Method for simultaneously reducing urethane and its precursors levels during Chinese liquor production process

Abstract

The present invention a method for simultaneously reducing urethane and its precursors levels during Chinese liquor production process, which relates to the field of fermented food production. The present invention is carried out through inoculating Bacillus amyloliquefaciens JP21 or combines with urease into the grains for fermentation. The content of EC and urea in the fermented grains after 5-day fermentation could reduce 30.16% and 50.05% respectively, With an addition of the B. amyloliquefaciens during grains fermentation, EC and urea levels are successfully controlled, and at the same time aroma and tastes of Chinese liquor hasn't been affected.

Claims

1. A method for reducing ethyl carbamate (EC) and its precursors levels, comprising inoculating 1-910.sup.7 CFU/g Bacillus amyloliquefaciens (B. amyloliquefaciens) into grains for fermentation; wherein g is gram of weight of the grains for fermentation; wherein said B. amyloliquefaciens is B. amyloliquefaciens JP21, which is deposited in China Center for Type Culture Collection in Wuhan University, Wuhan. Hubei. China on Sep. 19, 2016 with Accession No. CCTCC No: M 2016499.

2. The method of claim 1, wherein said B. amyloliquefaciens is inoculated before grain fermentation begins.

3. The method of claim 1, comprising inoculating 5-10 mL of B. amyloliquefaciens cell suspension/100 g grains into the grain fermentation.

4. The method of claim 1, comprising obtaining the B. amyloliquefaciens from inoculating into a LB medium and incubating at 37 C. for 24-48 h.

5. The method of claim 1, wherein said B. amyloliquefaciens is inoculated into grains with urease before the grain fermentation begins.

6. The method of claim 5, wherein said urease is produced from Lactobacillus reuteri.

7. The method of claim 1, the method comprising the steps of: 1) B. amyloliquefaciens collection: inoculating the B. amyloliquefaciens into LB medium, and incubating at 37 C. for 24-48 h; centrifuging the resulting broth, collecting stain precipitation and then resuspending by physiological saline; 2) strain inoculation: inoculating B. amyloliquefaciens cells suspension at concentration of 1-910.sup.7 CFU/g into grains for fermentation, wherein the volume of the B. amyloliquefaciens suspension is 5-10 mL/100 g grains; and 3) grains fermentation: incubating the grains under 28-30 C.

8. The method of claim 1, the method comprising the steps of: 1) strain inoculation: inoculating B. amyloliquefaciens cells suspension at concentration of 1-910.sup.7 CFU/g into grains for fermentation, wherein the volume of the B. amyloliquefaciens suspension is 5-10 mL/100 g grains; and 2) grains fermentation: incubating the grains under 28-30 C.

Description

BRIEF DESCRIPTION OF DRAWINGS

Figure Captions

(1) FIG. 1. EC and urea concentration of fermented grains that inoculated with B. amyloliquefaciens JP21 (1910.sup.6 CFU/g) and B. amyloliquefaciens JY06 (1910.sup.6 CFU/g) respectively;

(2) FIG. 2. EC and urea concentration of fermented grains that inoculated with B. amyloliquefaciens JP21 (1910.sup.7 CFU/g) and B. amyloliquefaciens JY06 (1910.sup.7 CFU/g) respectively;

(3) FIG. 3. Concentration of EC in distilled solution that prepared from fermented grains.

DETAILED DESCRIPTION

(4) Materials and Methods:

(5) 1. Urease Assay:

(6) 1) Construction of standard curve: 4 g/L ammonium chloride with volume of 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4 or 1.6 mL is mixed with distilled water to a final volume of 2 mL; 1 mL 10% acetocaustin is added so the reaction is terminated. 1 mL chromogenic agent I and 1 mL chromogenic agent II are added before incubated at 37 C. for 20 min; ultrapure water is added to the resulting solution to a final volume of 10 mL, and then absorbance of the solution is measured at 578 nm.

