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. 2020 Nov 24;9(1):87–98. doi: 10.1002/fsn3.1960

Nonvolatile taste compounds of Shanghai smoked fish: A novel three stages control techniques

Yu Zhou 1,2, Shunsheng Chen 1,2,3, Xichang Wang 1,2,3, Hongcai Zhang 1,2,3,4,✉
PMCID: PMC7802575  PMID: 33473273

Abstract

In this work, the effect of processing stages including first soaking (FS), frying after first soaking (FFS), and second soaking (SS) on nonvolatile taste compounds of Shanghai smoked fish was investigated using high‐performance liquid chromatography (HPLC) and automatic amino acid analyzer. Results showed that the contents of free amino acids (FAAs) ranged from 396.94 to 585.79 mg/100 g and 5′‐inosine monophosphate (IMP, as main umami nucleotide) from 215.91 to 284.56 mg/100 g in Shanghai smoked fish, respectively. Moreover, the contents of Glu and Gly as main umami amino acids ranged from 1.64 to 107.32 mg/100 g and 61.61 to 108.88 mg/100 g, respectively. TAV values of IMP, Asp, and Glu in Shanghai smoked fish reached 11.38, 2.73, and 21.46, respectively. The obvious difference could be observed using principal component analysis (PCA) in three processing stages of Shanghai smoked fish. Therefore, probing into the nonvolatile flavor of Shanghai smoked fish could not only enrich the theoretical basis of flavor chemistry in freshwater fish fields, but probe into the formation mechanisms of taste compounds in further study.

Keywords: ATP‐related compounds, free amino acids, grass carp, nonvolatile flavor

Removing the native unpalatable taste of grass carp is key for increasing its umami flavor and economic value. Therefore, the effect of processing stages including first soaking (FS), frying after first soaking (FFS), and second soaking (SS) on nonvolatile taste compounds of Shanghai smoked fish was investigated using high‐performance liquid chromatography (HPLC) and automatic amino acid analyzer.

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Highlights.

  • First report about the nonvolatile taste compounds of Shanghai smoked fish.

  • Three processing stages including FS, FFS, and SS were used for preparing the Shanghai smoked fish.

  • Synergetic effect of Maillard reaction and seasonings on tastes of Shanghai smoked fish was investigated.

  • Earthy‐musty tastes of grass carp were covered up as well as umami flavor was increased.

  • Electronic tongue could effectively distinguish the taste profiles of Shanghai smoked fish.

1. INTRODUCTION

Grass carp (Ctenopharyngodon idellus), together with black carp, silver carp, and bighead carp, are known as "the four major Chinese carps." Grass carp with abundantly nutritional values is one of the largest freshwater fish in China, accounting for approximately 71% of all freshwater aquaculture production (Xie et al., 2018). In 2018, the output of grass carp reached 55,043 million tons accounting for about 21.63% and ranking the first in freshwater fish (Xu, Wu, Guo, 2019). Grass carp usually grows in freshwater such as pond or lake, but bacteria with earthy smell are easily attached to plankton such as diatom and cyanobacteria, leading to accumulation of bad odor substances through food chain in grass carp (Zhong et al., 2011; Zhou & Wang, 2006). The earthy‐musty compounds mainly include 2‐methylisoborneol (2‐MIB), geosmin, trimethylamine, and hexanal (Robertson et al., 2005; Yang, Hu, et al., 2019; Yang, Shi, et al., 2019; Zhao, Wu, et al., 2015; Zhao, Shen, et al., 2015; Zhao, Zou, et al., 2015). Thus, removing the native unpalatable taste of grass carp is key for increasing its umami flavor and economic value.

In recently years, the deodorization methods of aquatic products consist of three categories: physical deodorization methods (embedding, adsorption, salt dissolution, masking, organic solvent extraction, irradiation, etc), chemical deodorization (acid‐base and antioxidant method), and biological deodorization (Hong et al., 2013; Yarnpakdee, et al., 2012; Fukami, 2006.; Hu & Pan, 2000; Kuley et al., 2012; Tomac et al., 2015; Giorgio et al., 2019). Physical deodorization methods include low‐cost of natural zeolite and active carbon adsorption, but time‐consuming and low efficiency limited their wide application (Kuley et al., 2012). Irradiation has not been widely used in aquaculture based on the consideration of food safety (Tomac et al., 2015). Although liquid‐liquid extraction was effective in fish oil deodorization at high‐temperature condition (70°C) (Song, Zhang, et al., 2018; Song, Wang, et al., 2018), the use of organic solvents resulted in damage of fish compositions and food safety problems was also the pitfall of this method.

Maillard reaction (MR) refers to the process that carbonyl compounds (reducing sugars) and amino compounds (amino acids and proteins) are polymerized and condensed into melanoids at certain conditions. It is particularly important for the formation of meat flavors (Dong et al., 2019; Thomas & Josephine, 1959; van den Ouweland, Demole & Enggist, 1989). Priazines, alcohols, and aldehydes, as the major flavor contributors, accounted for 38.86, 9.21, and 8.23% aroma of Maillard reaction products (MRPs) from Collichthys niveatus (C. niveatus) protein hydrolysates (Zhao, Wu, et al., 2015; Zhao, Shen, et al., 2015; Zhao, Zou, et al., 2015). The contents of total free amino acids (FAAs) increased from 53.36 nmol/kg in fresh grass carp to 65.03 and 72.18 nmol/kg in fried samples for 2 and 4 min, respectively, indicating frying significantly contributed to improving the taste and flavor compounds of grass carp (Li, Tu, Sha, et al., 2016; Li, Tu, Zhang, et al., 2016). Previous report also indicated that fishy smell in grass carp soup could be improved by masking function of garlic and ginger, known as "sensational deodorizing" (Li, Tu, Sha, et al., 2016; Li, Tu, Zhang, et al., 2016). Therefore, it was hypothesized that the synergistic effect of MR and seasonings could effectively remove fishy and earthy flavor of grass carp.

Shanghai smoked fish deeply loved by public is a traditional special dish with crispy crust and delicious taste. The attractive flavor of grass carp could be increased with the help of MR and seasonings. Wang et al., previously investigated the contents of free amino acids (FAAs), ATP‐related compounds (ATPs) of dead grass carp stored at 4°C for 12 hr (Wang et al., 2018). Few study focused on the nonvolatile flavor compounds of Shanghai smoked fish by adjusting the conditions of MR and the addition ratios of seasonings.

