Method for synchronously producing crude protein and biolipid through kitchen waste fermentation and application

Abstract

The invention provides a kitchen waste fermentation method based on a steam explosion technology. The method comprises the following steps: firstly, treating the kitchen waste by utilizing a steam explosion technology, so that macromolecular components such as starch, protein and fibers in the kitchen waste are degraded into relatively small molecular substances, and grease adsorbed in the small molecular substances is fully released; then inoculating enzymes and fermentation strains to carry out synchronous saccharification and fermentation on the kitchen waste, and converting nutritional ingredients such as fermentable sugar generated by degradation of starch and fibers and short peptides, amino acids and the like generated by degradation of proteins into microbial single-cell proteins; finally, protein powder and a biological oil product are respectively obtained through oil-water-residue three-phase separation. The invention provides a method capable of realizing efficient resource utilization of kitchen waste.

Description

Technical Field

[0001] The invention belongs to the field of resource utilization of organic waste, relates to a technology for resource utilization of kitchen waste, and specifically relates to a method and application of synchronously producing crude protein and bio-oil by fermenting kitchen waste. Background Art

[0002] The main components of food waste include rice, noodles, meat, bones, vegetables, fruit residues, etc. Since food waste is nutritious and contains a variety of proteins, fibers, sugars and oils, which are suitable for the growth of microorganisms, the resource utilization of food waste through fermentation technology has become one of the effective means of food waste treatment. At present, the production of biogas by anaerobic digestion of food waste, the production of fertilizers by aerobic fermentation, and the preparation of protein feed have gradually become the mainstream. The process of preparing feed protein by fermenting food waste is particularly popular due to its obvious economic value. However, due to the low content of sugar in food waste that can be directly fermented by microorganisms, the existing fermentation process for preparing feed protein generally has problems such as low protein content in the final product, the need to add auxiliary materials (such as wheat bran, etc.) to supplement sugar, high energy consumption for raw material sterilization, and insufficient utilization of fiber components in food waste. Therefore, how to improve the utilization rate of fiber components, thereby increasing the supply of fermentable sugars, simplify the fermentation process, reduce energy consumption, and ultimately increase the protein content of the final product and enhance the economic value of the product is the focus of urgent research and solution in the iterative upgrading of existing processes. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a method and application of synchronously producing crude protein and bio-oil by fermenting kitchen waste.

[0004] 1. In a first aspect, the present invention provides a method for simultaneously producing crude protein and bio-oil by fermenting kitchen waste, comprising the following steps:

[0005] S1. Screening the food waste to separate impurities and then coarsely crushing it;

[0006] S2. The crushed food waste is subjected to steam explosion treatment to obtain a food waste slurry;

[0007] S3. Adding enzyme preparations and fermentation bacteria to the food waste slurry for simultaneous saccharification and fermentation;

[0008] S4. The fermented food waste is squeezed to remove solid impurities to obtain an organic slurry;

[0009] S5. The organic slurry is subjected to three-phase separation to recover bio-oil and solid residue, and the solid residue is dried to obtain crude protein;

[0010] In step S2, the specific conditions of the steam explosion treatment are: treatment at a pressure of 0.1-1.5 MPa for 1-10 min.

[0011] Preferably, in step S1, the coarse crushing method includes any one of shear crushing, hammer crushing and tearing crushing.

[0012] Preferably, in step S3, the enzyme comprises at least one of saccharifying enzyme, amylase, cellulase, xylanase, pectinase and protease.

[0013] Preferably, the enzyme preparation is a compound of amylase, saccharifying enzyme, cellulase, xylanase, protease and pectinase, and the enzyme activity ratio of the saccharifying enzyme, amylase, cellulase, xylanase, pectinase and protease is 10:50:30:20:50:10. The ratio of the enzyme preparation to the food waste slurry is 170U:1g.

[0014] Preferably, in step S3, the fermentation bacteria include at least one of Bacillus licheniformis, Bacillus subtilis, Candida utilis, Saccharomyces cerevisiae, Enterococcus faecalis, Enterococcus faecium, Pediococcus acidilactici, Bacillus coagulans, Lactobacillus brevis, Lactobacillus fermentum and Aspergillus niger.

