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. Nutritional
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 activity
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 grains (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.
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