What Are Short Chain Fructooligosaccharides?

Oligofructose is stable in nature, safe and non-toxic when used as a feed additive, and is not digested by endogenous enzymes in the gastrointestinal tract, leaving no residue in the animal's body. It can improve the intestinal microflora, promote animal intestinal development, regulate protein and lipid metabolism, promote mineral absorption, enhance immunity, and has the effect of antibiotics without leaving residues in the body, does not produce drug resistance, and is called a prebiotic (microecological agent) [1].

1. Physicochemical properties of fructooligosaccharides

1.1 Structural composition

Fructooligosaccharides (FOS), also known as oligofructose, sucrose-fructose-trisaccharide oligosaccharides, etc., have the molecular formula G-F-Fn (G is glucose, F is fructose, n = 1–3). They are a general term for sucrose molecules that have been combined with several D-fructoses via β-1,2 glycosidic bonds to form sucrose-fructose-trisaccharides, sucrose-fructose-tetrasaccharides, sucrose-fructose-pentasaccharides and their mixtures [2] .

1.2 Sweetness

Fructooligosaccharides with a purity of 55% to 65% are about 60% as sweet as sucrose by mass; those with a purity of 96% are about 30% as sweet as sucrose and have a fresher sweetness than sucrose [3].

1.3 Viscosity

In the range of 0 to 70°C, the viscosity of fructooligosaccharides is similar to that of corn high fructose syrup, and decreases with increasing temperature [3].

1.4 pH value and thermal stability

When the environmental pH value is neutral, fructooligosaccharides are very stable at 120°C. Under acidic conditions (pH 3), they are highly susceptible to decomposition after 70°C, and their stability is significantly reduced [3].

1.5 Water activity

The water activity of oligofructose G is similar to that of sucrose, but slightly higher for oligofructose [3].

1.6 Other processing characteristics

It has good solubility, high temperature resistance, inhibition of starch aging, non-colorability, shape-giving properties, alkali resistance, water retention and stability, but is poor in non-hygroscopicity [3].

2 Physiological effects of oligofructose on animals

2.1 Optimizing the gastrointestinal tract flora

The microorganisms in the intestines of animals can be divided into three categories: one category is beneficial bacteria represented by Bifidobacterium; another category is harmful bacteria represented by Clostridium; and the remaining category is intermediate bacteria. When the beneficial flora is dominant, the microecology of the body is in balance; on the other hand, when the harmful flora is dominant, the animal body is in a state of sub-health or illness.

Bifidobacteria are a type of non-motile Gram-positive bacterium without spores that exists in the intestines of warm-blooded animals and humans. After years of research, it has gradually been recognized that bifidobacteria are beneficial intestinal bacteria that accompany animals throughout their lives. Bifidobacteria ferment oligofructose to produce short-chain fatty acids and some antimicrobials, which can inhibit the growth of exogenous pathogenic bacteria and indigenous spoilage bacteria in the intestine, reducing the production of toxic fermentation products and harmful bacteria. The reduction in the formation of toxic metabolites can greatly reduce the burden on the liver to break down toxins, thereby indirectly protecting the liver. The proliferating bifidobacteria also have the ability to enhance the animal's immune system and resist tumors, and can produce some nutrients that the animal's body needs [4].

2.2 Promote intestinal metabolism

Fructooligosaccharides can promote small intestinal peristalsis, accelerate the degradation and elimination of intestinal putrefactive substances. They can have the effect of moistening the bowels, improving the character of the feces, preventing and alleviating constipation. Fructooligosaccharides can rapidly proliferate bifidobacteria, forming a bacterial film on the intestinal mucosa that makes it difficult for pathogens to colonize. Bifidobacteria, while being cultivated, also ferment fructooligosaccharides in large quantities, producing acetic acid, propionic acid and lactic acid, which lower the pH of the intestinal lumen, directly inhibit the growth of pathogenic bacteria and accelerate peristaltic movement in the intestinal lumen. In addition, fructooligosaccharides are water-soluble, easy to eat, not absorbed by the body or harmful bacteria, can stimulate the rectal defecation reflex, and have a synergistic effect with bifidobacteria to detoxify and neutralize toxins. This detoxification method of microecological balance is very safe and effective, without any toxic side effects [4].

