Extraction optimization and amino acid analysis of edible dock protein

Edible dock is a new food raw material with high protein content, in order to explore the application value of edible dock protein, the basic components of edible dock were determined, including crude protein, crude starch, crude fat, water and ash. The extracted crude protein was scanned by UV-VIS full wavelength and the isoelectric point was determined. Edible dock protein was extracted by alkali extraction and acid precipitation method. The effects of pH (8, 9, 10, 11, and 12), solid-liquid ratio (1:15, 1:20, 1:25, 1:30, and 1:35 g/mL), extraction temperature (30, 35, 40, 45, and 50℃) and extraction time (15, 20, 25, 30, and 35 min) on the yield of edible dock protein were investigated by single factor experiment. The response surface experiment was designed by Box Behnken, and the pH, solid-liquid ratio and extraction temperature were selected as indexes. The influence of the three indexes on the yield of edible dock protein was as follows:B(pH) > A(solid-liquid ratio) > C(extraction temperature), and the influence of the interaction of all indexes on the protein yield was as follows:BC > AB > AC. The molecular weight of edible dock protein was determined by electrophoresis with sodium dodecyl sulfate and polyacrylamide (SDS-PAGE).The amino acid composition of the protein was determined and analyzed by amino acid analyzer. The results showed that the protein content of edible dock could reach about 30%, and the yield was 101.33 mg/g under the conditions of solid-liquid ratio 1:25 g/mL, extraction solution pH10.0 and extraction temperature 40.0℃. Electrophoresis image showed 3 bands near 55.2, 40.8 and 15.6 kDa, and the highest concentration was near 55.2 kDa. The amino acid composition analysis of edible dock protein showed that the content of glutamic acid and aspartate was higher; the content of cystine and methionine was lower. The essential amino acids accounted for 44.42% of the total amino acids. The amino acids of edible dock protein are complete, the pattern is good, and the nutritional value is high. This study can provide a certain theoretical basis for the supplement of human dietary protein.