Method for flocculating and modifying starch by using compound lactobacillus fermentation preparation

Abstract

The invention discloses a method for flocculating and modifying starch by using a compound lactobacillus fermentation preparation, and belongs to the technical field of starch flocculation modification. According to the method disclosed by the invention, the starch is fermented, flocculated and modified by utilizing a lactic acid bacteria compound fermentation preparation (comprising a leuconostoc mesenteroides SJ-14 fungicide and a leuconostoc citreum SJ-57 fungicide), adopting adaptive pretreatment and adopting specific fermentation conditions, so that the gelatinization performance of the fermented, flocculated and modified starch is improved, the viscosity is remarkably improved, and the starch has the advantages of high viscosity, high yield, high quality and the like. The sweet potato starch prepared by the method has better gel property and texture property, and the adhesiveness, elasticity and chewiness of the starch are obviously improved, so that the eating quality and taste of the sweet potato starch are improved.

Description

Technical Field

[0001] The invention relates to a method for modifying starch, in particular to a method for flocculating and modifying starch by utilizing a composite lactic acid bacteria fermentation preparation, and belongs to the technical field of starch flocculation modification. Background Art

[0002] At present, the traditional starch production process mainly involves washing and crushing starch source materials, and then using water as a medium to separate starch particles from non-starch components. The commonly used separation methods in the starch industry are mainly divided into five categories, namely: launder separation, centrifugal separation, centrifuge cyclone separation, full cyclone separation and sour pulp separation. These separation methods all use the differences in water solubility and density between starch particles and non-starch components to separate starch from fibers, soluble substances, etc. Among them, the first four separation methods all use physical effects such as gravity and centrifugal force to achieve separation, while the sour pulp separation method is a special processing method unique to my country, which mainly uses the action of microorganisms in the sour pulp fermentation process to separate starch.

[0003] However, the traditional method of producing starch still has the following shortcomings:

[0004] The viscosity of starch is relatively low, and the toughness, boiling resistance and palatability of the processed vermicelli (noodles) need to be improved, which in turn limits their edible quality and taste to a certain extent. At the same time, the production of starch using the acid pulp method is unstable due to the complex composition and numerous microorganisms in the acid pulp.

[0005] Although, the prior art "CN111154666A A strain of Leuconostoc citreum with starch agglutination activity" discloses that Leuconostoc citreum SFL-2-8 can promote starch agglutination and accelerate precipitation and separation of various starch slurries such as sweet potato starch and potato starch; "CN111254102A Leuconostoc citreum and its application in precipitating starch slurry" discloses that Leuconostoc citreum WSJ-57 can quickly and fully precipitate starch and improve starch production efficiency; "CN111154667A A high-density culture method of a lactic acid bacteria with starch agglutination effect" discloses that the lactic acid bacteria is Leuconostoc citreum SFL-2-8, which can achieve rapid amplification in a short time to obtain high-concentration bacteria, and the usage is less than 1 / 3 of the traditional "starch slurry", and has high stability. This lays a good foundation for the application of the strain in industrial starch precipitation and separation; "CN112553270A A method for preparing low-calorie dextrin modified with α-1,3 glycosidic bonds" discloses that Leuconostoccitreum NRRL B-742 converts starch into low-calorie dextrin, etc. Summary of the invention

[0006] In order to solve the problems of low viscosity of starch prepared by the prior art, which leads to poor taste of subsequent products, the present invention proposes a method for flocculating and modifying starch using a composite lactic acid bacteria fermentation preparation. In this technical solution, starch is fermented by using a lactic acid bacteria composite preparation to accelerate the sedimentation rate of starch, and the gelatinization performance of the starch after fermentation and modification is improved, the viscosity after gelatinization is significantly improved, and the gelatinization properties and texture properties are better, and the adhesion, elasticity and chewiness are significantly improved, thereby improving the edible quality and taste of the starch.

[0007] In order to achieve the above technical objectives, the following technical solutions are proposed:

[0008] A method for flocculating and modifying starch using a composite lactic acid bacteria fermentation preparation, comprising: mixing starch, the composite lactic acid bacteria fermentation preparation and water evenly at a mass volume ratio of 1:20-30:1.5-3, fermenting at 25-37°C for 20-24h, and then freeze-drying for 40-48h to obtain flocculated and modified starch;

[0009] The lactic acid bacteria composite fermentation preparation includes a mixture of L. mesenteroides SJ-14 and L. citreum SJ-57 in a ratio of 1 to 4:1 to 4.

[0010] Furthermore, the number of viable bacteria in the Leuconostoc mesenteroides SJ-14 bacterial agent is 1×10 9 CFU / mL~5×10 9 CFU / mL.

[0011] Furthermore, the number of viable bacteria in the Leuconostoc citrinum SJ-57 bacterial agent is 1×10 9 CFU / mL~5×10 9 CFU / mL.

