Leaf protein concentrate and grass juice

Protein synthesis is one of the chief activities of the green part of the plant. Some forage crops produce leaf protein in large quantities of up to 5 tons per hectare - three to four times that of grain crops. The basic technology for separating the leaf protein from the fibrous part or the leaf has been known for about fifty years, but a technology for large-scale production was not developed until the 1970s. The basic steps for the production of leaf protein concentrate (LPC) are grinding the plant and separating the juice by pressing. The protein is dissolved in the juice, after which it is coagulated, usually by heating, and then dried. The machinery needed for large-scale production is expensive, the minimum economical output being about 10 tons of leaf protein per hour - which means that about 5000 hectares are needed for the commercial production of LPC. Smaller machinery has been designed for use at the village level. 

Dried LPC contains about 40% crude protein, of which about three quarters is true protein. The amino acid composition is remarkably constant regardless of the green fodder used. The biological value of leaf protein lies between that of soybean and that of milk. The product is green and presents no palatability problems when included in mixed feeds. 

The recommended level of LPC in diets depends on both the raw material and the processing method; LPC from green cereal fodder, rye grass and marrowstem kale has been shown to cause fewer problems than that from lucerne. It seems possible to include LPC in the diets of poultry, pigs and calves at levels covering up to 30% of the protein allowances for these species. When using lucerne LPC, this level can under certain conditions create problems, in which case it is advisable to decrease the percentage of inclusion. 

Protein concentrate from sugar beet tops has given poor results and cannot be recommended until the processing method is changed. At higher levels of inclusion in poultry diets LPC may depress feed intake and increases the incidence of wet droppings. The carcasses of poultry reared on LPC diets are yellower, which in some countries can create market resistance. The LPC preparations now being manufactured are very dusty, which can cause problems in handing. 

A milk replacer for calves based on LPC gave very good results. It contained 20% LPC, 12.3% fish protein concentrate (FPC), 48.7% dried whey, 15% animal fat and 4% minerals and vitamins. 

Liquid grass juice can be fed directly to pigs. The juice is readily extracted by mechanical pulping and squeezing on a belt press. The yield of juice is approximately 50% of the weight of the crop. The addition of sodium metabisulphite to the acidified juice at pH 4 permits long-term storage. Grass juice can replace three quarters of the soybean meal in pig rations. It is fed most simply in a ratio of 4:1 liquid to a meal consisting of 93% barley, 5% soybean meal and 2% minerals and vitamins. 

The residue from the extraction of the leaf protein from herbage still contains protein and can be used as roughage for cattle, although its palatability is fairly low. As most of the soluble minerals are also extracted with the protein, it is necessary to provide a mineral mix with the residue. 

					As % of dry matter
				DM	CP	CF	Ash	EE	NFE	Ca	P	Ref
Lucerne, aerial
part, fresh, USA				94.5	23.0	24.3	8.3	4.8	39.6			205
LPC from lucerne,
USA				95.1	36.7	0.7	13.4	6.9	42.3			"
Residue of lucerne,
USA				92.6	17.1	35.2	6.9	3.3	37.5			"
LPC from lucerne,
Sweden					42.0	3.0	16.0	3.0	36.0			478

References

205, 272, 478