[0015] Preferably, the fermentation strain is one of the following (a)-(b):

[0016] (a) the fermentation bacteria is a mixture of Bacillus subtilis, Bacillus licheniformis and Candida utilis, and the inoculation ratio of Bacillus subtilis, Bacillus licheniformis and Candida utilis is 1:1:1;

[0017] (b) The fermentation bacteria is a mixture of Bacillus subtilis, Saccharomyces cerevisiae and Candida utilis, and the inoculation ratio of Bacillus subtilis, Saccharomyces cerevisiae and Candida utilis is 1:1:1.

[0018] More preferably, the fermentation bacteria is a mixture of Bacillus subtilis, Bacillus licheniformis and Candida utilis, and the inoculation ratio of Bacillus subtilis, Bacillus licheniformis and Candida utilis is 1:1:1.

[0019] Preferably, in step S2, the specific conditions of the steam explosion treatment are: treatment at a pressure of 0.5-1.5 MPa for 1-10 min.

[0020] More preferably, in step S2, the specific conditions of the steam explosion treatment are: treatment at a pressure of 1 MPa for 5 minutes.

[0021] Preferably, in step S3, the specific conditions of the fermentation are: fermentation at 28-40° C. for 24-120 h.

[0022] Preferably, the specific conditions of the fermentation are: fermentation at 36° C. for 48 h.

[0023] In a second aspect, the present invention provides application of the method described in producing crude protein and / or bio-oil using food waste.

[0024] The present invention has the following beneficial effects: (1) Before steam explosion of food waste, the method of the present invention only needs to perform coarse crushing, and the material is sterilized and finely crushed simultaneously by steam explosion. Since no special fine crushing process such as pulping or homogenization is required, energy consumption is saved. In addition, compared with the traditional high temperature and high pressure sterilization method, steam explosion has lower energy consumption. (2) Steam explosion will cause the protein, starch, fiber and other components in the material to degrade, generate short-chain small molecules, so that the adsorbed oil is fully released, and at the same time increase the nutrients required for the growth of fermentation microorganisms, promote microorganisms to convert various nutrients into single-cell proteins, thereby increasing the protein content of the final product. (3) When using steam explosion to treat food waste, no additional chemical reagents need to be added, no additional pollution is generated, and the reagent consumption cost is saved. (4) Since the steam explosion process accelerates the degradation of fiber components, the subsequent enzymatic hydrolysis efficiency is improved, more fermentable sugars are provided for fermentation microorganisms to use, and no auxiliary materials are required to supplement sugar during the fermentation process, which simplifies the production process and reduces costs. (5) The method of the present invention can simultaneously produce bio-oil and protein powder, thereby achieving harmless treatment of food waste and efficient resource utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 . Process flow chart of the present invention.

[0026] Figure 2 . Effects of different steam explosion pressures on the growth of fermentation bacteria and the protein content of fermentation products.

[0027] Figure 3 . Effects of different steam explosion times on the growth of fermentation bacteria and the protein content of fermentation products.

[0028] Figure 4 . Crude protein content in fermentation products of different fermentation bacteria strains.

[0029] Figure 5 . Crude protein content in fermentation products of mixed strain fermentation.

[0030] Figure 6 . Crude protein content of mixed strain fermentation products at different fermentation temperatures.

[0031] Figure 7 . Crude protein content of mixed strain fermentation products at different fermentation times.

[0032] Figure 8 . Effect of added enzymes on the crude protein content of fermentation products. DETAILED DESCRIPTION

[0033] The following specific embodiments are further explanations of the present invention, in order to provide a better understanding of the present invention, but the embodiments do not constitute any form of limitation to the present invention.

[0034] Unless otherwise specified, the reagents used in the examples are conventional reagents in the art and can be purchased through commercial channels. The experimental operations not specifically described in the examples are conventional operations in the art or can be understood or known by those skilled in the art based on the existing technology or common knowledge they master.

[0035] The food waste described in the embodiment of the present invention is the remaining food waste collected from catering enterprises in Xindu District of Chengdu City, and its main component contents are as follows: water content 73.2%, dry matter content 26.8%, including total sugar 18.0%, crude oil 25.8%, crude protein 23.0%, and fiber 28.3%.