2.3 Regulating nitrogen metabolism in the body

Feeding rats inulin (a natural ingredient containing a large amount of fructooligosaccharides) promoted the expansion of the cecum and the acidification of the cecal contents. Inulin had no effect on net nitrogen balance, but significantly inhibited nitrogen digestibility, which indicates that nitrogen excretion was shifted from the kidneys to the intestines. The balance between urea nitrogen transfer (plasma-caecum) and ammonia nitrogen transfer (caecum-plasma) was positive, indicating that inulin caused positive urea nitrogen deposition in the caecum. When fed a diet containing inulin, the transfer of urea nitrogen is high, but most of it is reabsorbed in the form of ammonia, indicating that the bacteria have a low utilization rate. Inulin increases the concentration of free amino acids in the cecum, but the cecum reabsorbs very little amino acids, so inulin significantly increases fecal nitrogen excretion and inhibits urinary nitrogen excretion. However, there is no effect on the total utilization rate of protein. Inulin can effectively promote the transfer of urea nitrogen to the intestine because it affects the osmotic pressure of the small intestine, thereby increasing the amount of urea at the end of the ileum. It is also possible that inulin increases the decomposition of urea by promoting the reproduction of urea-decomposing bacteria or by promoting the diffusion of urea nitrogen [4].

2.4 Enhances the body's immune system

Fructooligosaccharides have been considered to be an immune enhancer that can improve the immune function of animals, mainly through the following aspects: (1) promoting the proliferation of bifidobacteria and enhancing the immune function of animals. Tests have shown that ingesting live or dead bifidobacteria can increase the body's antibody levels and activate the phagocytic activity of macrophages, which is important for improving the body's ability to fight infections and preventing, inhibiting and killing tumor cells. The colonization of lactobacilli and bifidobacteria in the intestinal wall can stimulate the body to produce a specific immune response. Fructooligosaccharides have immunological adjuvant and immunomodulatory effects. Fructooligosaccharides have a synergistic effect on lipopolysaccharides, which can enhance cellular and humoral immune functions. In addition, fructooligosaccharides also have an antigenic effect, which can cause a direct antibody response. 3) It can activate the body's humoral and cellular immunity. 4) Fructooligosaccharides have a disease-preventing function [4].

2.5 Improves fat metabolism

Fructooligosaccharides lower cholesterol and neutral fat and improve lipid metabolism. In addition to accelerating cholesterol metabolism by proliferating bifidobacteria and turning it into fecal sterols that can only be excreted in the stool, fructooligosaccharides, like all fibers, promote intestinal peristalsis, absorb bile acids, and reduce the synthesis and absorption of cholesterol. In addition, oligofructose is not absorbed by the body and cannot be synthesized into fat by the “glycolipid metabolism” pathway. It can be used to prevent simple fat deposition caused by excessive neutral fat [4].

2.6 Promotes mineral absorption

Fructooligosaccharides can promote the absorption of minerals such as calcium, magnesium and iron. Tests on rats have shown that the intake of fructooligosaccharides can significantly improve the body's absorption of important minerals such as calcium, magnesium and iron, and even increase bone mineral density, which is of great significance for preventing osteoporosis. Fructooligosaccharides as food can significantly prevent the decrease in hematocrit and hemoglobin in rats after surgery. This shows that oligofructose can promote the absorption of iron and magnesium in the rat colon. Oligofructose promotes iron absorption mainly in the ileum. Consumption of oligofructose can prevent anemia after gastrectomy, and the effect is better than inulin. Consumption of oligofructose can increase the volume of the rat's femur and the concentration of mineral calcium and magnesium, indicating that oligofructose can promote the absorption of calcium and magnesium [5].

2.7 Effect on gastrointestinal histology

Howard et al. found that adding oligofructose to the diet of suckling piglets resulted in faster cell proliferation in the mucosa of the cecum and colon than in the control group, and also prevented atrophy of the mucosal epithelium. It is believed that this is because oligofructose, after being metabolized by bacteria, provides short-chain fatty acids as an energy source for mucosal cell proliferation. Leavit et al. reported as early as 1978 that the intermediate metabolic product of cells, butyrate, is the preferred raw material for the growth of normal colon cells, and can promote the formation of normal cells by stabilizing DNA and repairing damage. Choi found that the length of intestinal microvilli was longer than that of the control group after adding oligofructose to the diet of 3-day-old chicks. As for the effect of long-term addition of oligofructose to the feed on the gastrointestinal tract, further research is needed. Bacillus and Bifidobacterium can inhibit the growth of Salmonella [6].

3 Production process of oligofructose

3.1 Microbial fermentation method for producing oligofructose

The industrial production method of oligofructose is mainly microbial fermentation. A strain that can produce high yields of oligofructose was selected from soil and rotten beets. This strain belongs to the mold. During the experiment, the starting bacteria were fermented to obtain a fermentation broth.