(7) 2) Determination of samples: 1 mL enzyme and 1 mL 3% urea is mixed and incubated at 37 C. for 15 min, 1 mL 10% acetocaustin is added so the reaction is terminated; chromogenic agent I and 1 mL chromogenic agent II are added before incubated at 37 C. for 20 min; ultrapure water is added to the resulting solution to a final volume of 10 mL and absorbance of 578 nm is measured.

(8) Chromogenic agent I: 15 g phenol and 15 g sodium nitroferricyanide are dissolved and diluted to a constant volume of 250 mL, stored at 4 C.

(9) Chromogenic agent II: 13.125 g NaOH and 7.5 mL sodium hypochlorite are dissolved and diluted to a constant volume of 250 mL, stored at 4 C.

(10) Enzyme activity is calculated through the formula below:

(11) $\mathrm{Enzyme}\mathrm{activity}=\frac{An}{15k}\left(U/\mathrm{mL}\right);$ A: UV spectrophotometric value; n: Dilution times; k: slope of standard curve.

(12) 2. Urethanase Assay:

(13) 1 mL of urethanase and 1 mL 3% urethane is mixed and incubated at 37 C. for 15 min, then 1 mL 10% acetocaustin is added to terminate the reaction; chromogenic agent I and 1 mL chromogenic agent II are added before incubated at 37 C. for 20 min; ultrapure water is added to the resulting solution to a final volume of 10 mL, and then the absorbance of the solution is measured at 578 nm. The enzyme activity is calculated according to the formula below:

(14) $\mathrm{Enzyme}\mathrm{activity}=\frac{An}{15k}\left(U/\mathrm{mL}\right);$ A: UV spectrophotometric value; n: Dilution times; k: slope of standard curve.

(15) The standard curve is prepared with the same procedure with that of urea assay with the replacement of ethyl carbamate to urea.

(16) 3. Determination of Urea in Broth (EXAMPLE 3):

(17) 1 mL of microbial culture is centrifuged at 8000 rpm, 400 L supernatant, 600 L xanthydrol and 100 L 0.1 moL/L HCl are mixed and react in dark for 30 min, then 0.22 m organic filter membrane is used for filtration before determination. The method of determination is disclosed in the paper that published on March 2011 with name of Determination of urea in rice wine by high performance liquid chromatography fluorescence detector.

(18) 4. Determination of EC in Broth (EXAMPLE 4):

(19) 4 mL of microbial culture is centrifuged at 8000 rpm, 2 mL supernatant and 100 L D5-ethyl carbamate are mixed and then transferred to extraction column for 15 min standing. 15 mL dichloromethane solution is used to elute at about 1 mL/min flow rate, the eluted solution is concentrated by nitrogen to 0.5 mL at room temperature and subsequently add methanol to constant volume of 2.00 mL, after been purified by 0.45 m organic membrane, the result solution is obtained for GC-MS the analysis. The method for determination of ethyl carbamate is according to Chinese national food safety standards with code of GB 5009.223-2014.

(20) 5. Determination of EC or Urea in Fermented Grains (EXAMPLE 5):

(21) 1) determination of urea: 10 g fermented grains and 20 mL sterile water are mixed and ice incubated for 30 min under sonic oscillator treatment, the resulting mixture is centrifuged at 8000 rpm for 5 min, supernatant is collected for HPLC analysis. The method of analysis is disclosed in the paper that published on March 2011 with name of determination of urea in rice wine by high performance liquid chromatography fluorescence detector.

(22) 2) determination of EC: 10 g fermented grains and 20 mL sterile water are mixed and incubated for 30 min, then sonic oscillator treated for 30 min, the resulting mixture is centrifuged at 8000 rpm for 5 min, supernatant is collected for EC analysis. The method for determination of ethyl carbamate is according to Chinese national food safety standards with code of GB 5009.223-2014.