Therefore, the present study was designed to study on the effects of first soaking (FS), frying after first soaking (FFS) and second soaking (SS) on the taste compounds of Shanghai smoked fish. A detailed study on the water‐soluble compounds of Shanghai smoked fish could not only enrich the theoretical knowledge of flavor chemistry of freshwater fish, but have a profound contribution to the development of freshwater fish processing techniques.

2. MATERIALS AND METHODS

2.1. Materials

Standards of adenosine triphosphate (ATP), adenosine diphosphate (ADP), 5′‐inosine monophosphate (IMP), and hypoxanthine (Hx) were purchased from Sigma. Standards of 5′‐adenosine monophosphate (AMP) and hypoxanthine riboside (HxR) were purchased from Tokyo Chemical Industry (TCI) Co., Ltd., Japan. KH2PO4, K2HPO4 and methanol (chromatographic grade), perchloric acid, KOH, trichloroacetic acid (TCA), and NaOH were from Sinopharm Chemical Reagent Co., Ltd, Shanghai, China. The 17 amino acids mixtures (chromatographic grade) were bought from National Institute of Metrology, China‐Institute of Stoichiometry and Analytical Sciences, Beijing, China.

The live grass carps (about 2.5 kg/tail), chive, ginger, cooking wine (Wangzhihe Food Co., Ltd), salt (China Salt Co., Ltd), pepper (Haoshihui condiment Co., Ltd), soy sauce (Haitian seasoning Food Co., Ltd), sunflower seed oil (Jinlongyu Food Co., Ltd), five‐spice powder (Weihaomei Food Co., Ltd), and sugar (Fengyiyuan Food Co., Ltd) were purchased from NGS Supermarket (No.570, Guzong Road, Pudong New Area).

2.2. Preparation of Shanghai smoked fish

Grass carps alive were timely stunned, killed, scaled, gutted, rinsed, and filleted (length × width × height, 9 × 1.5 × 1.5 cm) after transporting to the laboratory. Seasonings formula of preparing Shanghai smoked fish is shown in Table 1. Processing stages of Shanghai smoked fish could be divided into three stages including FS, FFS, and SS. The detailed treatment process was shown below. (a) grass carp was soaked in the seasoning mixtures including cooking wine (20%), salt (1.5%), chive (2%), ginger (1%), garlic (1%), pepper (1%), and soy sauce (5%) for 30 min. (b) grass carp after FS treatment was fried on the electric frying pan (HY‐81, Nanhai Poffey Electrical and Mechanical Equipment Co., Ltd.) at 180°C for 5 min. (3) Grass carp after FFS treatment was soaked for 10 min in boiling water (60%) containing sunflower seed oil (5%), five‐spice powder (0.1%), sugar (3%), and soy sauce (10%) in nonstick pot (Hertz Electric Appliances Co., Ltd.). Both liquid and oil of soaking and frying fish fillets were drained by kitchen paper.

Table 1.

Seasonings formula of preparing Shanghai smoked fish

Treatment process Formula
FS A0 A1 A2 A3 A4 A5 A6 A7 A8
FFS B0 B1 B2 B3 B4 B5 B6 B7 B8
SS C0 C1 C2 C3 – – – – –
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A0–A8: no adding; cooking wine; cooking wine + salt; cooking wine + chive; cooking wine + ginger; cooking wine + garlic; cooking wine + pepper; cooking wine + soy sauce; all seasonings.

B0–B8: no adding; cooking wine; cooking wine + salt; cooking wine + chive; cooking wine + ginger; cooking wine + garlic; cooking wine + pepper; cooking wine + soy sauce; all seasonings.

C0–C3: all seasonings + plant oil; all seasonings + plant oil + sugar; all seasonings + plant oil + sugar +soy sauce; all seasonings + plant oil + sugar +soy sauce + five‐spice powder.

All seasonings represented cooking wine + salt +chive + ginger +garlic + pepper +soy sauce.

Abbreviations: FFS, frying after first soaking; FS, first soaking; SS, second soaking.

2.3. ATP‐related compounds (ATPs) analysis of Shanghai smoked fish

ATP‐related compounds were determined based on previous procedures described by Yokoyama et al. (Yokoyama et al., 1992). The 5 g of fish fillets was accurately weighed before adding 10 ml of cold perchloric acid (10%, v/v), and then centrifuged (H2050R, Xiangyi Co., Ltd.) at 10,000 rpm at 4°C for 15 min after homogenization for 2 min. The same treatment process was repeated twice except for adding 5 ml of cold perchloric acid (5%, v/v).

The collected supernatants were combined and adjusted to pH 6.50 with 1 mol/L KOH, and then stood for 30 min. The supernatants were diluted to 50 ml, shaken and filtered through a 0.22 μm membrane. All operating conditions were conducted at 4°C.

Amounts of ATPs were determined by high‐performance liquid chromatography (HPLC) (W2690/5, Waters Co., Ltd) according to previous report (Qiu et al., 2015). ODS‐SPC18 column (4.6 mm × 250 mm, 5 μm) was employed for the separation of ATPs at 28°C. The mobile phase A and B were 0.05 mol/L KH2PO4 and K2HPO4 (1:1, v:v), and methanol, respectively. To improve the separation efficiency of ATPs, the flow rate and detection wavelength was set as 1.0 ml/min and 254 nm, respectively.

2.4. Free amino acids (FAAs) analysis of Shanghai smoked fish

The concentration of FAAs was analyzed by an automatic amino acid analyzer (L‐8800, Hitachi) based on previously reported method with slight modifications (Jia et al., 2017). Samples (2 g) were homogenized with 15 ml of 15% TCA and stood for 2 hr, then centrifuged at 10,000 rpm at 4°C for 15 min. The obtained sediment (5 ml) was adjusted to pH 2.0 with 3 mol/L NaOH and diluted to 10 ml before filtration through a 0.22 μm filter membrane.

2.5. Electronic tongue analysis of Shanghai smoked fish

Samples (2 g) were homogenized with 25 ml ultrapure water, and stood for 15 min, followed by centrifugation at 10,000 rpm for 10 min at 4°C. The sediment was filtered through a 0.22 μm membrane for further analysis (Yang, Hu, et al., 2019; Yang, Shi, et al., 2019). Samples were diluted 80 times before Electronic tongue (Alpha M.O.S., Astree, France) analysis based on previously reported conditions (Yang, Hu, et al., 2019; Yang, Shi, et al., 2019). The 120 s response value on each sensor was selected as the original data of electronic tongue.

