3.2. Effect of liquefaction temperature on the course of simultaneous saccharification and fermentation process
The assessment of fermentation dynamics by the CO2 release during SSF showed no significant differences in the course of the fermentation as affected by the liquefaction temperature ( data not shown). The concentration of reducing sugars in mashes liquefied at initial and peak temperature of gelatinization (T0 and Tp respectively) grew in the first day of the SSF (Fig. 1), for the other variants of experiment no such phenomenon was observed. The highest rate of reducing sugars utilization was observed in the mashes hydrolyzed at final temperature of gelatinization ( Tf), its concentration decreased to ca. 6 g L1 after 48 h of the SSF and did not significantly change by the end of the process. The final concentration of reducing sugars in other variants of experiment was similar (ca. 16–19 g L1). The glucose utilization profile was almost identical as reducing sugars (Fig. 2a). The changes in concentration of other carbohydrates (maltose, maltotriose, dextrins (DP4+)) in all studied variants of experiment were similar throughout the simultaneous saccharification and fermentation (Fig. 2a, b and c respectively). Its concentrations were established after 24 h and did not significantly change by the end of the process. The ethanol formation dynamics during studied SSF experiments is shown in Fig. 3. It was observed that slightly higher concentration of ethanol was obtained in mashes liquefied at final temperature of gelatinization (Tf) after subsequent hours of the process. The final concentration of ethanol ranged ca. 129 g L1 (ca. 16.2% v/v) for Tf variant and ca. 124–126 g L1 (15.7–15.9% v/v) in other variants of experiment. The ethanol production lasted by the second day of fermentation and did not change significantly by the end of the process. It was observed that the lowest glycerol concentration was obtained in waste wheat–rye bread mashes enzymatically liquefied at the final temperature of gelatinization (Tf) and it ranged ca. 11.8 g L1, in the case of other variants its concentration ranged ca. 12.5 g L1 for T0 and ca. 13.1 g L1 for Tp and T85 (Fig. 4a). There were found small amount of lactic acid (ca. 1.3–1.7 g L1) at the beginning of the fermentation in all studied samples (Fig. 4b), its concentration did not significantly change throughout the SSF process.
The increase in the concentration of reducing sugars and glucose within the first day of the SSF for mashes liquefied at initial and peak temperature (T0 and Tp respectively), not observed in other experimental variants, was caused by the higher rate of dextrins hydrolysis than utilization of sugars by the yeast. This was probably due to higher content of soluble dextrins (as determined by HPLC) and non-dissolved solids which probably contain some high-molecular, insoluble glucose polymers which were subsequently hydrolyzed during the SSF. This was observed earlier by Zhang et al. [32]. After the fermentations were completed some quantities of residual dextrins were determined unhydrolyzed in the mashes. This was probably caused by loss of glucoamylase activity due to insufficient temperature or a decrease in pH the medium. This could be avoided by increasing the glucoamylase dosage at the beginning of the fermentation [33]. Higher ethanol production dynamics in mashes liquefied at final temperature of gelatinization (Tf), in comparison to mash liquefied at 85 C, could be explained by lower, initial concentration of monomeric sugars which caused lower osmotic pressure upon the yeast cells [34]. On the other hand lower dynamics of ethanol production in mashes T0 and Tp in comparison to Tf could be explained by
3.2. ผลของอุณหภูมิการ liquefaction ของกระบวนการหมักและ saccharification พร้อมThe assessment of fermentation dynamics by the CO2 release during SSF showed no significant differences in the course of the fermentation as affected by the liquefaction temperature ( data not shown). The concentration of reducing sugars in mashes liquefied at initial and peak temperature of gelatinization (T0 and Tp respectively) grew in the first day of the SSF (Fig. 1), for the other variants of experiment no such phenomenon was observed. The highest rate of reducing sugars utilization was observed in the mashes hydrolyzed at final temperature of gelatinization ( Tf), its concentration decreased to ca. 6 g L1 after 48 h of the SSF and did not significantly change by the end of the process. The final concentration of reducing sugars in other variants of experiment was similar (ca. 16–19 g L1). The glucose utilization profile was almost identical as reducing sugars (Fig. 2a). The changes in concentration of other carbohydrates (maltose, maltotriose, dextrins (DP4+)) in all studied variants of experiment were similar throughout the simultaneous saccharification and fermentation (Fig. 2a, b and c respectively). Its concentrations were established after 24 h and did not significantly change by the end of the process. The ethanol formation dynamics during studied SSF experiments is shown in Fig. 3. It was observed that slightly higher concentration of ethanol was obtained in mashes liquefied at final temperature of gelatinization (Tf) after subsequent hours of the process. The final concentration of ethanol ranged ca. 129 g L1 (ca. 16.2% v/v) for Tf variant and ca. 124–126 g L1 (15.7–15.9% v/v) in other variants of experiment. The ethanol production lasted by the second day of fermentation and did not change significantly by the end of the process. It was observed that the lowest glycerol concentration was obtained in waste wheat–rye bread mashes enzymatically liquefied at the final temperature of gelatinization (Tf) and it ranged ca. 11.8 g L1, in the case of other variants its concentration ranged ca. 12.5 g L1 for T0 and ca. 13.1 g L1 for Tp and T85 (Fig. 4a). There were found small amount of lactic acid (ca. 1.3–1.7 g L1) at the beginning of the fermentation in all studied samples (Fig. 4b), its concentration did not significantly change throughout the SSF process.The increase in the concentration of reducing sugars and glucose within the first day of the SSF for mashes liquefied at initial and peak temperature (T0 and Tp respectively), not observed in other experimental variants, was caused by the higher rate of dextrins hydrolysis than utilization of sugars by the yeast. This was probably due to higher content of soluble dextrins (as determined by HPLC) and non-dissolved solids which probably contain some high-molecular, insoluble glucose polymers which were subsequently hydrolyzed during the SSF. This was observed earlier by Zhang et al. [32]. After the fermentations were completed some quantities of residual dextrins were determined unhydrolyzed in the mashes. This was probably caused by loss of glucoamylase activity due to insufficient temperature or a decrease in pH the medium. This could be avoided by increasing the glucoamylase dosage at the beginning of the fermentation [33]. Higher ethanol production dynamics in mashes liquefied at final temperature of gelatinization (Tf), in comparison to mash liquefied at 85 C, could be explained by lower, initial concentration of monomeric sugars which caused lower osmotic pressure upon the yeast cells [34]. On the other hand lower dynamics of ethanol production in mashes T0 and Tp in comparison to Tf could be explained by
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