The aim of feed processing mainly to improve the nutrient utilisation of the feed, especially that of starch. Feed processing also reduces dust, toxins and improves gastrointestinal function. The digestion of starch can be improved by:
- Exposing the starch to microbes and enzymes: this can be done by cracking the pericarp of the seed as well as through various chemical treatments which are non-thermal processes.
- Increasing the surface area exposed to microbes and enzymes: this can be done by decreasing the size of the food particles. This is a non-thermal process.
- Improving enzyme efficiency: this can be done by increasing starch hydration and through the gelatinisation of the starch granules which are thermal processes.
Non-Thermal Processing Methods
Cracking, Crushing and Grinding
A hammer mill may be used to crush and grind grain. A hammer mill is a machine that has a series of spinning hammers which shatter the grain. The particles have an inconsistent size but there is a high throughput.
A roller mill may also be used. This is a machine that consists of rotating cylinders with smooth, grooved or corrugated surfaces. This machine has a slower throughput than the hammer mill but the particles are more uniform in size. In addition, the machine can be adjusted to vary the amount of processing and steam can be combined with the rolling.
Steam rolling is also known as flaking and is useful because the steam is used to soften the grain before it is rolled.
The advantages of cracking, crushing and grinding include the fact that starch is exposed, digestion is improved and a mixture of coarse and fine particles. However, this method of processing is costly, the vitamins are oxidised. Rancidity and dust are also most common and there is an increased risk of choke or vomiting as well as acidosis.
Clipping
Clipping removes the pointed, fibrous ends of oats. This exposes the starch to digestion and increases the energy and protein density of the feed. However, this does increase the cost of the feed, vitamins are oxidised and some of the benefits of fibre in the gastrointestinal tract are lost.
Crumbling
Crumbling is used to reduce the particle size of pelleted feeds and is usually used with fish, young pigs and poultry.
Chemical Processing
Chemical processing uses sodium hydroxide, ammonia or urea to soften the husk of the grain. The advantage of this method is that it doesn't expose the endosperm to rapid fermentation and so decreases the risk of acidosis. In addition, this method of processing reduces palatability which reduces the incidence of gorging.
However, this process can be quite expensive, palatability is reduced and their is a risk of toxicity.
Thermal Processing
Thermal processing is used to improve the efficiency of digestive enzymes.
Hot Soaking and Boiling
This method is used to soften hard grains which improves digestibility and palatability and reduces dust. However, vitamins are destroyed during the process and nutrients may be leached into water. The process is also quite labour intensive.
Steam Rolling and Flaking
Steam provides heat and moisture and this softens the grain. The more steam that is applied to the grain, the bigger the flake and the larger the surface area. More steam also leads to gelatinisation and increased digestibility. This process improves palatability, lessens dust and creates larger particle sizes.
The disadvantage to this process is that the increase in digestibility is only marginal, it is quite costly, vitamins are lost and the contents of the grain are exposed to oxidisation.
Canning
Canning involves the mixing of ingredients to form a mix that contains lots of moisture. The mix is then cooked at a high temperature and sealed in a can.
Baking
This involves the mixing of the ingredients to form a dough which is then spread in to thin sheets and baked in an oven. The sheets are then allowed to cool before they are processed into pieces and packaged.
Popping
This involves heating the grain which causes the water vapour in the grain to expand. This causes the starch granules to swell, fracture and gelatinise and the endosperm to rupture. This improves starch digestibility.
Micronisation
There are several steps to this process. First, the grain is soaked to soften the husk and improve starch hydration. The grain is then heated with infrared burners which causes the water vapour to expand. This causes the endosperm to rupture while the starch granules swell, fracture and gelatinise. Finally the grain is rolled to crack the husk and increase the surface area.
Micronisation improves starch digestibility, palatability, decreases the amount of dust, creates a larger particle size and the heat destroys some toxins and insects. However, the process can be expensive and the contents are exposed to oxidation which reduces the shelf live of the product. Vitamins and additives may also be lost in the process and their may be a reduction in protein digestibility.
Extrusion and Expanding
In this process, the feed is ground and then heat, moisture and pressure is applied. This destroys the starch's crystalline structure to form an amorphous blob. Starch hydration is also achieved and the gelatinisation of the starch and some proteins also occurs. The advantages of this process is that it greatly improves starch digestibility of the grain, protein digestibility may also be improved and undegradeable protein is increased. The process also reduces the amount of dust, and destroys toxins and insects. It also allows the food to be shaped and makes them easy to chew.
The process can be expensive, however, and some amino acids, vitamins and additives are lost and the shelf life is reduced. Extruded feed also has an unusual texture and may not be palatable in some animals, protein digestibility may also be reduced.
Pelleting
In pelleting, the ingredients are mixed, exposed to steam, and the resulting hot wet mash is forced into a pellet die (a sheet of metal with holes in it). The feed then emerges looking like spaghetti strands which are then cut into pellets. The pellets are cooled, dried and screened to remove the fine particles.
Pelleting improves starch digestibility and palatability of the grain. The process also cuts down on the amount of waste, dust and storage space. The heat used destroys some toxins and insects and the pellets are easier to handle and chew.
The down-side to the process is its cost and the requirement for special storage. Vitamins and additives are also lost and there is a reduced chewing time which may increases the risk of acidosis.
That's all for now, let me know if you have any questions :)
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