To prevent the carryover effects, ultrapure water was used for cleaning after test and cleaning period was 10 s. Each sample was determined 8 times and the last three data were analyzed by principal component analysis (PCA).

2.6. Calculation of taste activity value (TAV)

TAV represented the ratio of the content of flavor substances in samples to their corresponding taste threshold.

TAV=The ratio of the content of flavor substancesCorresponding taste threshold (1)

where TAV > 1 means this substances contributed significantly to flavor and TAV < 1 means not significant (Gunlu & Gunlu, 2014).

2.7. Statistical analysis

All data were represented by means ± standard deviations (SD) of three independent replicates. The data analysis was performed using Microsoft Excel 2010 and SPSS Statistics 17.0. The Duncan's test of one way ANOVA was used for significant differences analysis. Original data were collected and analyzed by PCA after electronic tongue analysis.

3. RESULTS AND DISCUSSION

3.1. Effects of FS on ATPs contents

Inosine monophosphate, GMP, and AMP are key components of strong umami taste (Chen & Zhang, 2007; Johnson et al., 2013). As shown in Table 2, results showed that IMP contents of A0–A8 were 215.91, 156.59, 180.05, 164.91, 175.84, 200.32, 199.48, 275.57, and 270.20 mg/100 g, respectively. Among them, IMP contents of cooking wine and soy sauce soaking sample were the lowest and highest, respectively. Although the contents of AMP in each sample were low, AMP has synergistic effects with IMP, Glu, and Asp on increasing umami of Shanghai smoked fish (Zhang et al., 2019). IMP contents of samples decreased significantly after soaking in cooking wine, but increased significantly after soaking in soy sauce. TAV of IMP in all samples after FS treatment were greater than 1, among them, soy sauce soaking sample was 27.55%, higher than that of fresh fish, indicating soy sauce and other seasonings contributed to the tastes of Shanghai smoked fish (Lioe et al., 2010). The main reason was that cooking wine with organic acids decreased the pH of fish (Lin et al., 2012; Zhao, Wu, et al., 2015; Zhao, Shen, et al., 2015; Zhao, Zou, et al., 2015), which promoted the degradation of IMP (Thanh & Peter, 1985). In addition, Asp and Glu were recognized as main synthesis substances of ATPs in soy sauce, that is, IMP was synthesized at first, and then converted into AMP and GMP (Lin et al., 2015; Moffatt & Ashihara, 2002). Studies have shown that IMP with strong umami could not only increase sweetness and meat flavor, but inhibit salty, bitter, and burnt flavor of fish. Therefore, IMP was the main umami nucleotide in FS process (Huang et al., 2019).

Table 2.

Contents of ATP‐related compounds in first soaking and frying for preparing Shanghai smoked fish (mg/100 g)

Samples ATP ADP AMP TAV IMP TAV Hx HxR
A0 15.38 ± 2.94c 14.32 ± 2.06c 13.54 ± 0.38e 0.27 215.91 ± 4.53c 8.64 15.13 ± 1.16d 20.97 ± 0.21e
A1 4.73 ± 1.58ab 6.76 ± 0.97b 7.29 ± 0.81d 0.15 156.59 ± 1.68a 6.26 9.20 ± 0.23c 11.68 ± 0.70b
A2 2.88 ± 0.92a 3.10 ± 0.31a 3.48 ± 0.38a 0.07 180.05 ± 3.66b 7.20 3.41 ± 0.11ab 14.28 ± 0.79c
A3 2.71 ± 0.08a 2.73 ± 0.50a 2.99 ± 0.03a 0.06 164.91 ± 3.28ab 6.60 3.20 ± 0.05a 8.92 ± 0.38a
A4 3.20 ± 0.22ab 3.14 ± 0.02a 3.35 ± 0.02a 0.07 175.84 ± 3.34b 7.03 3.41 ± 0.07ab 12.88 ± 0.22bc
A5 3.78 ± 0.62ab 3.54 ± 0.61a 4.54 ± 0.51b 0.09 200.32 ± 16.59c 8.01 3.31 ± 0.11a 14.19 ± 0.73c
A6 6.02 ± 0.70b 6.47 ± 0.21b 7.87 ± 0.39d 0.16 199.48 ± 4.05c 7.98 3.88 ± 0.29ab 25.18 ± 1.31f
A7 5.17 ± 0.20ab 5.73 ± 0.58b 6.09 ± 0.09c 0.12 275.57 ± 11.52d 11.02 3.91 ± 0.00ab 19.38 ± 0.28d
A8 5.98 ± 0.74b 6.06 ± 0.60b 5.96 ± 0.25c 0.12 270.20 ± 4.99d 10.81 4.34 ± 0.14b 24.88 ± 0.78f
B0 12.31 ± 1.40jk 9.54 ± 0.30ij 14.91 ± 0.98i 0.30 384.93 ± 11.33k 15.40 3.89 ± 0.10i 28.48 ± 0.46i
B1 10.46 ± 1.00i 11.29 ± 0.63jk 15.64 ± 0.24ij 0.31 359.19 ± 6.69jk 14.37 4.12 ± 0.11i 30.45 ± 0.27j
B2 14.25 ± 0.59k 10.97 ± 1.08ijk 14.79 ± 0.93i 0.30 376.49 ± 14.38k 15.06 4.47 ± 0.11j 39.09 ± 0.69m
B3 12.97 ± 0.06jk 10.62 ± 0.83ijk 17.05 ± 1.16jk 0.34 379.17 ± 11.11k 15.17 4.55 ± 0.20jk 35.37 ± 0.09kl
B4 11.81 ± 0.72ij 10.28 ± 0.06ijk 14.73 ± 0.72i 0.29 360.29 ± 5.30jk 14.41 4.69 ± 0.06jkl 34.64 ± 0.86k
B5 16.75 ± 1.38l 11.94 ± 1.37k 18.76 ± 0.87k 0.38 375.53 ± 7.56k 15.02 4.83 ± 0.02klm 40.19 ± 1.20m
B6 12.84 ± 0.59k 9.33 ± 0.15i 14.42 ± 0.30i 0.29 322.25 ± 10.26i 12.89 4.90 ± 0.00lm 37.17 ± 0.60l
B7 10.09 ± 1.11i 10.72 ± 0.85ijk 16.00 ± 1.03ij 0.32 337.89 ± 15.77ij 13.52 5.04 ± 0.29m 34.29 ± 1.09k
B8 9.14 ± 1.09j 11.53 ± 0.03k 15.69 ± 0.94ij 0.31 370.11 ± 19.58k 14.80 4.85 ± 0.10klm 35.84 ± 1.23kl
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A0–A8: no adding; cooking wine; cooking wine + salt; cooking wine + chive; cooking wine + ginger; cooking wine + garlic; cooking wine + pepper; cooking wine + soy sauce; all seasonings.

