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).