Chemical and biochemical components of Beach pea (Lathyrus maritimus L.)

Chavan, Uttam Dnyanu (1998) Chemical and biochemical components of Beach pea (Lathyrus maritimus L.). Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Physico-chemical properties of Beach pea (Lathyrus maritimus L.) seeds were evaluated and their proximate composition determined. Results were also compared with those of green pea (Pisum sativum L.) and grass pea (Lathyrus sativus L.). Beach pea seeds had a very low grain weight, density, hydration capacity, hydration index, swelling capacity and swelling index as compared to green pea and grass pea. The contents of crude protein (% N x 6.25, 29.2%), crude fibre (12.0%), reducing sugars (0.2%), total phenolics (1.2%), ash (3.0%), and total free amino acids (0.6%) of beach pea were substantially higher than other peas examined. The contents of cysteine (1.6%), methionine (1.1 %), and tryptophan (0.3%) in beach pea proteins were low, but still higher than those in green pea and Canadian and Indian grass peas. Beach pea lipids were dominated by linoleic acid (69.1%), similar dominance of linoleic acid was observed in green pea (45.1 %) and Canadian grown grass pea (57.0%). The major macroelements of beach pea were potassium (475.8 mg/100g), phosphorus (413.2 mg/100g), magnesium (179.7 mg/100g), and calcium (144.2 mg/100g). The content of microelements, namely manganese, zinc, and iron in beach pea was 3.5, 3.0 and 9.4 mg/100g, respectively. -- Samples of beach pea (Lathyrus maritimus L.) seeds and plant parts were analyzed in order to determine their chemical composition, total and free amino acids as well as minerals. The crude protein content of beach pea plant parts varied from 10.7 to 28.0%, soluble proteins 190.2 - 709.0 mg/100g, lipid 1.3 - 6.0%, ash 2.2 - 6.8%, crude fibre 10.7 - 35.5%, soluble sugars 0.1 -12.2%, starch 0.8 - 26.5%, carbohydrate 55.8 - 81.5% and phenolic compounds 0.5 - 3.0%. The amino acid profile of seed proteins and other plant parts of beach pea showed that they were deficient in sulphur-containing amino acids. Tryptophan was another limiting amino acid in plant parts, except in leaves (1.35 g/16g N). The content of free amino acids was highest in branches and stems (3147.9 mg/100g) and lowest in pod shells (150.7 mg/100g). Beach pea plant parts were a good source of minerals such as K, P, Ca, Mg, Na, Fe and Zn. -- The biochemical composition of seeds and pod shells of beach pea was determined during growth and maturation. The content of crude and soluble protein, soluble sugars and phenolics was high in the fresh green seeds and pod shells, but these decreased rapidly during seed maturation. Meanwhile, the corresponding content of starch increased in seeds and decreased in pod shells. Glutamic acid was the predominant amino acid in seeds and aspartic acid was dominant in pod shells. Levels of arginine, alanine, and threonine were highest in fresh green seeds. Methionine and cysteine content increased during seed maturation, but declined in pod shells. Free amino acid content decreased rapidly during the latter stages of seed maturation. Potassium, calcium, sodium, phosphorus were the predominant minerals in fresh green seeds and pod shells, but iron content was highest in mature pod shells relative to that of other stages of maturation. Major changes in colour (pigment interchanges) also occurred during maturation. -- Acetone-water (7:3, v/v) mixture containing 1% concentrated HC1 served best for extraction of condensed tannins as compared with other solvents used in this study. Air classification of beach pea cotyledons and hulls concentrated protein content in cotyledons up to 35% and starch up to 37%. Meanwhile, the content of total phenolics and condensed tannins was reduced by up to 0.93 and 5.76%, respectively, in cotyledons of beach pea. -- Beach pea hulls were also extracted with 70% (v/v) acetone containing 1% concentrated HC1 in order to isolate, fractionate and partially characterize the compounds responsible for antioxidative activity of hulls. The UV absorption maxima showed that flavonoids were present in all three isolated fractions (I-III). β-Carotene-linoleate model system studies indicated that antioxidant activity of separated fractions and crude extract were in the order of fraction III > crude extract > fraction II > fraction I. Silica gel TLC plates sprayed with a solution of β-carotene and linoleic acid indicated that many of the individual compounds present were antioxidative in nature. Furthermore, separation of fraction III on a semi-preparative HPLC showed the presence of (+) catechin and (-) epicatechin as the main phenolic compounds present. -- Methanol-ammonia-water extraction system efficiently removed β-N-oxalylamino-L- alanine (BOAA) and reduced the content of non-protein nitrogen, phenolics and condensed tannins from beach pea seeds with a concomitant increase in protein content of the processed meal. -- The nitrogen solubility of beach pea seeds was lowest at pH 4.5. The content of glutelin in beach pea seeds, its cotyledons and hulls was higher than those of green and grass pea seeds. Meanwhile, the corresponding albumin and globulin were lower than those of green pea and Canadian grass pea. Albumin fraction contained the highest amount of sulphur-containing amino acids as compared to those of other protein fractions and the amount of these amino acids was higher in beach pea than those of other peas examined. Poly aery lamide gel electrophoresis (PAGE) results of protein isolates as well as protein fractions showed that major storage proteins of beach pea were in the range 22 - 40 kDa and 43 - 116 kDa. -- Beach pea protein isolates prepared using sodium hydroxide had 87% protein, while those extracted with sodium hexametaphosphate had 85% protein. Functional properties, such as water binding, fat binding, foaming, foam stability, emulsion, emulsion stability and in-vitro digestibility (pepsin-trypsin; 80.6 - 82.6% and pepsin-pancreatin; 78.6 - 79.2%) of beach pea protein isolates were comparable to those of green pea and grass pea protein isolates. Starch from beach pea was isolated and its physicochemical properties compared with those of green pea and grass pea starches. The yield of beach pea starch was 12.3 % on a whole seed basis. The shape of the granules was round to elliptical, with granules 6-17 μm in diameter. Scanning electron micrographs (SEM) revealed the presence of smooth surfaces with many granules occurring in clusters. The total amylose content of beach pea starch was 29%, of which 5.9% was complexed by native lipids. The X-ray diffraction pattern of beach pea starch was of the "C" type and the X-ray intensities were much weaker than in other legume starches. The starch exhibited a restricted two stage swelling pattern and moderate amylose leaching. Native granules of beach pea were hydrolyzed readily by a 2.2 N HC1 solution (49% in 20 d) and porcine pancreatic α- amylase (35% in 24 h). The gelatinization temperature range was 60-74.2 °C and the enthalpy of gelatinization was 1.6 Cal/g. The results showed that starch chain associations within the amorphous and crystalline domains of beach pea starch are much weaker than those in green pea and grass pea starches.

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