B0–B8: no adding; cooking wine; cooking wine + salt; cooking wine + chive; cooking wine + ginger; cooking wine + garlic; cooking wine + pepper; cooking wine + soy sauce; all seasonings.

All seasonings represented cooking wine + salt +chive + ginger +garlic + pepper + soy sauce.

Different superscript letters (a‐m) in the same column indicate a significant difference (p < .05).

Abbreviations: ADP, adenosine diphosphate; AMP, 5′‐adenosine monophosphate; ATP, adenosine triphosphate; Hx, hypoxanthine; HxR, hypoxanthine riboside; IMP, 5′‐inosine monophosphate; TAV, taste activity value.

On the contrary, Hx could interact with certain amino acids and peptides, resulting in little bit of bitterness in Shanghai smoked fish and thus causing undesirable smells (Qiu et al., 2015). The Hx contents in fresh grass carp (A0: 15.13 mg/100 g) were higher than other FS samples (A1–A8: 9.20, 3.41, 3.20, 3.41, 3.31, 3.88, 3.91, and 4.31 mg/100 g, respectively), indicating masking function of seasonings on unfavorable taste compounds of grass carp.

3.2. Effects of FFS on ATPs contents

Table 2 shows the contents of ATPs in FFS of grass carp. Although the contents of AMP in FFS were low, significantly higher than that of FS samples. AMP acting as a good flavor enhancer in aquatic foods could suppress bitterness and produce pleasant sweetness and saltiness (Qiu et al., 2015). IMP contents of B0–B8 reached 384.93, 359.19, 376.49, 379.17, 360.29, 375.53, 322.25, 337.89, and 370.11 mg/100 g, respectively. IMP contents of FFS with cooking wine and pepper were the lowest, but fried grass carp were the highest (Table 2). Compared with FS samples, the contents of IMP in FFS were increased by 78.28, 129.38, 109.10, 129.93, 104.90, 87.47, 61.55, 22.61, and 36.98% respectively. TAV of IMP of each sample was greater than 12, higher than that of the FS samples (Table 2), showing high‐temperature frying mainly contributed to the tastes of grass carp. The main reason was the accumulation of IMP degraded from ATP by high‐temperature frying (Cui, 2001).

3.3. Effects of SS process on the content of ATPs

Second soaking was applied to enhance the tastes of grass carp after FS and FFS treatment. Figure 1a shows the ATPs contents of grass carp were affected by SS process. IMP contents of C0–C3 were 263.99, 267.96, 274.35, and 284.56 mg/100 g, respectively. IMP contents of SS samples soaked with plant oil and water were the lowest, and that of Shanghai smoked fish final products were the highest (Figure 1a). Plant oil, sugar, and water had no significant effect on IMP content, except for soy sauce. The main reasons were that soy sauce contained the tasting ATPs (Lioe et al., 2010), and Asp and Glu contributed to the synthesis of new IMP, which was consistent with the results in FS‐ and FFS‐treated samples. Moreover, TAV of IMP of each treated sample was more than 10 (Figure 1b), which further indicated that soy sauce was helpful for increasing umami taste of grass carp.

FIGURE 1.

FIGURE 1

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(a) Contents of ATP‐related compounds (mg/100g), and taste activity value (TAV) of AMP and IMP (b) in second soaking for preparing Shanghai smoked fish. C0, C1, C2, and C3 represented all seasonings + plant oil, all seasonings + plant oil + sugar, all seasonings + plant oil + sugar + soy sauce and all seasonings + plant oil + sugar +soy sauce + five‐spice powder, respectively. All seasonings represented cooking wine + salt + chive + ginger + garlic + pepper + soy sauce. ATP: adenosine triphosphate; ADP: adenosine diphosphate; AMP: 5′‐adenosine monophosphate; IMP: 5′‐inosine monophosphate; Hx: hypoxanthine; HxR: hypoxanthine riboside

The degradation order of ATP was successively ATP > ADP > AMP > IMP > HxR > Hx (Wang et al., 2018). The certain umami ATPs are also produced with the degradation of ATP. TAV of IMP in A0, A8, B8, and C3 was 8.64, 10.81, 14.80, and 11.38, respectively (Table 2 and Figure 1b). Previous studies have shown that IMP had strong umami (Johnson et al., 2013), so it was the main umami ATPs in Shanghai smoked fish, contributing significantly to its tastes.

Contents of AMP were significantly lower than that of IMP. AMP contents of FS samples were the lowest with no significant difference (p > .05) compared with other samples (Table 2, Figure 1b). Although the content of AMP in each sample was low, AMP had synergistic effects with IMP, Glu, and Asp (Zhang et al., 2019), leading to savory taste of fish. Bitter Hx has adverse effect on tastes of grass carp, Hx content in Shanghai smoked fish reduced to one third of that in fresh grass carp, indicating that SS treatment could greatly improve the bitterness of grass carp. Three reasons might be accounted for the improvement of savory and palatability taste. (a) ATPs exhibited better stability under neutral conditions than acidic or alkaline conditions (Cui, 2001), meanwhile cooking wine promoted ATP degradation by reducing the pH of matrix. (b) high‐temperature frying accelerated ATPs decomposement with a rapid IMP accumulation (Qiu & Yue, 2016), and (c) taste ATPs was used as umami reinforcing agent after adding soy sauce (Lioe et al., 2010).

