Method for processing steam pretreated straw feed catalyzed by endogenous lactic acid

Abstract

The application discloses a processing method of straw feed by endogenous lactic acid catalysis and steam pretreatment. The main component of crop straw is lignocellulose, and the compact structure of the lignocellulose hinders hydrolysis and fermentation in the rumen. Steam pretreatment can effectively destroy the compact structure and improve the feeding value. In the steam pretreatment process, water-soluble sugar in the straw is easily degraded into inhibitors such as hydroxymethyl furfural, which is harmful to the health of ruminants and feeders, and causes waste of sugar. Lactic acid anaerobic fermentation is simple and easy to operate, and lactic acid produced thereby is easy to be used by ruminants. In the application, solid-state fermentation is carried out during the storage period of the straw, water-soluble sugar in the straw is converted into lactic acid, and then the raw material is subjected to steam pretreatment to produce feed. The endogenous conversion produced lactic acid can effectively catalyze the hydrolysis of hemicellulose and acetyl group in the pretreatment process, improve the digestibility of the feed, reduce the resource waste of water-soluble sugar, and greatly reduce the generation of hydroxymethyl furfural.

Description

[Technical Field]

[0001] This invention relates to the field of crop straw feed production and processing, and is a method for processing straw feed by steam pretreatment catalyzed by endogenous lactic acid. [Background Technology]

[0002] my country is a major agricultural country with a large output, wide distribution, and diverse types of crop straw, with straw resources reaching 700 million tons annually. The main components of straw are cellulose, hemicellulose, and lignin. The high degree of polymerization and crystallization of cellulose macromolecules, along with the entanglement of hemicellulose and the coating of lignin, results in a very dense structure of straw biomass, which affects its efficiency as a direct feed resource for ruminants.

[0003] Steam pretreatment or steam explosion pretreatment can effectively destroy the structure of lignocellulose under high temperature and high pressure, causing lignin to melt, acetyl groups to break, and some polysaccharides to hydrolyze into oligosaccharides and monosaccharides, thereby improving the digestibility of cellulose and hemicellulose in the rumen. Therefore, it can be used as an effective feed processing method in industrialization. Feed produced from crop straw using this method has shown good results in in vitro gas production experiments, in vivo digestion experiments, and animal feeding experiments.

[0004] Agricultural straw raw materials often contain a certain amount of water-soluble sugars. Taking corn straw as an example, the content of water-soluble glucose and fructose is generally greater than 2%. These sugars are synthesized by chloroplasts in plant leaves or stem stem cells through photosynthesis and are mainly used to maintain seed starch synthesis. However, during the high-temperature reaction process of steam pretreatment, these water-soluble sugars are usually degraded into hydroxymethylfurfural, which is toxic to ruminants and livestock workers, and also results in a great waste of water-soluble sugar resources.

[0005] This invention first converts water-soluble sugars into heat-resistant lactic acid during the raw material storage stage, while simultaneously lowering the pH of the raw material to effectively prevent contamination by microorganisms during storage. During pretreatment, this lactic acid acts as a catalyst, catalyzing the cleavage of acetyl groups and the hydrolysis of hemicellulose, improving the digestibility of the material as feed, and allowing the lactic acid to be utilized by ruminants. Furthermore, the reduction in water-soluble sugar content minimizes the generation of hydroxymethylfurfural during pretreatment, avoiding waste of sugar resources. [Summary of the Invention]

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for processing straw feed by steam pretreatment catalyzed by endogenous lactic acid.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A method for processing straw feed using steam pretreatment catalyzed by endogenous lactic acid, comprising the following specific steps:

[0009] (1) The crop straw raw material is coarsely cut, sand and gravel are removed and crushed, the solid content is adjusted and lactic acid bacteria are inoculated, and the water-soluble sugar contained in the straw is used as a substrate for solid fermentation to produce lactic acid; (2) The straw containing lactic acid obtained in step (1) is steam pretreated, and then the pretreated straw is used as feed or feed additive.

[0010] The advantages of this invention are as follows: Under the same pretreatment conditions, compared with traditional steam pretreatment, the endogenous lactic acid-catalyzed steam pretreatment process hydrolyzes hemicellulose into more monosaccharides and oligosaccharides, improving the digestibility of cellulose and hemicellulose in feed, which is beneficial to the digestion and utilization of feed by ruminants; it reduces the production of hydroxymethylfurfural, which is beneficial to the health of ruminants and feeders; the lactic acid produced in the solid-state fermentation process can also be converted and utilized by ruminants, avoiding the degradation and waste of water-soluble sugar resources. [Attached Image Description]

[0011] Figure 1 The effect of solid-state fermentation on the digestibility of corn stalks after steam pretreatment;

[0012] Figure 2 The effect of solid-state fermentation on the hydroxymethylfurfural content in corn stalks after steam pretreatment;

Detailed Implementation Methods

[0013] The following provides a specific embodiment of the steam pretreatment method for processing straw feed catalyzed by endogenous lactic acid according to the present invention.

