INTRODUCTIONSeed proteins can be broadly classified into two categories: housekeeping proteins and storage proteins. Seed storage proteins are group of proteins synthesized mainly during seed development, serve as a major nitrogen reserve which are utilized during germination of the seed. They are the source of necessary free amino acids and nitrogen to the growing plant with the sole purpose of providing proteins (nitrogen and sulphur source) required during germination(Chua et al., 2008). These are a complex mixture of different proteins which differ in structure, size, shape, amino acid composition, solubility and other physiological, functional, nutritional, nutraceutical and nutragenomic properties. Storage proteins are generaly found as aggregates in protein bodies of the seed and no significant data/reports available on their enzyme activity.
Osborne (1924) classified seed storage proteins based on their solubility as:Albumins: Extractable in water Globulins: Extractable in dilute salt solutionProlamins: Extractable in aqueous alcoholGlutelins: Extractable in weak alkali or acid or dilute SDS solutionsSeed storage proteins of grain crops meet the dietary protein requirement, thus playing a major role as a source of dietary protein for humans as well as livestock (Shewry, Napier & Tatham, 1995; Mandal. S., & Mandal, 2000; Bojórquez-Velázquez et al., 2016).
Because of the abundance of these storage proteins, they are mainly responsible for the nutritional quality of the human diet. Apart from nutritional qualities, seed proteins gain special importance due to their ability to influence the functional quality, which inturn determines the end use of grain in food processing (Bojórquez-Velázquez et al., 2016). Seed storage proteins accumulate in the cotyledon and embryo of dicotyledonous plants and in the endosperm of monocotyledonous plants. Salt-soluble globulins are the predominant storage protein in legumes and are grouped under two classes, 7S and 11S globulins, while alcohol-soluble prolamins are the major storage proteins in cereals. Oats and rice are exceptional, in which the major storage proteins are globulin-like.
GlobulinBased on their sedimentation coefficients, globulins are classified into two groups: 7S or vicilins and 11S or legumins (Shewry et al., 1995; Tandang-Silvas, Tecson-Mendoza, Mikami, Utsumi, & Maruyama, 2011). Legumins are the most extensively studied seed storage proteins, because they are the most widely distributed in nature, being present in both monocot and dicotyledonous seedsShewry et al., 1995; Tandang-Silvas et al., 2011).
The 11S globulins are hexameric proteins of 275–450 kDa and have 50–60 kDa monomers, which are composed of an acidic ( a ) subunit (30–40 kDa) and a basic (b) subunit (20–25 kDa) linked by a single disulfide bond highly conserved among plant legumins (Kshirsagar, Fajer, Sharma, Roux, & Sathe, 2011; Tandang-Silvas et al., 2011). The 11S globulin monomers are synthesized as a sin-gle precursor protein, from which the signal sequence is separated co-translationally.
The resultant proglobulins are assembled into trimers in the endoplasmic reticulum and transported to protein storage vacuoles, where they are cleaved to form acidic and basic subunits linked by a disulfide bond. After this cleavage, the trimers assemble into stable mature hexamers. Unlike vicilins, 11S globu-lins are usually non-glycosylated, with some exceptions such as a -conglutin from lupin, cocosin from coconut and Cal-1 from cof-fee (Batista-Coelho et al.
, 2010; Duranti, Consonni, Magni, Sessa, & Scarafoni, 2008; García, Arocena, Laurena, & Tecson-Mendoza, 2005)Oilseed proteinsThe world production of oilseeds was estimated to be —-million tonnes during 2015. Oil seeds have been the backbone of agricultural economy of India from time immemorial. The total oil seed production in India was estimated as e —-million tonnes of during 2015 (FAO).
The most important oilseed crop grown in India are groundnut, rapeseed and mustard, sesame, linseed, safflower, castor, sunflower, niger, soybean and oil palm (reference). Due to inadequate supply of animal proteins, there is a need for palnt proteins to be utilized for food and feed purposes. Hence, increasing attention is on oilseeds as an alternative nutirion source. After extraction of oil from oilseeds, large amount of oilseed cake/meal is generated as a waste by-product.
These waste by-product with good amount of protein content, can be used as a protein source. These can contribute to a large extent as a food protein source for human consumption. The seed storage proteins fraction contribute to the protein quality of the protein extracted from these oil seed meal/cake. Most of the oil seeds have globulin as the predominat seed storage protein. The protein isolate prepared from a oil seed meal (with globulin as the major protein), will contain globulin as predominat protein in it. India is a vast country having a wide range of oilseed variety that is exploited commercially. Oilseeds occupy very important position in the Indian agricultural economy.
The varieties of oilseeds grown in India are ground nut, soybean, sesame, sunflower, cotton, safflower, mustard, etc. Oilseed storage proteins are generally rich source of nitrogen. In oilseeds, large amount of proteins are present in protein bodies (Pernollet and Mosse, 1982).
Utilization of protein from unconventional sources of vegetable origin, including oilseeds for edible purposes has been explored. The oilseed proteins are categorized into 2 group’s namely low and high molecular weight fractions and based on the sedimentation coefficient the protein fractions are designated as 11S, 7S, 2S protein (Prakash and Rao, 1988). Storage protein: Oil PalmOil palmOil palm is a species of particular economic importance as it provides one of the most important sources of edible oil, most cost-effective feedstock for biodiesel and also animal feed (Sauyee et al.
, 2011). In oil palm, there are two important species in the genus Elaeis, E. guineensis that has its centre of origin in Africa and the South American species, E. oleifera. As a drupe, each oil palm fruit is made up of three major layers: an outer epicarp, a middle fibrous mesocarp from which palm oil is extracted and a hard breakable endocarp, known as the shell, which encloses the kernel.