Regulation of quality and biogenic amine production during sufu fermentation by pure Mucor strains

LWT - Food Science and Technology 117 (2020) 108637

Contents lists available at ScienceDirect

LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt

Regulation of quality and biogenic amine production during sufu fermentation by pure Mucor strains

T

Bing Yanga,b, Yue Tana,b, Jianquan Kana,b,∗ a b

College of Food Science, Southwest University, 2 Tiansheng Road, Beibei, Chongqing, 400715, PR China Laboratory of Quality & Safety Risk Assessment for Agro-products on Storage and Preservation (Chongqing), Ministry of Agriculture, Chongqing, 400715, PR China

A R T I C LE I N FO

A B S T R A C T

Keywords: Sufu Pure-culture fermentation Mucor Biogenic amines Quality control

Natural fermentation of sufu yields large amounts of biogenic amines (BAs) and other risk factor, which pose significant health risks. To improve the safety and quality of sufu, we investigated sufu fermentation by three microbial strains, Actinomucor elegans, Mucor wutunkiao, and Mucor racemosus, and monitored the dynamics change of each risk factor during sufu fermentation. Results showed that the moisture content, pH, NaCl, amino acid nitrogen content, and total acid content of all samples were at normal levels for mature sufu products. The H2S and total volatile base nitrogen (TVB-N) levels in Mucor racemosus fermented sufu (MRFS) were lower than those in other mucor fermented sufu. And pure mucor fermentation significantly reduced the benzoic acid content. Different mucor strains and fermentation processes contributed to different BAs levels in the final sufu products. The levels of common BAs cadaverine, spermidine, spermine, histamine, and tyramine were significantly lower (p < 0.05) in MRFS than in sufu fermented with other mucor strains. Through these results, the main step of risk factor generation during sufu fermentation was identified, which can be useful for producing sufu products with good quality and low levels of BAs through pure-culture fermentation.

1. Introduction Sufu, a traditional Chinese fermented soybean product, is made from soybean curd (tofu) fermented in saline and other dressing mixtures. Sufu has a spreadable, creamy consistency and a distinctive flavor. It has been eaten in a cheese-like manner since the Wei Dynasty (220–265 CE) in China (B. Z. Han, Wang, Rombouts, & Nout, 2003). It can be divided into several types according to its production method, color, flavor, and other qualities. The most common type of sufu is mould-fermented by Actinomucor, Mucor, and Rhizopus mould species (B.-Z. Han, Rombouts, & Nout, 2001; Ray, El Sheikha, & Kumar, 2014). Mould-fermented sufu is made in three steps: (1) Solid tofu is fermented using a pure bacterial or fungal fermentation starter culture (fungal culture is most common) to create fermented tofu (called maopi or pehtze), (2) the fermented tofu is salted, and (3) the salted, fermented tofu is ripened in a saline dressing mixture for some period of time. Most sufu in China, especially domestic sufu, is produced by traditional fermentation. Therefore, its safety and stability cannot be guaranteed. Previous studies indicated that there are potential health safety risks with commercially fermented traditional Chinese sufu products. During fermentation, biogenic amines (BAs) are formed. BAs are organic, alkaline, low-molecular weight compounds containing nitrogen.

∗

They are formed by the decarboxylation of amino acids or the amination and transamination of aldehydes and ketones. The BAs most commonly found in foods are putrescine, cadaverine, tryptamine, 2phenylethylamine, spermidine, spermine, histamine and tyramine. Excessive intake of BAs can lead to nausea, sweating, migraine, respiratory distress, hot flashes, heart palpitations, and other adverse reactions (Guan et al., 2013). Thus, regulating BA content is necessary to ensure the safety of sufu products. Typical BAs found in soybean products include putrescine, histamine, and cadaverine, and they have been abundantly detected in commercial sufu products (Toro-Funes, Bosch-Fuste, Latorre-Moratalla, Veciana-Nogués, & Vidal-Carou, 2015). At present, there have been a few reports on methods of reducing BAs content in sufu. Selecting an appropriate starter culture, optimizing fermentation conditions, and incorporating appropriate additives can reduce the generation of BAs and improve the quality of fermented foods (Z. F. Liu et al., 2011). Sufu is high in protein content, which can be broken down by enzymes and/or bacteria to form volatile, basic nitrogen. Sulfhydryl amino acids react with desulfhydrylase to form volatile sulfur-containing compounds such as H2S, and free amino acids are decarboxylated to generate biogenic amines (Yang, Ding, Qin, & Zeng, 2016). These compounds are often used as indicators of freshness in

Corresponding author. College of Food Science, Southwest University, No. 2 Tiansheng Road, Beibei District, Chongqing, 400715, PR China. E-mail address: [email protected] (J. Kan).

https://doi.org/10.1016/j.lwt.2019.108637 Received 26 June 2019; Received in revised form 4 August 2019; Accepted 15 September 2019 Available online 16 September 2019 0023-6438/ © 2019 Elsevier Ltd. All rights reserved.

LWT - Food Science and Technology 117 (2020) 108637

B. Yang, et al.

animal-based food products, but excessive levels reduce the nutritional value and edibility of food, and pose significant health risks. Benzoic acid is usually added as a preservative to sufu products, but excessive levels could also pose a health risk. Here, we aimed to analyze the dynamics of each risk factor during tofu fermentation, determine the main step of risk factor generation, and put forward informed and appropriate control measures. We selected three types of pure microbial strain starter cultures for sufu fermentation and evaluated whether they could effectively reduce BA content and produce high quality sufu. We tracked the content of H2S, TVB-N, and aflatoxin throughout the fermentation process, as well as the water content, pH, free ammonia nitrogen, and total acid content. Comparing the quality and BA content of the fermented sufu obtained using each of the pure mucor strains, we were able to determine suitable strains for safe sufu fermentation.

2 d, the tofu maopi was submerged in 10% brine. After marinating for 5 d, the tofu maopi was rinsed with 10% brine and drained. Finally, the dried tofu maopi was placed in a glass container, and the fermentation mixture was added. The fermentation mixtures of AE fermented sufu (AEFS), MW fermented sufu (MWFS), and MR fermented sufu (MRFS) contained NaCl 10% (w/v) and ethanol 12% (v/v). The mixtures were packed into sealed bags and placed in a constant temperature incubator at 25 °C, 90% humidity for 80 d. During the pre-fermentation stage (S1–S10), samples were taken every 6 h. During the curing stage (S11–S16), samples were taken daily. During the post-fermentation stage (S17–S25), samples were taken every 10 days. All samples were pulverized for further analysis.