3.4. Effects of FS process on the content of FAAs

It is well‐known that FAAs are important water‐soluble flavor components in foods (Chen & Zhang, 2007). They not only had own flavor characteristics, but synergized with other FAAs to produce different taste sensations (Weng, 2011). As shown in Table 3, FAAs contents of A0‐A8 reached 396.94, 419.54, 427.46, 439.88, 412.05, 418.48, 408.03, 464.44, and 421.02 mg/100 g, respectively, among them, the contents of flavor amino acids accounted for 28.33, 30.64, 33.76, 32.48, 33.08, 29.80, 37.01, 39.98, and 38.66%, respectively. The contents of Phe and Tyr in the two soy sauce soaked samples were higher than that without soy sauce soaking. Phe and Tyr, as important flavor components, were bitter aromatic amino acids, which have been found to be important flavor components in soy sauce in recent years (Chen & Zhang, 2007; Lioe et al., 2010). Contents of flavor amino acid, except for Pro, were significantly higher than that of fresh grass carp, among them, the contents of Asp and Glu were increased after soy sauce soaking (Lioe et al., 2010). Chen & Zhang also showed that Gly, Glu, and Ala contributed to the major sweetness of fish (Chen & Zhang, 2007). The TAV of Glu in fresh grass carp was less than 1, but FS samples were greater than 4 (Table 5). Although the TAV of Asp, Ser, Gly, and Ala were lower than 1 before and after FS, they all increased and had synergistic effect on the flavor of grass carp. The main reasons why FS process could improve the contents of umami were that (a) ethanol in cooking wine (Wang, 2005) and seasonings (salt, chive, ginger, garlic, etc) entered into fish cells through capillaries and intercellular spaces because protein structure was destroyed and promoted the dissolution of amino acids (Pei et al., 2014). (b) Asp and Glu as main FAAs in soy sauce were permeated into fish meat, as well as the decomposition of histones in grass carp.

Table 3.

Contents of free amino acids in first soaking and frying for preparing Shanghai smoked fish (mg/100 g)