Example 1: Isolation of B. amyloliquefaciens JP21

(23) 1. Strain Isolation and High Throughput Screening;

(24) (1) Isolation of microbes in fermented grains: 0.85% saline and fermented grains is mixed at quality ratio of 1:1.6, the suspension is gradient diluted and plated on the MRS agar medium and YPD agar plate, respectively. The MRS medium is placed at 37 C., and the YPD medium is placed at 30 C. for at least 24 h until single colonies appeared on the plate.

(25) (2) Isolation of strains with capability of utilizing urea or urethane: The colonies on MRS medium and YPD medium are transferred to MRS medium and YPD medium. Both MRS and YPD medium contains 10 g/L urea or urethane, respectively. The strains that been transferred to MRS medium are incubated at 37 C. and the strains been transferred to YPD medium are incubated at 30 C.

(26) (3) Picking and cultivation of strains: 250 L MRS medium is added into each well of 96-well plate, colony been surrounded with purple circle on the plate is transferred to 96-well plate using QPix420 automated microbial screening system, each colony is transferred to three wells and separately incubated at the optimal condition for 24 h. The culture broth is centrifuged at 6000 rpm for 10 min; strain cells are resuspensed with saline and transferred with 1% inoculation amount to medium containing chromogenic agent and urea or urethane. After been incubated for 24 h, strains in the color-changed well that changed from yellow to purple are the candidate strains.

(27) 2. Identification of the Strains:

(28) the candidates are streaked and incubated to colonies, a single colony is transferred to MRS medium and incubated at 37 C. for 24 h; strains are collected, genome of the strain is extracted. The 16S rDNA sequence of the candidate strain is amplified using universal primers. From the blast results from NCBI database, the strain has high homology with B. amyloliquefaciens, and is designated as B. amyloliquefaciens JP21.

Example 2: Enzyme Production of B. amyloliquefaciens JP21

(29) (1) Enzyme preparation: B. amyloliquefaciens JP21 (been screened from EXAMPLE 1) and B. amyloliquefaciens JY06 (been screened from the soy sauce mash, with code CCTCC No: M 2015423.) are both incubated in the medium at 37 C. for 24 h. 50 mL culture broth is centrifuged at 4000 rpm for 10 min, supernatant has been discard and cells precipitate are collected, the precipitate is washed by citrate buffer solution for twice, resuspended by 50 mL solution, and then ice incubated for 30 min before cell broken for 120 s, thus crude enzyme is obtained.

(30) (2) Enzyme assay: The activity of urease and urethanase of the crude enzyme is determined. As it shows that the urease produced from B. amyloliquefaciens JP21 is 0.46 U/mL, and the urethanase is 0.28 U/mL, while no urease or urethanase activity has been detected from crude enzyme produced by B. amyloliquefaciens JY06.

Example 3: Degradation of Urea by B. amyloliquefaciens JP21

(31) (1) Seed culture preparation: B. amyloliquefaciens JP21 and B. amyloliquefaciens JY06 are both incubated in the medium at 37 C. for 24 h. 50 mL culture broth is centrifuged at 4000 rpm for 10 min, supernatant has been discard and cells precipitate are collected, the precipitate is washed by citrate buffer solution for twice, resuspended by 50 mL solution, and then seed culture is obtained.

(32) (2) Inoculation and grains fermentation: The seed culture (with the strain concentration of 610.sup.7 CFU/mL) is inoculated at 1% volume ratio into the medium containing 10 g/L urea and 5 g/L glucose, and then incubated at 37 C. for 24 h. The urea concentration in the culture broth is detected through HPLC.

(33) (3) Results: It is found that, urea in culture broth of B. amyloliquefaciens JP21 is 8.7 g/L, which is at a reduction rate of 13% compared with the initial urea content, while no urea reduction is found in broth of B. amyloliquefaciens JY06.

Example 4: Reduction of EC by B. amyloliquefaciens JP21

(34) Step (1) is carried out according to EXAMPLE 3.

