The essence of food fermentation

ferment

Fermentation means that microbial cells directly give electrons released by oxidation of organic matter to an intermediate product that is not comp

ferment

Fermentation means that microbial cells directly give electrons released by oxidation of organic matter to an intermediate product that is not completely oxidized by the substrate itself, and at the same time release energy to produce various metabolites. Under fermentation conditions, organic matter is only partially oxidized, so only a small part of energy is released. Oxidation during fermentation is accompanied by the decrease of organic matter. The reduced organic matter comes from the catabolism of the initial fermentation, that is, no external electron acceptor is needed. The phenomenon of fermentation has been known for a long time, but it is nearly 200 years to understand its essence. The word fermentation in English comes from Latin fervere, which means "stirring". It describes the phenomenon when yeast acts on juice or malt extract. The modern definition of fermentation is: the reaction process of producing and accumulating a large number of specialized metabolites through the growth, culture and chemical changes of microorganisms (or animal and plant cells).

Basic information

Chinese name: Fermentation

ferment

Also known as fermented grains.

Pronunciation: fā jiào

Definition: some kind of decomposition process of organic matter by organisms.

Application: food industry, biological and chemical industry.

Basic meaning

name

ferment

Boiling phenomenon is caused by carbon dioxide produced by sugar degradation in leachate under anoxic conditions. In biochemistry, the anaerobic respiration process of yeast is called fermentation. The fermentation we are talking about now has been given different meanings for a long time.

Fermentation is a chemical reaction and physiological change of life, and it is a process in which various biochemical reactions are continuously decomposed and synthesized according to the genetic information of life itself to obtain energy to maintain life activities.

Fermentation products refer to substances that can regulate metabolism to achieve balance during the reaction process or when the reaction reaches the end point.

In fact, fermentation is also a kind of breathing, but breathing eventually produces CO2 and water, and fermentation eventually obtains various metabolites.

definition

The Chinese word "fermentation" represents a process as a noun and an action as a verb.

(1) "fermentation" strictly defined by microbial physiology;

The process that organic matter is degraded into oxidation products by biological oxidation and releases energy is collectively called biological oxidation.

Microbial physiology divides biological oxidation into respiration and fermentation, and respiration can be further divided into aerobic respiration and anaerobic respiration. Therefore, fermentation is a way of biological oxidation.

Fermentation is a biological oxidation mode: under the condition of no exogenous final electron acceptor, the oxidation of energy organic compounds by heterotrophic microbial cells is coupled with the reduction of endogenous organic compounds (which have been metabolized by cells). Generally, metabolic energy ATP is obtained by horizontal phosphorylation of substrates (substrates of kinases) instead of electron transfer and electron transfer phosphorylation in electron transfer chains including cytochrome. The primary electron carrier NAD, which releases electrons from energy organic compounds, directly donates electrons to endogenous organic electron acceptors in the form of NADH, thus regenerating NAD and reducing the latter to fermentation products (products of incomplete oxidation).

NAD in cells is limited. If NAD, as a primary electron carrier, can't be regenerated, it can't be recycled, and there will be fewer and fewer effective electron carriers, so the dehydrogenation reaction can't continue. Therefore, the regeneration of coenzyme NAD is a necessary condition for biological oxidation (including fermentation) to continue.

(2) Fermentation defined in industrial production-"industrial fermentation"

In industrial production, any industrial production realized through microbial life activities is generally called "fermentation". Fermentation as defined in this way is "industrial fermentation". Industrial fermentation depends on the life activities of microorganisms, which are supported by metabolic energy provided by biological oxidation, so industrial fermentation should cover all the ways of biological oxidation in microbial physiology: aerobic respiration, anaerobic respiration and fermentation.

In the past century, with the progress of science and technology, the fermentation technology has undergone epoch-making changes, from the stage of using the original microorganisms in nature to the new stage of transforming them into microorganisms with special properties according to human wishes to produce fermented products that human needs.

(3) The technical term "fermentation"

In life, the word "fermentation" is often associated with cakes, fried dough sticks, steamed buns and steamed buns made of dough, or with moldy and rotten food.

