Raw products
Resulting from the peeling
The amount of peels resulting from the peeling of potatoes depends on many factors including the size of potatoes, their maturity and the methods of peeling: it was reported to vary from 2 to 50% (El Boushy et al., 2000).
Abraded peels
Abraded peels are raw potato peels of potato obtained through abrasion (scrapping) in the processing of crisps. They contain less starch than steam peels. Once abraded, the potatoes are washed and the abraded peels are transported with water. The byproduct has thus a low DM content. It can be later pressed or contrifuged (Crawshaw, 2004).
Resulting from screenings
Potato slurry/ potato filter cake
Filter cake is a raw by-product that consists of fine particles of potato pumped from settling or clarifier tanks to remove part of the water. It has a low DM content (12% to 15%) and 6% to 75% of that is starch. Due to its starch content, potato slurry is an unstable product under aerobic conditions. The starch can rapidly ferment during storage: it yields simple sugars suitable for bacteria developement, acidification occurs and CO2 is released, accounting for digestible energy losses. Bacteria are half aerobic and half facultative anaerobic groups. If storage is not adequately done, some of these bacteria and molds can produce toxins or pathogenic bacteria may develop and become an issue for the health of the animals fed on potato slurry (Bradshaw et al., 2002).
Screen solids from process water/potato waste
These are raw small potatoes and slices, white waste, nubbins, hopper box that are removed by screening or settling. They are mostly fed to ruminants (Crawshaw, 2004; El Boushy et al., 2000).
Potato starch
This by-product is recovered in process water after the uncooked potato have been cut, sliced chipped and have released the starchy content of damaged cells. This starch is recovered from cold water. It remains uncooked and makes a valuable source of slow-release energy for ruminants though it goes only seldom to feed markets (Crawshaw, 2004).
Potato pulp from starch extraction
For starch extraction, potatoes are rasped and washed in cold water so that the starch exsudates. Potato pulp remains after extraction of starch and of protein water solubles. Per 100 kg potatoes, starch extraction yields 3-3.5 kg dried potato pulp, 16-20 kg starch, and 3.2-5.8 kg protein water solids (Boucqué et al., 1988; Treadway, 1987; Howerton et al., 1948).
Cooked products
The production of french fries or crisps involves steam-peeling, cooking/blanching or deep-frying. Steam peels, lye caustic peels, culled fries, culled crisps, hash browns, crowns, batter, crumbles, nubbins are by-products that have undergone heat treatment and may have been added oil, seasoning salts etc. Heat treatments gelatinize starch that becomes readily digestible and deep-frying in oil increases energy amount (Crawshaw, 2004).
Resulting from the peeling
Potato feed/steam peel
Potato feed or steam potato results from the peeling process occurring during the production of chips (french fries) or potato dehydration. In this process steam at 200°C and pressure are used for a few seconds to remove the outer peel from potatoes. Steam increases moisture and gelatinizes starch contained in the peel. Peel is removed by a scrubber. Steam has a sanitation effect as it has anti-microbial effect or bacteriostatic effect (Bradshaw et al., 2002; van Lunen et al., 1989). The product has a porridge-like aspect and it is recommended to store it in special tanks or in bunker silo where it forms a firm gel. It can be used a sealing substance for moist feeds prone to decay during ensiling. It has been used to seal silos of brewer's grains, sugar beet pulp, grass and maize silage. A layer of 30-40 cm potato feed has been advised for adequate sealing of silos (Decruyenaere et al., 2005). However, the potato feed layer requires to be sheeted in order to prevent birds, cats and vermin contamination and comply with safety rules of storage (Crawshaw, 2004).
Lye caustic peel
In the lye peeling process, potatoes are washed with a hot (76-99°C) sodium hydroxide (5-20% NaOH) solution and then mechanically peeled yielding about 14% solids (El Boushy et al., 2000; Hinman et al., 1978). Peels resulting from lye peeling are alkaline and require neutralization before use as animal feed. Thanks to the chemical treatment, lye caustic peels have a low microbiological load and do not spoil during storage provided pH remains high (Hinman et al., 1978).
Resulting from screenings/trimming
Prime potato puree
Prime potato puree (PPP) is recovered after potatoes are sliced, chipped or diced and after ungelatinized potato starch has been extracted. The remaining starchy material is washed with hot water which gelatinizes the starch and increases its digestibility and passage rate. This starchy material may contain some peels removed by steam peeling which bring fibre and protein and makes PPP very different from potato starch. Because processes are very variable, PPP composition is also very variable and should be assessed prior to formulating rations (Crawshaw, 2004).
The PPP has high moisture content and may be centrifuged to reduce water content. Because reducing moisture in the PPP decreases its pumpability in pig liquid feeding, it is thus important that PPP moisture content remains between 17-23% for pig feeding while it can be drier in ruminants feeding (Crawshaw, 2004).
Culled fries, culled crisps, hash browns, crowns, batter, crumbles, nubbins
These are partially or fully-cooked by-products separated from final products because they do not comply with the size or colour standards of food-grade products. However, they have the same nutritive value as fries or crisp. They are highly energetic feeds containing not only high level of gelatinized starch but also of oil (up to 20%). Those products are considered to have higher energy level than any animal feed but oils and fats. The oil used for deep-frying affects the levels of saturated/unsaturated fatty acids with consequences on rumen microflora/microfauna and on methane emissions. Products cooked in rapeseed oil or sunflower oil may have defaunating effects, reduce methane emissions and thus limit the energy losses in ruminants (Crawshaw, 2004). Those by-products are also seasoned and may contain 0.5-1.75% sodium, the upper limit being an issue in pigs diet (Crawshaw, 2004). Potato hash is a mixture of potato skins, starch, fats and yellow maize obtained after the production of snacks. In South Africa, potato industry yields 50 t/day of potato hash that can be used in animal feeding (Nkosi et al., 2011).
Potato mash/ dried potato meal/ potato flakes/potato granules
Those products are obtained after the cooking of potatoes in the processing of chips or of dehydrated puree, potato flour and in the process of artificial chips like "Pringles" reconstituted from potato puree. Those potato by-products have high energy level, high amount (75%) of highly digestible starch (gelatinized) but also good quality protein, little fibre and some minerals (Crawshaw, 2004). They can be used in pigs diets and in ruminants diets provided the ration has enough fibre to prevent acidosis and enough rapidly available N to improve protein synthesis in the rumen (Crawshaw, 2004)..
Mixtures of by-products
Potato puree feed (PPF)
Potato puree feed is a combination of potato feed (steam peel) and prime potato puree. The mixture is easy to prepare, contains 15-16 % DM and the two components do not separate in the silo. As a mixture, PPF combines advantages and restrictions of both components: it contains cooked and partially cooked materials, it has the starch content of PPP and protein and fibre content of potato feed. It is thus recommended for both ruminants and pigs (Crawshaw, 2004).