(35) (2) Inoculation and grains fermentation: seed culture is obtained and inoculated into the medium containing 10 g/L urea and 5 g/L glucose, and then incubated at 37 C. for 24 h.

(36) (3) Results: The EC concentration in the culture broth is detected. It is found that, EC in broth of B. amyloliquefaciens JP21 is 9.2 g/L, which is at a reduction rate of 8% compared with the initial EC content, while broth of B. amyloliquefaciens JY06 shows no EC reduction.

Example 5: Effect of Inoculation Size on Grains for Fermentation

(37) (1) Cells preparation: Colony of B. amyloliquefaciens JP21 is picked and inoculated into LB medium, after been incubated at 37 C. for 24 h, culture broth is centrifuged at 8000 rpm for 5 min; strains are collected and resuspended by sterile saline.

(38) (2) Grains fermentation: The cells suspension at a final concentration of 1910.sup.7 CFU/g is inoculated to the grains with different volume of 5, 10, 20, and 30 mL, respectively. The resulting grains are incubated and fermented at 2830 C. for 5 days.

(39) (3) Results: Condition of fermented grains is observed. It shows that, each of the 100 g fermented grains that with 20 mL or 30 mL inoculation volume changed from solid to semi-solid after 5 days anaerobic fermentation, which is greatly distinguished from the real fermentation condition. Besides, the fermented grains with 20 mL or 30 mL inoculation volume shows the odor, acid characteristics of rancidity, indicating microbial system of the fermented grains has been changed. On the contract, each of the 100 g fermented grains with 5 mL or 10 mL inoculation volume keeps normal morphology and smell, which is consistent with normal fermented grains.

Example 6: Comparison of the Urea and EC Reduction Capability of B. amyloliquefaciens JY06 to that of B. amyloliquefaciens JP21

(40) (1) Culture preparation: B. amyloliquefaciens JP21 and B. amyloliquefaciens JY06 are cultivated according to EXAMPLE 5.

(41) (2) Inoculation: The bacterial culture is centrifuged at 8000 rpm for 5 min, strains are collected and resuspended in 0.85% NaCl. The cells suspension at a final concentration of 1910.sup.6 CFU/g is inoculated into the grains with volume of 510 mL.

(42) (3) Grains fermentation: The grains prepared from step (2) is incubated and fermented at 2830 C. for 5 days.

(43) Control: Grains without strains inoculation that incubate and ferment under the same condition according to step (3) is set as the control. The initial concentration of EC and urea in grains is 15 g/kg and 20 mg/kg, respectively.

(44) (4) Results: Content of EC and urea in the fermented grains is determined (as shown in FIG. 1). The EC concentration of fermented grains for the control maintains at about 15 g/kg, while EC in fermented grains that inoculated with 1910.sup.6 CFU/g B. amyloliquefaciens JP21 and JY06 are 11 g/kg and 14 g/kg, respectively, indicating the significant reduction of EC during the fermentation by the addition of 1910.sup.6 CFU/g B. amyloliquefaciens JP21, while B. amyloliquefaciens JY06 shows little effects on the reduction of EC.

(45) The urea concentration of fermented grains (Control) decreases from 20 mg/kg to 19 mg/kg, while the final urea concentration in 5-days fermented grains that inoculated with 1910.sup.6 CFU/g B. amyloliquefaciens JP21 and JY06 are 17 mg/kg and 19 mg/kg, respectively, indicating a slight reduction of urea in grains by B. amyloliquefaciens JP21 and B. amyloliquefaciens JY06.

Example 7: Effect of Addition of B. amyloliquefaciens JY06 and B. amyloliquefaciens JP21 on Urea and EC Reduction

(46) (1) Culture preparation is carried out according to EXAMPLE 6.

(47) (2) Inoculation: The bacterial culture is centrifuged at 8000 rpm for 5 min; strains are collected and resuspended in 0.85% NaCl. The cells suspension at a final concentration of 1910.sup.7 CFU/g is inoculated to the grains with volume of 510 mL, respectively.