As a professional vocabulary, "fermentation" not only covers making dough into cakes, fried dough sticks, steamed bread and steamed buns, but also refers to the industrial production of wine and alcoholic beverages, food and food additives, feed and feed additives, medicines and chemical raw materials through fermentation.

trait

The biggest difference between fermentation and other chemical industries is that it is a chemical reaction carried out by organisms. Its main features are as follows:

1. Generally speaking, the fermentation process is a biochemical reaction at normal temperature and pressure, which is safe and requires simple conditions.

2. The raw materials used in fermentation are usually starch, molasses or other agricultural and sideline products, and a small amount of organic and inorganic nitrogen sources can be added to react. Microorganisms can selectively use the nutrients they need, because there are different kinds. Based on this characteristic, wastewater and waste can be used as raw materials for fermentation to transform and renew biological resources.

3. The fermentation process is completed by biological automatic regulation, and the reaction is specific, so a single metabolite can be obtained.

4. Due to the biological reaction mechanism, some complex compounds can undergo highly selective chemical conversion reactions such as oxidation and reduction at specific sites, and more complex polymer compounds can also be produced.

5. It is very important to prevent and control the pollution of miscellaneous bacteria in the fermentation process. In addition to strict disinfection and air filtration, the reaction must be carried out under aseptic conditions. If mixed bacteria are polluted, the production will suffer huge economic losses, and if phage is infected, it will cause greater harm to fermentation. Therefore, maintaining aseptic conditions is the key to the success or failure of fermentation.

6. Microbial strains are the basic factors of fermentation. Through mutation and strain screening, high-yield excellent strains can be obtained, and products that are difficult to produce by conventional methods can be obtained by making full use of production equipment.

7. Compared with other industries, industrial fermentation has the advantages of less investment, quick effect and remarkable economic benefits.

Based on the above characteristics, industrial fermentation has attracted more and more attention. Compared with traditional fermentation technology, modern fermentation engineering has more advantages than the above fermentation characteristics. In addition to using microorganisms, animal and plant cells and enzymes can also be used, and artificial "engineering bacteria" can also be used for reaction; The reaction equipment is not only a conventional fermentor, but a variety of bioreactors are used instead, with high degree of automation and continuity, which improves and innovates the fermentation level on the original basis.

reaction

The process of fermentation reaction varies according to the utilization of different sugars and the production of products. Taking the production of alcohol from glucose as an example, the following explains the process of wine fermentation, which is also the most classic fermentation reaction:

Chemical formula: c6h12o6 → 2c2h5oh+2co2+2atp (released energy: 1 18kJ/mol) Text formula: sugar (glucose, fructose or sucrose) → alcohol (ethanol)+carbon dioxide+energy (ATP).

type

According to the characteristics of fermentation and the different requirements of microorganisms for oxygen, fermentation can be divided into several types:

1, divided by fermentation raw materials: sugar fermentation, petroleum fermentation and wastewater fermentation.

2. According to fermentation products: such as amino acid fermentation, organic acid fermentation, antibiotic fermentation, alcohol fermentation, vitamin fermentation, etc.

3. According to the forms of fermentation, there are solid fermentation and liquid submerged fermentation.

4. According to the fermentation process, there are batch fermentation, continuous fermentation and fed batch fermentation.

5. According to the different demand for oxygen in the fermentation process, it can be generally divided into anaerobic fermentation and aeration fermentation.

culture

Microorganisms are a large class of organisms, including bacteria, viruses, fungi and some small protozoa. Although small, it is closely related to people's lives. Microorganisms can be described as "ubiquitous, ubiquitous" in nature, covering a variety of beneficial and harmful, widely involving health, medicine, industry and agriculture, environmental protection and many other fields. Guangzhou Agriculture and Animal Husbandry Development Co., Ltd. specializes in separating and purifying production strains.

Prokaryotes: bacteria, actinomycetes, spirochetes, mycoplasma, rickettsia, chlamydia.

Eukaryotes: fungi, algae, protozoa.

Cell-free classes: viruses and subviruses.

cultivate

In industry, the fermentation process is under strict control, which is called culture, namely batch culture, fed-batch culture, semi-continuous culture and continuous culture.

Batch culture

Batch fermentation is the simplest fermentation process. After inoculating the strain in the culture medium, there is no need to add or take out anything except ventilation and exhaust. In the whole process, the parameters such as bacterial concentration, nutrient concentration and product concentration change with time.

