Extracting oil from seeds and fruits leaves behind a valuable byproduct that is rich in protein and can contain some residual oil – and anti-nutritional factors – depending on the extraction method.
Soybean meal remains the major protein source for intensively reared animals worldwide. Rapeseed meal is claiming a good part of its glory, because the need for the European Union to decrease its dependency on soybeans, and on the heavy use of rapeseed oil to create bio-diesel – with the two perhaps politically connected.
Whether the insurgence of rapeseed meal will become permanent is a matter of debate but, for the moment, it is a force to be reckoned with, at least in the European Union. Nevertheless, this discussion is not about these two major protein sources, but about ingredients that, given the opportunity, can replace them, either at the same efficiency or at a lower cost; rarely both aspects are possible.
Here, we will focus on five alternative proteins that also originate from the oil extraction industry as byproducts. Although the raw materials may also be used, with some thermal or other processing, it is the residual meal that interests us here as it is usually more economical and more widely available than, say, extruded seeds that have a more local appeal.
Before expanding on these five alternative protein sources, it is important to note that the oil extraction process will affect the residual oil concentration, the final protein concentration and quality, and the potency of any anti-nutritional factors.
In general, solvent extraction imparts more heat on the residual meal byproduct. Heat can deactivate some anti-nutritional factors, but if excessive it can damage the useful proteins, too. Also, solvent extraction leaves behind the least residual oil and concentrates the most protein fraction. On the opposite side is cold pressed extraction, with several intermediate processing methods also being employed. So, not all protein meals are created equal.
The degree of decortication (hull removal) dictates the final meal’s fiber concentration. In reverse, the degree of addition of hulls at the end of the process dictate the protein concentration of the byproduct.
High-fiber products (up to 40%) are directed to ruminant feeding, whereas high-protein products (up to 35%) are reserved for inclusion in feeds for monogastrics. Apart from the fiber issue, sunflower meal has no other major issues – perhaps that of seasonal availability is an important one – and as such it can be used quite freely in all feeds.
Inclusion rates are limited not only by its fiber concentration, but also by the need to balance its protein profile, which is limiting in lysine.
Cottonseeds are known for their fuzzy appearance, which is nothing more than pure cellulose (fiber). The degree of removal of those fibers dictates the use of the resulting byproduct after oil extraction.
Raw seeds yield a meal with as much as 25% fiber, making it suitable only for ruminant feeding, whereas partial and complete fiber removal yield meals with 15% and 7% crude fiber, respectively.
Apart from fiber, the other major issue of cottonseed meal is the presence of gossypol, a toxic substance that cannot be deactivated by heating – although there are other nutritional means around it. In general, cottonseed meal – of any type – is reserved for ruminants because they are not (as) sensitive to gossypol as monogastrics. As such, cottonseed meal can be used up to 0.5% of their live weight, and as a matter of fact, high-oil meals are preferred.
In reality, not much cottonseed is being crushed for oil because it is prized as an oil- and fiber-rich and stable seed extremely suitable for feeding high-yielding dairy cows.
Linseed oil is used mainly for industrial purposes and, as such, the majority of it is extracted by the solvent method.
The resulting byproduct is rich is protein (30-35%), which is deficient in lysine and methionine, and poor in oil (less than 2%), which is rich in alpha-linolenic acid (50% of total), an omega-3 fatty acid. Linseeds contain cyanogenic glycosides and as such they require heat treatment to ensure the volatile and highly toxic hydrogen cyanide evaporates.
There are many different varieties, and those least offensive can become usable even through pelleting of the feeds. Cold-pressed linseed meal should be avoided, but if some form of heat treatment is applied, then it might be suitable for feeding. Ruminants, which benefit the most from the mucilage proteins of linseed, also suffer the most from the cyanogenic glycoside problem.
Conservative inclusion figures are advised (2-5% in monogastrics and 0.1% of live weight in ruminants), unless quality is assured, in which case, excellent quality linseed can be used up to 10% in monogastric feeds and up to 0.5% of live weight in ruminants.
Sesame oil is highly valued for its refined taste and high oleic acid concentration. White sesame varieties are the most commonly used for mechanical oil extraction, although other sesame varieties – some of them bitter – exist.
The resulting sesame meal is rich in quite rancidity-resistant oil (5-10%) and protein (40-50%). The latter is especially rich in methionine – something that is lacking in soybean meal – and also in tryptophan, a particularly expensive amino acid in free form. The only major concern with sesame meal is the concentration of oxalic acid, which is minimal in white seeded varieties.
Good quality sesame meal can be fed up to 10% in diets for poultry and pigs and up to 0.3% of live weight in ruminants. Higher levels are possible but require further dietary fine-tuning.
Peanut oil can be extracted from raw peanuts as harvested or after removal of the husk. The former process yields a high-fiber byproduct (up to 25% crude fiber) suitable only for ruminants. If the husk is removed, the fiber concentration of peanut meal drops to about 5%, making it suitable for inclusion in feeds for monogastrics. For the latter, it is important to use only meal derived from solvent extraction as, without proper heat treatment, the anti-nutritional factors (mainly trypsin inhibitors) are not deactivated.
Good quality peanut meal, which is quite tasty, contains about 45% protein (deficient in methionine) and it can be used up to 20% in diets for monogastrics and up to 0.3% of live weight in ruminants.
As with anything new, it is important to begin with a conservative approach, as far as inclusion rate is concerned, with unknown feed ingredients. As knowledge and experience is combined with a sufficient degree of characterization (laboratory analyses, origin, processing, etc.), and with satisfactory animal performance response, higher inclusion rates are possible.
It is best to avoid combining too many uncommon ingredients unless their inclusion rate is minimal (less than 5%) to avoid combining problems. Feeds that contain too many such ingredients usually follow the less than 5% rule of thumb aiming to reduce cost by using byproducts of usually unknown origin and thus quality.