The cells in the fermentation broth were crushed in an ice bath using an ultrasonic crusher, and the supernatant was centrifuged to obtain an enzyme solution. An enzyme solution, a sucrose solution with a concentration of 25 g/100 mL, and a disodium hydrogen phosphate-citric acid buffer were taken for the enzyme reaction. The analysis results show that the conversion rate of sucrose to sucralose (the main component of oligofructose) can reach more than 85%. During the reaction, because by-products have a certain inhibitory effect on the reaction, if a certain amount of counter-inhibitory substance (such as glucose oxidase, etc.) can be added, the conversion rate of oligofructose will be higher [7]. At the same time, according to the composition of the reaction products, a unique separation process is used to achieve a product purity of 82%. The selected strain is used as the fructooligosaccharide-producing strain, and the production process is as follows.

(1) Production equipment: seed fermentation tank, ultrasonic crusher, centrifuge, heating device, feeding device, reactor, drying and purification device, crushing and packaging device, etc.

(2) Process description: The optimal fermentation process conditions are: initial pH 6.0, temperature 30°C, time 25h. The intracellular and extracellular enzymes of this bacterium are both active and basically equivalent. Therefore, the cells are broken up using an ultrasonic crusher, and the intracellular and extracellular enzymes are collected for enzymatic reactions. The optimal enzymatic reaction conditions are: temperature 50°C, pH 6.0, time 1 h, initial substrate (sucrose) concentration 25 g/100 mL. This bacterium has a high yield, and the production process is simple and easy to implement.

3.2 Production of fructooligosaccharides by immobilized cell fermentation

The advantages of using immobilized cell fermentation are that it can be continuous, makes full use of the active bacteria, is highly automated and easy to operate. To use immobilized cell fermentation, the cells must first be immobilized. The immobilized bacterial cell process is as follows: the fermentation broth obtained after culturing the strain is separated to obtain a wet bacterial cell, and the bacterial cell is added to a pre-prepared sodium alginate solution with a mass fraction of 6% to 8%. The mixture is stirred evenly under vacuum, and then sprayed or passed under pressure through a 0.6 mm hollow tube to allow the homogeneous mixture to fall into a 0.5 mol/L 0.5 mol/L CaCl2 solution, so that it forms gel beads. After hardening for 20-30 minutes, it is filtered and loaded into a fixed-bed column or fluidized-bed reactor [3].

3.3 Enzyme or immobilized cell method for producing oligosaccharides

The oligofructose obtained by enzymatic or immobilized cell method for producing oligofructose is not high, about 50% to 60%. The reason is that the enzymatic method produces oligofructose while generating a by-product glucose, which inhibits the further conversion of sucrose, so the product contains a considerable amount of glucose and unacted sucrose. Using Aspergillus niger and other enzymes (isomerase, glucose oxidase) co-encapsulated or synergistic methods, in the production of fructooligosaccharides, the by-product glucose isomerization or oxidation, thereby lifting the inhibitory effect of glucose, and obtained fructooligosaccharides with contents of 63% and 71% respectively [6].

3.4 Production of fructooligosaccharides by the double enzyme method

The double enzyme method for producing fructooligosaccharides uses fructose transferase to convert sucrose to produce ordinary fructooligosaccharides as a raw material. Under the conditions of 30°C and pH 5, glucose oxidase and catalase are used in a synergistic reaction with 30% of the total sugar. After 17 hours of aeration under the above conditions, fructooligosaccharides are obtained [8].

4. Methods for the separation and purification of fructooligosaccharides

4.1 Chromatography

Chromatography is a method that uses a specific adsorbent to separate and purify 55% fructooligosaccharides by the principle of adsorption chromatography. After the processes of adsorption, washing, elution and concentration, a slurry or powder of fructooligosaccharides with a fructooligosaccharide content of over 95% can be obtained, and the separation effect is relatively good. However, this process requires the use of organic solvents, resulting in high production costs. The adsorption carrier is also limited, which is far higher than the price of chicory oligofructose and lacks market competitiveness [9].

4.2 Resin fluidized bed processing equipment

The use of resin fluidized bed processing equipment to purify 55% oligofructose is a method that has been newly developed in Japan and South Korea in recent years. The key part of this method lies in the design and manufacture of the equipment. With properly designed equipment, oligofructose can be purified with a purity of over 95%, and all materials can be fully utilized with minimal waste. Although the equipment investment is relatively high, large-scale continuous production can be achieved, and the operation is simpler and more practical, with a tendency towards cleaner production [9].