[0036] The activation described in the following examples refers to inoculating the strain into a liquid culture medium and culturing and activating the culture medium at 37° C. and 200 rpm for 24 h.

[0037] The mixed enzymes described in the following Examples 1-5 and Example 7 refer to an enzyme mixture added in the following amounts: 10 U of amylase, 50 U of saccharifying enzyme, 30 U of cellulase, 20 U of xylanase, 50 U of protease and 10 U of pectinase per gram of substrate.

[0038] The crude protein content described in the following examples is the crude protein content in the dry matter of the fermentation solid residue; the specific method for determining the crude protein content is determined in accordance with the first method 5.2 automatic Kjeldahl nitrogen analyzer method in the national standard GB5009.5-2016 "National Food Safety Standard Determination of Protein in Food".

[0039] Example 1. Effects of different steam explosion pressures on the growth of fermentation bacteria and the protein content of kitchen waste

[0040] 1. Weigh 100 g of kitchen waste, sieve and remove impurities such as metals, cloth, and plastic bags, then coarsely crush it and put it into the steam explosion chamber of the steam explosion equipment. Set the steam explosion pressure to 0.1, 0.5, 1.0, 1.5, and 1.8 MPa, respectively, and maintain the pressure for 10 min for steam explosion.

[0041] 2. Collect the exploded kitchen waste in a triangular bottle, add the enzyme mixture and connect it to OD 600= 0.5 of Bacillus subtilis 1 mL, fermented at 37 ° C for 48 h.

[0042] 3. After the fermentation is completed, the number of live bacteria in the fermentation system is calculated by the plate count method; the fermentation solid residue is collected by centrifugation and its crude protein content is determined.

[0043] The results are as follows Figure 2 As shown, when the steam explosion pressure is 0.1-1.5 Mpa, compared with the control group (Ctrl) that is directly fermented without steam explosion, the number of live bacteria and the content of crude protein in the fermentation system are significantly increased, especially when the steam explosion pressure is 1 Mpa, the number of live bacteria and the content of crude protein are the highest; when the steam explosion pressure is 1.8 Mpa, which exceeds the limited range of the present invention, the crude protein content in the fermentation system is not significantly increased compared with the control group, and the number of live bacteria is also significantly decreased. The results of this embodiment suggest that steam explosion can effectively improve the fermentability of restaurant kitchen waste, significantly increase the content of bacterial protein, and improve the comprehensive utilization value of restaurant kitchen waste.

[0044] Example 2. Effects of different steam explosion times on the growth of fermentation bacteria and the protein content of kitchen waste

[0045] The experimental steps of this embodiment are different from those of embodiment 1 in that the steam explosion pressure is set to 1 Mpa and maintained for 1, 5, 10, and 15 minutes respectively. The remaining steps are the same as those of embodiment 1.

[0046] The results are as follows Figure 3 As shown in the figure, when the steam explosion pressure was maintained for 1-10 min, the crude protein content in the fermentation system increased significantly. When the maintenance time was 5 min, the number of live bacteria and protein content in the system were the highest. However, when the pressure maintenance time continued to extend, the crude protein content and the number of live bacteria decreased significantly.

[0047] Example 3. Effect of steam explosion of food waste fermented with a single fermentation strain on protein content

[0048] 1. Steam explosion of kitchen waste was performed at a pressure of 1 MPa for 5 min.

[0049] 2. Weigh 30 g of steam-exploded food waste and inoculate the following fermentation strains: Bacillus subtilis, Bacillus licheniformis, Candida utilis, Saccharomyces cerevisiae, Bacillus coagulans, Enterococcus faecalis, Pediococcus acidilactici, Aspergillus niger, Aspergillus oryzae, 1 mL OD 600 The suspension was 0.5% and cultured at 37°C for 96 h. The crude protein content in the fermentation sample was determined (the results are shown in Figure 4 as shown).

[0050] Example 4. Effect of mixed strain fermentation steam explosion on protein content of kitchen waste

[0051] 1. Steam explosion of kitchen waste was performed at a pressure of 1 MPa for 5 min.

