Structure-function relationship of black cumin seeds protein isolates: Amino-acid profiling, surface characteristics, and thermal properties

[Display omitted] •The extraction of black cumin seeds proteins was optimized using response surface methodology.•The black cumin seeds proteins isolate showed a semi-crystalline structure.•FTIR analysis revealed the typical peaks of protein.•Black cumin seeds proteins were thermally stable until approximately 90 °C.•Black cumin seeds proteins presented peculiar functional properties. The aim of the present investigation was to determine the chemical composition, the amino-acid profiling, the structural characteristics and the functional properties of protein isolates of two black cumin seeds varieties. Response surface methodology (RSM) was firstly carried out to determine optimal conditions of proteins extraction from black cumin seeds. Results indicated that the meal to solvent ratio, pH and extraction time were stated as the main influencing factors to obtain protein isolates of black cumin seeds. The protein content of cumin seeds protein isolates varied between 68.76%–78.41% showing the predominance of glutamic acid (12.73–14.59 %), aspartic acid (5.28–5.62 %) and arginine (4.94–5.49 %) amino acids. X-ray diffraction patterns of the protein isolates showed a semi-crystalline structure. Structural characterization by FTIR analysis showed the typical peaks of protein, namely, amide I, amide II and amide III. The thermal properties of protein isolates were investigated by differential scanning calorimetry. A denaturation temperature ranged from 88.11 °C to 90.65 °C. Black cumin seeds protein isolates were able to decrease the interfacial tension (down to 17.62 mN/m) leading to an interesting emulsifying (up to 159.53 m2/g) and foaming (up to 145.54 %) properties as function of pH.