2. Materials and methods

The selected soybeans (1000 g) were washed and soaked in 4000 mL of water at room temperature for 8 h. Then, the soaked soybeans were ground with 10 L of water. The soymilk was strained using a 100 mm screen and incubated at 98 ± 2 °C for 5 min. Then, the appropriate amount of sodium benzoate was added to the soymilk and stirred to dissolve. After cooling to 80 °C, 100 mL of MgCl2 solution was gently added with stirring, and the mixture was incubated at 80 °C for 40 min. The uncongealed tofu was pressed into molds and the tofu was stacked to squeeze out additional water. The tofu with benzoic acid was then either inoculated with Mucor racemosus or not inoculated (control) and fermented under identical conditions.

2.3. Fermentation with benzoic acid preservative

2.1. Preparation of starter culture strains The pure culture strains used in this study, Actinomucor elegans 41355 (AE), Mucor wutunkiao 40854 (MW), and Mucor racemosus 40491 (MR), were purchased from the China Center of Industrial Culture Collection (Beijing, China). Each strain was grown in potato-dextro agar (PDA) at 25–30 °C for 3 d. Then, 1 mL of stroke-physiological saline solution was added to PDA to obtain a spore suspension, which was then mixed into bran medium and incubated at 25–30 °C for 3 d before use. 2.2. Preparation of tofu

2.4. Physicochemical analysis of sufu

Sufu fermentation included three steps: pre-fermentation, curing, and post-fermentation (Fig. 1). First, tofu was cut into cubes (3 cm × 3 cm × 2 cm), and arranged leaving some space around each cube. The prepared AE, MW, and MR suspensions were sprayed onto the tofu cubes and then cultured in incubators at 30 °C, 25 °C and 25 °C, respectively. The tofu maopi was then removed from the incubator and the fimbria was removed from the surface. The tofu maopi was placed into a glass container and cured with NaCl (10%, w/w). After curing for

Moisture content was determined using the standard gravimetric method described by AOAC, Association of Official. NaCl content was determined by the modified Volhrad method (AOAC 2000; Method no. 935.47) (AOAC, 2007). Free amino nitrogen was measured using the formalin titration method (Suo et al., 2015; Tan et al., 2019). Approximately 10 g of sufu was homogenized with 90 mL of distilled water. Then, the pH value of the supernatant was determined using a pb-10 pH meter (Sartorius, Germany).

Fig. 1. Sufu production process. 2

LWT - Food Science and Technology 117 (2020) 108637

B. Yang, et al.

During post-fermentation (S17–S25), pH gradually decreased as total acid content increased. The observed changes in pH and total acid content were similar with results of previous research (Tan et al., 2019). These results demonstrated that appropriate fermentation occurs during this process. AAN is an important index reflecting the protein utilization rate in raw materials and is used to judge the fermentation end point in fermented foods (Lopetcharat, Choi, Park, & Daeschel, 2001). The AAN content of MWFS was higher than that of AEFS and MRFS. These results may be due to differences in the protease activity of different mucor strains. Previous reports indicated that the protease activity of MW (261.6 U/g) is higher than that of AE (236.8 U/g) and MR (162.7U/g) (Ran & Kan, 2015). Therefore, MW had a beneficial effect on the production of AANs, thus shortening the fermentation cycle compared with AE and MR fermentation. During the curing stage, the AAN content in the salt billet was negatively correlated with the NaCl content; the higher the NaCl content, the lower the AAN content. During the postfermentation stage, the total acid content increased as fermentation time increased. This may be due to the production of a large amount of acidic substances which lead to an increase in total acid during the fermentation process (Marcotte, Taherian, Trigui, & Ramaswamy, 2001). Soup base directly impacts the color, flavor, and taste of sufu, and can also inhibit the growth of mucor, bacteria, and other fungi. Additionally, sufu soaked in soup base is not only good for storage and transportation, but also good for sales. As shown in Fig. 2, during the post-fermentation stage the soup base had a trend towards increased total acid content and decreased pH, which is consistent with the changes in total acid and pH observed in sufu. The AAN content in the soup base increased as fermentation time increased. This was because the AAN in sufu dissolved into the soup base, as further confirmed by the decrease in AAN content in sufu.

2.5. Tracking potential sufu risk factors H2S content was determined by methylene blue colorimetry (Yang et al., 2016). TVB-N content was determined using the Semimicro determination of nitrogen method (Li et al., 2019; Yang et al., 2016). Aflatoxin content was measured using an ELISA kit according to the manufacturer's instructions (Andy Biotechnology Co. LTD. Changsha, China). Benzoic acid content was determined using high performance liquid chromatography (Agilent Technologies. Madrid, Spain) (Q. Liu, Hong, Han, Hwang, & Lee, 2012). 2.6. Determination of BA content The BA content of sufu samples was determined according to methods reported by Endo (1983) and Tan et al. (2019). Detailed methods are described in reference to the supplementary material. 2.7. Statistical analysis All measurements were performed in triplicate and analyzed using analysis of variance (ANOVA) with SPSS 20.0 (IBM SPSS Statistics for Windows, IBM Corp., USA), with contrast tests applied to the data to determine differences among the means. The criterion for statistical significance was p < 0.05. Results were expressed as the mean ± standard deviation (SD). 3. Results and discussion 3.1. Physicochemical properties The changes in moisture content, pH, NaCl, AAN content, and total acidity in sufu fermented by the different mucor strains are shown in Fig. 2 and Table A1 (see Supplemental material). The variability of each of these indexes for the sufu fermented by AE (AEFS), MW (MWFS), and MR (MRFS) were similar, but their contents were different. China's national standards stipulate that the physicochemical indexes of mature white fermented bean curd are limited to NaCl content ≥6.5 g/100 g, moisture content ≤75%, AAN content ≥0.35 g/100 g, and total acid content ≤1.30 g/100 g (China, 2007). Our results indicated that each physicochemical index of AEFS, MWFS, and MRFS reached the national standard for mature fermented sufu. The physicochemical properties of the three types of sufu are shown in Fig. 2. The ranges of each property among all samples were as follows: moisture content; 66.13% −82.31%, pH; 5.14–6.70, NaCl content; 2.729–12.26 g/100 g, AAN; 0.011–0.361 g/100 g, and total acidity; 0.013–0.288 g/100 g. The average pH of MWFS was significantly higher than that of AEFS and MRFS at post-fermentation stages (p < 0.05). There was large variation in the moisture content, pH, and total acid content among sufu samples at the S25 stage (finished product sufu), which is in close agreement with the findings of Rong-Fa Guan (Guan et al., 2013). World Health Organization (WHO) reported that most manufacturing plants do not strictly control the composition of their products. NaCl content has reported impacts on structural, chemical, and microbial changes during the sufu ripening process (B.-Z. Han, Cao, Rombouts, & Nout, 2004; B. Z. Han et al., 2003), and higher NaCl content can inhibit the formation of BAs in fermented food products (Guan et al., 2013). Therefore, the influence of NaCl on the formation of BAs in the sufu production process may need further study. The pH and total acid content are important factors in the normal fermentation of sufu and have a significant effect on the quality of the final product. During the early stage of pre-fermentation (S1–S3), the pH decreased due to amino acid and fatty acid accumulation from mucor fermentation. However, with the accumulation of peptides and ammonia compounds by intensive protein hydrolysis, the pH increased at later stage. Changes in total acid content contrasted changes in pH.

