Feed safety has become a hot spot in the world. Many well-known feed enterprises have established a HACCP control system to ensure feed safety. Due to the lagging construction of China's feed standard system, many operational technical specifications have not yet been established. For the testing of feed additives and illegal drugs, there is still a lack of authoritative and versatile methods. Therefore, for most feed mills in China, there is a lack of feed safety measures and methods. To this end, it is necessary to provide feed producers with more effective information to help them ensure the quality of the feed and improve the safety of the feed. This paper analyzes the pollution problem of drugs in the process of feed processing, and proposes countermeasures for the feed production and processing enterprises.
Drug contamination during feed processing means that a certain amount of drug or drug-containing feed remains in a certain process during processing, and is mixed into the next batch (or even several batches) of feed, that is, residual drug (or drug-containing feed). ) caused pollution to the next batch of feed.
1. Analysis of the causes of pollution during feed processing
Drug contamination of feed can occur during feed processing, transport and storage. However, the processing is mainly in the following aspects.
1.1 Vacuum system
In the processing workshops of large and medium-sized feed mills, the vacuum system is distributed in various main processes in the processing process, with the aim of reducing the dust generated in the processing, purifying the production environment and reducing the risk of dust explosion. For the collected dust, it is generally returned to the feed for economic reasons, but the dust is delayed to return to the same batch of feed, or the design of the dust collection system is unreasonable, resulting in excessive absorption of drugs and excipients. Or adhere to the dust collection system due to static electricity or moisture and enter the next batch of dust.
1.2 batching system
Accurate ingredients are the premise and guarantee for the strict implementation of production formulas. Especially the accurate measurement of drug additives that have a direct impact on feed safety is very important. Once errors are not found in time, it can not be compensated in the follow-up section, which will bring serious pollution. .
1.3 Mixer System
The mixing process is a process of evenly distributing the various components and is the main link of drug contamination. The main reason is that the mixing time setting is unreasonable, the expected mixing effect is not achieved, and the mixing unevenness or excessive mixing phenomenon occurs; the design and construction of the horizontal mixer are improper, the stirring spiral belt (or paddle) and the mixer are mixed. The gap between the inner wall and the bottom is too large, resulting in incomplete discharge and residual feed. Vertical mixers often remain in the lower spiral tube or the wall of the discharge port and cannot be discharged. The mixing machine port cannot be closed or the gasket is damaged. In addition, the feed viscosity is large (adding molasses and fat) to the inner wall of the mixer, or static electricity is attached to the inner wall of the mixer, the top end and the air return tube.
1.4 Buffer warehouse
Buffer bins are the processing capacity between the balance equipment, which is conducive to the production of continuous equipment, but too shallow or too small volume, poor design, or attached due to static electricity or moisture, can not completely remove residual feed, resulting in drug contamination.
1.5 conveyor
Long transport distances and excessive use of horizontal conveying equipment may result in residual contamination. The main reason is that the horizontal conveying equipment is poorly designed or constructed, and the bottom gap is too large to accumulate the feed, or is not completely cleaned and adhered due to static electricity or moisture.
1.6 Bucket
The residual drug caused by the bucket lifter is generally small, but the feed may adhere to the residual bucket or the base due to static electricity, moisture, and viscosity, etc., and may also cause pollution.
1.7 silo
The drug contamination caused by the silo is mainly caused by poor design or construction (slope is less than 60 degrees). In addition, frequent knocking causes internal undulations, resulting in bridging and attachment, plus incomplete removal of residual feed, and the use of the same warehouse with drug-containing and non-medicated feeds, resulting in contamination of feed drugs.
1.8 processing sorting
Processing ordering is to sequentially arrange the order of feeds of different types or different formulations under the conditions of existing processing equipment. Due to operations, production technology, production equipment, etc., the feed products produced in the previous batch will definitely affect the products that are subsequently produced. Therefore, incorrect production sequencing is also the cause of contamination of feed drugs.
2 How to reduce or prevent drug contamination in feed processing
After analyzing the causes of drug contamination in the feed, it is necessary to take improvement measures. Usually, as long as the production sequencing or adjustment of the mechanical equipment is corrected, the problem can be significantly reduced. For some manufacturers, it may be necessary to repair and replace machinery, or even complete a complete production system. In order to avoid the problem of drug contamination, the conventional improvement measures adopted in combination with actual production mainly include the following aspects:
2.1 production process design
When designing the feed processing technology, it is necessary to shorten the conveying distance as much as possible, use less horizontal conveying equipment, and use the dispenser and the self-flowing form as much as possible. For horizontal conveying equipment, a scraper conveyor with self-cleaning function should be used whenever possible. Under the conditions of the process requirements, minimize the number of material upgrades and the number of transition hoppers. The suction and dust removal system should be equipped with an independent wind network as much as possible. The metering and addition of the dosing compound premix should be arranged as far as possible in the upper part of the mixer. If it must be lifted or transported after metering and weighing, pneumatic conveying must be used.
2.2 Develop an appropriate feed production ranking table
The purpose of correct sorting is to "anti-cross-contamination." The general principle is to produce the drug-free feed first, and then to produce the drug-containing feed; add the same drug to the same animal feed, and process the feed with high drug content, and then process the drug with low drug content; the same type of animal Animal-free feeds, such as sow lactation (pre-stage) feeds, are produced without drug-based feeds, and are manufactured in batches after the manufacture of the drug-restricted period. However, when the sales volume of a certain drug-containing feed is much higher than that of the drug-free feed, it is conceivable to set up a completely separate dedicated production line to minimize the risk of cross-contamination. The sorting method should be applied to the entire machining system, from the beginning of the crushing bin to the end of the finished bin.