[0012] Furthermore, the preparation method of the Leuconostoc mesenteroides SJ-14 bacterial agent comprises:

[0013] 1) Use a sterile inoculating loop to take a loop of Leuconostoc mesenteroides SJ-14 bacterial solution from a -80°C cryopreservation tube and streak it on an MRS agar plate, then incubate it at 37°C for 24 hours;

[0014] 2) Use a sterile inoculating loop to take a single activated colony on the MRS agar plate, add it to 10 mL of MRS liquid culture medium, and culture it at 37°C for 16 to 18 hours to obtain an activated bacterial solution of Leuconostoc mesenteroides SJ-14;

[0015] 3) Using a pipette, take the activated bacterial solution at a 1% inoculation volume and inoculate it into MRS liquid culture medium, and expand the culture at 37° C. until the end of the bacterial growth exponential phase (16 to 18 hours), thereby obtaining the culture solution of Leuconostoc mesenteroides SJ-14 after expansion culture;

[0016] 4) The culture fluid of the expanded cultured Leuconostoc mesenteroides SJ-14 was separated from the culture medium by centrifugation, and resuspended in a sterile 0.1 M PBS solution to obtain a Leuconostoc mesenteroides SJ-14 bacterial agent.

[0017] Furthermore, the preparation method of the Leuconostoc citrinum SJ-57 bacterial agent comprises:

[0018] 1) Use a sterile inoculating loop to take a loop of Leuconostoc citrinum SJ-57 bacterial solution from a -80°C cryopreservation tube and streak it on an MRS agar plate, then incubate it at 37°C for 24 hours;

[0019] 2) Use a sterile inoculating loop to take a single activated colony on the MRS agar plate, add it to 10 mL of MRS liquid culture medium, and culture it at 37°C for 16 to 18 hours to obtain an activated bacterial solution of Leuconostoc citrinum SJ-57;

[0020] 3) Using a pipette, take the activated bacterial solution at a 1% inoculation volume and inoculate it into MRS liquid culture medium, and expand the culture at 37° C. until the end of the bacterial growth exponential phase (16 to 18 hours), to obtain the expanded culture of Leuconostoc citrifolia SJ-57 culture medium;

[0021] 4) The culture fluid of Leuconostoc citrinum SJ-57 after the expanded culture is separated from the culture medium by centrifugation, and resuspended in a sterile 0.1 M PBS solution to obtain a Leuconostoc citrinum SJ-57 bacterial agent.

[0022] Furthermore, the preparation method of the lactic acid bacteria composite fermentation preparation comprises:

[0023] 1) Adjust the OD of Leuconostoc mesenteroides SJ-14 inoculum 600 OD of the Leuconostoc citrinum SJ-57 inoculant 600 equal;

[0024] 2) Mix the intestinal bacteria agent of Leuconostoc mesenteroides SJ-14 and the lemon bacteria agent of Leuconostoc citrinum SJ-57 at a ratio of 1 to 4:1 to 4 to obtain a lactic acid bacteria composite fermentation preparation.

[0025] Furthermore, the method for preparing the starch comprises:

[0026] Wash fresh sweet potatoes, peel them, and cut them into small pieces; add water, mix, and crush (using a crusher) at a mass volume ratio of sweet potato pieces (kg) to water (L) of 1:1.2-1.5, and filter with a 100-mesh filter to remove fibers and other impurities to obtain starch slurry;

[0027] The starch slurry is washed with water for 3 to 5 times, then allowed to stand, the upper clear liquid is removed, and the lower precipitate is centrifuged at a speed of 4000 to 6000 g for 10 to 15 minutes to obtain starch.

[0028] In this technical solution, the water involved is all pure water.

[0029] The beneficial technical effects brought about by adopting this technical solution are:

[0030] The invention utilizes a lactic acid bacteria composite fermentation preparation (including a Leuconostoc mesenteroides SJ-14 bacterial agent and a Leuconostoc citrifolia SJ-57 bacterial agent), adopts a suitable starch pretreatment, and adopts specific fermentation conditions to ferment, flocculate, and modify the starch, thereby ensuring that the gelatinization performance of the starch after fermentation, flocculation, and modification is improved, the viscosity is significantly increased, and the starch has better gel properties and texture properties, and the adhesion, elasticity, and chewiness of the starch are significantly improved, thereby improving the edible quality and taste of the sweet potato starch. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The Fourier transform infrared spectra (FT-IR) of starch after fermentation of different lactic acid bacteria compound fermentation preparations;

[0032] Figure 2 This is the X-ray diffraction spectrum (FT-IR) of starch after fermentation with different lactic acid bacteria composite fermentation preparations. DETAILED DESCRIPTION

[0033] The present invention is further illustrated below through the description of specific implementation modes, but this is not a limitation of the present invention. Those skilled in the art can make various modifications or improvements based on the basic idea of ​​the present invention, but as long as they do not deviate from the basic idea of ​​the present invention, they are all within the scope of the present invention.

