The researchers said the aim of the study was to apply a mild extraction process to produce protein concentrates that comply with EU organic farming methods. They used four different crops - red clover, clover grass, alfalfa and oilseed radish - as feedstocks.
Based at Denmark’s Aalborg University and the University of Aarhus, along with consultancy, Biotest Aps, the academics said their approach yielded a dry organic product containing up to 46% of crude protein and a balanced amino acid profile, comparable with soybeans.
“Moreover, the presence of lactic acid in the protein product might increase the value of these products.”
The authors said they studied the recovery of proteins from the crops into their respective protein concentrates and assessed them for protein extraction yields, while subsequently evaluating them in terms of amino acid composition.
Extraction of proteins contained in green biomass like grass requires an initial wet fractionation step in which the fresh biomass is pressed with a mechanical press (Kamm et al., 2009) or by extrusion (Colas et al., 2013a), they explained.
The team used a new type of extraction method that includes lactic acid fermentation to trigger a pH decrease and hence, the precipitation of proteins (Kiel et al., 2015). They said that, in this way, the extraction method does not require the use of inorganic acids or organic solvents and the product contains lactic acid, which may be beneficial for animal gut health.
Some 6kg of dry organic protein product was obtained per ton of clover grass and oil seed radish, while 13kg of dry organic protein product could be produced per ton of red clover and alfalfa in the biorefinery process, said the authors.
The dry protein products had a favorable amino acid composition for poultry feeding, they added.
Moreover, methionine contents between 7.8 and 9.1 g/kg DM were obtained in the protein products, said the team.
The protein concentrates were said to account for 6.7%, 3.1%, 8.4%, and 2.8% of the total wet weight in the fresh red clover, clover grass, alfalfa and oilseed radish, respectively.
The CP recovery in the protein concentrates was 23.4% for red clover, 17.1% for clover grass, 15.1% for alfalfa and 12.1% for oilseed radish, noted the academics.
The authors said that larger protein extraction yields could be achieved in the protein concentrates if the screw-pressing step was modified along with optimal pH precipitation.
They stressed that further investigations are needed for full evaluation of the feed quality of the protein products for monogastric animals and of the cost effectiveness of the biorefinery process in order to generate a feed product that is able to compete with current market prices.
GMO-free soy protein challenges
Increasing difficulties to obtain GMO-free organic soy protein, which is currently the main feed source in organic agriculture, is hindering this sector in the EU, said the authors.
They said the EU organic sector tends to source soybeans mainly imported from Asia in order to ensure GMO free products. There is a pressing need, they argue, to develop moresustainable organic farming systems based on the utilization of locally produced feeds.
“Actually, Denmark has the highest market share for organic egg production, namely 22% of the total egg production as percentage of the total market share in Denmark (Danish Poultry Council, 2014).
“There is an urgent need of finding alternative protein sources for the organic farming sector and particularly for monogastric animals, which have specific requirements for certain amino acids.”
The authors note an increasing interest in the use of legumes in crop rotations for their multiple benefits with respect to less use of fertilizer, pesticides and a high biomass yield.
Lupins v grasses
However, they said while legumes like faba beans, peas and lupin can grow in temperate climates and could increase the amount of locally grown protein sources for organic poultry, the content of methionine and cysteine, essential for poultry, are low compared to soybeans (Petterson, 2000), and therefore not useful as an alternative to soybeans.
“In addition, the value of grain legumes as [a] protein source in organic poultry diets are also dependent on the content of anti-nutritional factors (ANFs) such as protease inhibitors, lectins and tannins, as well as the content of non-starch polysaccharides (NSP), which can vary among cultivars and limit the inclusion level.”
Alternatively, extraction of proteins from green grasses holds promise for organic pig and poultry farming, they wrote.
“Proteins from organically grown green biomass extracted in the biorefinery concept can particularly be utilized to satisfy the imminent demand for protein rich organic feed for monogastric animals. The amino acid profiles of proteins extracted from green leaves are generally comparable with those from current protein sources like soybeans, meat, fish or eggs except for lower methionine content (Aletor et al., 2002).”
Plant proteins are mainly concentrated in the leaves. Rubisco (ribulose 1, 5-bisphosphate carboxylase) is the most abundant soluble protein in green biomass (Lamsal et al., 2007), explained the authors.
Source: Journal of Cleaner Production
Title: Lactic acid fermentation for refining proteins from green crops and obtaining a high quality feed product for monogastric animals
Authors: M.Santamaría-Fernández, B. Molinuevo-Salces, P.Kiel, S. Steenfeldt, H.Uellendahl, M.Lübeck