mainly composed of glycine, isoleucine, valine, leucine, arginine, phenylalanine, histidine, tyrosine, lysine, glutamic acid, serine, alanine, threonine, aspartic acid, and methionine. The second principal component was mainly composed of proline, aspartic acid, and serine. And the third principal component was mainly composed of methionine (Table11).


## 3.7. Comprehensive Evaluation

A comprehensive evaluation model was established based on the contribution rates of the eigenvalues corresponding to the three principal components of hydrolyzed amino acids and the four principal components of free amino acids. The free amino acid model wasF = 0.445F1 + 0.329F2 + 0.120F3 + 0.106F4. The hydrolyzed amino acid model was F′ = 0.392F1′ + 0.346F2′ + 0.262F3′. A comprehensive score was calculated for each sample, followed by ranking and evaluating the amino acid content of each sample. It can be seen from Table 12 that the comprehensive scores of hydrolyzed amino acids and free amino acids of Agrocybe chaxinggu edible fungus powder were greater than those of other varieties, indicating that the comprehensive quality of hydrolyzed amino acids and free amino acids of this variety was higher, and it is a variety with better amino acid quality.Table 12
Comprehensive scores of 5 edible funguses powder.
SampleFree amino acidHydrolyzed amino acidComprehensive scoreRankComprehensive scoreRankAgrocybe chaxinggu edible fungus powder2.04012.0271Pleurotus citrinopileatus edible fungus powder0.06531.1802Flammulina velutipes edible fungus powder0.7332−0.8444Lentinus edodes edible fungus powder−1.4245−0.3813Hericium erinaceus edible fungus powder−1.4134−1.9795


## 4. Conclusions and Discussion

In this study, the composition and content of free amino acids and hydrolyzed amino acids ofAgrocybe chaxinggu edible fungus powder, Pleurotus citrinopileatus edible fungus powder, Flammulina velutipes edible fungus powder, Lentinus edodes edible fungus powder, and Hericium erinaceus edible fungus powder were analyzed. The results showed that the total amount of hydrolyzed amino acids contained in the 5 edible fungus powders was between 2.583 and 14.656 g/100 g. The total amount of free amino acids contained in the 5 edible fungus powders was between 0.550 and 2.612 g/100 g. The total amount of hydrolyzed amino acids was relatively large, which may be caused by the simultaneous thermal degradation and Maillard reaction, which hydrolyzed macromolecular proteins or polypeptides into small molecular amino acids. Comparative analysis of the mass fractions and composition of amino acids indicated that Pleurotus citrinopileatus edible fungus powder best met the ideal protein standard. The delicious taste of edible fungus powder is determined by the balance and mutual influence of different free amino acids, which play an important role in the taste of edible fungus powder. In this study, the TAV of free amino acids of five edible fungus powders was evaluated. The TAV of amino acids is related to water solubility. Water-soluble amino acids may be partly due to hydrolysis, or may be due to water-solubility in nature, which was related to the structure and properties of the amino acids themselves [36]. The most significant free amino acid that affects the taste of the 5 edible fungus powders which can be screened out was the glutamic acid in the umami amino acid. And Flammulina velutipes edible fungus powder has the most outstanding umami. However, the amino acids alone might not be good enough to be responsible for the taste. Fatty acids might also contribute a lot in forming the taste. The taste of edible fungus powder was systematically evaluated, and the results of fatty acids need to be determined later [37]. PCA extracted four principal components from 16 free amino acids with a cumulative variance contribution rate of 100%, and extracted three principal components from 16 hydrolyzed amino acids with a cumulative variance contribution rate of 99.143%, which can better reflect the comprehensive information on the quality of the 5 edible fungus powders. A comprehensive evaluation model was established, and the comprehensive quality of amino acids in Agrocybe chaxinggu edible fungus powder was the best. This paper only studies the amino acid compositions and contents of 5 edible fungus powders at present. Further research will collect more edible fungus powder samples to determine their amino acid composition and content in order to establish a more detailed edible fungus powder quality evaluation system, laying a theoretical foundation for the development of edible fungus resources.



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*Source: 3618002-2022-04-07.xml*