[0034] In the following examples, Leuconostoc citreum SJ-57 (L. citreum SJ-57) was deposited in the General Microbiology Center of China National Microbiological Culture Collection Administration on December 20, 2019, with the deposit number CGMCC No. 19201.

[0035] Example 1

[0036] Use a sterile inoculation loop to take a loop of bacterial solution from a -80℃ cryopreservation tube and streak it on an MRS agar plate. Incubate it at 37℃ for 24h. Use a sterile inoculation loop to take a single activated colony on the MRS agar plate, add it to 10mL MRS liquid culture medium, and incubate it at 37℃ for 18h. Use a pipette to take the activated bacterial solution and inoculate it into MRS liquid culture medium at a 1% inoculation rate. Expand the culture under the same conditions for 18h until the end of the bacterial growth exponential phase. Place it in a 4℃ refrigerator for later use.

[0037] The bacterial liquid was Leuconostoc mesenteroides SJ-14 (L. mesenteroides SJ-14) and Leuconostoc citreum SJ-57 (L. citreum SJ-57) preserved in the laboratory. The number of viable bacteria after expansion culture was 1×10 9 CFU / mL. The two strains were resuspended in PBS solution and adjusted to the same OD 600 (range 1.2-1.6), and prepared as a lactic acid bacteria compound fermentation preparation in a 1:1 ratio.

[0038] Fresh sweet potatoes were washed, peeled, and cut into small pieces. The sweet potato pieces were mixed with water at a ratio of 1:1.5 (g / mL), and crushed in a crusher. The resulting mixture was filtered with a 100-mesh nylon cloth to remove fibers and other impurities to obtain starch slurry. The slurry was washed with distilled water for 3 times and left overnight. The supernatant was skimmed off, and the lower starch slurry was centrifuged at a speed of 6000g for 15 minutes to obtain starch.

[0039] The extracted starch was mixed with the lactic acid bacteria composite fermentation preparation and water in a ratio of 1:25:2 (g; mL; mL) and fermented at 25°C for 24 hours. The starch obtained after fermentation (SJ-14:SJ-57-1:1) was freeze-dried for 48 hours and collected.

[0040] Example 2

[0041] Use a sterile inoculation loop to take a loop of bacterial solution from a -80℃ cryopreservation tube and streak it on an MRS agar plate. Incubate it at 37℃ for 24h. Use a sterile inoculation loop to take a single activated colony on the MRS agar plate, add it to 10mL MRS liquid culture medium, and incubate it at 37℃ for 18h. Use a pipette to take the activated bacterial solution and inoculate it into MRS liquid culture medium at a 1% inoculation rate. Expand the culture under the same conditions for 18h until the end of the bacterial growth exponential phase. Place it in a 4℃ refrigerator for later use.

[0042] The bacterial liquid was Leuconostoc mesenteroides SJ-14 (L. mesenteroides SJ-14) and Leuconostoc citreum SJ-57 (L. citreum SJ-57) preserved in the laboratory. The number of viable bacteria after expansion culture was 1×10 9 CFU / mL. The two strains were resuspended in PBS solution and adjusted to the same OD 600 (Range 1.2-1.6), prepared as a lactic acid bacteria compound fermentation preparation in a ratio of 1:2.

[0043] Fresh sweet potatoes were washed, peeled, and cut into small pieces. The sweet potato pieces were mixed with water at a ratio of 1:1.5 (g / mL), and crushed in a crusher. The resulting mixture was filtered with a 100-mesh nylon cloth to remove fibers and other impurities to obtain starch slurry. The slurry was washed with distilled water for 3 times and left overnight. The supernatant was skimmed off, and the lower starch slurry was centrifuged at a speed of 6000g for 15 minutes to obtain starch.

[0044] The extracted starch was mixed with the lactic acid bacteria composite fermentation preparation and water in a ratio of 1:25:2 (g; mL; mL) and fermented at 25°C for 24 hours. The starch obtained after fermentation (SJ-14:SJ-57-1:2) was freeze-dried for 48 hours and collected.

[0045] Example 3

[0046] Use a sterile inoculation loop to take a loop of bacterial solution from a -80℃ cryopreservation tube and streak it on an MRS agar plate. Incubate it at 37℃ for 24h. Use a sterile inoculation loop to take a single activated colony on the MRS agar plate, add it to 10mL MRS liquid culture medium, and incubate it at 37℃ for 18h. Use a pipette to take the activated bacterial solution and inoculate it into MRS liquid culture medium at a 1% inoculation rate. Expand the culture under the same conditions for 18h until the end of the bacterial growth exponential phase. Place it in a 4℃ refrigerator for later use.