3.2. H2S content As shown in Fig. 3a, the tofu maopi had no H2S. The sufu H2S content in each group increased rapidly during the pre-fermentation stage. At the end of the pre-fermentation stage, the content of H2S in MRFS was significant higher than that of the other two groups. During the curing stage, the H2S content in each group was significantly reduced at S11 compared with that at the end of the pre-fermentation stage. The high pre-fermentation levels may be due to the addition of salt, which dehydrated the sufu. Then, during the curing stage, the water-soluble H2S is dissolved in the soup base, leading to a decrease in sufu H2S content. During the post-fermentation stage, the content of H2S in the sufu and soup bases of each group showed an increasing trend at first (S17–S18), and then decreased. With extended post-fermentation time, the H2S content gradually increased. This may be because the H2S was absorbed and utilized by saccharomycetes in the fermented sufu, leading to greater consumption of H2S than production and thus overall reduction in the total quantity. 3.3. Total aflatoxin content Changes in total aflatoxin content during fermenting are shown in Fig. 3c–d. No aflatoxin was detected in tofu (S1). During the pre-fermentation stage, the total aflatoxin content in the AEFS group increased gradually, while no aflatoxin was detected in the MWFS and MRFS groups (S1–S5). At the end of the pre-fermentation stage, the total aflatoxin content in the AEFS, MWFS, and MRFS groups increased to 0.488 μg/kg, 0.351 μg/kg, and 0.098 μg/kg, respectively. However, aflatoxin was not detected in the soup bases or in the sufu during the post-fermentation stage (data not shown). The World Health Organization (WHO) stated that foods containing more than 15 μg/kg of aflatoxin could cause harm to humans. Our results indicated that the total aflatoxin content in sufu was lower than this standard limit 3

LWT - Food Science and Technology 117 (2020) 108637

B. Yang, et al.

Fig. 2. (a–b) Changes in sufu water content obtained from fermentation with different mucor. (c–d) Changes in sufu pH obtained from fermentation with different mucor. (e–f) Changes in sufu NaCl content obtained from fermentation with different mucor. (g–h) Changes in sufu AAN content obtained from fermentation with different mucor. (i–j) Changes in sufu total acid content obtained from fermentation with different mucor. A: pre-fermentation, B: curing stage, C: post-fermentation (sufu), D: post-fermentation (soup bases).

4

LWT - Food Science and Technology 117 (2020) 108637

B. Yang, et al.

Fig. 3. (a–b) Changes in sufu H2S content at various stages; (c–d) Changes in total aflatoxins contents in sufu at various stages; (e–f) Changes in sufu TVB-N levels at various stages. A: pre-fermentation; B: curing stage; C: post-fermentation (sufu); D: post-fermentation (soup bases).

during the curing stage (S11–S16) may be due to the inhibition of protease activity by salt or/and alcohol (Kilinc, Cakli, Tolasa, & Dincer, 2006). During S17–S18, the moisture content of sufu increased, resulting in a decline in TVB-N levels, while the TVB-N levels in the soup base increased rapidly. Significant increases in TVB-N levels were observed in the three types of mucor fermented sufu and soup bases during the post-fermentation stage (S18–S25). The AEFS group had significantly lower final TVB-N content (S25) than MWFS (p < 0.05). Thus, suitable strain fermentation can effectively control the TVB-N content in fermented sufu.

throughout the entire fermentation process. 3.4. TVB-N value As shown in Fig. 3e–f, TVB-N was not detected in sufu at S1. However, the TVB-N content increased rapidly with increased fermentation time (S3–S10). At the end of the pre-fermentation stage, the TVBN levels were significantly higher in AEFS than in MWFS and MRFS. During the curing stage, the TVB-N levels were lower than at the end of the pre-fermentation stage. There was no significant change in TVB-N levels during the whole curing stage. TVB-N levels are related to the degradation of proteins. Nitrogen-containing compounds, such as proteins, peptides, and amino acids, are deaminated or decomposed by enzymes and converted into amino acids and volatile nitrogen (El Jalil, Faid, & Elyachioui, 2001). Table salt and alcohol have inhibitory effects on this protease activity. Therefore, the slow increase in TVB-N content

3.5. Benzoic acid content The change in sufu benzoic acid content is shown in Fig. 4a–b. Commercially produced tofu contains about 300 mg/kg benzoic acid. During the pre-fermentation stage with each of the mucor strains, the 5

LWT - Food Science and Technology 117 (2020) 108637

B. Yang, et al.

Fig. 4. (a–b) Changes in sufu BA contents at various stages; (c–d) Changes in sufu water and BA contents during pre-fermentation in a simulation experiment in which sodium benzoate was added. A: pre-fermentation; B: curing stage; C: post-fermentation (sufu); D: post-fermentation (soup bases).

At the end of fermentation, the benzoic acid contents in the tofu maopi with and without mucor fermentation were 191.25 mg/kg and 582.09 mg/kg, respectively. These results showed that the final benzoic acid content was not related to decreased water content, but might be determined by microorganism consumption during fermentation. Additionally, pure mucor fermentation significantly reduced the benzoic acid content.

benzoic acid content in the raw sufu was significantly reduced. At the end of the pre-fermentation stage, the benzoic acid content in the AEFS, MWFS, and MRFS were reduced to 25%, 12.5%, and 16.7%, respectively, compared with the tofu maopi. During the curing stage, the benzoic acid contents in the sufu samples with each of the three types of mucor showed decreasing trends with increased curing time. During the post-fermentation period, the benzoic acid content in each of the different kinds of sufu solids and soup bases showed the same trend. On the 80th day of post-fermentation, AEFS had the greatest benzoic acid content (52.3000 ± 0.443 mg/kg), followed by MRFS (27.676 ± 0.883 mg/kg) and MWFS (11.933 ± 0.360 mg/kg). Previous studies have not detected benzoic acid in raw soybeans, but found that the benzoic acid content in douchi gradually increased with increased fermentation time. Both sufu and douchi are made from microbial fermentation of soybeans, thus, fermented sufu may also contain benzoic acid (Shen, 2012). However, in this study, benzoic acid was found in the tofu maopi, and then the content of benzoic acid decreased sharply during the pre-fermentation process, which was opposite to the previous findings about douchi benzoic acid content. Therefore, we designed a validation test to further investigate the change in benzoic acid content of tofu maopi with and without Mucor racemosus inoculation. As shown in Fig. 4c–d, the results indicated that the moisture content of sufu with and without mucor fermentation decreased with increased pre-fermentation time. The benzoic acid content in the tofu maopi with exogenously added benzoic acid was 600 mg/kg.