[0014] Example 1

[0015] Air-dried corn stalks were coarsely chopped into 0.1-10cm lengths, and large stones and gravel were removed. The stalks were then directly crushed using a hammer mill until the particles could pass through a 1cm inner diameter sieve. At this point, the raw material contained 24.7 mg / g DM of glucose and 32.0 mg / g DM of fructose. The hydroxymethylfurfural content in the feed was 0%, and the cellulase hydrolysis yield was 23.9%.

[0016] Example 2

[0017] Air-dried corn stalks were coarsely chopped into 0.1-10cm lengths, and large stones and gravel were removed. The stalks were then directly crushed using a hammer mill until the particles could pass through a 1cm inner diameter sieve. At this point, the raw material contained 24.7 mg / g DM of glucose and 32.0 mg / g DM of fructose. Water was added to adjust the solid-liquid ratio to 2:1. After mixing, *P. acidilactici* TY112 seed bacteria were inoculated, compacted, and placed in sealed bags for anaerobic fermentation at 28℃ for one week. At this point, the lactic acid yield was 25.7 mg / g DM. The hydroxymethylfurfural content in the feed was 0%, and the cellulase hydrolysis yield was 23.1%.

[0018] Example 3

[0019] Air-dried corn stalks were coarsely chopped into 0.1-10cm lengths, and large stones and gravel were removed. The stalks were then directly pulverized using a hammer mill until the particles could pass through a 1cm inner diameter sieve. At this point, the raw material contained 24.7 mg / g DM of glucose and 32.0 mg / g DM of fructose. The corn stalks were then pretreated with water at a 2:1 solid-liquid ratio at 120℃ and 0.10MPa for 5 minutes. At this point, the hydroxymethylfurfural content in the feed was 0%, and the cellulase hydrolysis yield was 23.8%.

[0020] Example 4

[0021] Air-dried corn stalks were coarsely chopped into 0.1-10cm lengths, and large stones and gravel were removed. The stalks were then directly crushed using a hammer mill until the particles could pass through a 1cm inner diameter sieve. At this point, the raw material contained 24.7 mg / g DM of glucose and 32.0 mg / g DM of fructose. Water was added to adjust the solid-liquid ratio to 2:1, and the mixture was thoroughly mixed. Lactic acid bacteria (P. acidilactici TY112) were then inoculated, compacted, and placed in sealed bags for anaerobic fermentation at 28℃ for one week. The lactic acid yield was 25.7 mg / g DM at this stage. The corn stalk material after solid-state fermentation was then pretreated at 120℃ and 0.10MPa for 5 minutes; at this point, the hydroxymethylfurfural content in the feed was 0, and the cellulase hydrolysis yield was 25.4%.

[0022] Example 5

[0023] Air-dried corn stalks were coarsely chopped into 0.1-10cm lengths, and large stones and gravel were removed. The stalks were then directly pulverized using a hammer mill until the particles could pass through a 1cm inner diameter sieve. At this point, the raw material contained 24.7 mg / g DM of glucose and 32.0 mg / g DM of fructose. The corn stalks were then pretreated with water at a 2:1 solid-liquid ratio at 140℃ and 0.26MPa for 5 minutes. At this point, the feed contained 0.14 mg / g DM of hydroxymethylfurfural, and the cellulase hydrolysis yield was 25.6%.

[0024] Example 6

[0025] Air-dried corn stalks were coarsely chopped into 0.1-10cm lengths, and large stones and gravel were removed. The stalks were then directly crushed using a hammer mill until the particles could pass through a 1cm inner diameter sieve. At this point, the raw material contained 24.7 mg / g DM of glucose and 32.0 mg / g DM of fructose. Water was added to adjust the solid-liquid ratio to 2:1, and the mixture was thoroughly mixed. Lactic acid bacteria (P. acidilactici TY112) were then inoculated, compacted, and placed in sealed bags for anaerobic fermentation at 28℃ for one week. The lactic acid yield was 25.7 mg / g DM at this stage. The corn stalk material after solid-state fermentation was then pretreated at 140℃ and 0.26MPa for 5 minutes; at this point, the hydroxymethylfurfural content in the feed was 0.07 mg / g DM, and the cellulase hydrolysis yield was 30.2%.