[0047] The bacterial liquid was Leuconostoc mesenteroides SJ-14 (L. mesenteroides SJ-14) and Leuconostoc citreum SJ-57 (L. citreum SJ-57) preserved in the laboratory. The number of viable bacteria after expansion culture was 1×10 9 CFU / mL. The two strains were resuspended in PBS solution and adjusted to the same OD 600 (range 1.2-1.6), and prepared as a lactic acid bacteria compound fermentation preparation in a ratio of 2:1.

[0048] Fresh sweet potatoes were washed, peeled, and cut into small pieces. The sweet potato pieces were mixed with water at a ratio of 1:1.5 (g / mL), and crushed in a crusher. The resulting mixture was filtered with a 100-mesh nylon cloth to remove fibers and other impurities to obtain starch slurry. The slurry was washed with distilled water for 3 times and left overnight. The supernatant was skimmed off, and the lower starch slurry was centrifuged at a speed of 6000g for 15 minutes to obtain starch.

[0049] The extracted starch was mixed with the lactic acid bacteria composite fermentation preparation and water in a ratio of 1:25:2 (g; mL; mL) and fermented at 25°C for 24 hours. The starch obtained after fermentation (SJ-14:SJ-57-2:1) was freeze-dried for 48 hours and collected.

[0050] Example 4

[0051] Use a sterile inoculation loop to take a loop of bacterial solution from a -80℃ cryopreservation tube and streak it on an MRS agar plate. Incubate it at 37℃ for 24h. Use a sterile inoculation loop to take a single activated colony on the MRS agar plate, add it to 10mL MRS liquid culture medium, and incubate it at 37℃ for 18h. Use a pipette to take the activated bacterial solution and inoculate it into MRS liquid culture medium at a 1% inoculation rate. Expand the culture under the same conditions for 18h until the end of the bacterial growth exponential phase. Place it in a 4℃ refrigerator for later use.

[0052] The bacterial liquid was Leuconostoc mesenteroides SJ-14 (L. mesenteroides SJ-14) and Leuconostoc citreum SJ-57 (L. citreum SJ-57) preserved in the laboratory. The number of viable bacteria after expansion culture was 1×10 9 CFU / mL. The two strains were resuspended in PBS solution and adjusted to the same OD 600 (Range 1.2-1.6), prepared as a lactic acid bacteria compound fermentation preparation in a ratio of 1:4.

[0053] Fresh sweet potatoes were washed, peeled, and cut into small pieces. The sweet potato pieces were mixed with water at a ratio of 1:1.5 (g / mL), and crushed in a crusher. The resulting mixture was filtered with a 100-mesh nylon cloth to remove fibers and other impurities to obtain starch slurry. The slurry was washed with distilled water for 3 times and left overnight. The supernatant was skimmed off, and the lower starch slurry was centrifuged at a speed of 6000g for 15 minutes to obtain starch.

[0054] The extracted starch was mixed with the lactic acid bacteria composite fermentation preparation and water in a ratio of 1:25:2 (g; mL; mL) and fermented at 25°C for 24 hours. The starch obtained after fermentation (SJ-14:SJ-57-1:4) was freeze-dried for 48 hours and collected.

[0055] Example 5

[0056] Use a sterile inoculation loop to take a loop of bacterial solution from a -80℃ cryopreservation tube and streak it on an MRS agar plate. Incubate it at 37℃ for 24h. Use a sterile inoculation loop to take a single activated colony on the MRS agar plate, add it to 10mL MRS liquid culture medium, and incubate it at 37℃ for 18h. Use a pipette to take the activated bacterial solution and inoculate it into MRS liquid culture medium at a 1% inoculation rate. Expand the culture under the same conditions for 18h until the end of the bacterial growth exponential phase. Place it in a 4℃ refrigerator for later use.

[0057] The bacterial liquid was Leuconostoc mesenteroides SJ-14 (L. mesenteroides SJ-14) and Leuconostoc citreum SJ-57 (L. citreum SJ-57) preserved in the laboratory. The number of viable bacteria after expansion culture was 1×10 9 CFU / mL. The two strains were resuspended in PBS solution and adjusted to the same OD 600 (range 1.2-1.6), and prepared as a lactic acid bacteria compound fermentation preparation in a ratio of 4:1.

[0058] Fresh sweet potatoes were washed, peeled, and cut into small pieces. The sweet potato pieces were mixed with water at a ratio of 1:1.5 (g / mL), and crushed in a crusher. The resulting mixture was filtered with a 100-mesh nylon cloth to remove fibers and other impurities to obtain starch slurry. The slurry was washed with distilled water for 3 times and left overnight. The supernatant was skimmed off, and the lower starch slurry was centrifuged at a speed of 6000g for 15 minutes to obtain starch.

[0059] The extracted starch was mixed with the lactic acid bacteria composite fermentation preparation and water in a ratio of 1:25:2 (g; mL; mL) and fermented at 25°C for 24 hours. The starch (SJ-14:SJ-57-4:1) obtained after fermentation was freeze-dried for 48 hours and collected.

