I. Foreword
For a long time, human beings have a contradictory mentality of mold and hostility; beneficial molds play an indispensable role in food processing, pharmaceuticals, pollution prevention, etc., but the second metabolite produced by the toxin-producing mold-mycotoxin For the livestock industry, it is a very sensitive and thorny issue. It is estimated that about 25% of the world's cereals are contaminated with mycotoxins before and after harvesting, while Taiwan is densely populated, land prices are high, and the grain required for livestock feeding has a low self-sufficiency rate, most of which depend on imports. From the recovery of grain from the field to the production of feed, the problem of toxin production must be recognized and countermeasures.
Animals are likely to consume mycotoxins during the feed intake process, so mycotoxin contamination is also a very important public health problem.
Second, the conditions of mold growth
Mold can grow when the nutrients in the grain or feed contain available nutrients at the appropriate temperature, water activity and oxygen conditions.
1. Nutrient
Mold growth requires a carbon source and a nitrogen source. The intact grain is structurally composed of cellulose or polyesters to protect carbon and nitrogen sources. If the grain is intact, the growth of the mold is slow. The structural damage or cracks caused by the grain during processing cause the kernels to lose the cellulose barrier of the corn shaft; in addition, the growth of the mold can be accelerated by pests in the field or during storage. Bullerman et al. (1984) pointed out that corn is exposed to drough stress, insect damage, and mechanical damage, increasing the chance of mold attack; causing mold to form a point of attack in vulnerable nucleoli. The growth of mold in the feed also causes a loss of the metabolic energy value of the amino acid, vitamins and feed.
2. Temperature
Temperature is an important factor in determining the growth of mold in feed or grain. Although mold can survive at different temperatures, there are certain limits to the temperature required for growth and production, aspergillus (Aspergillus) and Penicillium ( Penicillum) prefers to grow under warm conditions and Fusarium must be at a lower temperature. Aspergillus flavus grows at a temperature of 36-38 ° C, and its range can range from 6 ° C to 46 ° C. In laboratory culture, the optimal amount of aflatoxin production is 25 ° C, and below 7.5 ° C or above 40 °C has no toxin formation, and cyclical temperature changes also contribute to the production of aflatoxin. This is a toxin-producing bacterium that reduces the decomposition of toxins, because the balance between the production and decomposition of toxins is in a state of storage. Changes will affect their final production.
In the microenvironment of corn in the barn, because of its respiration, it increases the moisture content and generates heat spots, which promotes the production of large amounts of toxins. Although it can be forced to drive wind to reduce this situation, but also Supply oxygen required for mold growth.
3. Oxygen
The mold is an obligate aerobic organism, so its proliferation and growth can be controlled under anaerobic conditions, but it is impractical due to the high cost of the equipment. Mold can still breathe when the oxygen concentration is as low as 4%, reduce the amount of oxygen, increase the amount of carbon dioxide can inhibit the activity and production of mold. Or when filling the barn with nitrogen to 99% or more, the effect of removing moisture and oxygen to prevent mildew is obtained.
4. Water-active
When the grain moisture content exceeds 13-14% and the relative humidity (RH) is 80-85%, it is very suitable for the proliferation of mold. The water activity (Water Activity, Aw) is used to represent the substrate moisture, which more fully expresses the distribution of water in the environment. Water activity means that the water in the grain or feed has a certain water vapor pressure at a certain temperature, and the ratio thereof is the ratio of the saturated water vapor pressure value of the pure water at the temperature; or at a certain temperature, In a closed barn, one percent of the relative humidity at equilibrium is reached.
Water activity = vapor pressure of moisture in cereals (t ° C) / water vapor pressure of pure water (t ° C)
= Balance relative humidity / 100
Molds can grow under different water activities, and some molds such as Monasus sp. can grow at Aw 0.62. Moisture movement in the grain is another source of moisture. When the grain is lower or higher than the ambient temperature, moisture is moved or agglomerated due to ventilation in the barn. Therefore, the feed or grain is stored in a safe humidity, and when the water is reaggregated, the mold will regenerate. After the starch or protein grain is pulverized, if the feed is exposed to 80% RH, the surface moisture of the grain will increase from 18% to 18% by rehydration. The raw materials are grown from crops, harvested and pulverized to form a relationship between the feed molds and their symbiotic detoxification. In the quality control system, there are 6 SIGMA (3.4 parts per million non-performing rate quality control management) to carry out enterprise production standards, toxin management. This concept should also be used to operate.
Third, the use of agents and specific toxin enzyme preparations
In recent years, various antifungal agents have been used in diets to control mold growth and prevent the formation of mycotoxins. The role of the fungicide depends on its dispersion and penetration in the matrix. The use of propionic acid and gentian violet has the effect of delaying the production of aflatoxin and the spore formation of Aspergillus parasiticus, and the antifungal effect of propionic acid is superior to that of calcium propionate. In addition to being effective in inhibiting mold, propionic acid also inhibits the proliferation of coli forms and S. cerevisiae. However, the use of such organic acids is highly corrosive to operators, and the use of α-rays as an alternative fungicide can meet economic and safety needs.
Fourth, the use of adsorbents
The best time to use the anti-fungal agent should be the storage of the grain after harvesting. After being shipped from the United States to Taiwan for unloading, the addition time is not enough. The use of anti-mold agent increases the cost burden and has been added to the grain. The mycotoxin present does not have a degradation effect. In addition, although it can be detoxified by ammoniation, this method has not been approved by the US Food and Drug Administration (FDA).
The use of various adsorbents to adsorb mycotoxins already present in cereals or feed appears to be the last line of defense, using adsorbents to specifically or non-specifically adsorb mycotoxins to reduce their risk to livestock. It has been found that adsorbents such as zeolite, bentonite, bleaching clay can be removed from fat and the harm of T-2 toxin and Zerallenone in piglets. Such adsorbents have a common feature; they are all aluminosilicate compounds that have the ability to ion exchange.
Philips et al. (1987, 1988) found in vitro that aluminas, zeolites, silica, phyllosilicates and chemically modified leaf silicates can be combined with aflatoxin B1 (AFB1) in aqueous solution and removed. And the chemically modified leaf silicate works best. Recently, many reports have reported that hydrated sodium calcium alumino silicate (HSCAS) is used to improve the toxic effects of aflatoxin on livestock and poultry, such as in dairy cows, pigs, chickens, and sheep. This selective chemical adsorbent binds tightly to the aflatoxin to form a stable HSCAS-aflatoxin complex in the gastrointestinal tract, thereby reducing the bioavailability of aflatoxin, which is estimated to be 483 nm per mg of HSCAS. AFB1 binding. The adsorption of HSCAS only specifically adsorbs aflatoxin, and has no adsorption effect on T-2 toxin, ochratoxin A and Diacetoxyscirpenol. The possible mechanism is that the aflatoxin B or G series (AFB1, B2, B2a, G1, G2, G2a) contains a β-ketolactone or an α-bislactone ring (α-bislactone). Preferred adsorptivity, and the β-carbonyl system of aflatoxin forms a stable compound with the metal ions of the HSCAS edge site. In addition, HSCAS has a reduced effect on the utilization of Zn in the diet, but has no effect on the utilization of phosphorus, manganese, vitamin A and B2, and has a slight impact on mineral metabolism in the body. The use of gene cloning to produce special enzyme preparation methods is the latest method to achieve efficient and rapid degradation of toxins.
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