Second-Generation Bioethanol from Coconut Husk

Table 3

Comparison of hydrolysis methods and maximum final sugar concentrations.

Reference	Pretreatment	Hydrolysis strategy	Enzymes	Enzyme concentration	Conditions	Maximum Sugars concentration
[52]	Microwave-assisted-alkaline	SSF	Cellusclast® 1.5 L and Pectinex® Ultra SP-L	n.a.	30°C, 150 rpm, 96 h, TS 2.5%	n.p.
[27]	2 steps with NaOH	SHF	Celluclast ®1.5L and Novozyme 188 (Novozymes A/S; Denmark)	15 FPU·(g substrate)^−1 and 15 IU·(g substrate)^−1	50°C, 140 rpm, 72 h, pH 4.8, TS 5%	22.8 g glucose·L^−1
		SSF			37°C, 72 h, pH 5.5, TS 5%	n.p.
		[53]			Microwave-assisted-alkaline	Only hydrolysis	Cellusclast ®1.5 L and Pectinex ® Ultra SP-L	0.5% (v/v) each	35°C, 150 rpm, 5 days, TS 1%	2.8 g TRS ·L^−1
Autohydrolysis	Aprox 0.7 g TRS ·L^−1
H2SO4	Aprox 0.7 g TRS ·L^−1
NaOH	Aprox 1.4 g TRS ·L^−1
[31]	Alkaline hydrogen peroxide + alkaline delignification	SSF mature coconut fiber	Cellic®CTec2 and HTec2	30 FPU·(g substrate)^−1, 75 CBU·(g substrate)^−1 and 130 IU·(g substrate)^−1	30°C, 48 h, TS 4%	Aprox 19 g glucose·L^−1
		SSSF mature coconut fiber			Prehydrolysis: 50°C, 8 h; SSF: 30°C, 40 h; TS 4%
[61]	No pretreatment.	Only hydrolysis	Non-enzymatic hydrolysis with subcritical water			3.4 g monosaccharides ·(100 g substrate)^−1
[47]	H2SO4	Only hydrolysis	Celluclast ® and Novozyme 188 (Novozymes A/S; Denmark)	0.33 mL of each	50°C, 150 rpm, 72 h, pH 4.8, TS 0.1-2%	1.2 g TRS ·L^−1
[32]	Autohydrolysis TS 10%	SSF green coconut shell	Cellic® CTec2 and HTec2	30 FPU·(g substrate)^−1, 75 CBU·(g substrate)^−1 and 130 IU·(g substrate)^−1	30°C, 48 h, TS 4%	Aprox 13 g glucose·L^−1
		SSSF green coconut shell			Prehydrolysis: 50°C, 12 h; SSF: 30°C, 36 h,; TS 4%
[28]	NaOH	SHF	Non-enzymatic hydrolysis with 1-4% (v/w) H2SO4, 121°C, 2 h			8.4% (w/v) glucose
[46]	NaOH	SHF	Cellulase® 26921, Novozyme188 (Novozymes A/S; Denmark) and enzymes from coconut husk isolated fungi	7.5 FPU·(g substrate)^−1	50°C, 96 h, pH 5	50 mM TRS
[49]	NaOH	SHF	Accelerase® 1500	2% (v/v)	50°C, 150 rpm, 72 h. TS 1%	8.7 g TRS ·L^−1
[33]	Hydrothermal catalyzed with NaOH	SSF	Cellic® CTec2 and HTec2	30 FPU·(g substrate)^−1, 75 CBU·(g substrate)^−1 and 130 IU·(g substrate)^−1	30°C, 48 h, TS 4%	Aprox 16 g glucose·L^−1
		SSSF			Pre-hydrolysis: 50°C, 12 h; SSF: 30°C, 36 h, TS 4%
[50]	NaOH	SHF	AlternaFuel® CMAX	3.75, 7.5 and 15 FPU·(g substrate)^−1	50°C, 200 rpm, 96 h, pH 6, TS 17%	8.7% (w/v) sugars
[51]	Acid-alkaline	Only hydrolysis	Celluclast ®1.5 L	20.0 FPU·(g substrate)^−1, 20.0 CBU·(g substrate)^−1 and 10.0 XU·(g substrate)^−1	50°C, 150 rpm, 72 h, TS 5%	Aprox 9 g TRS ·L^−1
	Alkaline hydrogen peroxide TS 4%					Aprox 11 g TRS ·L^−1
[54]	Acidified aqueous glycerol	SSF	Enzyme from T. reseei	10 FPU·(g substrate)^−1	37°C, 120 rpm, 96 h	n.p.
	Aqueous glycerol
[62]	No pretreatment.	Only hydrolysis	Non-enzymatic hydrolysis with subcritical water + CO2			1.7 g monosaccharides ·(100 g substrate)^−1
[48]	NaOH	SHF	AlternaFuel® CMAX	15 FPU·(g substrate)^−1 each time	50°C, 200 rpm, 96 h, pH 6, TS 24 and 29%	9.7% (w/v) sugars
[29]	NaOH + Tween® 80; Autohydrolysis	Only hydrolysis	T. reesei ATCC 26921, β-glucosidases and xylanases	20.0 FPU·(g substrate)^−1, 20.0 CBU·(g substrate)^−1 and 10.0 FXU/·(g substrate)^−1	50°C, 150 rpm, 96 h, TS 5%	0.5 g TRS ·(g substrate)^−1; 0.1 g TRS ·(g substrate)^−1
[30]	NaClO2- C2H4O2/ autohydrolysis	Only hydrolysis	Cellic® CTec2 and HTec2	10 FPU·(g substrate)^−1, 30 CBU·(g substrate)^−1 and 40 IU·(g substrate)^−1	50°C, 150 rpm, 96 h, TS 4%	Aprox 24 g glucose·L^−1

n.a.: not available or present; TS: total solids loadings (w/v); n.p.: not present because of SSF or SSSF; values obtained from liquor after enzymatic hydrolysis but not used for fermentation (SSF and SSSF).