3.6. Biogenic amine contents During the sufu fermentation process, the total biogenic amine (BA) contents during the fermentation stage are shown in Table 1. The results showed that a small amount of total BAs (about 30 mg/kg) were detected in the tofu (S1). In the pre-fermentation stage, the BA content rapidly increased with increased pre-fermentation time. With continued fermentation time, the BA content in each of the three fermented sufu types decreased significantly at the curing stage (S11) compared with the end of pre-fermentation stage (S10). The main reason for this decrease is that the BAs in sufu dissolve in the soup bases. With increased sousing time, the BA content in each of the three sufu samples gradually increased. During the post-fermentation stage, the moisture content of the sufu soaked in the soup bases increased at S17–S18, and the BA content was diluted and thus decreased, while the BA content in the soup bases increased rapidly. The BA contents in sufu increased slowly with continued post-fermentation time. The results of this experiment 6

206.351 ± 1.561cA 47.351 ± 1.660lA 58.510 ± 2.723kA 48.500 ± 1.878lA 58.753 ± 7.055kA 65.901 ± 1.958kA 77.856 ± 6.887jA 89.070 ± 1.444iA 106.920 ± 5.14gA

3.886 ± 0.776fgF 1.745 ± 0.010fgF 12.584 ± 1.509dCD 3.101 ± 0.517fgF 3.659 ± 2.229fgE 6.464 ± 0.408efD 9.086 ± 2.228deCD 11.455 ± 0.527dD 13.848 ± 0.449dC

S17 S18 S19 S20 S21 S22 S23 S24 S25 MWFS S1 S2 S3 S4 S5 S6 S7 S8 S9 S10

7

5.423dA 8.726jA 2.506iA 9.139iA 4.496hA 7.743hA 7.867gA 10.15gA 1.961gA

318.235 108.580 120.052 123.385 145.642 145.029 175.115 165.434 171.636

0.446 ± 0.022lD

40.9210.626bcC 10.624 ± 1.289hD 36.686 ± 2.258cdB 25.826 ± 0.660eB 20.262 ± 1.177fgB 15.902 ± 7.005gB 23.512 ± 1.786efC 35.587 ± 3.279dB 36.441 ± 1.246cdB

6.913 ± 0.372iB

S17 S18 S19 S20 S21 S22 S23 S24 S25 MRFS S1

± ± ± ± ± ± ± ± ±

397.651 ± 1.241aA 58.441 ± 2.467kA 104.771 ± 2.278jA 190.573 ± 0.626fA 340.799 ± 13.85cA 323.703 ± 12.27dA

0.597aB 1.085hD 0.438fgD 0.358fgC 2.421bcBC 0.067bC

± ± ± ± ± ±

56.874 10.196 20.149 19.818 41.230 42.246

S11 S12 S13 S14 S15 S16

NDlD NDlE NDlD NDlD NDlD 61.235 ± 2.522kA 174.053 ± 7.297gA 277.765 ± 11.41eA 378.066 ± 5.805bA 397.554 ± 9.200aA

346.247 ± 1.485aA 98.124 ± 10.342hA 128.566 ± 7.509fA 87.909 ± 2.617iA 181.673 ± 5.942dA 209.424 ± 1.561cA

70.498 ± 0.629aB 3.820 ± 0.784fgE 2.129 ± 0.207fgE 1.262 ± 0.311fgE 3.794 ± 0.702fgF 4.025 ± 0.557fgF

S11 S12 S13 S14 S15 S16

NDiD NDiE NDiD NDiD 6.739 ± 1.886hC 23.441 ± 3.956efC 56.174 ± 9.595aB 42.920 ± 2.175bB 60.278 ± 0.903aB 57.446 ± 1.767aB

NDmD NDmD NDmE 161.325 ± 9.192eA 325.499 ± 3.074bA 349.212 ± 3.928aA

NDhD 0.443 ± 0.005gC 0.461 ± 0.002gD 32.398 ± 8.484cC 52.625 ± 1.452bB 72.700 ± 7.986aB

AEFS S1 S2 S3 S4 S5 S6

CAD

PUT

N0.

NDiE

NDaG NDaF NDaG NDaF NDaG NDaE NDaG NDaF NDaG

NDaG NDaE NDaG NDaE NDaF NDaF

NDaD NDaE NDaD NDaD NDaD NDaF NDaE NDaE NDaF NDaG

5.899 0.379 0.333 0.368 0.358 0.356 0.372 NDfG NDfF

± ± ± ± ± ± ±

0.005bE 0.003eG 0.037eF 0.012eG 0.037eF 0.038eF 0.000eF

NDfG NDfF NDfG 2.055 ± 1.060dE 2.886 ± 0.599cF 7.026 ± 1.013aE

NDfD NDfD NDfE NDfF NDfF NDfG

TRY

± ± ± ± ± ±

1.030deD 0.922cC 1.652fgC 0.577deC 2.385cC 1.253aC

± ± ± ± ± ±

± ± ± ± ± ± ± ± ± 0.916efgE 1.039fgD 1.802fgE 5.544defC 0.931efgD 0.179efgD

0.289aA 0.403bcA 0.322deB 2.033bB 0.621deD 2.477gD 6.382fgD 3.021deD 5.113efgE

NDcE

12.142 ± 0.126efgE 18.298 ± 1.855cdC NDhG NDhF NDhG NDhE NDhG NDhF NDhG

12.485 10.426 10.499 14.578 12.094 12.282

NDhD 31.232 19.907 15.049 22.675 15.834 10.136 10.288 15.898 12.700

23.268 ± 0.140abC 8.430 ± 0.105hiD 10.094 ± 2.220ghD 9.663 ± 0.214ghD 21.664 ± 1.681bcC 12.324 ± 0.518efC 9.958 ± 0.530ghCD 3.147 ± 0.028jF 2.828 ± 0.015jE

13.437 20.682 10.692 12.977 21.323 24.166

NDjD NDjD NDjE 0.855 ± 0.199kE 6.861 ± 0.246iD 14.654 ± 1.169dD

PHE

0.012cC 0.009cC 0.007cD 0.042cE 0.013cE 0.013cF

± ± ± ± ± ± ± ± ±

± ± ± ± 0.025cG 0.018cG 0.036cF 0.005cG 0.004cF 0.023cF 0.038cF 0.739bF 0.390aD

0.091 0.009cF 0.033cG 0.014cG

cF

± 0.005cF

± ± ± ± ± ±

± ± ± ± ± ± ±

0.073 0.060cE 0.022cF 0.064cD 0.033cF 0.840bE 2.989aF

cF

5.107 ± 0.305bC

NDdG NDdF 0.511 0.580 0.421 0.479 0.486 1.703 4.885

NDdG NDdE NDdG NDdE NDdF NDdF

0.529 ± 0.012cC NDdE NDdD NDdD NDdD NDdF NDdE NDdE NDdF NDdG

0.624 0.560 0.485 0.508 0.431 0.424 0.483 3.843 6.493

0.521 NDdF 0.321 0.585 0.611 0.637

0.529 0.524 0.517 0.495 0.526 0.530

SPD

Table 1 Changes in biogenic amines contents (mg/kg) of sufu obtained from different mucor during fermentation.