[0060] Comparative Example 1

[0061] Fresh sweet potatoes were washed, peeled, and cut into small pieces. The sweet potato pieces were mixed with water at a ratio of 1:1.5 (g / mL), and crushed in a crusher. The resulting mixture was filtered with a 100-mesh nylon cloth to remove fibers and other impurities to obtain starch slurry. The slurry was washed with distilled water for 3 times and left overnight. The supernatant was skimmed off, and the lower starch slurry was centrifuged at a speed of 6000g for 15 minutes to obtain starch.

[0062] The starch (Control) was freeze-dried for 48 h and then collected.

[0063] Comparative Example 2

[0064] Use a sterile inoculation loop to take a loop of bacterial solution from a -80℃ cryopreservation tube and streak it on an MRS agar plate. Incubate it at 37℃ for 24h. Use a sterile inoculation loop to take a single activated colony on the MRS agar plate, add it to 10mL MRS liquid culture medium, and incubate it at 37℃ for 18h. Use a pipette to take the activated bacterial solution and inoculate it into MRS liquid culture medium at a 1% inoculation rate. Expand the culture under the same conditions for 18h until the end of the bacterial growth exponential phase. Place it in a 4℃ refrigerator for later use.

[0065] The bacterial liquid was Leuconostoc mesenteroides SJ-14 (L. mesenteroides SJ-14) preserved in the laboratory, and the number of viable bacteria after expansion culture was 1×10 9 CFU / mL. Resuspend the strain in PBS solution and adjust to the same OD as the lactic acid bacteria composite fermentation preparation. 600 (Range between 1.2-1.6).

[0066] Fresh sweet potatoes were washed, peeled, and cut into small pieces. The sweet potato pieces were mixed with water at a ratio of 1:1.5 (g / mL), and crushed in a crusher. The resulting mixture was filtered with a 100-mesh nylon cloth to remove fibers and other impurities to obtain starch slurry. The slurry was washed with distilled water for 3 times and left overnight. The supernatant was skimmed off, and the lower starch slurry was centrifuged at a speed of 6000g for 15 minutes to obtain starch.

[0067] The extracted starch was mixed with L. mesenteroides SJ-14 PBS solution and water in a ratio of 1:25:2 (g; mL; mL) and fermented at 25° C. for 24 h. The starch (SJ-14) obtained after fermentation was freeze-dried for 48 h and collected.

[0068] Comparative Example 3

[0069] Use a sterile inoculation loop to take a loop of bacterial solution from a -80℃ cryopreservation tube and streak it on an MRS agar plate. Incubate it at 37℃ for 24h. Use a sterile inoculation loop to take a single activated colony on the MRS agar plate, add it to 10mL MRS liquid culture medium, and incubate it at 37℃ for 18h. Use a pipette to take the activated bacterial solution and inoculate it into MRS liquid culture medium at a 1% inoculation rate. Expand the culture under the same conditions for 18h until the end of the bacterial growth exponential phase. Place it in a 4℃ refrigerator for later use.

[0070] The bacterial liquid was Leuconostoc citreum SJ-57 (L. citreum SJ-57) preserved in the laboratory, and the number of viable bacteria after expansion culture was 1×10 9 CFU / mL. Resuspend the strain in PBS solution and adjust to the same OD as the lactic acid bacteria composite fermentation preparation. 600 (Range between 1.2-1.6).

[0071] Fresh sweet potatoes were washed, peeled, and cut into small pieces. The sweet potato pieces were mixed with water at a ratio of 1:1.5 (g / mL), and crushed in a crusher. The resulting mixture was filtered with a 100-mesh nylon cloth to remove fibers and other impurities to obtain starch slurry. The slurry was washed with distilled water for 3 times and left overnight. The supernatant was skimmed off, and the lower starch slurry was centrifuged at a speed of 6000g for 15 minutes to obtain starch.

[0072] The extracted starch was mixed with L. citreum SJ-57 PBS solution and water in a ratio of 1:25:2 (g; mL; mL) and fermented at 25° C. for 24 h. The starch (SJ-57) obtained after fermentation was freeze-dried for 48 h and collected.

[0073] 1. Analyze the structure of starch by Fourier transform infrared spectroscopy (FT-IR). Use Fourier transform infrared spectrometer at 4000-400 cm-1 The spectral curve is recorded within the scanning range with a resolution of 4cm -1 The scanning times are 64 times, and the results are shown in Figure 1 .

[0074] Depend on Figure 1 It can be seen that the natural starch and the starch fermented by the strain are at 4000-400cm -1 The absorption peak positions and shapes in the wavenumber region are similar, and no new absorption peaks are found in the spectrum after fermentation, indicating that the short-range ordered structure of starch is not affected after fermentation. -1 The absorption intensity showed an increasing trend, indicating that fermentation strengthened the hydrogen bonds between and within starch molecules. The short chain lengths produced during fermentation have strong intermolecular interactions and bring them together. By calculation, the 995 / 1020cm -1 and 1047 / 1020cm -1 The results showed that the starch had a higher crystallinity and structural order after fermentation with lactic acid bacteria compound fermentation agent, and the structural stability of starch was the highest when the compound fermentation agent was SJ-14:SJ-57-4:1, and the gel performance was also the highest.