4.3 Membrane filtration to separate oligofructose

The membrane filtration process was originally used for water treatment. With the improvement of the membrane process and changes in membrane pore size technology, it has gradually been introduced into the field of material separation and purification and used in industrial production, achieving good economic benefits. Hebei Welkin Pharmaceutical Co., Ltd. cooperated with other companies to research the use of membrane filtration equipment and obtained oligofructose with a content of about 80%, which has a high yield. If the separation continues, oligofructose with a content of more than 90% can also be obtained.

5 Application of oligofructose in feed

In the early 1980s, foreign scholars began to take an interest in the beneficial bacteria that are naturally found in the intestines of animals. They sought to find a substance that could promote the growth and reproduction of beneficial bacteria in the intestines, but would not be absorbed and utilized by harmful bacteria and the livestock themselves. It was discovered that short-chain sugar substances, also known as functional oligosaccharides, had this function. In the mid to late 1980s, Japan was the first to develop it into a feed additive for use in the feed industry.

The animal nutrition community in China only came into contact with this type of additive in the late 1990s. Fructooligosaccharides themselves do not have a significant effect on the animal body. Their effect is mainly due to their proliferative effect on bifidobacteria in the animal body, which increases the growth rate of bifidobacteria, and accordingly, under the condition that the total bacterial count in the animal intestine remains the same, harmful bacteria in the intestine are inhibited to varying degrees. In addition, functional oligofructose has the effect of increasing daily weight gain, feed conversion rate, disease resistance of the animal body, and reducing the number of pathogenic bacteria such as Escherichia coli and Salmonella in the digestive tract and livestock products. Functional oligofructose is one of the feed additives with great development potential [10].

6 Current development constraints

The development of oligofructose in China is mainly affected by two factors: one is the level of production technology. Oligofructose fermentation has been successful, but the conversion rate is low, and the extraction technology restricts the industrial production process; the other is economic benefits. The sales of oligofructose are affected by the competition from other oligosaccharides (malt oligosaccharides, soy oligosaccharides), and the economic benefits are not obvious, thus affecting its development [6].

7 Prospects for application

For half a century, the application of antibiotics has greatly promoted the rapid development of the animal husbandry industry, but their side effects have also become increasingly apparent. The extensive use of antibiotics has caused endogenous infection or superinfection in animals to become increasingly serious, which has weakened the immune function of livestock and poultry, and may even pose a threat to human health through the food chain. As a new type of feed additive, oligosaccharides can be specifically utilized by beneficial bacteria in animals, inhibiting harmful flora and playing a role similar to antibiotics. Oligofructose is abundant and inexpensive, making it one of the most important types of oligosaccharide additive. As people gain a deeper understanding of oligofructose and conduct more research, its application prospects will certainly become more and more promising [11].

References:

[1] Huang Haiqing, Wang Yizhen. Application and research progress of oligofructose in animal nutrition [J]. Feed Wide Angle, 2002 (16): 26-27.

[2] Xu Xilin, Lin Qingsheng, Lai Fengying. Production of fructooligosaccharides from sucrose fermentation [J]. Food Industry Science and Technology, 1997 (4): 34-37.

[3] Wang Shihua, Peng Limin, Zhang Hui, et al. Development and application of fructooligosaccharides [J]. China Dairy Industry, 2002 (2): 31-34.

[4] Tang Shengqiu, Dong Xiaoying, Zou Xiaoting. Oligofructose and its application in animal nutrition [J]. Additive World, 2003 (10): 40-42.

[5] Yang Yuange, Luo Faxing. Oligofructose - a new type of functional food base [J]. Sugarcane Sugar Industry, 2002 (3): 35-39.

[6] Wang Shihua, Bai Wenzhao, Luo Jinhua, et al. Application of oligofructose in feed [J]. Cereals, Oils and Feed Industry, 2002 (3): 25-26.

[7] Tang Jun, Zhang Haitao. Properties of oligofructose and new fermentation process for its production [J]. Chemical Industry and Engineering Technology, 1999, 20 (2): 11-12.

[8] Wang Duoren. Development of oligofructose [J]. Guangxi Sugarcane, 2002(4): 29-34.

[9] Li Xiuqin, Yang Xinghui, An Suxin. Purification method of oligofructose [J]. Hebei Chemical Industry, 2003(1): 4-7.

[10] Lin Qinlu, Qin Dan, Jin Yanghai. Production and application of functional factors of oligofructose [J]. Chinese Food and Nutrition, 2002 (4): 20-22.

[11] Yao Jianguo, Xia Dong, Li Ruzhi. A new type of feed additive, oligofructose [J]. Additive World, 2000 (5): 15-16.