± ± ± ± ± ± ± ± ±

± ± ± ± ± ±

± ± ± ± ± ±

0.525deE 0.383deE 1.138deE 0.044fE 0.129fE 0.078fE 0.233deE 0.252cdE 1.087aD

0.151deE 0.174bcD 0.270bD 1.937deD 2.732bcE 1.402deE

0.508deB 1.194deB 0.240deC 0.092deE 0.941fD 0.285deE

± ± ± ± ± ± ± ± ±

± ± ± ± ± ±

0.019hiF 0.023iE 0.100hiE 0.32iD 0.077iE 0.283iC 0.463hiE 0.332ghDE 0.500cDE

0.502fgF 0.584cdD 0.674cF 0.109fgD 0.200eE 0.036hiE

6.964 ± 0.015eB

4.337 3.922 4.456 4.145 3.917 4.275 4.330 5.185 8.726

5.950 7.453 7.573 5.570 6.464 4.358

6.622 ± 0.508eB 12.226 ± 0.44aD 12.731 ± 0.46aC 11.083 ± 0.12bC 9.188 ± 0.487cC 8.614 ± 0.732cE 8.796 ± 0.558cD 8.822 ± 0.351cD 6.715 ± 0.106deE 6.197 ± 1.334efF

5.922 5.500 5.980 4.583 4.414 4.722 5.407 6.557 9.417

5.800 6.674 6.892 6.229 6.698 6.250

6.622 5.887 6.188 5.689 4.995 5.893

SPM

NGfE

49.313 44.559 29.948 28.140 15.149 15.660 34.741 15.701 25.740

46.111 24.008 27.868 55.299 50.318 50.734

NDkD 18.655 19.497 20.833 26.452 27.830 27.735 27.078 36.167 48.477

14.396 13.736 29.810 37.702 38.097 29.850 25.842 21.291 18.737

14.375 14.069 13.888 13.860 14.661 14.579

NDhD NDhD 12.937 14.623 15.903 14.449

HIS

± ± ± ± ± ± ± ± ±

± ± ± ± ± ±

± ± ± ± ± ± ± ± ±

± ± ± ± ± ± ± ± ±

± ± ± ± ± ±

± ± ± ±

1.085abB 1.985bB 1.157deC 1.083efB 0.478jC 1.277jB 4.424cdB 1.795jC 6.721fgC

0.546bC 5.521ghC 3.201efC 8.025aB 7.828abB 3.428abB

1.056hiB 0.551hiA 1.661hiA 2.866fgA 3.068efB 2.084efC 1.767efC 7.264cC 5.726abC

0.076gD 0.241gC 2.869bB 0.389aB 2.330aB 1.551bB 2.259cB 1.262dB 0.716fB

0.327gD 0.148gC 0.171gC 0.336gC 0.847gD 0.957gD

0.407 0.200gD 0.372fC 0.504gD

gB

± ± ± ± ± ± ± ± ±

± ± ± ± ± ±

± ± ± ± ± ± ± ± ± ±

± ± ± ± ± ± ± ± ±

± ± ± ± ± ±

± ± ± ± ± ±

0.301cdeD 0.090ijkCD 0.497klD 0.696jklC 0.098lD 0.453lB 0.397lD 0.117lCD 0.070lD

2.026cdeD 0.575bcB 1.699eB 2.060hC 2.206deC 0.377bcdC

0.343hA 0.052hijC 0.086hijB 0.207hiB 0.469gB 1.215gC 2.466fC 0.694cdB 3.099aC 1.218abD

0.568deB 2.114cB 0.776hiC 0.165hiC 0.327hiD 0.297iC 0.486iC 0.141hiC 0.489iC

0.973bC 3.159eB 1.750fB 3.643deB 0.646deB 0.814cdB

0.343ghA 1.232gA 0.407fA 3.437bB 2.564aB 1.248aC

11.406 ± 0.023gA

35.565 14.062 12.493 12.716 11.813 11.514 11.632 11.467 11.263

36.363 36.862 34.201 16.502 34.524 36.603

16.550 14.698 14.859 15.024 22.209 22.628 32.172 36.503 40.328 38.690

36.911 40.019 14.627 13.979 14.341 13.321 13.049 14.032 13.199

50.054 34.653 29.992 36.833 37.172 37.711

16.550 18.245 30.198 47.599 53.381 54.696

TYR

± ± ± ± ± ± ± ± ±

± ± ± ± ± ±

0.676 1.136 4.317 2.258 10.73 3.299 8.428 2.070 5.886

2.934 10.94 4.461 7.177 9.484 0.642

± ± ± ± ± ± ± ± ±

± ± ± ± ± ±

5.000 5.566 2.373 11.08 5.967 16.05 9.905 13.31 7.570

3.709 7.259 4.891 2.938 13.39 15.82

(continued on next page)

30.837 ± 0.627

460.512 200.045 204.146 194.791 197.204 192.859 249.815 235.076 258.691

555.435 147.386 205.061 302.338 485.429 469.925

23.701 ± 0.176 76.811 ± 1.763 66.994 ± 0.957 61.989 ± 1.366 87.263 ± 5.105 159.583 ± 2.923 309.065 ± 16.55 403.377 ± 19.60 537.453 ± 9.198 561.064 ± 12.53

297.257 117.721 132.423 118.403 141.717 133.362 142.053 149.394 171.442

500.931 178.022 192.480 161.712 268.818 303.818

23.701 ± 0.176 25.099 ± 0.489 50.301 ± 0.190 262.985 ± 19.91 459.789 ± 1.993 512.134 ± 13.16

Total BA

B. Yang, et al.

LWT - Food Science and Technology 117 (2020) 108637

0.481 ± 0.062hE 2.581 ± 0.344fE 4.624 ± 0.343fD 15.927 ± 0.341bB 1.111 ± 0.059gE 10.344 ± 0.287cdC 4.635 ± 0.086fD 4.221 ± 0.039fD 3.408 ± 0.171fD

32.780 ± 0.648aC 0.179 ± 0.001hF NDiF 0.265 ± 0.000hE 1.137 ± 0.176gD 0.988 ± 0.024hF

