Enzyme-assisted extraction of proteins from macroalgae Gracilaria dura, investigation of bioactive and technofunctional properties and identification of proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis

In the present thesis, process conditions of ultrasound-assisted enzymatic extraction of proteins from red macroalgae Gracilaria dura were optimized using response surface methodology (RSM). The effects of extraction time, enzyme/substrate ratio (E/S) and ultrasonic applying time were investigated on protein content, total phenolic content (TPC) and antioxidant activity (AOA) of the extracts. The chemical composition of G. dura was determined. Then, effect of pH was investigated on % protein solubility and zeta potential value. In addition, identification studies of protein extracts obtained under optimum extraction conditions were carried out using sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) technique. Furthermore, technofunctional properties (water holding capacity (WHC), oil holding capacity (OHC), emulsion stability (ES) were investigated. According to the results of the study, G. dura contained 11.97±0.05% protein, 0.32±0.06% fat, 24.30% carbohydrate, 45.50±0.73% ash and crude fiber 17.93±1.06%in dry weight (dw). Protein solubility (~58%) of G. dura was highest at pH 13. Protein content, TPC and AOA of the protein extracts obtained under optimum conditions (ultrasonic applying time: 257.57 seconds, E/S: 2.5 (g/g) and extraction time: 22.62 hours) were 188.71 mg/g dw, 64.33 mg gallic acid equivalent (GAE)/g dw and 54.24 mg Trolox equivalent (TE)/g dw, respectively. In addition, WHC, OHC, EA, ES and FC values of the protein extracts were 195%, 568%, 44%, 75% and 12.5%, respectively. On the other hand, the protein extracts did not exhibit FS. Furthermore, the protein extracts from G. dura had protein fractions with molecular weights of 11 and 25 kDa. In conclusion, it can be said that G. dura may has a potential to be applied to oil-based food formulations due to its good level of OHC.