Abstract:
Leaf protein concentrate (LPC) can be utilized as ingredients of vegetarian diets, additional nutrients for human food and feed industries. Most LPC has been produced from vegetables and cereals including peanut, cassava, and morning glory, while LPC from aquatic plants were hardly found. Duckweed is an aquatic plant that grows fast and contains high amount of organic nitrogen as protein. In this research, total protein content (TPC) from 4 species of duckweed in Thailand including Wolffia globosa, Lemna minor, Spirodela polyrrhiza, and Azolla pinnata were determined by Kjeldahl method. The highest amount of TPC (27.45±0.02 % (w/w) dry weight of duckweed) was found in Wolffia globosa. The extracted protein from this duckweed was further processed into the leaf protein concentrate (LPC) by pH adjustment (pH 3-6) and thermal precipitation (37-80 °C). The highest yield of LPC (69.96±0.10 % (w/w)) was extracted by thermo-coagulation at 80 °C and pH 4. The chemical analysis of LPC components consisted of 69.96 % (w/w) protein, 8.96 % (w/w) fat, 8.84 % (w/w) carbohydrate, 5.66 % (w/w) moisture, 4.06 % (w/w) fiber, and 2.49 % (w/w) ash. Moreover, heavy metals were analyzed by Air-C2H2 Flame Atomic Absorption Spectrometry, and found 2.37 mg/l Mn, 2.29 mg/l Fe, and 2.16 mg/l Zn. For the analysis of protein fraction, some essential amino acids were found including 8.07 % (w/w) glutamic acid, 6.53 % (w/w) aspartic acid, and 5.87 % (w/w) leucine. Moreover, functional properties of LPC were investigated. It was found that solubility of LPC was from 30.49±1.39 to 32.75±2.97 % (w/v) under the pH range from 4 to 6, and increased significantly at pH values higher than 7 (34.72±0.97 % w/v). The maximum solubility of LPC was found at pH 12. The LPC-oil emulsion was considerated when SDS was supplemented and decreased in 3-fold within 10 minutes after mixing. Decreasing in foam stability was observed within 10 minutes and constanted at (96.14±0.61% w/v). The viscosity of LPC (22.3±3.86 cP). The results of this study are helpful for formulating the future food-supplements such as whey protein.