ND NDiF 3.557 ± 0.195fD 1.617 ± 0.063gD 8.118 ± 4.300deD 14.204 ± 7.141bcC 30.000 ± 8.581aB

iF

TRY

NDcF NDcG 0.616 ± 0.008bE 0.622 ± 0.001aE NDcG NDcE NDcE NDcF NDcF

NDcG NDcG NDcF NDcF NDcE NDcG

ND NDcF NDcF NDcE NDcF NDcF NDcF

cF

PHE ± ± ± ± ± ± ±

0.426 0.009cD 0.010cE 0.006cD 0.004cE 0.004cE 0.003cE

bD

1.500 0.494 1.050 1.559 0.687 0.734 4.051 1.592 0.635

± ± ± ± ± ± ± ± ±

0.019cD 0.086dF 0.485cE 0.145cD 0.098dF 0.132dD 5.175bD 0.842cE 0.300dE

1.151 ± 0.002cF 1.145 ± 0.001cE 1.486 ± 0.559cE 3.658 ± 5.457bD 25.857 ± 0.41aB 1.460 ± 0.28cE

3.874 1.712 1.512 1.485 1.164 1.153 1.156

SPD

NGiF 4.328 4.411 4.311 4.644 NGiE NGiE NGiF NGiF

4.175 4.518 3.616 3.656 3.688 NGiG

9.137 9.657 7.465 7.554 7.926 4.549 4.265

SPM

± ± ± ±

± ± ± ± ±

± ± ± ± ± ± ±

0.141gE 0.188gD 0.285gC 0.078fD

0.029gE 0.031fgD 0.050hD 0.073hD 0.121hC

0.026 0.030aC 0.061dC 0.084dC 0.034cD 0.034fgD 0.027gD

bB

20.637 14.766 15.462 16.805 15.747 NGfE NGfE NGfF NGfF

12.846 14.237 13.071 14.561 21.482 20.122 ± ± ± ± ±

± ± ± ± ± ± 0.767abC 1.281eD 1.929eC 2.922deB 0.606eC

0.142eD 0.028eB 0.397eC 2.885eC 6.491aB 6.358abD

NG NGfF NGfF NGfE 17.492 ± 0.058cdB 13.464 ± 0.043eC 12.946 ± 0.060eC

fF

HIS

33.633 46.767 34.714 29.767 31.352 10.636 14.180 10.369 10.059

13.366 12.027 17.289 21.263 25.223 42.475

11.502 12.215 13.802 13.305 13.396 12.534 13.568

TYR

± ± ± ± ± ± ± ± ±

± ± ± ± ± ±

± ± ± ± ± ± ±

0.713bB 9.393aA 1.490bB 13.01bcA 2.001bcA 0.012gC 1.929fC 0.405gC 0.641gC

0.08fgD 0.035gC 3.864efB 1.743deB 2.183cdB 2.58aB

0.063 0.050gB 0.040fgB 0.050fgB 0.060fgC 0.069gC 0.025fgC

gA

145.422 ± 2.961 127.195 ± 14.56 150.874 ± 4.031 140.321 ± 14.11 98.295 ± 1.853 64.218 ± 7.611 73.849 ± 6.513 85.314 ± 1.835 110.124 ± 4.671

215.791 ± 1.137 73.972 ± 0.573 62.538 ± 3.602 74.656 ± 8.429 149.043 ± 11.33 150.162 ± 14.16

31.706 ± 0.325 36.367 ± 0.225 51.902 ± 0.801 41.378 ± 0.931 102.478 ± 4.203 134.431 ± 5.528. 217.540 ± 8.189

Total BA

Sufu obtained using the following mucor: AEFS-Actinomucor elegans fermented sufu, MWFS-Mucor wutunkiao fermented sufu and MRFS-Mucor racemosus fermented sufu. Putrescine (PUT), Cadaverine (CAD), Tryptamine (TRY), 2-Phenylethylamine (PHE), Spermidine (SPD), Spermine (SPM), Histamine (HIS) and Tyramine (TYR). Mean values ± standard deviations from triplicate analysis. ND: not detected. Means with different lower case letters with in the same column for significant differences (p < 0.05). Means with different upper case letters with in the same line for the same fermentation time point among different groups stand for significant differences (p < 0.05).

± ± ± ± ± ± ± ± ±

0.527eB 2.339fgC 2.728cA 0.785eA 0.676hC 4.464hB 1.153gB 1.605dA 2.165bA

± ± ± ± ± ± ± ± ±

32.864 25.219 54.643 34.181 15.650 14.194 23.422 40.237 61.848

2.301bA 2.582defB 2.143dB 1.166dA 0.750efgB 3.172efgA 1.241fgA 0.863efgB 1.624deB

56.306 33.039 35.355 37.149 29.104 28.310 27.561 28.895 34.174

S17 S18 S19 S20 S21 S22 S23 S24 S25

75.163 ± 0.659aB 4.303 ± 0.064ijD 3.965 ± 1.159jD 4.355 ± 1.520ijD 24.569 ± 4.367fgB 27.021 ± 2.596fC

± ± ± ± ± ±

0.231aA 0.543dA 0.586gA 5.192fgA 11.671cA 7.091bA

76.310 37.563 23.111 26.898 47.087 58.097

S11 S12 S13 S14 S15 S16

0.302 ± 0.039 0.122 ± 0.016lE 1.140 ± 0.033jkE 1.564 ± 0.022jkD 7.433 ± 0.475iD 27.387 ± 3.037fB 77.113 ± 0.485aA

lE

6.891 ± 0.015 12.661 ± 0.206hA 24.427 ± 0.761gA 15.853 ± 0.896hA 46.949 ± 0.391cA 61.139 ± 0.114bA 78.493 ± 0.153aA

CAD

S2 S3 S4 S5 S6 S7 S8

iC

PUT

N0.

Table 1 (continued)