2.3 Electrostatic adhesion
To eliminate static electricity, you can install a ground wire on the affected machine, or buy a non-electrostatic premix, or add liquid material to control dust to reduce static electricity. Alternatively, an oscillator may be attached to a portion where the feed is easily attached to shake off the deposit.
2.4 Dust collection system
The air flow rate and flow pressure of the dust collecting net are correctly designed, and more time is allowed to clean the dust in the entire system. Or use liquid materials to reduce dust. The dust collected during the production of the drug-containing feed can be discarded (can also be played back to the next feed containing similar drugs).
2.5 Mixer Residue
For food-containing feeds, a high uniformity mixer should be used. Or adjust the spacing of the stirring spiral belt or the stirring paddle and the bottom plate to the existing mixer. The easiest way is to install a plastic brush on the stirring spiral belt or install an air cleaning nozzle to remove any remaining feed. It is also critical to correctly determine the order and timing of the feed, typically when the mixer is full of 1/2 to 3/4.
2.6 Bucket machine residue
For the residual of the bucket lifter, you can consider adjusting the base of the bucket lifter to reduce the height of the feed bucket and make it clearer. Or install an air cleaning nozzle. In addition, the inner surface and the transition surface must be clean and smooth.
2.7 Residues in the feed bin
In addition to the science to be designed for the silo, when the type of feed stored changes, it should be checked and cleaned manually. Either install an oscillator or use air to remove residual feed.
2.8 Residues in , granulators and dryers
For the residue in the dryer, it can be solved by paying attention to the timely removal. However, the residue in the conditioner and the granulator can be solved by "flushing". "Flushing" is the use of a certain amount of a raw material, such as corn flour, soybean meal or wheat bran, to remove the residue from the previous processing of pharmaceutical or animal-derived feed. “Flushing†should not only be applied to the cleaning of the conditioner and granulator, but should start from the warehouse to be pulverized and run through the entire production process. Regularly check the processing equipment to confirm the effectiveness of the flushing procedure. The used scouring material should be labeled and stored for reuse in the feed that can be used.
Feed safety is a systems engineering. In addition to paying attention to the drug contamination in the processing discussed above, there are many other aspects of influence. In addition, a sound quality management system and system are also important aspects that affect feed safety. Feed processing enterprises should pay attention to it in many aspects.
3 Cross-contamination metrics
The measure of cross-contamination occurring in feed mills is a very difficult problem in the world feed industry. Although the overall goal of the feed mill is to reduce cross-contamination, however, for the measurement of cross-contamination, laws and regulations cannot be established without giving an accurate measurement method, nor can the feed mill be instructed to detect cross-contamination.
3.1 Uniformity and cross-contamination
Homogenity, defined as "the difference in particle content in a sample." Cross-contamination is defined as "carry-over" between adjacent batches. Uniform and cross-contamination are two related and different concepts when evaluating feed quality and safety. For example, the smaller the particle size of the feed, the better the mixing uniformity, that is, the mixing effect is good, the uniformity is high, and the coefficient of variation (CV) is low. However, too fine particles are at risk of cross-contamination. Some of the fines may be transferred to the next equipment and the next batch, causing contamination of the next batch. If the pellets of the feed are too large, mixing may be problematic, but the chance of cross-contamination is small. For the current general practice of uniformity, the coefficient of variation of the mixer is required to be less than 5%. But no scientific research shows that more than 5% is dangerous for animals and humans. Most feed scientists believe that the coefficient of variation is between 5% and 10%, and the production performance is the same. The biggest influencing factor for cross-contamination is drugs. The view is that the easiest way to solve cross-contamination is to use no antibiotics in the formula and not to have cross-contaminating ingredients.
3.2 Measurement of cross-contamination
For the cross-contamination quantification problem, as with the problem of determining the mixing uniformity, the tracer and assay protocol are first selected. Cross-contamination and quantitative cross-contamination can only be judged if a tracer is selected. Therefore, the selection of appropriate tracers and assays is conducive to the development of laws and regulations and to guide the production of feed mills. The tracers currently used vary from country to country. According to the source, it can be divided into exogenous tracers. Such as bismuth, colored iron particles, methyl violet and cobalt carbonate. Endogenous mimics have antibiotics or other pharmaceutical ingredients, as well as salt. But in Europe, salt has gradually been replaced by other reliable ingredients. It is generally considered that the conditions for the determination of cross-contamination ideal tracers:
1 Non-toxic in the range of determination of uniformity and cross-contamination;
2 does not exist in the feed ingredients;
3 has no effect on animal organs and nutrition;
4 can be mixed in solid form, evenly mixed in the application range of /kg;
5 contains at least 106 particles per gram;
6 is stable in processing engineering, especially in the process of heating and extrusion granulation;
7 analysis method is simple, reliable, and highly reproducible;
8 analysis and detection concentration is 0.5%;
9 can be used for pre-mixed feed and full-price feed;
10 can not be recycled.
4 Conclusion
The problem of feed cross-contamination is quite serious in China and one of the factors affecting feed safety. For the measurement of cross-contamination, there is no ready-made method in China, but there is no relevant laws and regulations for cross-contamination, and there is relatively little research on this aspect.
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