Amino acid types Taste Treatment process Threshold (mg/100 g)
A0 A1 A2 A3 A4 A5 A6 A7 A8
Asp* Umami/sour (+) 0.58 ± 0.02a 0.64 ± 0.01bc 0.64 ± 0.02b 0.64 ± 0.02b 0.66 ± 0.02bc 0.57 ± 0.03a 0.70 ± 0.02c 1.45 ± 0.03d 1.63 ± 0.04e 3
Thr# Sweet (+) 10.07 ± 0.06bc 9.91 ± 0.16ab 10.85 ± 0.12d 10.87 ± 0.17d 10.33 ± 0.22c 9.54 ± 0.22a 10.81 ± 0.10d 12.83 ± 0.11f 11.54 ± 0.28e 260
Ser* Sweet (+) 4.99 ± 0.18a 4.92 ± 0.19a 5.77 ± 0.12b 5.78 ± 0.19b 5.44 ± 0.19b 4.73 ± 0.16a 6.22 ± 0.13c 8.26 ± 0.12e 7.66 ± 0.09d 150
Glu* Umami/sour (+) 1.64 ± 0.11a 21.10 ± 0.05b 23.42 ± 0.15c 23.64 ± 0.21c 20.98 ± 0.33b 23.30 ± 0.23c 30.42 ± 0.30d 53.79 ± 0.23f 41.45 ± 0.71e 5
Gly* Sweet (+) 61.61 ± 0.04c 60.30 ± 0.26b 69.03 ± 0.16g 66.65 ± 0.37f 65.26 ± 0.10e 54.34 ± 0.27a 67.04 ± 0.43f 69.15 ± 0.22g 63.72 ± 0.17d 130
Ala* Sweet (+) 8.20 ± 0.36a 7.83 ± 0.16a 10.92 ± 0.10d 10.21 ± 0.35c 10.00 ± 0.22c 9.21 ± 0.25b 14.46 ± 0.12e 17.83 ± 0.14g 16.24 ± 0.06f 60
Cys Bitter/sweet/sulfur (−) 0.91 ± 0.04abc 0.84 ± 0.06ab 0.95 ± 0.03bc 0.99 ± 0.02c 0.99 ± 0.02c 0.83 ± 0.07a 0.88 ± 0.05abc 0.94 ± 0.06abc 0.87 ± 0.02ab ND
Val# Sweet/bitter (−) 6.13 ± 0.09ab 5.77 ± 0.16a 6.41 ± 0.09b 6.39 ± 0.17b 6.09 ± 0.13ab 6.20 ± 0.33ab 6.14 ± 0.09ab 8.26 ± 0.14d 7.25 ± 0.35c 40
Met# Bitter/sweet/sulfur (−) 1.72 ± 0.05ab 1.61 ± 0.10a 1.92 ± 0.08c 1.76 ± 0.12abc 1.84 ± 0.09bc 1.70 ± 0.04ab 1.84 ± 0.07bc 2.48 ± 0.06e 2.18 ± 0.04d 30
Ile# Bitter (−) 3.34 ± 0.22a 3.37 ± 0.17ab 3.87 ± 0.12c 3.84 ± 0.09c 3.82 ± 0.04c 3.54 ± 0.14abc 3.67 ± 0.18bc 5.48 ± 0.13e 4.87 ± 0.01d 90
Leu# Bitter (−) 5.72 ± 0.06ab 5.53 ± 0.17a 6.11 ± 0.12cd 6.17 ± 0.18d 5.90 ± 0.17abcd 5.75 ± 0.08abc 5.95 ± 0.15bcd 8.49 ± 0.29f 7.67 ± 0.07e 190
Tyr Bitter (−) 4.98 ± 0.27a 5.21 ± 0.16ab 5.77 ± 0.16bc 5.57 ± 0.41bc 5.56 ± 0.16bc 5.71 ± 0.22bc 5.35 ± 0.16abc 5.78 ± 0.24c 5.52 ± 0.08abc ND
Phe# Bitter (−) 3.22 ± 0.14abc 2.99 ± 0.08b 3.40 ± 0.10cd 3.29 ± 0.17bc 3.63 ± 0.18d 3.21 ± 0.11bc 2.82 ± 0.15a 5.24 ± 0.11f 4.46 ± 0.03e 90
Lys# Sweet/bitter (−) 20.61 ± 0.03ab 22.16 ± 0.17de 21.17 ± 0.29bc 21.31 ± 0.30c 20.11 ± 0.32a 22.23 ± 0.35e 21.13 ± 0.17bc 23.70 ± 0.13f 21.62 ± 0.34cd 50
His Bitter (−) 221.96 ± 0.90f 227.05 ± 0.65g 216.61 ± 0.64e 230.65 ± 0.56h 211.85 ± 0.39d 227.96 ± 0.63g 192.10 ± 0.60b 198.92 ± 0.77c 185.56 ± 47a 20
Arg Sweet/bitter (+) 5.82 ± 0.31ab 6.56 ± 0.11cde 6.12 ± 0.09abc 6.19 ± 0.11bcd 5.59 ± 0.45a 7.09 ± 0.22e 6.32 ± 0.08bcd 6.65 ± 0.32cde 6.73 ± 0.03de 50
Pro* Sweet/bitter (+) 35.45 ± 0.22e 33.74 ± 0.18c 34.514 ± 0.11d 35.94 ± 0.18f 33.99 ± 0.09c 32.57 ± 0.32bc 32.16 ± 0.14ab 35.19 ± 0.20e 32.07 ± 0.13a 300
Subtotal 396.94 419.54 427.46 439.88 412.05 418.48 408.03 464.44 421.02
Taste amino acid acids (%) 28.33 30.64 33.76 32.48 33.08 29.80 37.01 39.98 38.66
Amino acid types Taste Treatment process Threshold (mg/100 g)
B0 B1 B2 B3 B4 B5 B6 B7 B8
Asp* Umami/sour (+) 1.21 ± 0.04a 1.28 ± 0.03a 1.47 ± 0.03b 1.24 ± 0.05a 1.22 ± 0.03a 1.22 ± 0.02a 1.54 ± 0.04b 4.81 ± 0.04c 4.89 ± 0.04c 3
Thr# Sweet (+) 20.49 ± 0.24c 22.02 ± 0.28e 19.84 ± 0.39b 21.26 ± 0.24d 15.55 ± 0.28a 23.60 ± 0.08g 22.59 ± 0.12f 26.13 ± 0.08h 21.32 ± 0.08d 260
Ser* Sweet (+) 11.16 ± 0.28b 12.54 ± 0.03c 13.63 ± 0.12d 12.19 ± 0.25c 9.51 ± 0.08a 15.33 ± 0.29f 14.41 ± 0.08e 19.34 ± 0.07g 15.15 ± 0.12f 150
Glu* Umami/sour (+) 3.83 ± 0.04a 32.66 ± 0.16d 43.17 ± 0.13f 31.39 ± 0.18c 26.44 ± 0.19b 41.18 ± 0.08e 43.21 ± 0.03f 87.77 ± 0.25h 68.31 ± 0.49g 5
Gly* Sweet (+) 110.20 ± 0.36b 129.92 ± 0.13e 147.50 ± 0.12h 125.81 ± 0.23d 95.06 ± 0.15a 143.50 ± 0.08g 139.45 ± 0.45f 148.65 ± 0.14i 113.29 ± 0.08c 130
Ala* Sweet (+) 18.31 ± 0.20b 20.85 ± 0.02d 25.66 ± 0.02e 19.34 ± 0.08c 14.58 ± 0.55a 28.76 ± 0.49g 26.33 ± 0.04ef 34.21 ± 0.49h 26.53 ± 0.41f 60
Cys Bitter/sweet/sulfur (−) 1.98 ± 0.03b 2.24 ± 0.05d 2.10 ± 0.04c 2.07 ± 0.03bc 1.47 ± 0.03a 2.40 ± 0.04e 2.36 ± 0.02e 2.80 ± 0.03f 1.99 ± 0.06b ND
Val# Sweet/ bitter (−) 12.25 ± 0.26b 13.46 ± 0.12c 13.55 ± 0.03c 12.11 ± 0.24b 9.36 ± 0.04a 13.96 ± 0.03d 13.52 ± 0.24c 18.87 ± 0.07f 14.50 ± 0.27e 40
Met# Bitter/sweet/sulfur (−) 3.28 ± 0.08b 3.66 ± 0.03cd 3.47 ± 0.07bc 3.55 ± 0.04c 2.32 ± 0.07a 3.85 ± 0.13de 4.12 ± 0.04f 5.15 ± 0.17g 3.90 ± 0.03e 30
Ile# Bitter (−) 6.47 ± 0.03b 6.98 ± 0.03c 7.01 ± 0.04c 6.89 ± 0.17c 4.97 ± 0.14a 7.29 ± 0.07d 7.41 ± 0.02d 10.87 ± 0.04f 8.49 ± 0.13e 90
Leu# Bitter (−) 9.40 ± 0.03b 10.14 ± 0.14c 10.00 ± 0.30c 9.48 ± 0.13b 7.20 ± 0.06a 10.66 ± 0.14d 10.67 ± 0.23d 15.73 ± 0.22f 12.63 ± 0.18e 190
Tyr Bitter (−) 7.55 ± 0.06c 8.25 ± 0.22d 7.13 ± 0.03b 8.18 ± 0.13d 5.18 ± 0.03a 9.07 ± 0.03e 9.22 ± 0.45e 9.86 ± 0.04f 8.37 ± 0.12d ND
Phe# Bitter (−) 4.52 ± 0.03c 5.02 ± 0.07d 4.26 ± 0.03b 4.92 ± 0.03d 2.98 ± 0.08a 5.91 ± 0.06e 5.81 ± 0.06e 8.55 ± 0.03g 7.55 ± 0.07f 90
Lys# Sweet/bitter (−) 25.11 ± 0.08b 26.00 ± 0.28c 27.58 ± 0.26d 25.03 ± 0.36b 19.82 ± 0.44a 31.40 ± 0.08f 29.61 ± 0.07e 35.05 ± 0.04g 27.61 ± 0.31d 50
His Bitter (−) 247.11 ± 0.40f 257.65 ± 0.43g 266.19 ± 0.59h 229.05 ± 0.85e 197.36 ± 0.45b 219.06 ± 0.44c 224.22 ± 0.77d 229.67 ± 0.83e 190.75 ± 0.98a 20
Arg Sweet/ bitter (+) 9.84 ± 0.12b 10.56 ± 0.08c 11.10 ± 0.06d 10.71 ± 0.03c 10.71 ± 0.06a 14.09 ± 0.05g 12.04 ± 0.04f 14.13 ± 0.08g 11.49 ± 0.03e 50
Pro* Sweet/ bitter (+) 24.31 ± 0.02c 25.87 ± 0.20e 27.33 ± 0.09g 25.56 ± 0.08d 19.59 ± 0.11a 26.62 ± 0.04f 25.39 ± 0.10d 28.53 ± 0.02h 23.34 ± 0.06b 300
Subtotal 517.03 589.10 630.99 548.79 440.59 597.90 591.90 700.14 560.11
Taste amino acid aaaacidacids (%) 32.69 37.88 41.01 39.27 37.77 42.92 42.29 46.18 44.90
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*: indicates taste amino acid; #: indicates essential amino acid; +: indicates good taste; ‐: indicates bad taste.

A0–A8: no adding; cooking wine; cooking wine + salt; cooking wine + chive; cooking wine + ginger; cooking wine + garlic; cooking wine + pepper; cooking wine + soy sauce; all seasonings.

B0–B8: no adding; cooking wine; cooking wine + salt; cooking wine + chive; cooking wine + ginger; cooking wine + garlic; cooking wine + pepper; cooking wine + soy sauce; all seasonings.