Microbial growth can be divided into lag period, logarithmic growth period, stable period and death period. In the lag period, bacteria do not divide but grow, because when the strain is inoculated into a new environment, the nucleic acid and enzyme in the cell are diluted, and the cell cannot divide at this time. When the concentration of substances related to cell division in cells reaches a certain level, cells begin to divide, and then cells grow rapidly, and the specific growth rate is almost constant. This period is called logarithmic growth period. With the growth of cells, nutrients in the culture solution decrease and wastes accumulate, which leads to the decline of cell growth rate and enters a deceleration period and a stable period. Finally, when the cell death rate is greater than the generation rate, it enters the death stage. For primary metabolites, they are synthesized and accumulated in the early logarithmic growth period, while secondary metabolites are synthesized in large quantities in the late logarithmic growth period and stable period.

Batch culture has the advantages of simple operation, short cycle, less chance of bacterial contamination and easy control of production process and product quality; However, the yield is low and it is not suitable for determining kinetic data.

fed batch culture

Fed-batch culture refers to adding fresh feed liquid in batch culture process to overcome the shortcomings of premature end of fermentation caused by insufficient nutrition. In this process, only the feed liquid is added and not taken out, so the volume of fermentation liquid at the end of fermentation is increased compared with that at the beginning of fermentation. This method is widely used in the actual production of factories.

In such a system, the substrate concentration can be kept low to avoid the hindrance of rapid utilization of carbon sources; The best growth and product synthesis conditions can be obtained by feeding control; The computer can also be used to control the reasonable feeding speed and stabilize the best production process. At the same time, because no material is taken out, the accumulation of products will eventually lead to the decline of specific productivity. Due to the addition of materials, the chance of bacterial contamination increases.

Semi-continuous culture

On the basis of fed-batch culture, intermittent release of part of fermentation broth (with release) is called semi-continuous culture. Some varieties use this method, such as tetracycline fermentation. Release a part of the fermentation broth, and then add a part of the feed liquor to dilute the metabolic harmful substances, which is beneficial to product synthesis and improve the total output. However, this will also lead to the dilution of precursor substances produced by metabolism and the increase of total extraction volume.

Continuous culture

In the process of fermentation, while adding fresh feed liquid, the same amount of fermentation liquid is released to keep the volume in the fermentation tank constant. After reaching the steady state, the concentrations of bacteria, products and restrictive matrix are constant throughout the process.

Controlling the dilution rate in continuous culture can optimize the fermentation process. Long fermentation period and high yield. However, if the strain is unstable, long-term continuous culture will cause strain degradation and yield reduction. The chances of feeding bacteria for a long time are also greatly increased. Therefore, this fermentation method is not commonly used in actual production.

Specific application

Solid state fermentation has a wide range of applications.

Traditionally, people use solid-state fermentation to produce bread, malt, distiller's yeast, alcoholic beverages, soy sauce, lobster sauce, mushrooms and other foods or to produce intermediate materials.

Modern research has found that some foods produced by solid-state fermentation contain physiologically active substances, which shows that solid-state fermentation has advantages in producing these foods and food additives. With the increasingly serious energy crisis and environmental problems, solid-state fermentation technology has aroused great interest with its unique advantages. Great progress has been made in solid-state fermentation and its application in resources, environment and protein feed, mainly in the successful development and application of biological feed, biofuel, biological pesticide, biotransformation, metabolic detoxification and bioremediation, which provides strong support for the sustainable development of solid-state fermentation and broad application prospects for the development of traditional technologies.

Alcohol fermentation and lactic acid fermentation

(1), pulverizing and removing stems.

Crushing: separating pulp from sweat.

Stem removal: the fruit stalk has a green stalk flavor, and unless extra tannins are needed in the wine, the fruit excrement will remain.

(2), alcohol fermentation and impregnation

After the grapes are broken and removed, they are transported to a fermentation container for fermentation. Yeast can be grape itself or artificially added. The fermentation process lasted for 4~ 10 days, and tannin and pigment in grape skin penetrated into grape juice.

The kneading process of tannin and pigment is called impregnation. Impregnation time varies from a few days to several weeks. Soft fermented "new wine" with low tannin content will have a short soaking time; When brewing red wine that can be stored for a long time, it will take a long time to soak because it needs enough tannins.