(48) (3) Grains fermentation: The grains prepared from step (2) is incubated and fermented at 2830 C. for 5 days.

(49) (4) Results: EC and urea content in fermented grains are determined (as shown in FIG. 2).

(50) The EC concentration of fermented grains (Control) maintains at about 15 g/kg, while EC in fermented grains with 1910.sup.6 CFU/g inoculation of B. amyloliquefaciens JP21 or JY06 is 10 g/kg and 14 g/kg, respectively, indicating inoculation of 1910.sup.7 CFU/g B. amyloliquefaciens JP21 greatly helps to reduce EC content during the grains fermentation while B. amyloliquefaciens JY06 showed little effects.

(51) The urea concentration of fermented grains (Control) decreases from 20 mg/kg to 19 mg/kg, while final urea concentration in 5 days fermented grains with 1910.sup.6 CFU/g inoculation of B. amyloliquefaciens JP21 and JY06 are 9 mg/kg and 20 mg/kg, respectively, indicating 1910.sup.6 CFU/g inoculation of B. amyloliquefaciens JP21 significantly reduces urea content during the fermentation while B. amyloliquefaciens JY06 showed little effects.

(52) (5) Scale-up fermentation: The cells suspension is inoculated at final concentration of 1910.sup.7 CFU/g into volume of 1 L grains for fermentation (each 100 g grains are inoculated with 510 mL cells suspension), and fermented under the same condition with above method. The results show that, content of both EC and urea reduces, meanwhile the flavor of the fermented grains has no significant changes.

Example 8: Comparison of the Effect of Urea and EC Reduction by B. amyloliquefaciens JY06 and B. amyloliquefaciens JP21

(53) (1) Culture preparation is carried according to EXAMPLE 7.

(54) (2) Inoculation: The culture broth is centrifuged at 8000 rpm for 5 min; strains are collected and resuspended by sterile saline. The cells suspension at a final concentration of 1910.sup.7 CFU/g is inoculated to the grains with volume of 510 mL, respectively.

(55) (3) Grains fermentation: The grains prepared from step (2) is incubated and fermented at 2830 C. for 70 days.

(56) (4) Results: EC and urea in fermented grains that fermented for 5 d, 20 d, and 70 d are determined. The initial content of EC and urea in grains are 32 g/kg and 39 mg/kg respectively. Concentration of EC in grains on day 20 increased dramatically, which may result from the production of ethanol production during the fermentation. (Table 1)

(57) (5) Reflux of fermented grains with ethanol: 20 g of fermented grains is mixed with deionized water and ethanol with a final concentration of 65%, the resulting mixture is transferred to a 250 mL flask and refluxed at 85 C. for 45 min to make sure the complete reaction of precursors with ethanol. The grains mixed with B. amyloliquefaciens JY06 or B. amyloliquefaciens JP21 are treated under the same condition. EC concentration of the resulting solution is determined through GC-MS. The EC concentration of the control is 89 g/kg, grains that inoculated with B. amyloliquefaciens JY06 and B. amyloliquefaciens JP21 leads to 73 g/L and 64 g/L after the reflux reaction, which indicating the reduction of EC by B. amyloliquefaciens JY06 and B. amyloliquefaciens JP21 during the liquor production process.

(58) TABLE-US-00001 TABLE 1 Concentration of EC and urea in fermented grains Stains for incubation Fermentation Time (d) EC Urea B. amyloliquefaciens 0 32 39 JY06 5 35 42 20 50 42 70 47 53 B. amyloliquefaciens 0 32 40 JP21 5 33 36 20 46 37 70 43 48 Control 0 32 40 5 38 41 20 53 42 70 52 53

Example 9: Effect of B. amyloliquefaciens JP21 and Urease on Urea and EC Reduction

(59) Since the rapid increase of EC during the initial 20 days fermentation, EC precursors in the fermented grains need to be reduced. The initial concentration of EC and urea of the grains in the present EXAMPLE 9 is 35 g/kg and 35 mg/kg, respectively.