All seasonings represented cooking wine + salt + chive + ginger + garlic + pepper + soy sauce.

Different superscript letters (a–i) in the same column indicate a significant difference (p < .05).

Abbreviation: ND, no determined.

Table 5.

Taste activity value (TAV) of amino acids of Shanghai smoked fish (mg/100 g)

Samples Asp Ser Glu Gly Ala Pro
A0 0.19 0.03 0.33 0.47 0.14 0.12
A1 0.21 0.03 4.22 0.46 0.13 0.11
A2 0.21 0.04 4.68 0.53 0.18 0.12
A3 0.21 0.04 4.73 0.51 0.17 0.12
A4 0.22 0.04 4.20 0.50 0.17 0.11
A5 0.19 0.03 4.66 0.42 0.15 0.11
A6 0.23 0.04 6.08 0.52 0.24 0.11
A7 0.48 0.06 10.76 0.53 0.30 0.12
A8 0.54 0.05 8.29 0.49 0.27 0.11
B0 0.40 0.07 0.77 0.85 0.31 0.08
B1 0.43 0.08 6.53 1.00 0.35 0.09
B2 0.49 0.09 8.63 1.13 0.43 0.09
B3 0.41 0.08 6.28 0.97 0.32 0.09
B4 0.41 0.06 5.29 0.73 0.24 0.07
B5 0.41 0.10 8.24 1.10 0.48 0.09
B6 0.51 0.10 8.64 1.07 0.44 0.08
B7 1.60 0.13 17.55 1.14 0.57 0.10
B8 1.63 0.10 13.66 0.87 0.44 0.08
C0 1.85 0.11 14.63 0.92 0.44 0.08
C1 2.25 0.11 18.26 0.98 0.47 0.08
C2 3.07 0.14 25.62 0.99 0.58 0.09
C3 2.73 0.11 21.46 0.84 0.49 0.08
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A0–A8: no adding; cooking wine; cooking wine + salt; cooking wine + chive; cooking wine + ginger; cooking wine + garlic; cooking wine + peppe and cooking wine + soy sauce; all seasonings.

B0–B8: no adding; cooking wine; cooking wine + salt; cooking wine + chive; cooking wine + ginger; cooking wine + garlic; cooking wine + pepper; cooking wine + soy sauce and all seasonings.

C0–C3: all seasonings + plant oil; all seasonings + plant oil + sugar; all seasonings + plant oil + sugar + soy sauce and all seasonings + plant oil + sugar + soy sauce + five‐spice powder.

All seasonings represented cooking wine + salt + chive + ginger + garlic + pepper + soy sauce.

3.5. Effects of FFS process on the content of FAAs

Maillard reaction between FAAs and sugars during cooking is essential for the development of desirable meaty aromas (Madruga et al., 2010). FAAs contents of B0–B8 were 517.03, 589.10, 630.99, 548.79, 440.59, 597.90, 591.90, 700.14, and 560.11 mg/100 g, respectively, among FAAs, the flavor amino acids accounting for 32.69, 37.88, 41.01, 39.27, 37.77, 42.92, 42.29, 46.18, and 44.90%, respectively (Table 3). FAAs contents of FFS samples were higher than that of FS samples, one possible reason was that the moisture contents of samples were greatly decreased during FFS (Li, Tu, Sha, et al., 2016; Li, Tu, Zhang, et al., 2016). Previous report also confirmed cooking did, in general, significantly increased the contents of amino acids compared with raw fish species (Erkan et al., 2010). The order of FAAs contents and percentages of flavor amino acids in grass carp was FFS > FS > fresh one. The main reasons were (a) the dissolution of amino acids was promoted by soaking treatment together with fast permeation of amino acids in soy sauce into fish meat. (b) FFS treatment accelerated the degradation of protein in grass carp tissues.

Free amino acids consumption was occurred in MR between FAAs and reducing sugars (Pei et al., 2014). The total FAAs contents of FFS were higher than that of FS (Table 3). Glu was recognized as main umami amino acids in FFS process and its contents in B0 were higher than that in A0, TAV of Glu was higher than 5 in FFS samples (B1–B8). TAV of Asp was higher than 1 in FFS with cooking wine and soy sauce soaking and FFS with all seasonings. TAV of Gly was also higher than 1 in most FFS samples (Table 5), indicating that FFS had an important contribution to the taste compounds of grass carp .

3.6. Effects of SS process on the content of FAAs

Free amino acids contents of C0–C3 were 598.05, 622.08, 697.66, and 585.79 mg/100 g, respectively, among them, flavor amino acids accounted for 44.50%, 47.30%, 49.99%, and 50.09%, respectively. The proportion of flavor amino acids in Shanghai smoked fish was the highest (Table 4). The main reasons were FS accelerated the oxidation and degradation of proteins (Li, Tu, Sha, et al., 2016; Li, Tu, Zhang, et al., 2016). Moreover, SS treatment was beneficial to the dissolution of FAAs, as well as crisp crust formation after FFS treatment promoted soaking solution penetrated into grass carp meat. Asp and Glu contents (TAV > 14) of in SS were higher that in FS and FFS (Table 5). Most of bitter FAAs such as Cys, Met, Tyr, and His decreased significantly in SS process. His contents were the highest among bitter amino acids in SS, which tasted bitter but could enhance the flavor effect and help to form the “meat flavor” characteristics of some aquatic products (Song, Zhang, et al., 2018; Song, Wang, et al., 2018). Therefore, SS treatment could improve the contents of FAAs and sweet/umami amino acids, significantly reducing the content of most bitter amino acids.

Table 4.