[0075] 2. The X-ray spectrum of starch was measured by X-ray diffractometer. The working conditions of the diffractometer were 40kV, 40mA. The diffraction angle (2θ) scanning range was 3° to 60°, the scanning step width was 0.02°, and the scanning rate was 4° / min. The measurement results are shown in Figure 2 .

[0076] Depend on Figure 2 It can be seen that the effect of treatment on starch structure is determined by XRD spectra of natural starch and fermented starch. The RC value is calculated by the ratio of peak area to total diffraction area. Compared with natural starch (RC = 32.71%), the relative crystallinity of starch after fermentation is significantly improved, mainly due to the hydrolysis of amorphous and partially crystalline regions during the fermentation process. α-Amylase effectively acts on crystalline and amorphous components during the hydrolysis of starch granules, and the ratio of crystalline area to amorphous area changes uncertainly. When the degree of damage to the amorphous region is greater than that of the crystalline region, the RC of starch tends to increase. When the degree of damage to the crystalline region exceeds that of the amorphous region, the crystallinity will increase. Therefore, the crystalline region is more resistant to the influence of fermentation than the loose amorphous region, and the influence of fermentation on starch structure may be mainly concentrated in the amorphous region of starch. The increase of organic acids during fermentation provides a suitable pH environment, which may help the starch chains in the amorphous region to form hydrogen bonds with the starch side chains.

[0077] 3. Determine the content of amylose in starch. The results are shown in Table 1.

[0078] Table 1 Amylose and amylopectin content of starch

[0079]

[0080]

[0081] As shown in Table 1, the difference in the content of amylose between natural starch and fermented starch is significant. The decrease in the content of amylose after fermentation of the composite lactic acid bacteria fermentation preparation may be due to the degradation of amylose by microbial fermentation, and the enzymes produced by bacteria destroy the amylose. The amorphous regions rich in amylose in starch granules may also be hydrolyzed by metabolites, resulting in the leaching of amylose. In addition, the lactic acid formed during the fermentation process may also contribute to the reduction of amylose.

[0082] 4. Determine the texture properties of starch gel by texture analyzer. Mix the starch sample with distilled water in a ratio of 3:4 to prepare a starch suspension. Then heat it to 100°C in a fixed film mold to obtain a warm paste cube with fixed length, width and height, and store it at 4°C for 24 hours to form a stable gel. Use P36 / R probe for measurement. Texture measurement conditions are: speed before measurement 1.0mm / s, measurement speed 1.0mm / s, speed after measurement 1.0mm / s, trigger force 5.0g, compression ratio 70%. Repeat the measurement for each sample at least 3 times. The measurement results are shown in Table 2.

[0083] Table 2 Gel texture parameters of starch

[0084] sample Adhesion(g) Elasticity Cohesion Adhesion(g) Chewing properties (mJ) Blank control <![CDATA[1.33±0.29 a ]]> <![CDATA[0.82±0.06 bcd ]]> <![CDATA[0.62±0.13 a ]]> <![CDATA[2182.27±770.52 ab ]]> <![CDATA[69.6±39.94 b ]]> SJ-14 <![CDATA[0.67±0.29 bc ]]> <![CDATA[0.84±0.01 abcd ]]> <![CDATA[0.79±0.12 a ]]> <![CDATA[3043.70±787.42 a ]]> <![CDATA[84.19±25.42 ab ]]> SJ-57 <![CDATA[0.67±0.29 bc ]]> <![CDATA[0.70±0.00 ef ]]> <![CDATA[0.71±0.03 a ]]> <![CDATA[1583.63±34.10 b ]]> <![CDATA[57.72±18.35 b ]]> SJ-14:SJ-57-1:1 <![CDATA[1.17±0.29 ab ]]> <![CDATA[0.88±0.02 d ]]> <![CDATA[0.55±0.11 a ]]> <![CDATA[2094.63±1022.4 ab ]]> <![CDATA[55.97±31.15 b ]]> SJ-14:SJ-57-1:2 <![CDATA[0.83±0.58 abc ]]> <![CDATA[0.88±0.00 cd ]]> <![CDATA[0.76±0.11 a ]]> <![CDATA[3270.47±596.8 a ]]> <![CDATA[123.01±25.59 a ]]> SJ-14:SJ-57-2:1 <![CDATA[1±0.50 abc ]]> <![CDATA[0.91±0.02 a ]]> <![CDATA[0.68±0.14 a ]]> <![CDATA[2300.53±530.48 ab ]]> <![CDATA[64.29±15.64 b ]]> SJ-14:SJ-57-1:4 <![CDATA[0.5±0.00 c ]]> <![CDATA[0.87±0.03 abc ]]> <![CDATA[0.69±0.14 a ]]> <![CDATA[2282.53±860.26 ab ]]> <![CDATA[62.06±26.52 b ]]> SJ-14:SJ-57-4:1 <![CDATA[1±0.00 abc ]]> <![CDATA[0.89±0.01 ab ]]> <![CDATA[0.70±0.05 a ]]> <![CDATA[3231.73±293.06 a ]]> <![CDATA[89.01±9.08 ab ]]>