(60) (1) Seed incubation: The Lactobacillus reuteri is inoculated into MRS medium, incubated at 30 C. for 72 h;

(61) (2) Preparation of crude enzyme: the culture broth of step (1) is centrifuged; cells are collected and resuspended using 20 mM, pH 7.0 PBS solution; 0.1 mm-diameter glass beads is added for wall-breaking, after cells' wall breaking, the resulting solution is centrifuged at 10000 rpm for 10 minutes, the supernatant is collected and crude enzyme is obtained.

(62) (3) Grains fermentation: The crude enzyme produced by L. reuteri and 15 mL cells suspension of B. amyloliquefaciens JP21 is inoculated into 150 g grains for fermentation, the final concentration of urease is 0.18 U/g grains, and the final concentration of B. amyloliquefaciens JP21 is 1910.sup.7 CFU/g. The grains after inoculation is fermented anaerobic at 2830 C. for 70 days, which is named as Group C.

(63) Meanwhile, the grains without B. amyloliquefaciens JP21 or urease inoculation is fermented under the same condition according to step (3), which is named as Group A.

(64) Grains only inoculated with B. amyloliquefaciens JP21 is fermented under the same condition according to step (3), which is named as Group B.

(65) The fermented grains from different groups that fermented for 0 d, 5 d, 10 d, 20 d, 30 d, 45 d, 60 d, and 70 d is collected at a quality of 10 g for EC and urea determination.

(66) (4) Results: As shown in Table 2, the urea content of fermented grains from Group A increases to 45 mg/kg during 70 days fermentation. Compared with the Group A, Group B shows 11% urea reduction for 70 days fermentation. Besides, the urea content in fermented grains from Group C decreases more than 60% during the initial 20 days, followed by minor decrease in the next 50 days. The urea content reduces 43% by urease and B. amyloliquefaciens JP21 when the fermentation is done. which indicating combination of urease and B. amyloliquefaciens JP21 is effective in elimination of urea.

(67) As shown in Table 2, EC concentration in fermented grains from Group A increases from 35 g/kg to 58 g/kg during the 70 days fermentation, while that decreases 16% in Group B and 32% in Group C. It can be concluded that, addition of urease and B. amyloliquefaciens JP21 can remarkably eliminate EC formation during grains fermentation.

(68) (5) Reflux of fermented grains with ethanol: The reflux reaction is carried out for fermented grains from different groups according to EXAMPLE 8. FIG. 3 shows that, EC content of the distilled solution from Group A is 99 g/kg, which is 41 g/kg higher than that from fermented grains (at end of the fermentation meanwhile the beginning of the distillation). Compared with the Group A, the content of EC in distilled solution decreases 25% in Group B and 52% in Group C, indicating B. amyloliquefaciens JP21 has capability of reducing EC concentration during the liquor production process including grains fermentation and distillation process. Moreover, inoculation of B. amyloliquefaciens JP21 and urease shows better effects.

(69) TABLE-US-00002 TABLE 2 Concentration of EC and urea in fermented grains Group Fermentation Time (d) EC(g/kg) Urea(mg/kg) Group A 0 35 35 5 37 39 10 39 43 20 53 46 30 49 44 45 55 40 60 57 41 70 58 41 Group B 0 35 35 5 30 34 10 34 36 20 44 41 30 43 35 45 48 36 60 46 37 70 48 41 Group C 0 35 35 5 26 12 10 27 13 20 30 18 30 28 20 45 30 20 60 32 23 70 36 26

(70) While the present invention has been described in some detail for purposes of clarity and understanding, one skilled in the art will appreciate that various changes in form and detail can be made without departing from the true scope of the invention. All figures, tables, appendices, patents, patent applications and publications, referred to above, are hereby incorporated by reference.