Extraction of proteins from fenugreek seeds by classical and ultrasonic methods, characterization of obtained protein isolates and usage in cupcake production

In this thesis, proteins from fenugreek seeds were extracted using both classical extraction and ultrasonic-assisted extraction (UAE) processes under different conditions to determine the optimal conditions that ensuring the highest extraction efficiency. The coagulated protein percentage, water-holding capacity, oil-holding capacity, foaming properties (foaming capacity and foam stability), emulsification properties (emulsion activity, emulsion stability, and emulsion capacity), and solubility properties of protein isolates obtained under all extraction conditions in classical extraction and UAE processes were determined. The molecular weights, amino acid compositions, structural, and thermal properties of protein isolates obtained under optimal extraction conditions were determined. Additionally, characterized protein isolates of fenugreek seeds were used for cupcake production. The pH and solid-solvent ratio in the classical extraction process and the sonication amplitude (%) and solid-solvent ratio in the UAE process were chosen as independent process variables. The highest yield in the classical extraction process (94.3±0.3%) was achieved at a pH of 11.47 and a solid-solvent ratio of 34.50 g/L, while the highest efficiency (98.8±0.5%) was obtained at a sonication intensity of approximately 67.51% and a solid-solvent ratio of 43.83 g/L in the UAE process. The obtained yield in the UAE process was found to be higher compared to classical extraction, and it was determined that a higher extraction yield was achieved in 8 times shorter processing time. According to the characterization results, it was found that the properties of the protein isolates obtained by UAE, except for emulsion activity, were higher than those obtained by classical extraction. The molecular weights and structural properties of protein isolates obtained by UAE and classical extraction processes were found to be quite similar. For both protein isolates, three distinct bands (46, 59, and 80 kDa) were obtained in the range of 22-175 kDa. The protein's secondary structures were determined using Fourier Transform Infrared (FT-IR) spectra, revealing a high presence of β-sheet structures in fenugreek seeds protein isolates. The thermal properties of protein isolates were determined using Differential Scanning Calorimetry (DSC). The denaturation temperatures for protein isolates obtained by classical extraction and UAE processes were calculated as ~119°C and 135°C, and the denaturation enthalpies were 28 mJ/g and 53 mJ/g, respectively. Additionally, the amino acid composition of the fenugreek seeds protein isolate was determined, and it was found to be rich in essential amino acids (317.97 g amino acids/kg protein isolate). The protein isolates obtained by classical extraction and UAE processes were used for cupcake production, and the color properties, moisture content, water activity, cooking yield, bulk density, hardness, volume, symmetry and uniformity indices values of the cakes, as well as the consistency and density values of the dough, were determined. Overall, it was determined that the addition of fenugreek seeds protein isolate did not adversely affect the properties of the dough and cupcakes. According to the sensory analysis results, cupcakes with 10% protein isolate showed superiority in terms of appearance, crust color, texture, taste, aroma, and overall acceptance compared to other samples.