Thermal Analysis. In: Nielsen SS, editor. Food Analysis. Boston: Springer US; 2010. pp. 555-71. [DOI: 10.1007/978-1-4419-1478-1_31]

Fenugreek (Trigonella foenum graecum) seed protein isolate: extraction optimization, amino acid composition, thermo and functional properties

BACKGROUND

With increasing demand for new protein sources, research on plant protein extraction and evaluation of the functional properties of protein isolates is necessary. In this study, pH and NaCl concentration, as two parameters affecting protein extraction of fenugreek seed, was investigated and the condition of fenugreek protein isolate (FPI) extraction was optimized using response surface methodology.

RESULTS

FPI had significantly (P< 0.05) higher protein and essential amino acid content (891.00 and 387.41 g kg(-1) , respectively) compared with soy protein isolate (SPI). FPI was rich in Asp and Glu, confirming the presence of bands in the acidic region (30-39 kDa) of its electrophoretic pattern. Differential scanning calorimeter thermography of both FPI and SPI showed two peaks with high denaturation temperature, confirming the presence of high protein content and hydrophobic amino acids. Protein solubility, foaming capacity, foam stability and emulsion stability of FPI were higher than SPI; moreover, both FPI and SPI showed pH-dependent protein functionalities.

CONCLUSION

Fenugreek seed protein extraction was optimized by control of pH and NaCl concentration. FPI could be used as a protein source with remarkable functional properties.

Can the thermodynamic melting temperature of sucrose, glucose, and fructose be measured using rapid-scanning differential scanning calorimetry (DSC)?

The loss of crystalline structure in sucrose, glucose, and fructose has been shown to be due to the kinetic process of thermal decomposition (termed apparent melting), rather than thermodynamic melting. The purpose of this research was to investigate whether or not it is possible to scan quickly enough to suppress the kinetic process of thermal decomposition and reach the thermodynamic melting temperature of these sugars using a new rapid-scanning DSC. Indium, a thermodynamic melting material, and sucrose, glucose, and fructose were analyzed at three heating rates from 1 to 25 °C/min using standard DSC and at seven heating rates from 50 to 2000 °C/min using rapid-scanning DSC. Thermodynamic melting was achieved when the onset temperature (T(m onset)) of the endothermic peak leveled off to a constant value independent of heating rate. The T(m onset) for indium was constant (156.74 ± 0.42 °C) at all heating rates. In the case of fructose, the T(m onset) increased considerably until a heating rate of approximately 698 °C/min, after which the average T(m onset) for the remaining three heating rates was constant at 135.83 ± 1.14 °C. Thus, 135.83 °C is proposed to be the thermodynamic melting temperature of fructose. It is important to note that the heating rate at which this thermodynamic melting temperature is achieved is most likely influenced by the type and amount of trace components (e.g., water and salts) contained in the fructose, which are known to vary widely in sugars. In the case of sucrose and glucose, thermodynamic melting temperatures were not able to be obtained, because the upper limit heating rate used was not fast enough to suppress thermal decomposition and achieve thermodynamic melting, perhaps due to the higher apparent T(m onset) for sucrose and glucose compared to that for fructose.