[0085] As shown in Table 2, compared with ordinary starch, the gel properties of the fermented modified starch are improved, with better gel properties and texture properties. Adhesion, elasticity and chewiness are significantly improved. When the ratio of SJ-14 to SJ-57 in the composite lactic acid bacteria fermentation preparation is 1:2, the chewiness of the starch gel is the best, and the adhesiveness is also the best. The method provided by the present invention improves the edible quality and taste of starch.

[0086] 5. Prepare the starch into vermicelli (write the steps for preparing vermicelli here) and test its properties.

[0087] The color of vermicelli was measured by a colorimeter. The vermicelli sample was placed in a measuring pan, and the L*, a* and b* of the sample were measured respectively. The experiment was repeated three times, L* represents white / black, a* represents red / green, and b* represents yellow / blue. The measurement results are shown in Table 3.

[0088] Table 3 Chromaticity value of vermicelli

[0089] sample L* a* b* ΔE Blank control <![CDATA[-21.48±1.13 b ]]> <![CDATA[1.03±0.46 a ]]> <![CDATA[4.44±1.19 a ]]> <![CDATA[22.07±1.03 b ]]> SJ-14 <![CDATA[-24.65±2.01 bc ]]> <![CDATA[0.56±0.35 a ]]> <![CDATA[3.23±0.19 b ]]> <![CDATA[24.87±2 ab <!-- 7 -->]]> SJ-57 <![CDATA[-25.04±3.25 bc ]]> <![CDATA[0.38±0.46 a ]]> <![CDATA[3.18±0.25 b ]]> <![CDATA[25.24±3.26 ab ]]> SJ-14:SJ-57-1:1 <![CDATA[-25.49±0.78 c ]]> <![CDATA[0.09±0.19 a ]]> <![CDATA[3.15±0.3 b ]]> <![CDATA[25.69±0.77 ab ]]> SJ-14:SJ-57-1:2 <![CDATA[-23.12±0.82 bc ]]> <![CDATA[0.14±0.22 a ]]> <![CDATA[3.02±0.43 b ]]> <![CDATA[23.32±0.85 ab ]]> SJ-14:SJ-57-2:1 <![CDATA[-26.34±0.33 c ]]> <![CDATA[0.62±1.52 a ]]> <![CDATA[3.35±0.73 b ]]> <![CDATA[26.59±0.25 a ]]> SJ-14:SJ-57-1:4 <![CDATA[-17.74±3.24 a ]]> <![CDATA[1.5±1.02 a ]]> <![CDATA[3.01±0.35 b ]]> <![CDATA[18.06±3.33 c ]]> SJ-14:SJ-57-4:1 <![CDATA[-24.11±2.01 bc ]]> <![CDATA[1.42±0.85 a ]]> <![CDATA[3.14±0.41 b ]]> <![CDATA[24.37±2.01 ab ]]>

[0090] As shown in Table 3, compared with ordinary starch, the vermicelli prepared from fermented modified starch shows differences in color. Compared with vermicelli prepared from ordinary starch, vermicelli prepared from fermented modified starch has a brighter color and higher whiteness. On the contrary, vermicelli prepared from ordinary starch has a yellower appearance. The method provided by the present invention improves the appearance and color of starch vermicelli.

[0091] 6. Determine the broken rate of vermicelli. Take 20 vermicelli samples with a length of 10 cm, boil them in 500 mL of boiling distilled water for 20 minutes, and record the total number of broken vermicelli after cooking. Calculate the broken rate of vermicelli according to the formula:

[0092]

[0093] The measurement results are shown in Table 4.

[0094] Table 4 Breakage rate of vermicelli

[0095]

[0096]

[0097] As shown in Table 4, compared with ordinary starch, the vermicelli prepared from fermented modified starch has better tensile properties. Through the broken rate test, we found that after cooking in boiling water for 20 minutes, the broken rate of vermicelli prepared from ordinary starch is much higher than that of vermicelli prepared from fermented modified starch, and when the ratio of SJ-14 to SJ-57 in the composite lactic acid bacteria fermentation preparation is 1:2, the broken rate of vermicelli is the lowest. It shows that the method provided by the present invention effectively improves the toughness and cooking characteristics of starch vermicelli.

