Starch-Protein Extraction and Separation it from Green Pea

Abstract

Legume is important food in healthy nutrition as a source of complex carbohydrates, proteins and dietary fibre, having significant amounts of vitamins and minerals, and high energetic value. It contains high amount of slowly digestible starches (SDS), and legumes have relatively low glycemic index (GI ~ 30).

There are many varieties of pea with different properties and composition, smooth or wrinkled seeded. Pea starch contains more amylose than commonly used starches therefore it is suitable material for producing biodegradable packages, paper and corrugated boards.

Garden (green) pea, cultivar Kashan (Kashan green pea), was tested for starch and protein extraction in laboratory. Hulled pea contained 31.2 % of starch with high content of amylose, 32.3 % of proteins and 2.0 % of lipids in dry matter.

The results were obtained with 8 experiments coming from dehulled and unhulled pea. At first the seeds were either milled (and the flour was sieved in some experiments) and then mixed with water or a liquidizer was used to disintegrate the seeds in water. After that, proteins were dissolved at pH 9.0 adjusted using 1M NaOH solution. Starch and fibre were separated using a laboratory centrifuge. The procedure was repeated 2x. The dissolved proteins were acidified at the isoeletric point pH 4.5 and the precipitate was re-dispersed using 1M NaOH solution and then again precipitated by an acid.

As expected, the isolated starch coming from dehulled seeds was of a higher purity compared with the unhulled ones. The best purity - 78% of starch in dry matter with the lowest content of proteins (3.7 %) and lipids (0.35 %) in dry matter was detected when using soft fraction of flour from dehulled seeds. Higher yield of proteins was obtained from the fraction of flour retained on a sieve.