Plant Proteins and their Quality, Essential Amino Acids and Limiting Amino Acids

Plant Proteins and their Quality, Essential Amino Acids and Limiting Amino Acids

(1) Between 10 and 30 % of the protein in forage is converted into human food by ruminants, whereas 40 to 60 % of the protein can be extracted. The approximate consequences of fractionating forage crop rather than using it as fodder.

(2) Leaves are the main site of protein synthesis and there are losses during translocation to other parts of a plant.

(3) When LP is made, the crop is harvested when less mature than when silage is made, and much less mature than when hay is made or a conventional crap is taken, the cost of harvesting is greater but an immature crop is not at risk for so long from diseases and pests.
(4) Crops that regrow several times after being cut young, or perennial crops, maintain cover on the ground, this enables fuller use to be made of sunlight and protects the ground from erosion.
(5) The fibrous residue contains the protein that was not extracted. Depending on the processing conditions, it can have two to five times as great a percentage of dry matter as the original crop and can therefore be dried to produce conserved ruminant feed economically.

Species and varieties selected for seed production or for a use other than LP extraction have been the source of most of the LP made in bulk. If varieties, possibly of species not at present used in agriculture, were investigated, yields would probably be greater than those so far attained.

Cowpea (Vigna unguiculata) gave 895 kg/ha in 80 days i.e., more than 4 tons if that rate could have been maintained for a year. In short term experiments yields as great as 17 kg of extracted protein per ha per day have been claimed.

Separation of Extract from Fiber:
The yields given above were measured on 4 to 5 kg samples of leaf taken from within a crop, pulping them in the unit designed for IBP (Davys & Pixie, 1969), pressing a sample in the unit similarly designed (I3avys, Pixie & Street, 1969) and measuring the amount of protein perceptible from the extract with trichloroacetic acid. In large-scale work it is usually advantageous to re-extract the fiber, this can give half as much protein again as a single extraction, but it would be difficult in the laboratory to get quantitative and repeatable results from a double extraction. The manner in which increasing skill in agronomy and processing have increased yields at Rothamsted

Separation of Protein from Extract:

Heat coagulation is generally accepted as the most satisfactory method for making a protein curd. Green, predominantly ‘chloroplastic’, protein coagulates at 50 to 60 °C, if that is separated; colourless ‘cytoplasmic’ protein separates at 70 °C. No more protein coagulates on further heating, but heating to 100 °C is probably advantageous in other ways it ensures a more nearly sterile product and it inactivates leaf enzymes more completely. When steam is injected into a stream of juice, heating takes place in 1 or 2 seconds; this produces had, easily filtered cured, and there is less enzyme action before inactivation. Chlorophyllase rich plants such as lucerne and wheat show the importance of this; the chlorophyll in LPs made by heating to 80 °C was almost completely hydrolysed to chlorophyllide, whereas there was little hydrolysis during quick heating to 100 °C (Arkcoll & Holden, 1973).

Bengal Gram:

The Bengal gram or chick pea (Cicer arietinum) has two principal cultivated types; the brown or yellow   brown deshi type and, the white seeded Kabuli type. Variation in their nutritive values are presented in table.

Table: Composition of two types of Bengal Gram:


Crude Protein (%)

Ether Extracts (%)

Crude Fiber (%)

Ash (%)

Carbohydrates (% by Difference)

Phosphorus (mg % / 100 g)

Calcium (mg/100 g)

Iron (mg/100 g)

Kabuli Type









Deshi Type









Red Gram:

Red gram or pigeon-pea is the second most widely cultivated pulse in India. Based on morphological characters, two forms, namely Cajanus cajon var. flavus, commonly known as tur and Cajanus cajan var. bicolor, known as arhar, have been described. The former type includes the commonly cultivated varieties, which are relatively dwarf and  bear yellow flowers and plain pods; the latter type includes most of the perennial types, which are generally late maturing, tall and bushy varieties.

Table: Methionine and Sulphuric Content of varieties of Red Gram


Methionine (mg/g)

Sulphur (mg/g)




























Commercial Varieties















Phaseolus Group:

Moong beans, urd beans and moth bean are considered to be native to India, having been originated from Phaseolus sublobatus which grows wild in India.