Claims

1. A method for flocculating and modifying starch using a composite lactic acid bacteria fermentation preparation, characterized in that: include: The starch, the lactic acid bacteria composite fermentation preparation and water are mixed evenly in a mass volume ratio of 1:20-30:1.5-3, fermented at 25-37°C for 20-24h, and then freeze-dried for 40-48h to obtain flocculated and modified starch; Among them, the lactic acid bacteria compound fermentation preparation includes the intestinal bacteria SJ-14 agent and the lemon bacteria SJ-57 agent in a ratio of 1 to 4:1 to 4.

2. The method for flocculating and modifying starch using a composite lactic acid bacteria fermentation preparation according to claim 1, characterized in that: The number of live bacteria in the Leuconostoc mesenteroides SJ-14 bacterial agent is 1×10 9 CFU / mL~5×10 9 CFU / mL.

3. The method for flocculating and modifying starch using a composite lactic acid bacteria fermentation preparation according to claim 2, characterized in that: The method for preparing the Leuconostoc mesenteroides SJ-14 bacterial agent comprises: 1) Use a sterile inoculating loop to take a loop of Leuconostoc mesenteroides SJ-14 bacterial solution from a -80℃ cryopreservation tube and streak it on an MRS agar plate. Incubate it at 37℃ for 24 h. 2) Use a sterile inoculation loop to take a single activated colony on the MRS agar plate, add it to 10 mL of MRS liquid culture medium, and culture it at 37°C for 16 to 18 hours to obtain an activated bacterial solution of Leuconostoc mesenteroides SJ-14; 3) Use a pipette to transfer the activated bacterial solution to MRS liquid culture medium at a 1% inoculation volume, and expand the culture at 37°C until the end of the bacterial growth exponential phase to obtain the culture solution of Leuconostoc mesenteroides SJ-14; 4) The culture fluid of the expanded Leuconostoc mesenteroides SJ-14 is separated from the culture medium by centrifugation, and resuspended in a sterile 0.1 M PBS solution to obtain a Leuconostoc mesenteroides SJ-14 bacterial agent.

4. The method for flocculating and modifying starch using a composite lactic acid bacteria fermentation preparation according to claim 1, characterized in that: The number of live bacteria in the Leuconostoc citrinum SJ-57 bacterial agent is 1×10 9 CFU / mL~5×10 9 CFU / mL.

5. The method for flocculating and modifying starch using a composite lactic acid bacteria fermentation preparation according to claim 4, characterized in that: The method for preparing the Leuconostoc citrinum SJ-57 bacterial agent comprises: 1) Use a sterile inoculating loop to take a loop of Leuconostoc citrinum SJ-57 bacterial solution from a -80℃ cryopreservation tube and streak it on an MRS agar plate. Incubate it at 37℃ for 24 h. 2) Use a sterile inoculation loop to take a single activated colony on the MRS agar plate, add it to 10 mL of MRS liquid culture medium, and culture it at 37°C for 16 to 18 hours to obtain the activated bacterial solution of Leuconostoc citrinum SJ-57; 3) Use a pipette to transfer the activated bacterial solution to MRS liquid culture medium at a 1% inoculation volume, and expand the culture at 37°C until the end of the bacterial growth exponential phase to obtain the expanded culture of Leuconostoc citrifolia SJ-57; 4) The culture fluid of Leuconostoc citrinum SJ-57 after expansion culture is separated from the culture medium by centrifugation and resuspended in a sterile 0.1 M PBS solution to obtain Leuconostoc citrinum SJ-57 bacterial agent.

6. The method for flocculating and modifying starch using a composite lactic acid bacteria fermentation preparation according to any one of claims 1 to 5, characterized in that: The preparation method of the lactic acid bacteria composite fermentation preparation comprises: 1) Adjust the OD of Leuconostoc mesenteroides SJ-14 inoculum 600 OD of the Leuconostoc citrinum SJ-57 inoculant 600 equal; 2) Mix the intestinal bacteria SJ-14 and the lemon bacteria SJ-57 at a ratio of 1-4:1-4 to obtain a lactic acid bacteria composite fermentation preparation.

7. The method for flocculating and modifying starch using a composite lactic acid bacteria fermentation preparation according to claim 6, characterized in that: And OD 600 It is 1.2 to 1.

6.

8. The method for flocculating and modifying starch using a composite lactic acid bacteria fermentation preparation according to claim 1, characterized in that: The method for preparing the starch comprises: Wash fresh sweet potatoes, peel them, and cut them into small pieces; add water, mix, and crush them in a mass volume ratio of sweet potato pieces to water of 1:1.2-1.5, and filter them with a 100-mesh filter to remove fibers and other impurities to obtain starch slurry; The starch slurry is washed with water for 3 to 5 times, then allowed to stand, the upper clear liquid is removed, and the lower precipitate is centrifuged at a speed of 4000 to 6000 g for 10 to 15 min to obtain starch.

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