Combining the effects of process design and pH for improved xylose conversion in high solid ethanol production from Arundo donax

AMB Express

Table 3 Summary of the fermentation performance during the shake flask fermentations

	4 g L⁻¹acetic acid
pH	5.0	5.5	6.0
Ethanol yield (g/g consumed sugars)	0.44 ± 0.01 ^A	0.43 ± 0.00 ^{A B}	0.40 ± 0.02^C
Ethanol yield (% of theoretical)	85.5 ± 1.2	83.8 ± 0.6	78.5 ± 3.6
Glycerol yield (g/g consumed sugars)	0.043 ± 0.007	0.042 ± 0.002	0.045 ± 0.004
Consumed xylose (%)	27.4 ± 1.9^C	38.7 ± 2.5 ^A	50.2 ± 1.2 ^B
Xylitol production (% of consumed xylose)	23.9 ± 0.2	25.2 ± 4.0	28.5 ± 2.6
Calculated carbon recovery ^a (including cell growth)	0.99 ± 0.00	0.99 ± 0.01	0.97 ± 0.04
	8 g L ⁻¹ acetic acid
pH	5.0	5.5	6.0
Ethanol yield (g/g consumed sugars)	0.43 ± 0.03 ^{A D}	0.43 ± 0.01 ^{A D}	0.42 ± 0.01 ^{B C D}
Ethanol yield (% of theoretical)	84.9 ± 5.4	84.5 ± 1.9	82.3 ± 0.9
Glycerol yield (g/g consumed sugars)	0.039 ± 0.009	0.042 ± 0.003	0.046 ± 0.000
Consumed xylose (%)	10.7 ± 1.2 ^D	37.0 ± 0.6 ^A	48.0 ± 2.0 ^B
Xylitol production (% of consumed xylose)	32.1 ± 7.8	23.8 ± 0.7	27.2 ± 2.0
Calculated carbon recovery ^* (including measured cell growth)	0.95 ± 0.04	0.99 ± 0.01	1.01 ± 0.02

^*Carbon recovery calculated according to Eq. 5 in material and methods, with CO₂ estimated based on ethanol production.
Yields are based on the final (48 hour) values, and standard deviations are based on duplicate experiments. All statistically compared mean values are denoted with one or several letters (A, B, C, D). Values labeled with the same letter are not significantly different at a confidence level of 95%. Note that in this table, yields for all six set-ups are compared.