[0052] 2. After activating Bacillus subtilis, Bacillus licheniformis, Candida utilis and Saccharomyces cerevisiae respectively, mix them in equal proportions according to the combination in Table 1 below, and take 1 mL OD 600 = 0.5 were inoculated into 30 g of steam-exploded food waste, and the enzyme mixture was added and cultured at 37 °C for 96 h.

[0053] Table 1. Combination and proportion of bacterial strains

[0054] Serial number Compound strains Proportion 1 Bacillus subtilis: Bacillus licheniformis 1:1 2 Bacillus subtilis: Saccharomyces cerevisiae 1:1 3 Bacillus subtilis: Candida utilis 1:1 4 Bacillus licheniformis: Saccharomyces cerevisiae 1:1 5 Bacillus licheniformis: Candida utilis 1:1 6 Saccharomyces cerevisiae: Candida utilis 1:1 7 Bacillus subtilis: Bacillus licheniformis: Candida utilis 1:1:1 8 Bacillus subtilis: Bacillus licheniformis: Saccharomyces cerevisiae 1:1:1 9 Bacillus licheniformis: Saccharomyces cerevisiae: Candida utilis 1:1:1 10 Bacillus subtilis: Saccharomyces cerevisiae: Candida utilis 1:1:1 11 Bacillus subtilis: Bacillus licheniformis: Saccharomyces cerevisiae: Candida utilis 1:1:1:1

[0055] 3. Determine the crude protein content in the fermentation sample.

[0056] Taking the steamed but uninoculated food waste (CK) as the control, the crude protein content of each combination is shown in Figure 5 As shown in the figure (CK is uninoculated food waste; 1-11 correspond to the bacterial species combinations in Table 1). The results showed that when Bacillus subtilis, Bacillus licheniformis and Candida utilis were mixed in equal proportions (combination 7) or Bacillus subtilis, Saccharomyces cerevisiae and Candida utilis were mixed in equal proportions (combination 10) for substrate fermentation, the obtained protein content was significantly improved compared with other combinations, especially the fermentation product of combination 7 had the highest protein content, indicating that when the three strains in combination 7 were fermented together, the three strains cooperated with each other, thereby synergistically promoting the production of crude protein in the system, while when the other combinations were used for strain compound fermentation, there was a certain antagonism between the strains, resulting in a significant decrease in the crude protein content in the system compared with fermentation using a single strain.

[0057] Example 5. Effects of different fermentation temperatures and fermentation times on the protein content of fermentation products

[0058] 1. Steam explosion of kitchen waste was performed at a pressure of 1 MPa for 5 min.

[0059] 2. Mix the activated Bacillus subtilis, Bacillus licheniformis and Candida utilis in equal proportions (1:1:1) as fermentation strains, and take 1 mL OD 600 = 0.5 was inoculated into 30 g of steam-exploded food waste, and an enzyme mixture was added. The following two groups of experiments were carried out: (1) fermentation at 28, 32, 36, and 40 °C for 72 h; (2) fermentation at 37 °C for 24, 48, 72, 96, and 120 h.

[0060] 3. Detect the crude protein content of the fermentation product.

[0061] The results are as follows Figure 6 and Figure 7 As shown in the figure, fermentation time and fermentation temperature have an important influence on the crude protein content in the fermentation product. When fermented at 28-40℃ for 24-120h, the crude protein content in the fermentation product is relatively high. When fermented at the optimal fermentation temperature of 36℃ and the optimal fermentation time of 48h, the crude protein content of the fermentation product is 36.0% and 37.0%, respectively.

[0062] Example 6. Effect of enzyme addition on the production of protein powder from fermented food waste

[0063] In this example, a mixed culture of activated Saccharomyces cerevisiae and Candida utilis and Pediococcus acidilactici were used as fermentation strains to compare the effects of adding or not adding commercial hydrolase on the production of protein powder by fermenting food waste.

[0064] Table 2 shows the fermentation strains used and the enzymes added. Take 1 mL of OD 600 = 0.5 activated bacterial suspension was inoculated into 30 g of steam-exploded food waste, and fermentation experiments were performed with or without the addition of hydrolase. The steam explosion conditions were 1 MPa pressure for 5 min, and the fermentation conditions were 37°C for 72 hours. The crude protein content of the fermentation product was detected. The results are as follows Figure 8 As shown in the figure (1-3 correspond to the numbers in Table 2), adding hydrolase can significantly increase the crude protein content of the fermentation product.

