The effect of extraction on ethanol production can be seen significantly from Fig. 13.5. Extracted seaweed produced higher ethanol percentage compared to non — extracted seaweed. Extracted seaweed yields 9.58% v/v of ethanol compared to 3.33% v/v of ethanol produced from non-extracted seaweed.

This is because by extraction (i. e. boiling the seaweed in hot water at 100% for 2 h), carbohydrates such as polysaccharide were released from the seaweed and dissolved in the slurry (Lin et al. 2000). In macroalgae biomass, it is known that it contains different types of carbohydrate mostly stored in the algae cell wall (Hu et al. 1998). The carbohydrates must be released and converted into simple sugars in order for the microorganisms to utilise these simple forms for bioethanol pro­duction (Philippidis and Smith 1995; Nguyen et al. 2009; Adams et al. 2009).

Fig. 13.5 Ethanol percentage for non-extracted and extracted seaweed

Hence, this makes the biomass pretreatment a crucial step. Without extraction, most carbohydrates are entrapped in the seaweed and not readily available for hydrolysis and subsequently for yeast to digest.

Figure 13.6 showed the comparison of the reducing sugar concentration in the slurry with or without extraction. The concentration of reducing sugar before fer­mentation was higher for experiment with extraction (8.10 mg/mL) compared to the one with no extraction (3.59 mg/mL). The concentrations of reducing sugar after fermentation for both experiments were similar, with extraction (1.96 mg/mL) com­pared to the one with no extraction (2.11 mg/mL). This showed that more sugar was utilised in the extracted sample (i. e. 6.14 mg/mL). Therefore, at this point, the extracted seaweed was expected to produce more ethanol compared to the non — extracted seaweed.