2. Materials and Methods
2.4. Discussion
Figure 2.12 Packed bed reactor operated: (a) without recycle and (b) recycling mode as a function of initial substrate concentration (S)
the CFW selected in the present study was found out to be semi-crystalline in nature and comprises of shorter glucose units, this indeed an advantage for the present enzymatic hydrolysis process as the enzyme load on splitting the longer chain polymer in the case of B-type will be significantly reduced in the A-type starch material [24]. TGA analysis outlined the similar depolymerization temperature of the CFW and pure starch implies the prevention of excessive energy burden observed in the case of other biomass [29]. TGA results substantiates that no significant differences with respect to the starch source of botanical origin and corroborates with a recent report [30] on the preparation of carboxyl methyl cellulose films with corn and cassava starch. Rheological analysis has shown the viscosity of the starch-aqueous system is due to the swollen nature of the starch, and the starch swells with an increase in temperature until its gelatinization point. Similar observation was reported in literature [30] highlighting that the normal starch, waxy starch, and high amylose starch all exhibited an increasing viscosity trend till 75 oC beyond which the viscosity was in downtrend. Thus, the gelatinized solution of the present CFW was found to be a suitable feedstock for saccharification through enzymatic hydrolysis.
Composition analysis demonstrated that the concentration of minerals was not observed to be inhibitory; instead, these minerals may support microbial activity in the fermentation, a process consecutive to enzymatic hydrolysis of CFW.
Tailor made CCN matrix was found to be the best suitable support matrix for hydrolysis of cassava fibre waste. For instance, the reduction in contact angle is highly favourable this is because the gelatinization of CFW was carried out in an aqueous environment, the enzyme support material should preferably be hydrophilic as that may reduce fluid flow resistance and thereby resulting in better enzyme-substrate contact to give enhanced enzymatic hydrolysis. Recently, polymer nanocomposite with graphene nanoplatelets was developed to increase the hydrophilicity of the polymeric
increase in the chitosan coating concentration resulted in a sharp reduction in the percentage elongation (Figure 2.8b), which enumerates the suitability of the CCN matrix as packing material in the packed bed reactors dealing with the enzymatic hydrolysis process. In order to handle the high inlet flowrate and shock loads in the packed bed system a packing material with excellent properties like high tensile strength and low elongation properties are solicited [37]. On top of all the aforementioned advantages, it is generally claimed that almost all the conventional immobilization support prepared using alginate or any other polymer suffers reduced relative activity due to mass transfer limitation.
However, such a mass transfer and other inherent limitations with support material were overcome by the tailor-made CCN matrix having very high surface area providing the intimacy between the enzyme and substrate complex [36, 37]. Also, enzymatic hydrolysis by immobilization outperformed the freely suspended system owing to the protection provided by the support material for α - amylase enzyme from harsh acidic environment.
Recyclability analysis has shown a slight reduction in the relative activity, which can be attributed to leaching of enzymes from the immobilized support and adsorption of the substrate onto the active sites thereby making them inaccessible for the next cycle of hydrolysis [10]. Recycle efficiency observed in the present study was significantly higher in comparison similar research studies reported in literature. Recently, a maximum of 80%
relative activity at the end of the 6th cycle for α-amylase immobilized on naringin functionalized magnetic nanoparticles was reported [10]. Finally, the packed bed studies established the scalability of the present system and its labile operation under both recycling and non-recycling mode.
Hence, the present study developed novel electrospun PLA and modified chitosan nanofiber immobilized with α - amylase for hydrolyzing highly viscous starchy solution
resulting from the CFW. As mentioned before, in section 3.2, the CCN matrix used in the present study was tailor-made to handle the viscous solution. For instance, the higher tensile strength needed to hold the huge pressure drop across the packed bed reactor was imparted by the addition of chitosan onto the PLA polymer. Further, the reduction in the elongation is an added advantage as it maintains the packing material to be intact throughout the operation of the packed bed reactor. Consecutively, reduced hydrophobicity and nano features associated with the packing material is an added advantage for the successful implementation of the present packing material in the pilot- scale packed bed reactor system. The abundance availability of the CFW and the ease associated with the automated production of CCN matrix through electrospinning process suggests the scalability of the present study for commercial production of fermentable sugars. Alternatively, the packed bed reactor system can be integrated as pretreatment hydrolysis unit in a biorefinery setup. Novel electrospun CCN matrix dealt in this present study as the support material could be extended for the immobilization of other industrially important enzymes like lipozyme, lipase and cellulase as these enzymes also handle viscous substrate such as cheese, vegetable oil and liquefied lignocellulose, respectively.