Contents of free amino acids in second soaking for preparing Shanghai smoked fish (mg/100 g)

Amino acid types Taste C0 C1 C2 C3 Threshold (mg/100 g)
Asp* Umami/sour (+) 5.54 ± 0.04a 6.76 ± 0.04b 9.20 ± 0.03d 8.19 ± 0.03c 3
Thr# Sweet (+) 22.13 ± 0.14c 20.94 ± 0.04b 24.93 ± 0.13d 19.87 ± 0.06a 260
Ser* Sweet (+) 15.80 ± 0.03a 16.20 ± 0.08b 20.39 ± 0.03d 16.49 ± 0.12c 150
Glu* Umami/sour (+) 73.14 ± 0.04a 91.28 ± 0.51b 128.11 ± 0.25d 107.32 ± 0.15c 5
Gly* Sweet (+) 119.85 ± 0.22b 126.78 ± 0.72c 128.89 ± 0.08d 108.88 ± 0.03a 130
Ala* Sweet (+) 26.33 ± 0.03a 28.19 ± 0.04b 34.80 ± 0.55d 29.31 ± 0.03c 60
Cys Bitter/sweet/sulfur (−) 2.21 ± 0.03c 1.87 ± 0.06b 2.23 ± 0.08c 1.66 ± 0.04a ND
Val# Sweet/bitter (−) 15.56 ± 0.61a 15.97 ± 0.04a 18.77 ± 0.05b 15.74 ± 0.21a 40
Met# Bitter/sweet/sulfur (−) 4.33 ± 0.04b 3.89 ± 0.04a 5.07 ± 0.04c 3.88 ± 0.03a 30
Ile# Bitter (−) 9.09 ± 0.05a 9.28 ± 0.24a 11.69 ± 0.21c 9.88 ± 0.03b 90
Leu# Bitter(−) 13.60 ± 0.04a 13.58 ± 0.34a 17.36 ± 0.26c 14.36 ± 0.24b 190
Tyr Bitter (−) 8.55 ± 0.24b 6.84 ± 0.07a 9.53 ± 0.03c 6.60 ± 0.03a ND
Phe# Bitter (−) 7.59 ± 0.44b 6.46 ± 0.04a 10.04 ± 0.06c 7.56 ± 0.09b 90
Lys# Sweet/bitter (−) 28.21 ± 0.06b 27.89 ± 0.04a 34.98 ± 0.07c 27.75 ± 0.07a 50
His Bitter (−) 208.75 ± 0.80c 209.30 ± 0.93c 199.28 ± 0.90b 173.49 ± 0.82a 20
Arg Sweet/bitter (+) 11.91 ± 0.03c 11.77 ± 0.03b 14.98 ± 0.06d 11.57 ± 0.06a 50
Pro* Sweet/bitter (+) 25.46 ± 0.08c 25.06 ± 0.07b 27.41 ± 0.05d 23.23 ± 0.04a 300
Subtotal 598.05 622.08 697.66 585.79
Taste amino acids (%) 44.50 47.30 49.99 50.09
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*: taste amino acid; #: essential amino acid; +: indicates good taste; ‐: indicates bad taste; ND: no determined. C0‐C3: all seasonings + plant oil; all seasonings + plant oil + sugar; all seasonings + plant oil + sugar +soy sauce; all seasonings + plant oil + sugar + soy sauce + five‐spice powder. All seasonings represented cooking wine + salt + chive + ginger + garlic + pepper + soy sauce. Different superscript letters in the same column indicate a significant difference (p < .05).

The delightful flavor amino acids in Shanghai smoked fish increased by 76.81% compared with fresh grass carp. The contents of His in Shanghai smoked fish were 27.94%, significantly lower than that of fresh fish in this work, which was consistent with previous report (Yue et al., 2016). The main reason was that Maillard reaction between aldehydes and His was greatly enhanced after soaking and frying (Cordoba et al., 1994). In addition, protein decomposition of grass carp tissues and lipid oxidation degradation after FFS treatment was enhanced (Wang, 2005). Therefore, FS, FSS, and SS had a synergistic effect on the improvement of earthy‐musty smell of grass carp and the increasement of total amounts of FAAs and flavor amino acid.

3.7. Electronic tongue analysis of Shanghai smoked fish

The electronic tongue response substances of Shanghai smoked fish at different processing stages are shown in Figure 3. PCA figure (Figure 2) could well reflect the completeness of difference information of taste profile of Shanghai smoked fish. Results showed that PC1 and PC2 were 84.85% and 13.51%, as well as total contribution rate of 98.36%. There was no overlap in PCA figures of Shanghai smoked fish, which indicated that three processing stage has obvious difference in the tastes of Shanghai smoked fish. The umami level of Shanghai smoked fish was the highest, showing FS, FFS, and SS treatment synergistically contributed to the tastes of grass carp and helped to improve its umami flavor.

FIGURE 3.

FIGURE 3

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Response substances of sour level, salinity, and umami of Shanghai smoked fish (mg/100g). A0 and B0: No adding; A8 and B8: all seasonings; C3: All seasonings + plant oil + sugar + soy sauce + five‐spice powder. All seasonings represented cooking wine + salt + chive + ginger + garlic + pepper + soy sauce

FIGURE 2.

FIGURE 2

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PCA chart of tasting Shanghai smoked fish. A0 and B0: No adding; A8 and B8: all seasonings; C3: All seasonings + plant oil + sugar + soy sauce + five‐spice powder. All seasonings represented cooking wine + salt + chive + ginger + garlic + pepper + soy sauce

4. CONCLUSIONS

Effect of treatment process including FS, FFS, and SS on the taste compounds of Shanghai smoked fish was in detail investigated in this work. Contents of taste ATPs, FAAs, and flavor amino acids in grass carp were successively increased by FS, FFS, and SS. IMP was the main umami ATPs in the three processing stages. Glu was the main umami amino acid in FS process. Glu and Gly were the main umami flavor amino acid in FFS process. Asp and Glu had the largest effect on the nonvolatile tastes of Shanghai smoked fish. The umami level of Shanghai smoked fish reached a maximum of 9.24, indicating seasonings contributed to taste active compounds, among them, cooking wine, salt, and soy sauce also played a certain role in the tastes of grass carp. This work indicated a new processing technique of preparing Shanghai smoked fish, which not only could cover up earthy‐musty smell of grass carp, but greatly increase its umami flavor.

CONFLICT OF INTEREST

The authors declare no conflict of interest.

AUTHOR CONTRIBUTIONS

Chen, S.S., Zhou, Y., Zhang, H.C., involved in design and conceptualization. Zhou, Y., Zhang, H.C. involved in manuscript writing and proofreading. Wang, X.C., Zhang, H.C., and Shi, W.Z. involved in experimental work, data analysis, and interpretation. All authors have read and agreed to the published version of the manuscript.

INFORMED CONSENT

Written informed consent was obtained from all study participants.

ETHICAL APPROVAL

This study was approved by the ethics committee of Shanghai Ocean University.

ACKNOWLEDGMENT

This research was supported by National Key Research and Development Program of China (No. 2017YFD0400105‐02).

Zhou Y, Chen S, Wang X, Zhang H. Nonvolatile taste compounds of Shanghai smoked fish: A novel three stages control techniques. Food Sci Nutr.2021;9:87–98. 10.1002/fsn3.1960

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available from the corresponding author upon reasonable request.

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Associated Data

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Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

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