Moong Bean or Green Gram (Phaseolus aureus):

The research work on the improvement of moong beans was started in India in 1925 with large collections of seed samples from different districts of the country and also from Burma. Pure line selection from the local materials resulted in some promising varieties, e.g., GG-127, GG-188, Krishna – 11, Khargone-1, Co. 1, Kopergaon, NP-23 and Jalgaon 781.

Urd Bean or Black Gram (Phaseolus mungo):
The earliest attempts to improve urd bean started in 1925, when 125 strains were isolated from the local bulks. Systematic improvement of urd was started in 1943. These efforts resulted in a number of promising varieties, both for dry areas, e.g. BG-379, B.R. 61, Mash-48, Mash 35-5, Khargone-3, T-27, T-65 and Sindh Kheda 1-1, and also for wetlands, e.g., ADT-1.
Moth Bean (Phaseolus acontifolius):
A breeding program on this crop was started in 1943 and 150 collections were made from the cultivated areas of the country. From single plant selections, two types, namely B-15 and B-18, were identified as good grain types and T-3 as a good fodder variety. Another variety No. 88, was identified as a better grain type, maturing in 120 days. These lines showed some improvement in yield, by 10-15 %, but no varieties resistant to diseases have been identified. Disease resistance and quality aspects are being considered in future breeding program.

Dolichos Beans:
Two major species of Dolichos, are commonly cultivated in India. One is Dolichos lablab, commonly known as walve or avare and the other Dolichos biflorus, known as horse gram or kulthi.

Walve or avare (Dolichos lablab):
Research work on improvement of avare has been carried out with the object of developing drought resistant, high yielding types with good quality pods. Some of the varieties e.g. Co. 1, Co. 5 and Co. 6, have shown wide adaptability and are being popularized in rotation with late paddy in areas where winters are mild.

Horse Gram or Kulthi (Dolichos biflorus):

Very little work has been done on the improvement of horse gram; however, as a result of single plant selections from the local bulks, a number of varieties recording 15-20 % more yield than local bulks have been developed. Some of the varieties e.g. BGM 1-1, No. 35, D.B. 7 have been found promising. Variety BGM-1 exhibited a high degree of virus resistance.

A breeding program for improvement of this crop (Vigna sinensis) has been in progress since 1940. A number of grain, fodder and vegetable varieties have been identified from time to time largely from collections made within the country or from abroad of the grain types, N.P. 2, N.P. 7, C-32, T-I, K-11, K-14; of the fodder varieties.

Pea or Matar:
There are two main types of cultivated pea (Pisum sativurn), namely the large, smooth or wrinkled seeded garden pea and the small, round or dimpled seeded field peas. While the former type is used as a table variety, the latter is used as pulse, whole or split.

Garden Pea:
A breeding program on the garden pea was initiated at the Indian Agricultural Research Institute in the thirties. Through single plant selection, the medium-tall, wrinkled-seeded variety NP-29 was developed which is still popular in the country for its quality. During the same period, green-seeded Hara Bauna and white round seeded Lucknow Poniya were popularized for general cultivation in northern India. In central India, where the winters are comparatively short, the variety Khapar Kheda became more popular. In the warm-temperate zone around the Himalayas, a smooth, white-seeded variety was popularized under the name Kala Nagini or Kanawari. In recent years, a few more varieties, e.g., Early Badger, Boneville and Perfection with very attractive pod size have been introduced for general cultivation.


Varietal improvement programs for this species (Lens esculntus), were initiated in India in 1924 by collecting mixed samples bought in bazaars all over the country. Single plant selections were picked up from the bulk population and sixty-six types were isolated. Some of these varieties e.g., N.P. 11, N.P. 47 (IARI), T-36, T-8 (UP), L-9-12 (Punjab) and B.R. 25 (Bihar).

Khesari or Teora:
The consumption of this pulse (Lathyrus satiyus), in large quantities leads to lathyrism because of the presence of, l-N- oxalyl amino alanire (βOAA). It is a very hardy crop and comes up well even under water logging and extreme drought conditions. Therefore in areas which are completely dependent on the monsoon, farmers insist on growing it.

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