B. Yang, et al.

LWT - Food Science and Technology 117 (2020) 108637

8

LWT - Food Science and Technology 117 (2020) 108637

B. Yang, et al.

many key functions in humans and animals, the consumption of foods containing high amounts of these amines may have toxicological effects (Kalac̆ & Krausová, 2005). For example, PHE, TRY, and TYR are associated with the development of hypertensive crises in certain patients, as well as diet-related migraine. BAs such as PUT, CAD, SPD, and SPM have no adverse effects on health by themselves, but they may react with nitrites to form carcinogenic nitrosamines, which are easily absorbed by the gastrointestinal tract where they inhibit the catabolism of toxic amines such as TRY, TYR, and PHE, thus enhancing toxicity (Kalac̆ & Krausová, 2005). Previous reports suggested that total food amine content of more than 1000 mg/kg is harmful to health (Santos, 1996). The United States Food and Drug Administration (USFDA) guidelines have a threshold of 50 mg/kg for HIS in seafood (Food & Administration, 2001). The average total amine levels in the three types of sufu were lower than this level: AEFS contained 171.442 ± 5.886 mg/kg, MWFS contained 258.691 ± 7.570 mg/kg, and MRFS contained 110.124 ± 4.671 mg/kg. The average HIS content of the three types of sufu were also well below the stipulated dangerous level of 50 mg/kg. Our results indicated that MRFS had the lowest total BA content and HIS content, and thus was most suitable for pure mucor fermentation of sufu due to its lowest risk. The formation of BAs in sufu products depends on several factors. One factor is the raw starting material, which may itself contain BAs. BAs are heat resistant and cannot be destroyed by freezing, cooking, or smudging (Tan et al., 2019). Thus, it is important to select raw materials without BAs. Another key factor is the microbial species introduced by contamination or intentionally added as fermentation starters (Su-Yeon, Hyeong-Eun, & Yong-Suk, 2017). In the traditional fermentation process, the culture contains a large number of microorganisms, such as Streptococcus lutetiensis, Lactococcus lactis, and Yarrowia lipolytica, some of which have been shown to secrete decarboxylase and produce BAs (Gu et al., 2018). A previous study showed that pure-fermentation technology avoids microbial contamination that may produce decarboxylase (Tan et al., 2019). It found that BA content is lowest in douchi, which is consistent with the fact that douchi has the lowest amino acid decarboxylase activity. The differences in manufacturing process and mucor strain could underlie the diversity of BAs observed in sufu in this study. Our BAs analyses revealed that the three types of selected mucor strains in our study, especially Mucor racemosus, are all suitable for sufu fermentation. The results of this work demonstrate a method to reduce BA content during sufu production and improve the safety and quality of the final product, in addition to providing beneficial guidance for the standardization of large-scale sufu production.

were consistent with the BA changes in purebred fermented sufu reported by Qiu et al. (2018). Slowing the BAs production speed during the post-fermentation stage may be related to the gradual decrease in the total microbial biomass during the post-fermentation stage (Shi & Fung, 2000). 3.7. Biogenic amine composition Biogenic amine (Putrescine (PUT), Cadaverine (CAD), Tryptamine (TRY), 2-Phenylethylamine (PHE), Spermidine (SPD), Spermine (SPM), Histamine (HIS), and Tyramine (TYR)) contents in the sufu samples are shown in Table 1. The major BAs in each type mucor fermented sufu were different. PUT, CAD, PHE, HIS, and TYR were the main BAs in AEFS and MWFS, while PUT, CAD, HIS, and TYR were the predominating BAs in MRFS (Table 1). The variation in BAs among different types of sufu samples from different mucor fermentations may result from the differences in the fermentation processes and microbiological composition (Qiu et al., 2018). BAs can form quickly if production process is contaminated by BA-forming bacteria (IBE, NISHIMA, & KASAI, 1992). HIS and TYR were derived from decarboxylated lysine and tryptophane, which were abundant in tofu (B.-Z. Han et al., 2004). In the pre-fermentation stage (S1), TYR was the major BA detected in all types of sufu samples, followed by SPM and SPD. Only MR was found to contain a small amount of PUT and CAD. No TRY or PHE were detected at the pre-fermentation stage in any of the sufu samples. During pre-fermentation, the BAs increased over time (S2–S6) in AEFS. In MWFS, PUT and CAD increased over S5–S10 and HIS and TYR increased over S1–S10, while PHE and SPM decreased over S3–S10. In MRFS, PUT, CAD, and TRY increased over S4–S8, while SPD and HIS decreased over S1–S8. In the curing stage, the PUT content rapidly decreased in S11–S14 and then increased in S14–S16 for all types of sufu. There was a trend of increased CAD over S14–S16 for AEFS and over S12–S16 for MWFS and MRFS. However, compared with the end of the pre-fermentation stage, the total of CAD in all types of sufu decreased after the curing stage. The SPD content increased over S12–S16 in AEFS and over S11–S15 for MRFS, but no CAD was detected in MWFS during the curing stage. HIS and TYR decreased over S11–S14 and then increased over S14–S16. The change in SPD was irregular throughout the curing stage for all types of sufu, with the content ranging from 3.616 ± 0.05 to 7.573 ± 0.674 mg/kg. During the postfermentation stage, AEFS and MRFS contained all of the BAs, however, MWFS had no TRY. In the early stages of post-fermentation, most of the BAs gradually decreased in all groups until the middle of the post-fermentation stage. At the end of post-fermentation, no TRY was detected in AEFS, no TRY or PHE were detected in MWFS, and no PHE, SPM, or TYR were detected in MRFS. Compared with traditionally fermented sufu products (Gu et al., 2018), the BA contents in our study were lower. This result showed that fermentation with selected strains of pure mucor was effective in decreasing BA contents in sufu products. A similar conclusion was reached by YK Park, Lee, & Mah, 2018. The CAD content in all sufu samples increased sharply during prefermentation, and then significantly decreased at the end of the curing stage. CAD was reported to be formed during the storage of sardine products containing 12% salt (10%–12% addition of salt in this study) at 30 °C, during which the number of halotolerant bacteria increased (Santos, 1996). The addition of NaCl enhances taste and also retards further growth of mucor or other harmful microbial contaminants in sufu. The mucor grows on the surface of the sufu maopi, with the mycelium hardly infiltrating into the sufu during the curing stage. Moreover, NaCl is involved in the transfer of mycelia-bound proteases from the mucor into the sufu (B.-Z. Han et al., 2004). The sufu maopi absorb salt and lose water after sousing, during which enzymes also diffuse and degrade. Thus, more BAs would be formed from amino acids by the microorganism produced enzymes (including decarboxylase) in the salted sufu. Although BAs such as PHE, TRY, TYR, and HIS are essential for

4. Conclusion Three different types of mucor strains as starter cultures to study the safety and quality of sufu. Results showed that the moisture content, pH, NaCl, AAN, and total acid content of all samples were at normal levels for mature sufu products. The total aflatoxin content in sufu were not detected in the post-fermentation period. The H2S, TVB-N, and BA contents in MRFS were lower than in AEFS and MWFS. Pure mucor fermentation could significantly reduce the BA contents in sufu. The total BA content was low (110.124 ± 4.671 mg/kg) in MRFS. Different mucor strains and fermentation processes contributed to different BA levels in the final sufu products. These findings demonstrated that the process conditions and selected mucor strain, especially Mucor racemosus (MR) adopted in this study, were suitable for the safe and rapid fermentation of sufu. In addition, These results suggested that sufu should be produced under strict sanitary conditions with suitable mucor strains to minimize BA contents. Further study is necessary to investigate how it changes in aspects of sufu production and storage, including the effects of Good Manufacturing Practice (GMP) or Hazard Analysis and Critical Control Point (HACCP), fermentation strain, storage temperature, NaCl concentration, and alcohol concentration in 9

LWT - Food Science and Technology 117 (2020) 108637

B. Yang, et al.

dressing mixture, impacting the formation of BAs in sufu.