(3), replace the container and squeeze the skin residue.

The purpose of changing the container is to separate the skin residue from the original wine and end the impregnation process. After removing the skin residue from the container, the wine is squeezed out. The wine squeezed from skin residue has dark color, high tannin content and bitter taste.

(4) lactic acid fermentation

In the process of red wine brewing, a kind of side fermentation called lactic acid fermentation is usually carried out. By-fermentation is to use lactic acid bacteria to transform sour malic acid in wine into softer and more stable lactic acid.

Produce monosodium glutamate

MSG is produced by fermentation all over the world. The raw materials for producing monosodium glutamate by fermentation are basically natural substances such as starch, sugar, acetic acid and molasses, so monosodium glutamate is not a chemically synthesized product.

Treatment of garbage by biological fermentation

BTA process can be widely used to treat biodegradable biological waste (organic part of waste) in domestic waste, wheeled garbage bin, agricultural waste and urban solid waste. Through BTA process, garbage can be converted into high-quality biogas and organic fertilizer (compost), and biogas can generate electricity and heat.

When BTA process treats garbage, the water used is basically the circulating water produced in the production process, and the excess water can be directly used for agricultural irrigation or further sewage cleaning treatment.

BTA single-stage fermentation system is commonly used. The fermentation of waste pulp is completed in a mixed fermentation reaction tank at one time. Considering the investment and operation cost, the existing fermentation equipment (such as fermentation tanks in sewage treatment plants and agricultural biogas plants) can directly transform and utilize this process. BTA single-stage fermentation system can be applied to existing waste treatment plants to expand production. If kitchen waste is to be treated, some BTA disinfection facilities need to be added.

There is also BTA multistage fermentation system, which is mostly used in factories with an annual processing capacity of more than 50,000 tons. In BTA multi-stage fermentation system, waste slurry is separated into solid and liquid substances by dehydration. The liquid phase contains soluble organic components and can be directly pumped into anaerobic fermentor (methane reactor). Since the dehydrated solid slag still contains undissolved organic components, it can be mixed with water again and pumped into the hydrolysis reactor. After about 4 days, these suspensions were dehydrated again, and then the liquid was partially injected into the fermentor (methane reactor). BTA multi-stage fermentation system creates the most ideal growth conditions for microorganisms through the degradation processes (acidification, hydrolysis and methane) in different reactors, and accelerates the degradation speed of organisms. It takes only a few days to convert 60%-80% of organic matter into methane gas.

Fermented food

brief introduction

Fermented food is a kind of food skillfully processed by beneficial microorganisms, which has a unique flavor and enriches our diet, such as yogurt, cheese, fermented wine, kimchi, soy sauce, vinegar, fermented soybeans, fermented milk, yellow wine, beer, wine, and even stinky tofu and stinky wax gourd. These are very attractive, mainly including grain fermented products, bean fermented products and dairy fermented products.

The origin of fermented food

As early as 3000 BC, the ancient nomadic people living in the Turkish plateau had already made and drunk yogurt. Now, after screening, people have determined the best strain for yogurt fermentation, and added new probiotics to yogurt to make it healthier.

After some vegetables are fermented, oxalic acid in vegetables is decomposed and protein is hydrolyzed to produce delicious peptides and amino acids. At the same time, new organic acids were produced.

Ordinary fermented food

There are mainly grain fermented products, bean fermented products and milk fermented products.

① Cereal fermented products include sweet noodle sauce, rice vinegar, rice wine, etc. These foods are rich in threonine and other ingredients, which can prevent memory loss. In addition, the main components of vinegar are various amino acids and minerals, which can lower blood pressure, blood sugar and cholesterol. In addition, there are steamed bread, bread, steamed stuffed bun, bread and so on.

② Fermented bean products include soybean paste, soy sauce, douchi, fermented bean curd, etc. Douchi is rich in antithrombotic components, which can prevent atherosclerosis and lower blood pressure. After fermentation, beans can participate in the synthesis of vitamin K and prevent osteoporosis.

(3) Milk fermented products such as yogurt and cheese contain lactic acid bacteria, which can inhibit the growth of intestinal spoilage bacteria, stimulate the immune system, mobilize the positive factors of the body, and effectively prevent cancer.