[0026] Example 7

[0027] Air-dried corn stalks were coarsely chopped into 0.1-10cm lengths, and large stones and gravel were removed. The stalks were then directly pulverized using a hammer mill until the particles could pass through a 1cm inner diameter sieve. At this point, the raw material contained 24.7 mg / g DM of glucose and 32.0 mg / g DM of fructose. The corn stalks were then pretreated with water at a 2:1 solid-liquid ratio at 160℃ and 0.52MPa for 5 minutes. At this point, the feed contained 0.33 mg / g DM of hydroxymethylfurfural, and the cellulase hydrolysis yield was 36.4%.

[0028] Example 8

[0029] Air-dried corn stalks were coarsely chopped into 0.1-10cm lengths, and large stones and gravel were removed. The stalks were then directly crushed using a hammer mill until the particles could pass through a 1cm inner diameter sieve. At this point, the raw material contained 24.7 mg / g DM of glucose and 32.0 mg / g DM of fructose. Water was added to adjust the solid-liquid ratio to 2:1, and the mixture was thoroughly mixed. Lactic acid bacteria (P. acidilactici TY112) were then inoculated, compacted, and placed in sealed bags for anaerobic fermentation at 28℃ for one week. The lactic acid yield was 25.7 mg / g DM at this stage. The corn stalk material after solid-state fermentation was then pretreated at 160℃ and 0.52 MPa for 5 minutes. At this point, the hydroxymethylfurfural content in the feed was 0.25 mg / g DM, and the cellulase hydrolysis yield was 38.4%.

[0030] Example 9

[0031] Air-dried corn stalks were coarsely chopped into 0.1-10cm lengths, and large stones and gravel were removed. The stalks were then directly pulverized using a hammer mill until the particles could pass through a 1cm inner diameter sieve. At this point, the raw material contained 24.7 mg / g DM of glucose and 32.0 mg / g DM of fructose. The corn stalks were then pretreated with water at a 2:1 solid-liquid ratio at 180℃ and 0.90 MPa for 5 minutes. At this point, the feed contained 1.20 mg / g DM of hydroxymethylfurfural, and the cellulase hydrolysis yield was 50.0%.

[0032] Example 10

[0033] Air-dried corn stalks were coarsely chopped into 0.1-10cm lengths, and large stones and gravel were removed. The stalks were then directly crushed using a hammer mill until the particles could pass through a 1cm inner diameter sieve. At this point, the raw material contained 24.7 mg / g DM of glucose and 32.0 mg / g DM of fructose. Water was added to adjust the solid-liquid ratio to 2:1, and the mixture was thoroughly mixed. Lactic acid bacteria (P. acidilactici TY112) were then inoculated, compacted, and placed in sealed bags for anaerobic fermentation at 28℃ for one week. The lactic acid yield was 25.7 mg / g DM at this stage. The corn stalk material after solid-state fermentation was then pretreated at 180℃ and 0.90 MPa for 5 minutes. At this point, the hydroxymethylfurfural content in the feed was 0.69 mg / g DM, and the cellulase hydrolysis yield was 52.7%.

[0034] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the concept of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for processing straw feed using steam pretreatment catalyzed by endogenous lactic acid, characterized in that, The specific steps are as follows: (1) The crop straw raw material is coarsely cut, sand and gravel are removed and crushed, the solid content is adjusted and lactic acid bacteria are inoculated, and solid anaerobic fermentation is carried out to produce lactic acid using the water-soluble sugar contained in the straw as a substrate; the lactic acid fermentation strain inoculated is a lactic acid bacteria that uses water-soluble sugar to ferment and produce lactic acid and meets the feed safety requirements. (2) The straw containing lactic acid obtained in step (1) is subjected to steam pretreatment, and then the pretreated straw is used as feed or feed additive; the steam pretreatment conditions are: 120℃, 0.10MPa for 5 min; or 140℃, 0.26MPa for 5 min; or 160℃, 0.52MPa for 5 min; or 180℃, 0.90MPa for 5 min; In step (1), the solid content of lactic acid solid fermentation is 30%-80% to avoid wastewater generation in subsequent pretreatment processes.

2. The method for processing straw feed using steam pretreatment catalyzed by endogenous lactic acid according to claim 1, characterized in that, In step (1), the crop straw is a biomass raw material containing water-soluble sugar, selected from one or a mixture of corn straw, wheat straw, rice straw, and corn cob.

3. The method for processing straw feed using steam pretreatment catalyzed by endogenous lactic acid according to claim 1, characterized in that, In step (2), the steam pretreatment is a high-temperature pretreatment using direct steam heating. The solid content of crop straw during pretreatment is 30%-80%, and no free wastewater is generated after pretreatment.

4. The method for processing straw feed using steam pretreatment catalyzed by endogenous lactic acid according to claim 1, characterized in that, In step (2), the pretreated straw is directly used as feed or feed additive for feeding ruminants.

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