production conditions for tyramine-and histamine-producing bacterial strains isolated from soybean paste (miso) starting materials. Eisei Kagaku, 38(5), 403–409. Kalac̆, P., & Krausová, P. (2005). A review of dietary polyamines: Formation, implications for growth and health and occurrence in foods. Food Chemistry, 90(1–2), 219–230. Kilinc, B., Cakli, S., Tolasa, S., & Dincer, T. (2006). Chemical, microbiological and sensory changes associated with fish sauce processing. European Food Research and Technology, 222(5–6), 604–613. Li, Y., Huang, J., Yuan, C., Ding, T., Chen, S., & Hu, Y. (2019). Developing a new spoilage potential algorithm and identifying spoilage volatiles in small yellow croaker (Larimichthys polyactis) under vacuum packaging condition. LWT-Food Secience and Technology, 106, 209–217. Liu, Q., Hong, I. P., Han, S.-B., Hwang, B. Y., & Lee, M. K. (2012). Analysis of antiadipogenic constituents of cordyceps militaris using high performance liquid chromatography-diode array detection in different samples: Comparison with anti-adipogenic activity. Natural Product Sciences, 18(3), 171–176. Liu, Z. F., Wei, Y. X., Zhang, J. J., Liu, D. H., Hu, Y. Q., & Ye, X. Q. (2011). Changes in biogenic amines during the conventional production of stinky tofu. International Journal of Food Science and Technology, 46(4), 687–694. Lopetcharat, K., Choi, Y. J., Park, J. W., & Daeschel, M. A. (2001). Fish sauce products and manufacturing: A review. Food Reviews International, 17(1), 65–88. Marcotte, M., Taherian, A. R., Trigui, M., & Ramaswamy, H. S. (2001). Evaluation of rheological properties of selected salt enriched food hydrocolloids. Journal of Food Engineering, 48(2), 157–167. Park, Y. K., Lee, J. H., & Mah, J.-H. (2018). Occurrence and reduction of biogenic amines in traditional asian fermented soybean foods: A review. Food Chemistry, 278, 1–9. Qiu, S., Wang, Y., Cheng, Y., Liu, Y., Yadav, M. P., & Yin, L. (2018). Reduction of biogenic amines in sufu by ethanol addition during ripening stage. Food Chemistry, 239, 1244–1252. Ran, C., & Kan, J. (2015). Research of fungus selection on whole-soybean sufu fermentation. China Condiment, (8), 1–4 (in chinese). Ray, R. C., El Sheikha, A. F., & Kumar, S. (2014). Oriental fermented functional (probiotic) foods. In R. C. Ray, & D. Montet (Eds.). Microorganisms and fermentation of traditional foods. Food biology series (pp. 283–311). Boca Raton, Florida, USA: Science Publishers Inc., CRC Press. Santos, M. S. (1996). Biogenic amines: Their importance in foods. International Journal of Food Microbiology, 29(2–3), 213–231. Shen, X. (2012). The formation mechanism research of Benzoic acid and Propionic acid in the traditional fermented muor douchi. Southwest university. Shi, X., & Fung, D. Y. (2000). Control of foodborne pathogens during sufu fermentation and aging. Critical Reviews in Food Science and Nutrition, 40(5), 399–425. Su-Yeon, K., Hyeong-Eun, K., & Yong-Suk, K. (2017). The potentials of Bacillus licheniformis strains for inhibition of B. cereus growth and reduction of biogenic amines in cheonggukjang (Korean fermented unsalted soybean paste). Food Control, 79, 87–93. Suo, H.-y., Zhao, X., Qian, Y., Chen, J., Li, j., Zhang, Y., et al. (2015). Changes in total sugar and amino acids, and formation of taste compounds in yongchuan douchi during fermentation. Food Science, 36(21), 100–104 (in Chinese). Tan, Y., Zhang, R., Chen, G., Wang, S., Li, C., Xu, Y., et al. (2019). Effect of different starter cultures on the control of biogenic amines and quality change of douchi by rapid fermentation. LWT-Food Secience and Technology, 109, 395–405. Toro-Funes, N., Bosch-Fuste, J., Latorre-Moratalla, M., Veciana-Nogués, M., & VidalCarou, M. (2015). Biologically active amines in fermented and non-fermented commercial soybean products from the Spanish market. Food Chemistry, 173, 1119–1124. Yang, J., Ding, X., Qin, Y., & Zeng, Y. (2016). Limit standards for protein decomposition products in sufu and douchi. Food Science, 37(6), 210–215 (in Chinses).

Conflicts of interest The authors declare no competing financial interest. Acknowledgement This study was financially supported by the Chongqing food and drug administration “Risk factor identification and safety assessment of chongqing real estate fermented soybean food in the process of production and processing” (Chongqing science and technology commission, No.159 [2016]) Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.lwt.2019.108637. References AOAC (2007). Association of official analytical chemists, official methods of analysis (18th ed.). washington, DC: Benjamin Franklin Station. China, M. o. C. o. t. P. s. R. o.. (2007). Fermented bean curd. Beijing: China Standards Press. El Jalil, M., Faid, M., & Elyachioui, M. (2001). A biotechnological process for treatment and recycling poultry wastes manure as a feed ingredient. Biomass and Bioenergy, 21(4), 301–309. Endo, Y. (1983). A simple method for the determination of polyamines and histamine and its application to the assay of ornithine and histidine-decarboxylase activities. Methods in Enzymology, 94, 42–47. Food, U., & Administration, D. (2001). Fish and fishery products hazards and controls guide. Washington, DC: Center for Food Safety and Applied Nutrition, US Food and Drug Administration 73. Guan, R. F., Liu, Z. F., Zhang, J. J., Wei, Y. X., Wahab, S., Liu, D. H., et al. (2013). Investigation of biogenic amines in sufu (furu): A Chinese traditional fermented soybean food product. Food Control, 31(2), 345–352. Gu, J., Liu, T., Sadiq, F. A., Yang, H., Yuan, L., Zhang, G., et al. (2018). Biogenic amines content and assessment of bacterial and fungal diversity in stinky tofu–A traditional fermented soy curd. LWT-Food Secience and Technology, 88, 26–34. Han, B. Z., Cao, C. F., Rombouts, F. M., & Nout, M. R. (2004). Microbial changes during the production of Sufu––a Chinese fermented soybean food. Food Control, 15(4), 265–270. Han, B. Z., Rombouts, F. M., & Nout, M. R. (2001). A Chinese fermented soybean food. International Journal of Food Microbiology, 65(1–2), 1–10. Han, B. Z., Wang, J. H., Rombouts, F. M., & Nout, M. R. (2003). Effect of NaCl on textural changes and protein and lipid degradation during the ripening stage of sufu, a Chinese fermented soybean food. Journal of the Science of Food and Agriculture, 83(9), 899–904. IBE, A., NISHIMA, T., & KASAI, N. (1992). Bacteriological properties of and amine-

10