[0065] Table 2. Fermentation strains and added hydrolytic enzymes

[0066] serial number Fermentation bacteria Hydrolases (30 U per gram of substrate each) 1 Pediococcus acidilactici Add saccharifying enzyme + amylase / no enzyme added 2 Saccharomyces cerevisiae + Candida utilis Added saccharifying enzyme / No added enzyme 3 Saccharomyces cerevisiae + Candida utilis Add saccharifying enzyme + cellulase / no enzyme added

[0067] Example 7. Production of fat and protein powder from food waste by steam explosion pretreatment and fermentation

[0068] 1. Take about 1 kg of food waste and perform steam explosion treatment under the conditions of 1 MPa pressure and pressure holding time of 5 min.

[0069] 2. After the activated Bacillus subtilis, Bacillus licheniformis and Candida utilis were mixed in equal proportions (1:1:1), the mixed bacterial suspension was inoculated at a ratio of 2 OD / 100 g of food waste, and the enzyme mixture was added and fermented at 36°C for 96 h.

[0070] 3. After the fermentation is completed, the fermentation is centrifuged at 2500×g for 5 min, and the upper oil phase and the lower solid residue are collected respectively. The mass of the oil phase is determined to be about 86.6 g; the crude protein content of the solid residue after drying is determined to be 39.0%.

Claims

1. A method for synchronously producing crude protein and bio-oil by fermenting kitchen waste, characterized in that: The following steps are involved: S1. Screening the food waste to separate impurities and then coarsely crushing it; S2. The crushed food waste is subjected to steam explosion treatment to obtain a food waste slurry; S3. Adding enzyme preparations and fermentation bacteria to the food waste slurry for simultaneous saccharification and fermentation; S4. The fermented food waste is squeezed to remove solid impurities to obtain an organic slurry; S5. The organic slurry is subjected to three-phase separation to recover bio-oil and solid residue, and the solid residue is dried to obtain crude protein; In step S2, the specific conditions of the steam explosion treatment are: treatment at a pressure of 0.1-1.5 MPa for 1-10 min.

2. The method according to claim 1, characterized in that In step S3, the enzyme preparation includes at least one of saccharifying enzyme, amylase, cellulase, xylanase, pectinase and protease.

3. The method according to claim 2, characterized in that The enzyme preparation is a compound of amylase, saccharifying enzyme, cellulase, xylanase, protease and pectinase, and the enzyme activity ratio of the saccharifying enzyme, amylase, cellulase, xylanase, pectinase and protease is 10:50:30:20:50:

10.

4. The method according to claim 1, characterized in that In step S3, the fermentation bacteria include at least one of Bacillus licheniformis, Bacillus subtilis, Candida utilis, Saccharomyces cerevisiae, Enterococcus faecalis, Enterococcus faecium, Pediococcus acidilactici, Bacillus coagulans, Lactobacillus brevis, Lactobacillus fermentum, Aspergillus niger and Aspergillus oryzae.

5. The method according to claim 4, characterized in that The fermentation strain is one of the following (a)-(b): (a) the fermentation bacteria is a mixture of Bacillus subtilis, Bacillus licheniformis and Candida utilis, and the inoculation ratio of Bacillus subtilis, Bacillus licheniformis and Candida utilis is 1:1:1; (b) The fermentation bacteria is a mixture of Bacillus subtilis, Saccharomyces cerevisiae and Candida utilis, and the inoculation ratio of Bacillus subtilis, Saccharomyces cerevisiae and Candida utilis is 1:1:

1.

6. The method according to claim 1, characterized in that In step S2, the specific conditions of the steam explosion treatment are: treatment at a pressure of 1 MPa for 5 minutes.

7. The method according to claim 1, characterized in that In step S3, the specific conditions of the fermentation are: fermentation at 28-40° C. for 24-120 hours.

8. The method according to claim 7, characterized in that The specific conditions of the fermentation are: fermentation at 36° C. for 48 hours.

9. Use of the method according to any one of claims 1 to 8 in producing crude protein and / or bio-oil from food waste.

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