TO EVALUATE THE EXTRACTION PROCESSES USING SOLVENT EXTRACTION TECHNIQUE FOR BIOACTIVE
3.3.2. Model and response surface analysis
3.3.2.2. Analysis of response surfaces
Effect of temperature on total phenolic content
Fig. 3.3 (a, b, c, and d) shows the effect of temperature on TPC of black and purple rice bran extract in acetone and ethanol solution. Extraction was carried out at different temperatures varied from 30-60 °C. The TPC in acetone solution was gradually increased (718.3-991.2 and 972-1060 mg GAE/100g) with an increase in the temperature from 30-60
°C for black and purple rice bran (Figs 3.3a and 3.3c). From the study, it can be observed that higher the extraction temperature, better the extraction rate. It may be attributed to higher solubility of TPC in acetone at higher extraction temperature. Moreover, it may possible that at higher temperature plant material became soft which enhance the mass transfer of TPC from plant tissue to solvent, thereby it also increases diffusion coefficient hence increases the TPC recovery.
Figs. 3.3b and 3.3d show a complex interaction between temperature and TPC in bran extract. The TPC extraction in ethanolic solution was affected moderately with the change of temperature. The total phenolic yield was increased with an increase in temperature from 30 to 45 °C. It may be due to the increases in solubility and rate of
However, in ethanolic solution when the temperature was above 45 °C, total phenolic yield decreased to 890.4 and 541.4 mg GAE/100 g for black and purple rice bran, respectively.
This may be due to the oxidative degradation and structural decomposition of phenolic compounds in the extract at high temperatures (Wang et al., 2008). A similar type of change was observed by the previous researchers (Spigno et al., 2007; Wang et al., 2008).
a) b)
c) d)
Fig. 3.3: Response surface plots for the effects of time and temperature on total phenolic content in a) acetone from black rice bran b) ethanol from black rice bran c) acetone from purple rice bran d) ethanol from purple rice bran.
Total phenolic content (mg GAE/100g) Total phenolic content (mg GAE/100g)
Total phenolic content (mg GAE/100g) Total phenolic content (mg GAE/100g)
Effect of extraction time on total phenolic content
In solvent extraction process, the selection of optimal extraction time is an important parameter, because of the time-dependent thermal degradation of the phenolic compounds. For this reason, a relationship was developed between extraction time and TPC as shown in Fig. 3.3 (a, b, c, and d). The effect of extraction time on TPC of rice bran extract in acetone solution is shown in Figs. 3.3a and 3.3c. It was observed from the figure that with an increase in the extraction time, there was a rapid increase in extraction yield from black and purple rice bran. From Fig. 3.3a, it was also observed that from black rice bran, the extraction yield of the phenolic compound was increased sharply than purple rice bran. However, in an ethanol solution, the extraction yield has shown (Figs. 3.3b and 3.3d) opposite behaviour for black and purple rice bran with time. For black rice bran the extraction yield was increased after a certain time, but, for purple rice bran, the reverse trend was observed. The increase in TPC of extract with the increase in extraction time can be explained by Fick’s law, which predicts the equilibrium condition between the solute and solvent after a certain time. But, the decrease in TPC with an increase in extraction time could be due to the structural changes and decomposition of polyphenols during the prolonged extraction (Liu et al., 2013). Furthermore, the change in extraction yield is due to the composition difference in extracted phenolic compounds from black and purple rice bran.
Effect of solvent concentration on total phenolic content
Fig. 3.4 shows an interaction between solvent concentration and TPC yield. It was observed from Fig. 3.4 (a, b, c and d) that in acetone and ethanol solution, the TPC increased with an increase in the solvent concentration up to a certain level (55 % and 62.5
% v/v) and decreases thereafter. This is probably due to the change in solubility of phenolic compounds in the mixture of acetone/ethanol and water which may due to the change in polarity of extractant. As water has a high dielectric constant, which leads to change in the polarities of the mixture with different solvent concentrations (Spigno et al., 2007). This phenomenon might also be attributed to the change of viscosity of extractant, which affect the mass transfer. Water has a higher viscosity than that of acetone and ethanol which enables the solvent to more completely penetrate the bran and thereby increases the TPC recovery (Sahin and Samli, 2013). Moreover, it is reported that water is acted as the plant swelling agent, while ethanol and acetone are believed to disrupt the bonding between
was observed by Sahin and Samli (2013) during the extraction of the phenolic compounds from olive leaf. Hence, a combination of organic solvent with water is more effective in the extraction of phenolic compounds than alcohol alone.
a) b)
c) d)
Fig. 3.4: Response surface plots for the effects of solvent composition and solvent to solid ratio on total phenolic content in a) acetone from black rice bran b) ethanol from black rice bran c) acetone from purple rice bran d) ethanol from purple rice bran.
Total phenolic content (mg GAE/100g) Total phenolic content (mg GAE/100g)
Total phenolic content (mg GAE/100g) Total phenolic content (mg GAE/100g)
Effect of solvent to solid ratio on total phenolic content
The influence of the solvent to solid ratio on TPC recovery from rice bran was investigated. Fig. 3.4 shows that initially increase of solvent to solid ratio from 5 to 12 (mL/g), enhances the total phenolic recovery from black and purple rice bran. It is due to the increase of concentration gradient which is the driving force in the solvent extraction process. This is consistent with mass transfer principles since the concentration gradient which is driving force is higher when a higher solvent to solid ratio used, leading to higher diffusion and increase the extraction yield (Mokrani and Madani, 2016). The same tendency of the parameter was also observed by Spigno and De Faveri (2009) for the phenols extraction from tea. However, after a certain ratio of solvent to solid (12 mL/g), there was a decrease in yield with the further increase of solvent to solid ratio. Similar types of the result were observed by a number of researchers (Chen et al., 2015; Chen et al., 2007). It may be attributed that at a high solvent to solid ratio, the high amount of solvent in the extraction system would not change the driving force anymore as the mass transfer is more confined into the solid interior (Zhang et al., 2008) and thereby decrease the recovery of TPC.