In this study, the determination of total proteins present in WSE was performed using the Bradford colorimetric method.
In the past it has been proven that the interference of carbohydrates present in the sample matrix significantly deviates the actual absorbance of the proteins, resulting in less accurate results if not primarily removed (Banik, Pal, Ghorai, Chowdhury, & Khowala, 2009).
Since the primary aim of these preliminary studies was to observe the hydrothermal degradation of proteins in SubCW and not quantify the exact amount of proteins in extract, carbohydrates present in WSE were not primarily precipitated and were analysed directly using the above mentioned method.
In contrast to the minimally hydrolysed triglycerides, total proteins (Fig. 2a) and carbohydrates (Fig. 2b) present in WSE show a much more different course.
From Fig. 2a it can be observed that after 5 min of extraction again the lower temperature kinetic curves (60 C and 100 C) show no dependence on extraction time. The highest amounts of water soluble proteins are obtained at 60 C equaling to approximately 30 wt.%. At temperatures higher than 100 C overall protein yield in WSE decreases significantly with increasing Te and at 160 C the concentration of proteins (wBSA) even starts to decrease with te.
The decrease of overall wBSA with increasing Te is probably a consequence of lower solubility of protein at higher temperatures, while the gradual decrease with extraction time at 160 C is possibly due to hydrolysis of proteins.
M/S ratio seems to have practically no influence on wBSA.
For total carbohydrates a quite similar pattern can be observed.
Again, for the lower temperature curves (60 C and 100 C), no influence of te can be observed, since carbohydrate concentration (wGLU) remains constant after 5 min of extraction. Oppositely a higher yield of total carbohydrates can be observed at TeP100 C, which indicates a higher carbohydrate solubility at higher temperatures.
At 130 C wGLU starts to decrease with te and the decrease is the highest at 160 C.
This decrease of wGLU not only indicates a decrease of carbohydrates in the sample but also a decrease of
present furfurals.
Furfurals are namely the main constituents formed in the phenol/sulfuric acid colorimetric method applied for determination of total carbohydrates. Therefore it can be presumed that products other than furfurals have formed during
extraction.
Since the carbohydrate profile of sunflower kernels consists mainly from hexose derivatives (glucose, sucrose, cellulose etc.) (Grompone, 2011) we can assume that after dehydration of the sugars mostly 5-hydroxymethyl furfural (5-HMF) is formed (Hayes, Fitzpatrick, Hayes, & Ross, 2008).
Afterwards, further dehydration of formed 5-HMF is possible in a second step, which produces levulinic acid and formic acid.
Due to the fact that at 130 C and 160 C the content of carbohydrates in extracts decreases with te it can be assumed that 5-HMF has been further degraded to organic acids.
When comparing the degree of hydrothermal degradation of proteins and carbohydrates (Fig. 2a and b) it can be observed that carbohydrates are more susceptible to SubCW induced reactions than proteins in the applied temperature range.
As already mentioned in Subsection 3.3, this difference could be a consequence of unequal solubilities of the two materials.
Furthermore, the reactivity could also be dependent on the ability of the water molecules to reach the reaction site i.e. on degree of crystallinity of the two materials etc.
Based on these observations, it can be concluded that hydrothermal degradation reactions of SubCW can indeed have a
more selective behaviour towards different types of chemical compounds as was assumed.
In this study, the determination of total proteins present in WSE was performed using the Bradford colorimetric method. In the past it has been proven that the interference of carbohydrates present in the sample matrix significantly deviates the actual absorbance of the proteins, resulting in less accurate results if not primarily removed (Banik, Pal, Ghorai, Chowdhury, & Khowala, 2009). Since the primary aim of these preliminary studies was to observe the hydrothermal degradation of proteins in SubCW and not quantify the exact amount of proteins in extract, carbohydrates present in WSE were not primarily precipitated and were analysed directly using the above mentioned method.In contrast to the minimally hydrolysed triglycerides, total proteins (Fig. 2a) and carbohydrates (Fig. 2b) present in WSE show a much more different course.From Fig. 2a it can be observed that after 5 min of extraction again the lower temperature kinetic curves (60 C and 100 C) show no dependence on extraction time. The highest amounts of water soluble proteins are obtained at 60 C equaling to approximately 30 wt.%. At temperatures higher than 100 C overall protein yield in WSE decreases significantly with increasing Te and at 160 C the concentration of proteins (wBSA) even starts to decrease with te.The decrease of overall wBSA with increasing Te is probably a consequence of lower solubility of protein at higher temperatures, while the gradual decrease with extraction time at 160 C is possibly due to hydrolysis of proteins.M/S ratio seems to have practically no influence on wBSA.For total carbohydrates a quite similar pattern can be observed. Again, for the lower temperature curves (60 C and 100 C), no influence of te can be observed, since carbohydrate concentration (wGLU) remains constant after 5 min of extraction. Oppositely a higher yield of total carbohydrates can be observed at TeP100 C, which indicates a higher carbohydrate solubility at higher temperatures.At 130 C wGLU starts to decrease with te and the decrease is the highest at 160 C. This decrease of wGLU not only indicates a decrease of carbohydrates in the sample but also a decrease ofpresent furfurals. Furfurals are namely the main constituents formed in the phenol/sulfuric acid colorimetric method applied for determination of total carbohydrates. Therefore it can be presumed that products other than furfurals have formed duringextraction.Since the carbohydrate profile of sunflower kernels consists mainly from hexose derivatives (glucose, sucrose, cellulose etc.) (Grompone, 2011) we can assume that after dehydration of the sugars mostly 5-hydroxymethyl furfural (5-HMF) is formed (Hayes, Fitzpatrick, Hayes, & Ross, 2008). Afterwards, further dehydration of formed 5-HMF is possible in a second step, which produces levulinic acid and formic acid. Due to the fact that at 130 C and 160 C the content of carbohydrates in extracts decreases with te it can be assumed that 5-HMF has been further degraded to organic acids.When comparing the degree of hydrothermal degradation of proteins and carbohydrates (Fig. 2a and b) it can be observed that carbohydrates are more susceptible to SubCW induced reactions than proteins in the applied temperature range. As already mentioned in Subsection 3.3, this difference could be a consequence of unequal solubilities of the two materials. Furthermore, the reactivity could also be dependent on the ability of the water molecules to reach the reaction site i.e. on degree of crystallinity of the two materials etc.Based on these observations, it can be concluded that hydrothermal degradation reactions of SubCW can indeed have amore selective behaviour towards different types of chemical compounds as was assumed.
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